Inverse palladocenes

Domain: neuroscience
Published: 2026-01-30
Editorial outcome: major_revision

Abstract
Metallocene research has influenced the development of organometallic chemistry, and the metal–nonmetal inverted half-sandwich structure (inverse metallocene) was very recently discovered. However, additional instances are required to propose the concept inverse metallocene and it remains uncertain whether metal five-membered ring structures analogous to the cyclopentadienyl anion structure exist. Herein we report the synthesis of a series of palladium analogs Pd8(PPh)2(PPh3)2(Ph2P=O)(S-Adm)5 (Pd8–P), Pd6(PPh)(PPh3)(S-Adm)6 (Pd6), Pd5(PPh)(S-Adm)4[(Ph2P)2O] (Pd5–O), and Pd5(PPh)(S-Adm)4[(Ph2P)2CH2] (Pd5–C), identify their fundamental metal building block named five-membered Pd aromatic ring, and reveal their conjugation‒photothermy correlation. In particular, we report an average NIR-II photothermal conversion efficiency per metal atom of 14.7% and the stability of the five-membered Pd aromatic ring, as illustrated by the fact that Pd5–C maintained photothermy performance for >10 heating–cooling cycles even after the ligands were removed. We further demonstrate the great potential of inverse palladocenes in areas such as laser shielding, high-temperature degradation, ignition, and temperature/light control. These results declare the research and application start of a type of materials named inverse palladocenes.

Introduction
The isolation and structural elucidation of ferrocene marked the inception of contemporary organometallic chemistry1–4. Since this milestone discovery, sandwich (or half-sandwich) metallocenes have been extensively reported5–8. The cyclopentadienyl anion (Cp, [C5H5]−) serves as the fundamental building block for this type of material. It comprises 6π electrons, adhering to the Hückel 4n+2 rule of aromaticity (Fig. 1a), and giving metallocenes unusual stability for practical applications in biology, pharmaceuticals, materials, etc9–14. However, the extension of this nonmetallic Cp to analogous metal five-membered rings, as well as the prospective metal aromaticity of the latter, requires further investigation. Interestingly, we recently produced an inverse metallocene-like structure15, in which the pentalene (C8H4) anion was replaced by a structurally similar two-fused and conjugated five-membered palladium (Pd5) ring, and the metal cation in metallocene was replaced by a nonmetal anion, as shown in Supplementary Fig. 1. The revealed nonmetal-to-metal ring coordination, as well as the aromatic Pd8 cation, was not previously reported16–19, which might indicate the emergence of a type of material: inverse metallocene. However, additional instances are required to validate a single case report. Specifically, it remains uncertain whether metal five-membered ring structures analogous to the Cp structure exist, which inspired this work.

Herein, we synthesized a series of inverse metallocene Pd nanoclusters, including Pd8(PPh)2(PPh3)2(Ph2P=O)(S-Adm)5 (Pd8–P for short), Pd6(PPh)(PPh3)(S-Adm)6 (Pd6 for short), Pd5(PPh)(S-Adm)4[(Ph2P)2O] (Pd5–O for short), and Pd5(PPh)(S-Adm)4[(Ph2P)2CH2] (Pd5–C for short), as well as the previously reported Pd8(PPh)2(PPh3)2(S-Adm)6 (Pd8–S for short). All of the nanoclusters comprised the Pd5 five-membered aromatic ring unit, demonstrating that Pd8–S is not the only example of an inverse metallocene material and that the five-membered aromatic metal ring is a fundamental metal building block for inverse metallocene (Fig. 1b). Moreover, nonmetal-aromatic ring to metallo-aromatic-ring π…π-like interactions were observed in the Pd5–C nanocluster20–30, indicating the border vagueness of metal and nonmetal aromatic rings. The five-membered aromatic Pd ring gave the series of inverse metallocene stability and ultrahigh NIR-II photothermal conversion efficiency (PCE). In addition, it was revealed that the photothermy was conjugation-related, and the smallest Pd5–C exhibited the highest NIR-II PCE up to 73.6% (irradiated at 980 nm) with an average PCE of 14.7% per Pd atom, which is much higher than that of previously reported photothermy materials31–35. The applications of Pd5–C in laser shielding, high-temperature degradation, ignition, and temperature/light control were also illustrated. The details are shown below.

Results
Synthesis of inverse palladocenes
Initially, we focused on the kinetics tuning of Pd8–S nanocluster synthesis to obtain inverse palladocenes featuring only a single five-membered metal ring unit (Supplementary Fig. 2). Unfortunately, our efforts resulted in the unexpected synthesis of Pd6 nanocluster, which was recently obtained by some other group36 according to the synthesis method of Pd8–S15 (the cited study focused on semihydrogenation catalysis, rather than chemical bonding). We then broke the Pd‒Pd bonds of the Pd8–S and Pd6 nanoclusters to obtain the target inverse palladocene (Supplementary Fig. 2). After 2 weeks of heating at 80 °C, the Pd8–S nanocluster remained unchanged except for a thiolate exchange with a [Ph2P=O]− group (from Ph3P oxidation), forming the Pd8–P nanocluster (Supplementary Fig. 3). In the case of the Pd6 nanocluster, two Pd‒Pd bonds in its three-membered ring were successfully cleaved with the two left triangular vertex Pd atoms protected by a bidentate (Ph2P)2O ligand, leading to the formation of Pd5‒O nanocluster (Supplementary Fig. 4). Note that, Pd5‒O can also be synthesized by a metal salt reduction method with relatively high yield via using Ph2PH(=O) and Ph2PCl as (Ph2P)2O ligand precursors (for detailed procedures, see Metal salt reduction method for the synthesis of Pd5‒O section of the Supplementary Information). Considering the presence of the protective (Ph2P)2O ligand (Supplementary Figs. 2 and 4) in the Pd5‒O nanocluster, we referred the synthesis of Pd8–S, but replacing PPh3 with the bisphosphine (Ph2P)2CH2 (DPPM) ligand, and fortunately achieved the direct synthesis of bisphosphine ligand-protected Pd5‒C nanocluster (see “Methods” for detailed synthesis). The thiolate type influences the final products due to the space and electronic effects, which influence the formation kinetics and thermodynamics of the products37. In our case, the space effect looks more prominent than the electronic effect since only very bulky 1-adamantanethiol led to the production of Pd5–C among the investigated thiolates. For the other thiols (including those with close electronic effects), they led to Pd nanoparticles or complexes as shown in the Supplementary Fig. 5. The synthesis routes for Pd8–P, Pd6, Pd5‒O, and Pd5‒C are illustrated in Fig. 2a and Supplementary Fig. 2, and plausible generation pathways for Pd8–P, Pd5‒O, and Pd5‒C are proposed in Supplementary Figs. 3 and 4. Moreover, density functional theory (DFT) calculations indicated that the Gibbs free energies for the transformations from Pd6 to Pd5‒O (and to Pd5‒C) (Fig. 2b) and from Pd8‒S to Pd8–P (Supplementary Fig. 6) were notably negative, demonstrating the transformation thermodynamic favorability.

Characterization of inverse palladocenes
The molecular compositions of the Pd8–P, Pd6, Pd5‒O, and Pd5‒C nanoclusters were all identified using electrospray ionization mass spectrometry (ESI‒MS), as shown in Fig. 2c‒f, and subsequently corroborated by single-crystal X-ray crystallography (SCXC). Specifically, one dominant ion peak at m/z 2763.02 was readily assigned to [Pd8(PPh)2(PPh3)2(Ph2P=O)(S-Adm)5Cs]+ (Fig. 2c; to assist ionization, cesium acetate was added to the nanocluster solution to form [cluster + ×Cs]×+ adducts before ESI‒MS analysis). The isotopic patterns, depicted in the inset of Fig. 2c, supported this assignment with a negligible deviation of 0.17 M/Z between experimental and theoretical values. This finding clearly illustrates that the transformation from Pd8–S to Pd8–P involved the substitution of one [S-Adm]− ligand in Pd8(PPh)2(PPh3)2(S-Adm)6 with one [Ph2P=O]− group (see Fig. 2c and Supplementary Fig. 7 for ESI‒MS comparison). ESI‒MS analysis also revealed the composition of the Pd6 nanocluster (Fig. 2d), with the predominant peak at m/z 2145.71 assigned to [Pd6(PPh)(PPh3)(S-Adm)6Cs]+. Similarly, the ion peaks of Pd5‒O and Pd5–C were attributed to {Pd5(PPh)(S-Adm)4[(Ph2P)2O]Cs}+ and {Pd5(PPh)(S-Adm)4[(Ph2P)2CH2]Cs}+, respectively. These assignments were also confirmed by comparing the isotopic patterns of the experimental and calculated results, as shown in the insets of Fig. 2d‒f. The number of Cs+ in these formulas corresponded precisely to the ion charge numbers, affirming the neutrality of the as-obtained species, which was further substantiated by the absence of any rational signal in the mass spectra when Cs+ was not added. Thus, the formulas of the resultant Pd nanoclusters were deduced to be Pd8(PPh)2(PPh3)2(Ph2P=O)(S-Adm)5, Pd6(PPh)(PPh3)(S-Adm)6, Pd5(PPh)(S-Adm)4[(Ph2P)2O], and Pd5(PPh)(S-Adm)4[(Ph2P)2CH2].

Given the exact compositions and the recognized formal oxidation states (OSs) of ligands [S-Adm]−, [PPh]2−, [Ph2P=O]−, and PPh3 (–1, –2, –1, and 0, respectively; note: the detailed analysis of the OS of phosphorus in inverse palladocenes is provided in the Analysis of the OS of phosphorus in inverse palladocenes section of the Supplementary Information)15,38, the average OSs of Pd in Pd8–P, Pd6, Pd5‒O, and Pd5–C were calculated to be +1.25, +1.33, +1.2, and +1.2, respectively, indicating the low OSs of Pd across all these nanoclusters39. Molecular orbital (MO) analysis verified the OSs of Pd in various inverse palladocenes. Taking Pd5–C as an example, the revealed three empty MOs is consistent with the total OS of its five Pd atoms (+6) (Supplementary Fig. 8). The low OSs of Pd were further authenticated using X-ray photoelectron spectroscopy (XPS) and natural population analysis (NPA) charge, as shown in Fig. 2g‒j and Supplementary Figs. 9‒12.

Geometric and electronic stuctures
SCXC definitively ascertained the compositions of the four Pd nanoclusters (Pd8–P, Pd6, Pd5‒O, and Pd5‒C) and revealed their structures, which were also well reproduced by DFT geometry optimization as shown in Supplementary Table 1, demonstrating the reliability of both the theoretical simulations and experimental results. As mentioned above, Pd8–S and Pd8–P differed solely in one ligand: [S-Adm]− versus [Ph2P=O]−. Pd8–P comprised two pseudo-coplanar metallic pentagon units interconnected by two shared Pd atoms, which was the same as that of Pd8–S15. In contrast, Pd5‒O, Pd5‒C, and Pd6 each fearured a single metallic pentagon unit (Fig. 3a). Among them, Pd5‒C distinguished itself from Pd5‒O by the substitution of the O atom in the bidentate phosphine of Pd5‒O with a CH2 unit. Pd6 incorporated an additional triangular unit alongside its coplanar metallic pentagon unit by sharing two Pd atoms. Overall, these nanoclusters demonstrate the metallic pentagon unit as the fundamental metal building block. The average Pd‒Pd distance within the metallic pentagon units remained consistent at 2.66 Å for Pd8–P, Pd5‒O, and Pd5‒C, consistent with the reported measurement for Pd8–S15. In contrast, Pd6 exhibited a longer mean Pd‒Pd distance of 2.70 Å (Fig. 3b), which can be explained as follows. The triangular unit in Pd6 had an average Pd‒Pd distance of 2.99 Å (Fig. 3c), surpassing that of the metallic pentagon unit and elongating the shared Pd‒Pd bond to 3.05 Å (Fig. 3a). Thus, the metallic pentagon unit in Pd6 had a longer average Pd‒Pd distance than that in Pd8–S, Pd8–P, Pd5‒O, and Pd5‒C nanoclusters. Meticulous inspection revealed that the five Pd atoms in all pentagon units deviated slightly from perfect coplanarity, and the deflection angles for noncoplanar atoms in Pd8–P, Pd8–S, Pd6, Pd5‒O, and Pd5‒C were 37°+35°, 35°+32°, 6°, 3°, and 1°, respectively (Fig. 3d and Supplementary Fig. 13), indicating the variation in five-membered ring conjugations. The conjugation disparity was also reflected in the bond length homogenization (Fig. 3a, e). To quantitatively assess this, a concept of nominal coplanar bond length standard deviation (Sncp) was introduced40,41, based on the coplanar five-membered ring formed after the projection of noncoplanar Pd atom(s) (see Supplementary Table 2 for the details). The Sncp values followed the sequence: Pd5‒C (0.078) < Pd5‒O (0.080) < Pd6 (0.201) < Pd8‒S (0.266) < Pd8–P (0.333), positively correlating with the deflection angles. The bond length homogenization and the deflection angle of noncoplanar atoms served as two pivotal physical parameters for evaluating the ring conjugation degree. In addition, the alignment between the sequence of deflection angles and that of nominal coplanar Pd–Pd bond length standard deviations corroborated the hierarchy of the conjugation degree order of Pd5‒C > Pd5‒O > Pd6 > Pd8‒S > Pd8–P (from largest to smallest). These are understandable given the differences in the protecting ligands or fused rings for the conjugated five-membered rings. For instance, in the comparison between Pd5‒C and Pd5‒O, the conjugation degree of the five-membered ring was lower in Pd5‒O than in Pd5‒C owing to the stronger electron-withdrawing capability of O compared to C42,43. Besides, the fused three- or five-membered ring exerts a dampening effect on conjugation, explaining why the conjugation degree of the five-membered ring of Pd5‒O was higher than that of Pd8–S or Pd8–P. The conjugation degree holds substantial implications for numerous physicochemical properties, which will be illustrated below.

Furthermore, DFT calculations were performed for the inverse palladocenes to provide insights into their electronic structure (Fig. 4). The electron localization functions (ELF) map, which provides the probability of finding electron pairs in a given region, suggested that the electrons were evenly distributed between each Pd−Pd pair in the five-, six-, and eight-membered ring units of all these compounds (Fig. 4c and Supplementary Fig. 14). Moreover, the theoretical calculations reveal that the five-membered ring in Pd5‒C is aromatic and is the basic unit of these systems (Fig. 4a). As supported by the adaptive natural density partitioning (AdNDP) method, all the Pd5 units have three 6c–2e AdNDP orbitals (Fig. 4b for Pd5‒C, Supplementary Fig. 15 for Pd5‒O, Pd6, Pd8–P, and refer to our previous work15 for Pd8–S), which agree with the 4n+2 rule in the five-membered aromatic ring (Cp and its analogues). Unlike classic d-transition metal metallocenes, wherein the interaction between Cp (or its analogues) and the metal atom involves strong covalent bonding with both Cp (and its analogues)-to-metal atom electron donation and metal atom-to-empty orbitals of Cp (and its analogues) δ-backdonation, inverse palladocenes have major orbital interactions comprising of ligand-to-metal atom coordination, where the Pd5 aromatic ring served as electron acceptor (Supplementary Fig. 16a; the energy decomposition analysis with natural orbitals for chemical valence (EDA-NOCV) of both metallocenes and inverse palladocenes are provided in the EDA-NOCV analysis of inverse palladocenes section of the Supplementary Information). Recently, Sun et al. synthesized two anionic clusters, [Cr5Sn20Sb2]4− and [(Cr)5Sn52Sb6]6−, both of which featured metal aromaticity in the chromium (Cr) segments within their cluster cores without connecting nonmetal atoms (Supplementary Fig. 16b)44. Dehnen et al. isolated a planar π-aromatic Bi5− ring with electron donating nature analogous to the Cp in contrast to our case (Supplementary Fig. 16c)45. The corresponding AdNDP orbital shapes and compositions revealed that Pd5 units featured unique nonmetal-to-metallo-aromatic-ring coordination arising from the orbital interactions between the centroid phosphorus (P) atom and the five adjacent Pd atoms. The aromatic properties of these systems were further supported by the isochemical shielding surface (ICSS), where the simulated [Pd5]6+ (all ligands were removed) and [Pd5(S-Adm)4(DPPM)]2+ (the [PPh]2‒ unit was removed) are analogous to the cases of aromatic [C5H5]‒ (Fig. 4d and Supplementary Fig. 17). Furthermore, the ICSSs of the total structural Pd5‒C, Pd5‒O, Pd6, Pd8‒P, and Pd8‒S are also in accordance with the characteristics of aromatic [C5H5]‒ or [C8H6]2‒, as shown in Fig. 4d and Supplementary Fig. 18. The series of compounds not only show environmental stability (water- and oxygen-resistant during the synthesis and use), but also exhibit rather thermostability and photostability (Supplementary Figs. 19 and 20), providing experimental support for their aromaticity.

An intriguing finding in the crystal structure was that one phenyl (Ph) motif of the DPPM ligand in the Pd5‒C was pseudo-parallel to the metallic pentagon unit of the adjacent Pd5‒C (face to face), separated by an inter-ring distance of 3.7 Å. This is formally similar to π…π stacking between organic aromatic rings (e.g., between Ph and Cp), indicating possible π…π-like interactions36 (Fig. 4a, e). Reduced density gradient (RDG) calculations revealed that the similar major van der Waals (vdW) interaction between Ph and Pd5 ring (Fig. 4f), and between Ph and Cp46 (Supplementary Fig. 21). These interactions were also corroborated by independent gradient model based on Hirshfeld partition (IGMH) analysis (Supplementary Fig. 22), which previously disclosed the unreported nonmetal-aromatic ring to metallo-aromatic-ring interactions23,47–51. Taken together, these results demonstrated that the metal-aromatic ring was comparable to the nonmetal-aromatic ring. Energy decomposition analysis (EDA) calculation on a simplified (Pd5‒C)2 dimer based on the crystal structure (Supplementary Table 3), reveals that electrostatic attraction between the phenyl group of the DPPM ligand and the adjacent metal five-membered ring dominates over orbital interactions induced by the electron transfer (accounting for 69.7% vs. 30.3%), which is further confirmed by the electrostatic potential distribution within the dimer. As shown in Supplementary Fig. 23, the plot of electrostatic potential surfaces suggests that the electrostatic potential is asymmetrically distributed among the Pd5‒C: the palladium five-membered ring is more negatively charged while the phenyl group of the DPPM ligand is relatively positive, facilitating their electrostatic attraction between the two moieties. The electrostatic attraction not only oriented all S-Adm ligands codirectional to the [PPh]2− ligands but also resulted in the one-dimensional self-assembly of Pd5‒C into an inverse palladocene supermolecule structure (Fig. 4e). Notably, this assembly adopted an orientation antipodal to that of the neighboring assemblies within the crystal lattice (Fig. 4g). However, such nonmetal-aromatic ring to metallo-aromatic-ring π…π-like interactions were absent in Pd5‒O, with all metallic pentagons in the lattice aligning parallel (Supplementary Fig. 24). This probably arose from intermolecular dense-packing induced by polarity, demonstrating that one atom difference in the ligand of inverse palladocene had a major effect on the intermolecular interactions (Supplementary Fig. 25). The intermolecular interactions considerably influenced the crystallographic arrangement, leading to the 2H arrangements of Pd8‒P and Pd5‒O, and the 4H arrangements of Pd5‒C and Pd6 (Fig. 3f).

Optical and electronic properties
The electronic structures of inverse palladocenes were experimentally investigated using ultraviolet/visible/near infrared (UV/Vis/NIR) spectrometry (Supplementary Figs. 26–29) and further explained by time-dependent (TD)‒DFT calculations (with PBE functional), as shown in Fig. 5 and Supplementary Figs. 30‒32. All of the nanoclusters exhibited NIR absorption characteristics. Specifically, Pd5‒C and Pd5‒O played intense experimental absorption bands within the wavelength window of ~850 to 1150 nm, peaking at 973 and 940 nm, respectively (Fig. 5a and Supplementary Fig. 27). Note that the absorptions of inverse palladocenes are solvent dependent. However, not only absorption intensities but also absorption maximum wavelengths don’t positively correlate with the solvent polarity as shown in Supplementary Fig. 29. Kohn‒Sham MO analysis revealed that the predominant contribution (96%) to the simulated Pd5‒C peak at 1050 nm originated from the highest occupied molecular orbital (HOMO) → the lowest unoccupied molecular orbital (LUMO) electronic transitions (Fig. 5b). This was similar to the calculated results of Pd5‒O, in which HOMO→LUMO electronic transitions accounted for the dominant contribution (94%) of the simulated peak at 1010 nm (Supplementary Fig. 30). In contrast, unlike their Pd5‒C and Pd5‒O counterparts, the NIR absorption peaks of Pd6 and Pd8‒P conspicuously blue-shifted into the NIR-I region (Supplementary Figs. 31 and 32). This shift was attributed to structural variations, particularly the presence of fused three-(Pd6) or five-(Pd8‒P) membered ring that reduce the aromaticity of the five-membered Pd ring, which is a common rule observed in organic conjugated systems52–54. The simulated Pd6 peak at 889 nm primarily (90%) arose from HOMO→LUMO electronic transitions, whereas the simulated Pd8‒P peak at 901 nm was attributed to both HOMO→LUMO electronic transitions (accounting for 40%) and HOMO-1→LUMO electronic transitions (accounting for 45%). Using Pd5‒C and Pd5‒O as examples, further disassembling along three axial directions by DFT calculations revealed that the y-axis transition of a metallic pentagon mainly contributed the lowest energy transition (α) (Fig. 5c, d and Supplementary Fig. 30c, d), reflecting in that the transition dipole moment ratios of x, y, and z (x:y:z) were 0.95:2.27:0.04 and 0.29:2.51:0.14 for Pd5‒C and Pd5‒O, respectively (Supplementary Table 4). The HOMO-LUMO gap of 1.09 eV matches well with the optical gap of Pd5‒C (1.18 eV) (Fig. 4b, Supplementary Figs. 27 and 33), which is consistent with the measured electrochemical gap of 1.60 V (Supplementary Fig. 34). Of note, the series of inverse palladocenes have close DPV profiles and electrochemical gaps with 1.63, 1.69, 1.59, and 1.68 V for Pd5‒O, Pd6, Pd8‒S, and Pd8‒P, respectively (Supplementary Fig. 34), providing further support for the existence of metal building block—five-membered aromatic metal ring, which plays the functional group-like55 role.

Photothermal properties
It is documented that dominant longitudinal transitions in metal nanorods56 or x-direction transitions in flat nanoclusters can result in strong photothermal effects15; however, it is unclear if such a major transition along the y-direction could also induce a notable photothermal conversion. Figure 6a shows that under 0.5 W/cm² laser irradiation, 80 μg/mL solutions of Pd5‒C or Pd5‒O exhibited a substantial temperature rise at 980 nm (which wavelength is close to the maximum NIR absorption wavelengths for the five inverse palladocenes: Pd5‒C, Pd5‒O, Pd6, Pd8‒S, and Pd8‒P), achieving PCEs of 73.6% and 68.1%, respectively (see Supplementary Information for detailed calculations). These values surpassed previously reported for nanoclusters and most other photothermal materials under identical irradiation wavelengths (Fig. 6b and Supplementary Table 9). For comparison, the PCEs of the remaining inverse palladocenes (Pd6, Pd8‒S, and Pd8‒P) were also investigated, revealing values of 51.8%, 24.1%, and 20.3%, respectively. Consequently, the PCE rankings among the five inverse palladocenes were Pd5‒C > Pd5‒O > Pd6 > Pd8‒S > Pd8‒P, which intriguingly mirrored their conjugation degree order, indicating the conjugation‒photothermy correlation and that the major photothermy was contributed from the five-membered Pd aromatic ring of inverse palladocenes. Specifically, Pd5 aromatic ring is the primary contributor of the NIR absorption, and thus strong conjugation within the Pd5 ring leads to intensive NIR absorption, enabling enhanced photothermal conversion in the NIR-II window.

To further verify the hypothesis that the five-membered Pd aromatic ring is the major photothermy contributor, we carried out a charge difference density analysis of Pd5‒C during its transition from the ground state to the excited state as shown in Supplementary Fig. 35. The analysis reveals that during the excitation process, electron transfer mainly occurs within the metallic Pd5 aromatic ring and partially involves those between Pd and the [SCH3]‒ ligands. We then computationally simulated the absorption spectrum of Pd5‒C by substituting the [SCH3]‒ ligand with F‒, Cl‒, Br‒, [OCH3]‒, or [SeCH3]‒ groups (Supplementary Fig. 36), which revealed the negligible change in the NIR peak, demonstrating the unessential influence of ligands on the electronic transition associated with the NIR absorption. Moreover, the unchanged photothermy performance for 10 heating–cooling cycles after ligand removal (Supplementary Figs. 37 and 38) served as a compelling evidence that the photothermy of Pd5‒C was dominated by the five-membered Pd aromatic ring. This finding demonstrates that merely five Pd atoms can achieve a remarkable 73.6% of light to heat conversion efficiency, suggesting an average of 14.7% per metal atom, which considerably outperforms that for other reported materials (Fig. 6c and Supplementary Table 10), demonstrating the uniqueness of the five-membered Pd aromatic ring. Notably, although the concentration only slightly affected PCE, it had considerable effect on the temperature rise. For instance, halving the Pd5‒C concentration to 40 μg/mL resulted in a temperature rise of 42.9 °C, whereas increasing it to 200 μg/mL increased the temperature to 65.4 °C (Fig. 6d; for the time-dependent temperature changes, see Fig. 6e and Supplementary Fig. 39). The Pd5‒C inverse palladocene also exhibited remarkable photothermal stability, as shown in Fig. 6e, with both 40 and 80 μg/mL Pd5‒C showing negligible loss in their maximum temperatures and UV/Vis/NIR spectra (Supplementary Fig. 40) after eight consecutive heating and cooling cycles. The Pd5‒C inverse palladocene even had good photothermal conversion performance under 1064 nm irradiation (0.5 W/cm²), with a temperature elevation of 18.1 °C. However, the photothermal conversion performance of Pd5‒C was relatively poor under 1208 nm irradiation because of the negligible absorption beyond 1100 nm (Fig. 6f; for time-dependent temperature changes, see Supplementary Fig. 41). Referring to the Jablonski energy level diagram (which indicates that a structure with relatively lower PCE might exhibit photoluminescence), we also attempted to investigate the photoluminescence properties of inverse palladocenes under different excitation wavelengths57. Unfortunately, no notable photoluminescence of inverse palladocenes was observed so far, as shown in Supplementary Fig. 42.

Our experiments demonstrated that the outstanding photothermy performance was applicable in multiple fields. One application is laser shielding. Figure 6g‒i show that Pd5‒C (2 mg/mL) effectively reduced 980 nm laser power from 500 to 9 mW, achieving an impressive shielding efficiency of 96.6% (calculated by the equation: R=(I0−I)/I0, where Ib is the permeated laser intensity of blank, I is the permeated laser intensity of the Pd5‒C solution, and I0 is the initial laser intensity). Reducing the concentration to 1.0 mg/mL still yielded a high shielding efficiency of 92.0%, and even for a dilute concentration of 50 μg/mL, the shielding efficiency reached 38.6%. Among the inverse palladocenes, Pd5‒C and Pd5‒O exhibited superior shielding performance for the 980 nm laser, which positively correlated with their PCEs (Fig. 6h and Supplementary Fig. 43a‒d) and conjugation degrees. Pd5‒C even had a good shielding ability for the 1064 nm laser, but performed less efficiently against the 1208 nm laser (Fig. 6i and Supplementary Fig. 43e, f), reflecting its limited absorption beyond 1100 nm.

Another application is for high-temperature degradation. For example, when Pd5‒C was encapsulated in polystyrene and exposed to 980 nm laser irradiation at 0.8 W/cm², it facilitated the degradation of the high ignition temperature polystyrene at ~368 °C (Fig. 6j and Supplementary Fig. 44). In addition, when Pd5‒C was loaded onto a cotton surface, it can ignite the cotton under identical irradiation conditions, suggesting a potential application in ignition (Fig. 6k and Supplementary Movie 1). Furthermore, Pd5‒C also displayed its applicability in temperature/light control, illustrated by the following experiment. When Pd5‒C was encapsulated in polyurethane (30 mg, 1 wt% of Pd5‒C, 0.2 mm thickness) and subjected to continuous 980 nm laser irradiation at 0.4 W/cm², the composite temperature rapidly increased over a stable range of 107.5‒108.5 °C, illustrating precise thermal management capabilities (Fig. 6l). Moreover, the aforementioned Pd5‒C/polyurethane film also exhibited excellent laser shielding performance (Supplementary Fig. 45), achieving a shielding efficiency of 81.8%. Overall, these findings demonstrate the great potential of inverse palladocene materials across a multitude of fields.

Methods
Materials
Pd(CH3COO)2 (99.9%), polystyrene (PS), and polyurethane (PU) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. 1-Adamantanethiol (Adm-SH, 99%), triphenylphosphine (PPh3), (Ph2P)2CH2 (DPPM), sodium borohydride (NaBH4, 99.8%), triphenylmethanethiol, 2-phenylethanethiol, benzenemethanethiol, cyclohexanethiol, 4-tert-butylphenylthiol, 2,4-dimethylbenzenethiol, toluene, dichloromethane (DCM), tetrahydrofuran (THF), N,N-dimethylformamide (DMF), and methanol were all purchased from Shanghai Chemical Reagent Co., Ltd. Pd8‒S nanocluster was prepared according to our previously report15. All chemicals were used as received. The water used in all experiments was ultrapure (resistivity 18.2 MΩ·cm), produced by a Milli-Q NANOpure water system.

Synthesis of Pd8(PPh)2(PPh3)2(S-Adm)6 (denoted as Pd8‒S)15
Pd(CH3COO)2 (50.0 mg, 0.223 mmol) and PPh3 (100.0 mg, 0.381 mmol) were co-dissolved in 8 mL of THF in a three-necked flask with continuous stirring for 5 min, accompanied by a solution color change from yellow to red. Then, a cold water solution containing NaBH4 (100.0 mg, 2.643 mmol) and Adm-SH (150.0 mg, 0.891 mmol) was immediately added all at once under vigorous stirring, accompanied by the solution color turn from red to dark. 25 min later, multi-sized Pd nanoclusters Pd x(PPh3)y(S-Adm)z were precipitated out and washed with excess methanol. The Pd x(PPh3)y(S-Adm)z nanoclusters were redissolved in toluene (10 mL) and water (5 mL) mixed solution and heated at 80 °C for 24 h. After this two-phase reaction was completed, the black organic solution was washed with methanol for three times. Pd8‒S was isolated from the crude product by preparative thin-layer chromatography (PTLC) in 10.0 mg (yield: 11%, based on the starting material Pd(CH3COO)2). Black single crystals suitable for X-ray diffraction analysis were obtained by slowly evaporating the mixture solution of Pd8‒S in DCM/methanol (4:3; 1 mL) for 3 days.

Synthesis of Pd8(PPh)2(PPh3)2(Ph2P=O)(S-Adm)5 (denoted as Pd8‒P)
Pd8‒S (3 mg, 1.16 × 10−3 mmol) and PPh3 (10.0 mg, 0.0381 mmol) were co-dissolved in 2 mL of toluene in a round-bottomed flask with continuous stirring and heated at 80 °C for over 2 weeks under air atmosphere. After the reaction was completed, the black solution was concentrated under reduced pressure to dryness. Pd8‒P was isolated from the crude product of 20 combined reaction batches by preparative thin-layer chromatography (PTLC) in 1.2 mg (yield: 2%, based on the starting material Pd8‒S). Black single crystals suitable for X-ray diffraction analysis were obtained by slowly evaporating the mixed solution of Pd8‒P in DCM/methanol (4:3; 1 mL) over 3 days.

Synthesis of Pd6(PPh)(PPh3)(S-Adm)6 (denoted as Pd6)
Pd(CH3COO)2 (50.0 mg, 0.223 mmol) and PPh3 (100.0 mg, 0.381 mmol) were co-dissolved in 8 mL of THF in a three-necked flask with continuous stirring for 5 min, accompanied by a solution color change from yellow to red. Then, a cold water solution containing NaBH4 (100.0 mg, 2.643 mmol) and Adm-SH (150.0 mg, 0.891 mmol) was immediately added all at once under vigorous stirring, accompanied by the solution color turn from red to dark. 10 min later, multi-sized Pd nanoclusters Pd x(PPh3)y(S-Adm)z (x, y, and z denote the number of the unit in a nanocluster, and x is larger than z) were precipitated out and washed with excess methanol. The Pd x(PPh3)y(S-Adm)z nanoclusters were redissolved in a toluene (10 mL) and water (5 mL) mixed solution and heated at 80 °C for 6 h (This process can turn the muti-sized Pd x(PPh3)y(S-Adm)z nanoclusters to narrowly distributed nanoclusters—size-focusing58. The use of a toluene/water mixed solvent can accelerate the size-focusing, possibly due to some hydrophilic byproducts that can migrate to the water phase, thus promoting the reaction. After this two-phase reaction was completed, the black organic solution was washed with methanol three times. Pd6 was isolated from the crude product by PTLC in 22.4 mg (yield: 30%, based on the starting material Pd(CH3COO)2). Black single crystals suitable for X-ray diffraction analysis were obtained by slowly evaporating the mixed solution of Pd6 in DCM/methanol (3:5; 1 mL) for 3 days.

Synthesis of Pd5(PPh)(S-Adm)4[(Ph2P)2O] (denoted as Pd5‒O)
Pd6 (3 mg, 1.49 × 10−3 mmol) and PPh3 (10.0 mg, 0.0381 mmol) were co-dissolved in 2 mL of toluene in a round-bottomed flask with continuous stirring and heated at 60 °C for over 2 weeks under air atmosphere After the reaction was completed, the black solution was concentrated under reduced pressure to dryness. Pd5‒O was isolated from the crude product of 20 combined reaction batches by PTLC in 1.5 mg (yield: 3%, based on the starting material Pd6). Black single crystals suitable for X-ray diffraction analysis were obtained by slowly evaporating the mixture solution of Pd5‒O in DCM/methanol (4:3; 1 mL) over 6 days.

Synthesis of Pd5(PPh)(S-Adm)4[(Ph2P)2CH2] (denoted as Pd5‒C)
Pd(CH3COO)2 (50.0 mg, 0.223 mmol) and DPPM (100.0 mg, 0.260 mmol) were co-dissolved in 8 mL of THF in a three-necked flask with continuous stirring for 5 min, accompanied by a solution color change from yellow to red. Then, a cold water solution containing NaBH4 (100.0 mg, 2.643 mmol) and Adm-SH (150.0 mg, 0.891 mmol) was immediately added all at once under vigorous stirring, accompanied by the solution color turn from red to dark. 30 min later, multi-sized Pd nanoclusters were precipitated out and washed with excess methanol. The precipitate was redissolved in toluene (10 mL) and water (5 mL), mixed solution and heated at 80 °C for 24 h. After this two-phase reaction was completed, the black organic solution was washed with methanol for three times. Pd5‒C was isolated from the crude product by PTLC in 9.8 mg (yield: 13%, based on the starting material Pd(CH3COO)2). Black single crystals suitable for X-ray diffraction analysis were obtained by slowly evaporating the mixed solution of Pd5‒C in DCM/methanol (5:4; 1 mL) over 5 days. Pd5‒C nanocluster could also be obtained by the ligand exchange reaction of Pd5‒O (3 mg, 1.77 × 10−3 mmol) and DPPM (10.0 mg, 0.026 mmol) in 2 mL of toluene and heated at 60 °C for 5 h under air atmosphere.

Note that, inverse palladocenes with planar aromatic Pd5 ring unit and unanticipated nonmental-to-metal aromatic Pd5 ring coordination are synthesized under aqueous-, oxygen-containing conditions and demonstrate remarkable stability in air atmosphere, distinctly differing from reported Pd clusters such as cubic Pd8(PAr)6 clusters59, planar Pd7 clusters60 and Pd4 clusters61 (which require strict anhydrous- and oxygen-free conditions for synthesis and most of them are sensitive to air atmosphere).

Construction of Pd nanoclusters/PS and Pd nanoclusters/PU composites
Pd nanoclusters (1 mg) and PS (100 mg) were co-dissolved in 1.5 mL of DCM and dropwise added into quartz grooves. After the volatilization of DCM, pressure was applied to the Pd nanoclusters/PS composites between two quartz sheets, and they were placed under reduced pressure in a vacuum oven for 12 h to fix their shape. To measure the PCE of Pd nanoclusters, the as-prepared Pd nanoclusters/PS films were shaped into 1 cm2 circular discs with a thickness of 0.20‒0.26 mm (detailed calculation procedures are provided in the Photothermal effects and efficiency calculation section of the Supplementary Information). The Pd nanoclusters/PU composites were constructed using a similar process as that for the Pd nanoclusters/PS composites; however, the PU needed to be dissolved in DMF instead of DCM at 90 °C for 12 h.

Characterization
All UV/Vis/NIR absorption spectra were acquired in the wavelength range of 190–1200 nm using a UV-2550 spectrophotometer. Electrospray ionization mass spectra (ESI‒MS) were recorded using a Waters Q-TOF mass spectrometer utilizing a Z-spray source. The sample was first dissolved in toluene (~0.5 g/L) and then diluted (2/1 v/v) with an ethanol solution containing 50 mmol of CsOAc. The sample was directly infused into the chamber at a flow rate of 5 μL/min. The source temperature was maintained at 70 °C, the spray voltage was 2.20 kV, and the cone voltage was adjusted to 60 V. The single crystal X-ray crystallography (SCXC) data of inverse palladocenes were collected using a Bruker D8 VENTURE CMOS PHOTON 100 diffractometer with a Helios MX multilayer monochromator using Ga Kα radiation (λ=1.34139 Å), while the (Ph2P=O) were collected using a XtaLAB Synergy R, HyPix four-circle diffractometer with a mirror monochromator using Cu Kα radiation (λ=1.54184 Å). 1H, 13C, and 31P NMR spectra were recorded with a Bruker Avance-400 spectrometer. The photoluminescence (PL) properties were recorded by a OmniFluo990 LSP using a xenon lamp as the excitation source under liquid nitrogen. X-ray photoelectron spectroscopy (XPS) was performed using a Thermo Scientific K-Alpha XPS spectrometer. Thermal gravimetric analysis (TGA) of Pd nanoclusters (~5 mg) was conducted in a N2 atmosphere (flow rate ~50 mL/min) on a TG/DTA 6300 analyzer (Seiko Instruments, Inc), with a heating rate of 10 °C/min. Scanning electron microscopy (SEM) characterization was carried out on a Hitachi SU8020 under an accelerating voltage of 10 kV. Transmission electron microscopy (TEM) characterization was carried out on a Tecnai G2 F20 under the accelerating voltage of 200 kV. Photothermal measurements were conducted using 980 nm (LSR980F-3W-FC), 1064 nm (LSR1064PD-3W-FC), and 1208 nm (LSR1208NL-1.5W-FC) lasers. The temperature was measured using a thermal imager infrared camera (Fotric 227S), with an error range of ±2.0 °C. Real-time temperatures and infrared photos were extracted from the video by FLIR tools software. Laser power was measured by HS1-USB 0516RI24U device with the software of Power Meter-USB. A conventional three-electrode system was used for differential pulse voltammetry (DPV) measurement. The saturated calomel electrode (SCE) (with saturated KCl solution) and carbon rods are used as a reference (RE) and counter electrode (CE), respectively. A Pt disk electrode (1 mm diameter) was used as working electrode (WE). The electrode potentials were controlled by a potentiostat (Zahner, Germen). The inverse palladocenes were dissolved in CH2Cl2/0.1 M Bu4NPF6 of that was constantly purged by N2 (99.99% Nanjing Special Gas Corp.) during the experiments. All electrochemical experiments were carried out at room temperature (ca. 25 °C).

Computational details
The geometry optimizations of the Pd5‒C, Pd5‒O, Pd6, Pd8‒S, and Pd8‒P inverse palladocenes were conducted by using density functional theory (DFT) with the ORCA 4.2.1 package62. The hybrid PBE0 functional and def2-SVP basis sets63,64 were adopted, where all-electron basis sets were used for H, C, P, and S atoms, while relativistic effective core potentials (RECP) with the associated valence basis set were applied for Pd atom. NBO 7.0 package65 was utilized to perform natural population analysis (NPA) and compute natural atomic orbitals (NAOs) for facilitating subsequent adaptive natural density partitioning (AdNDP)66 analyses. AdNDP analysis was calculated with Multiwfn 3.8 package67.

Atomic charge analyses, electron localization functions (ELF)68, and the energy decomposition analysis with natural orbitals for chemical valence (EDA-NOCV)69,70 calculations were performed with Perdew−Burke−Ernzerhof (PBE) functional based on single-point calculations by using ADF 2019.304 package71. The all-electron polarized triple-zeta (TZP) Slater-type basis sets were adopted for Pd atoms, and DZP Slater-type basis sets were adopted for other atoms72. The scalar relativistic (SR) effects were taken into account with the zero-order regular approximation (ZORA)73. Reduced density gradient (RDG)74,75 was calculated with the ORCA 4.2.1 package, in which the RDG curve was visualized by using Multiwfn 3.867 and VMD 1.9.3 software76. The isochemical shielding surfaces (ICSS) analysis was also performed with Multiwfn 3.8 software and visualized by VMD 1.9.3.

The Gibbs free energy calculations at T=298.15 K and P=1 atm were carried out by using PBE77 functional along with LANL2TZ ECP and basis set78,79 for Pd atoms, and all-electron basis set80,81 6–31G* for the rest of atoms. Vibrational frequency calculations were performed to obtain the thermal corrections over the quantum-mechanical energies. Based on the geometries optimized in the gas-phase, single-point calculations were further performed at the higher level of LANL2TZ(f)82 basis set for Pd atoms, and 6–311G*80,81 for the rest of atoms. Dispersion corrections were included in our calculations by employing the D3 version of Grimme’s dispersion with Becke-Johnson damping83. Solvent corrections using the SMD model84 were included by considering the reaction in toluene. All the calculations were performed using the Gaussian 16 package85 unless specified otherwise.

To better reproduce the experimental UV/Vis/NIR absorption spectrum, the simulation was carried out by using the Gaussian 16 package85 with the PBE77 functional for geometry optimization and TD‒DFT calculations. The ECP and basis set LANL2TZ78,79 were used for Pd atoms, and 6–31G* was used for others (H, C, S, and P)80,81. 200 singlet-to-singlet excitation energies were considered in the TD‒DFT calculations. The Kohn‒Sham molecular orbital analysis was performed by using Multiwfn 3.8 program67.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "You, Jiang, Zhao and colleagues report on the synthesis and properties of inverse palladocenes. This contribution follows\non the heels of https://doi.org/10.1002/anie.202313491 and essentially reports derivatization work (the Pd5 derivatives,\nrespectively), as the former manuscript also had already presented application for photothermal conversion in the NIR (850\nnm, yet lower efficiency) as well as detailed spectroscopy (XPS, XRD, detailed computations). From a synthetic chemist’s\nperspective, I hence consider the novelty rather low. Provided the editor judges the application section of sufficient impact to\nwarrant publication with Nat. Commun., I suggest the following revisions:\n1.) I struggled a lot to follow the manuscript. One issue is the excessive use of acronyms/substituents in text & figures, which\nobscures valuable information such as formal oxidation state, charge, etc. Another issue is imprecise language (e.g., PPh\nshould be referred to as a phosphinidene ligand, what do the authors mean with “the average charge state are …, indicating\nthe reduced state…”). NPA cannot assign an oxidation state (if that is what the authors mean), more informative would be an\nMO-diagram and/or computation of localized orbitals (e.g., NAOs) – how many d-electrons are in the cluster?; the MS section\nis quite long yet rather unimportant in sight of the scXRD data, etc.\n2.) I think the compounds should be put into context with Pd8(PAr)6 (https://doi.org/10.1002/advs.202400699) and\ncorresponding XPS data for Pd (and of course also P !). The authors assume (if I understandd right; and which could be also\nright) that PPh is a dianion, yet this other work substantiates a neutral charge? Generally, the work is not well embedded in\nthe field; e.g. (among various) why is Haytons planar Pd7 not mentioned\n(https://pubs.acs.org/doi/full/10.1021/acs.inorgchem.9b03276)? Or Crimmin’s Pd4\n(https://pubs.rsc.org/en/content/articlehtml/2019/sc/c9sc02750e)? The authors claim “a PCE of 15% per Pd, which is much\nhigher that that of previously reported materials”. Yet, what kind of materials are these? And what is their PCE? And so on…\n3.) The reaction profiles are confusing (stoichiometry is not balanced); please correct for one less significant digit. PBE-\nD3/631G* is not appropriate for computing energies (please add single points at higher level of theory).\n4.) The depiction of the phosphinidene with an arrow is confusing. It is a 4-electron donor (and not 2 electrons)\n5.) The TOC is overloaded for my taste\n6.) Fig. 5: The assignment of transitions is not clear (it should specified as MLCT/LMCT, pi-pi, etc.). Transition difference\ndensities would be much clearer. These seem NOT genuine HOMO-LUMO transitions (2.4 eV corresponds to 500 nm !)\n7.) Please give extinction coefficient in UV-Vis electronic absorption spectra.\n8.) UV-Vis, XPS spectra: Pick peaks\n9.) It would be great to better carve out structure-property relationships…\n10.) I did not get the point of Sncp -", "reviewer_2": "Metallocenes with layered structures have had a significant impact on the development of organometallic chemistry. In\nparticular, metallocenes with high catalytic activity and electrochemical redox ability play a very important role in their\napplications. This paper proposes a new group of compounds called \"Inverse palladocenes\", which are different from the\ngeneral \"palladocenes\", which are metallocenes based on palladium. These groups of materials have a high degree of\nnovelty in the fields of metal organic chemistry and cluster chemistry. Furthermore, these researches have already been\ninvestigated at a high level.\nMinor comments are shown below.\nComment 1\nWhat is the essential difference between Reference 15 (Angew. Chem. Int. Ed. 63, e202313491 (2024).) and this study?\nComment 2\nThere is a lack of information on the synthesis mechanism. What results would you get if the authors used a different\nthiolate? It is better to provide experimental evidence of the origin of (Ph2P)2O.\nComment 3\nIt is important to investigate the electronic state information in more detail. It is better to measure DPV or SWV.\nComment 4\nThe number of vibration intensities reproduced in the theoretical calculation for Fig. 5 seems to be too few. It would be better\nto try a more accurate calculation.\nComment 5\nThe experimental method is not explained enough. In particular, the reader does not know how the photothermal\nmeasurement was performed. Were inverse palladocenes supported on TiO2 used? Were inverse palladocenes mixed with\npolystyrene used?\nComment 6\nIs it possible to experimentally clarify the orientation dependence in the photothermal measurement using inverse\npalladocenes with a flat shape?\nComment 7\nIt is better to add the results of the comparison with reference materials in the calculation of PCE. How much PCE can be\nobtained with only polystyrene, only ligands, or only Pd precursors?\nComment 8\nThe shapes of the spectra in Fig.5a and S28 seem to be very different. Why does this difference occur? Is Pd5-C stable by\nlight?\nComment 9\nLooking at the TG results (Fig.S25), I think Pd5-C, Pd6, and Pd8-S are stable up to about 280°C. However, looking at the\nresults of the time-dependent temperature changes shown in Fig.S25, the temperature rises to a temperature higher than\ntheir decomposition temperatures. Can inverse palladocenes maintain their structure at such high temperatures?", "reviewer_3": "This manuscript presents a comprehensive study on the synthesis, characterization, and photothermal properties of a novel\nclass of Pd-based nanoclusters \"inverse palladocenes.\" The work is highly original and addresses an under-explored area\nin organometallic chemistry involving \"nonmetal-to-metal\" coordination and Pd aromaticity. The inverse palladocenes\ndemonstrate rigorous structural/electronic characterization and promising applications, particularly in photothermal\nconversion and laser shielding.\nThe study is in general well-organized and the major conclusions are supported by the results, which is suitable for the\naudience of Nature Communications. However, there are a few issues should be addressed:\n1. In Figure 4f, the RGD plot appears with many jagged edges, making it difficult to fully observe the π-π stacking interaction.\nWe kindly suggest considering an increase in the number of grid points to improve the visualization.\n2. Is there any electron transfer occurring between the phenyl group of the DPPM ligand and the nearby metal five-membered\nring? We kindly suggest calculating the orbital distribution based on the crystal structure to analyze the orbital or\nhole-electron distribution within the aggregate. Additionally, it may be helpful to calculate the electrostatic potential of\ninverse palladocycles for further analysis.\n3. Should the authors provide more details about the testing conditions for the absorption spectra of inverse palladocenes?\nFor instance, are the samples in the form of powder, thin films, or solutions? If the samples are in solution, it would be\ninteresting to explore how different polarities of solvents affect their absorption spectra. On the other hand, if the samples are\nin the form of powder or thin films, the author could investigate any differences in their absorption spectra under various\nconditions.\n4. The inverse palladocences synthesized by the author show diverse photothermal conversion capabilities. Referring to the\nJablonski energy level diagram, might a structure with relatively lower photothermal conversion efficiency exhibit\nphotoluminescence? If this material features near-infrared luminescence properties, its potential application could be greatly\nbroadened.\n5. The author noted that the photothermal conversion originates from the conjugation of the five-membered palladium\naromatic ring of inverse palladocences. However, we also observe five-membered palladium aromatic rings in Pd8 and Pd6.\nWhy Pd8 and Pd6 don't demonstrate sufficiently strong photothermal conversion capabilities?\n6. In the final paragraph of the article, the author mentions that Pd5-C encapsulated in polystyrene assist in the degradation\nof polystyrene at 368 °C. However, in supplementary figure 25, the Pd5-C decomposed at ~300 °C and reached a mass loss\nof 60% by ~50 °C. Considering this information, why the reaction might specifically occur at 368 °C?\n7. It is suggested to present the values involved in the PCE calculation in a table format for better clarity and organization.\n8. In which solution was the photothermal conversion tested (Figure 6a), water or toluene?"}, "author_response": "We thank the Editor and all the reviewers for their reading of the manuscript and helpful\nsuggestions. Below our po int-by-point response (or the words from the previous manuscript)\nis in blue, revisions (except for figures) are in red, and the page number mentioned in the\nmanuscript is referred to the version with revision marked.\nResponse to reviewer 1’ comments: pages 1-22\nResponse to reviewer 2’ comments: pages 22-37\nResponse to reviewer 3’ comments: pages 38-46\nReviewers’ comments:\nReviewer 1\nYou, Jiang, Zhao and colleagues report on the synthesis and properties of inverse\npalladocenes. This contribution follows on the heels of\nhttps://doi.org/10.1002/anie.202313491 and essentially reports derivatization work (the\nPd derivatives, respectively), as the former manuscript also had already presented\n5\napplication for photothermal conversion in the NIR (850 nm, yet lower efficiency) as\nwell as detailed spectroscopy (XPS, XRD, detailed computations). From a synthetic\nchemist’s perspective, I hence consider the novelty rather low. Provided the editor\njudges the application section of sufficient impact to warrant publication with Nat.\nCommun., I suggest the following revisions:\nResponse: Thank the reviewer for the comments. However, we are sorry for the\nevaluation “From a synthetic chemist’s perspective, I hence consider the novelty rather\nlow”, which is in strong contrast to the other two reviewers’ comments (see below).\nWe did synthesize the Pd (PPh) (PPh ) (S-Adm) (Pd –S for short) previously\n8 2 3 2 6 8\n(https://doi.org/10.1002/anie.202313491), which might indicate the emergence of a\nnovel type of material: inverse metallocene. However, we didn’t propose the concept\n“inverse metallocene” in that work since additional instances are required to validate a\nsingle case report. In particular, at that time it remained uncertain whether metal five-\nmembered ring structures analogous to the cyclopentadienyl anion (Cp) structure exist.\nHere we proposed the concept “inverse metallocene” and demonstrated that the five-\nmembered aromatic metal ring is a fundamental metal building block for inverse\nmetallocene by obtaining a series of new compounds using different methods, some of\nwhich are obviously different from the previous one as shown in Fig. 2a and\nSupplementary Fig. 2. For example, we synthesized Pd –O by a ligand-exchange\n5\nmethod starting from Pd , and we obtained Pd –C by two methods (one is the ligand-\n6 5\nexchange method, and the other is referred to the previous method but with the details\nmodified). Therefore, in term of synthesis, the current work is not a routine work as\n1\nstated by the reviewer.\nFor the photothermal study, this work has distinct differences with the previous\none as shown below: the longest laser irradiation wavelength was extended from the\nprevious 808 (not 850!) nm to 1208 nm, which is nontrivial for practical applications;\nthe high photothermal conversion efficiency (PCE) of 14.7% per metal atom was\nachieved, which considerably outperforms that for Pd –S and other reported materials\n8\nas displayed in Fig. 6c and Supplementary Table 9; a novel physical quantity—nominal\ncoplanar bond length standard deviation (S ) was introduced to evaluate the\nncp\nconjugation degree of inverse palladocenes and the conjugation-correlated photothermy\nwas revealed; importantly the application of photothermy was barely demonstrated in\nthe previous work except for simple imaging, here a lot of applications including laser\nshielding, high-temperature degradation, ignition and temperature control were\ndisplayed, demonstrating great potentials of inverse palladocenes for practical\napplications.\nExcept for the synthesis and photothermal investigations, we also performed\nstructure and optical property study and had some interesting findings in this work, for\nexample, it is found that single atom difference in the inverse palladocenes led to\ndramatic crystallographic arrangement change, and the nonmetal-aromatic ring to\nmetallo-aromatic-ring weak interactions existed in the crystal structure of Pd 5‒C.\nIn short, we have made great advances in the synthesis, structure, property and\nstructure-property correlation study of a novel type of materials, and we have further\nexpanded the application fields of this type of materials. Therefore, this work is not an\nessential derivatization report of the previous work, and its novelty should be\nreasonably evaluated.\nFig. 2a. The synthesis routes of Pd –P, Pd ‒O, and Pd –C.\n8 5 5\n8 5 5\nas their reaction equations (b).\nQuestion 1: I struggled a lot to follow the manuscript. One issue is the excessive use\nof acronyms/substituents in text & figures, which obscures valuable information such\nas formal oxidation state, charge, etc. Another issue is imprecise language (e.g., PPh\nshould be referred to as a phosphinidene ligand, what do the authors mean with “the\naverage charge state are…, indicating the reduced state…”). NPA cannot assign an\noxidation state (if that is what the authors mean), more informative would be an MO-\ndiagram and/or computation of localized orbitals (e.g., NAOs) – how many d-electrons\nare in the cluster? the MS section is quite long yet rather unimportant in sight of the\nSCXC data, etc.\nResponse: Thank the reviewer for the comments. We synthesized Pd (PPh)(S-\n4 2 2 2 5 5 4 2 2\nPd ‒O), Pd (PPh)(PPh )(S-Adm) (denoted as Pd ), Pd (PPh) (PPh ) (Ph P=O)(S-\n5 6 3 6 6 8 2 3 2 2\nAdm) (denoted as Pd ‒P), as well as Pd (PPh) (PPh ) (S-Adm) (denoted as Pd ‒S)\n5 8 8 2 3 2 6 8\nnanoclusters. The complete molecular formulas of these nanoclusters are explicitly\npresent in the Abstract, Introduction, and Methods sections. Additionally, their\nmolecular formulas are identified by ESI‒MS analysis within the “Characterization of\n3\ninverse palladocenes” section. By providing full molecular formulas upon first mention\nand using abbreviations thereafter, we ensure clarity regarding the compositions of the\nsynthesized materials while maintaining readability, consistent with standard scientific\npractice (abbreviated nanocluster formulas appear totally 295 times across the main text\nand Methods). Similarly, the oxidation states of palladium in these nanoclusters are\nthoroughly analyzed in the “Characterization of inverse palladocenes” section.\nTherefore, we don’t think that we intentionally obscure valuable information such as\nformal oxidation states, charges, or molecular formulas by using\nabbreviations/substituents in the text and figures.\nWe are sorry for some imprecise language in our manuscript, which have been\nmodified in the revised manuscript. The PPh have been modified to [PPh]2‒, denoting\nthe residual of PPh after the loss of two Ph groups. Also, S-Adm, and Ph P=O have\n3 2\nbeen modified to [S-Adm]− and [Ph P=O]−, respectively. We used Pd(CH COO) as the\n2 3 2\nPd precursor, in which the charge state of Pd is +2. The average charge states of Pd in\nPd –P, Pd , Pd ‒O, and Pd –C were calculated to be +1.25, +1.33, +1.2, and +1.2,\n8 6 5 5\nrespectively, thus it can be regarded that the Pd in all the inverse palladocenes is in a\nreduced state compared with that in the precursor Pd(CH COO) . That is what we mean\n3 2\nin the sentence “the average charge state are…, indicating the reduced state…”. We\ndidn’t mean that NPA can determine the oxidation state of Pd in various inverse\npalladocenes, and we provide them just for supporting the conclusion. Following the\nreviewer’s suggestion, we have provided additional MO data and discussion in the\nrevised manuscript as shown below. Given that Pd has a d10 electron configuration, the\nd-electron counts of Pd –S, Pd –P, Pd , Pd ‒O, and Pd –Care concluded to be 70, 70,\n8 8 6 5 5\n64, 44 and 44, respectively, on the basis of the charge state of Pd. MS is quite important\nfor the determination of precise composition, which not only provides verifications for\nthe SCXC data but also provides information (e.g. charge) sole SCXC can NOT afford,\nthus we give a detailed analysis of MS in the previous manuscript. Of course, we can\nshorten it if also required by the Editor due to the space limit.\nPages 6-7\n…Molecular orbital (MO) analysis verified the charge state of Pd in various inverse\npalladocenes. Taking Pd –C as an example, the revealed three empty MOs is consistent\n5\nwith the total charge state of its five Pd atoms (+6) (Supplementary Fig. 8)....\nSupplementary Figure 8. The 3d contour of the three unoccupied Kohn-Sham MOs\nfor Pd ‒C, derived from the in-plane Pd-4d atomic orbitals (AO). Note that due to the\n5\n4\nstrong metal-ligand orbital interaction, these three empty MOs also have unignorable\nligand components.\nQuestion 2: I think the compounds should be put into context with Pd (PAr)\n8 6\n(https://doi.org/10.1002/advs.202400699) and corresponding XPS data for Pd (and of\ncourse also P!). The authors assume (if I understand right; and which could be also right)\nthat PPh is a dianion, yet this other work substantiates a neutral charge? Generally, the\nwork is not well embedded in the field; e.g. (among various) why is Haytons planar Pd\n7\nnot mentioned (https://pubs.acs.org/doi/full/10.1021/acs.inorgchem.9b03276)? Or\nCrimmin’s Pd (https://pubs.rsc.org/en/content/articlehtml/2019/sc/c9sc02750e)? The\n4\nauthors claim “a PCE of 15% per Pd, which is much higher than that of previously\nreported materials”. Yet, what kind of materials are these? And what is their PCE?\nAnd so on…\nResponse: Thank the reviewer for the comments and so many questions. Inverse\npalladocenes represent a new type of materials, distinctly different from the mentioned\nclusters (Fig. R1). Therefore, we didn’t put them into context with the mentioned\nclusters in the previous manuscript. For clarity, we have added a discussion in the\nrevised manuscript as shown below. For the PCE data of various materials, we have\nprovided them in the previous manuscript, which are also copied below for the\nconvenience of the Editor and the reviewers.\nPages 25-26\n…Note that, inverse palladocenes with planar aromatic Pd ring unit and unanticipated\n5\nnonmental-to-metal aromatic Pd ring coordination are synthesized under aqueous-,\n5\noxygen-containing conditions and demonstrate remarkable stability in air atmosphere,\ndistinctly differing from reported Pd clusters such as cubic Pd (PAr) clusters56, planar\n8 6\nPd clusters57 and Pd clusters58 (which are sensitive to air atmosphere and require strict\n7 4\nanhydrous- and oxygen-free conditions for synthesis). Due to the exceptional stability\nof the inverse palladocenes, these novel materials provide great potentials for practical\napplications in common (aqueous-, oxygen-containing) conditions.…\nReferences\n8 6\n2400699 (2024).\nstabilized palladium nanocluster with a hexagonal aromatic Pd core. Inorg.\nSci. 10, 8083-8093 (2019).\n8 6 7\n(2020)), and Pd (d, Chem. Sci. 10, 8083–8093 (2019)).\nbetween various materials.\nLaser\nWavelength Temperature η\nSample State power Cycle Category\n(nm) changes (T) (%)\n(W/cm2)\naqueous\nAu NPs 2.4 514 2 °C in 6 min <10 NP nanoparticles\ndispersion\naqueous about 33 °C in six\nAu PBs 1.0 808 88.6 plasmonic\ndispersion 30 min cycles\naqueous about 31.5 °C six\nAu PBs 1.0 1064 80.8 plasmonic\ndispersion in 30 min cycles\naqueous about 26 °C in five\nAu NDs 0.4 1064 84.9 nanodumbbells\nsolution 5 min cycles\naqueous about 34.5 °C five\nAuNCs@SiO2 0.5 1064 82.2 nanochains\nsuspension in 5 min cycles\naqueous\nAu/TiO2 0.5 532 11.5 °C NP NP nanoparticles\nsolution\naqueous 40 °C in 10\nSi-GO 4.0 532 NP NP nanoparticles\nsolution min\naqueous\nNS-40 0.32 532 12 °C in 6 min 42.8 NP nanoparticles\nsolution\naqueous\nNS-60 0.32 532 9 °C in 6 min 30.6 NP nanoparticles\nsolution\naqueous 52 °C in 10\nAu NPs 0.34 532 62.9 NP nanoparticles\nsolution min\naqueous about 17.5 °C six\nGA-CuFeSe2 0.27 532 79.6 nanoparticles\nsolution in 10 min cycles\nAu NP-Packed\nsolid 0.15 532 220 °C in 2 s NP NP nanoparticles\nSpheres\nAuNP–mTHPC aqueous\n0.015 532 0.3 °C in 2 min NP NP nanoparticles\ncomplex solution\naqueous\nACA 1.3 532 10 °C in 6 min NP NP nanoparticles\nsolution\nthree inorganic\nGO solid 1.3 532 17 oC in 30 s NP\ncycles materials\n6\ntoluene\nAu37(CHT)23 0.25 650 12 oC in 5 min 30.3 NP nanoclusters\nsolution\ntoluene 17.2 oC in 5\nAu48(CHT)26 0.25 650 42.9 NP nanoclusters\nsolution min\naqueous 15−36.8 °C in three organic\nTNMs 1.0 660 41.0\nsolution 10 min. cycles materials\nchloroform 39.1 °C in 6 six\nAg155 0.1 660 NP nanoclusters\nsolution min cycles\ntoluene\nAu42 1.0 808 27 °C in 5 min. NP NP nanoclusters\nsolution\naqueous About 35.2 °C ten MOF-based\nUiO-66@PAN 1.5 808 21.6\nsolution in 10 min cycles materials\nfive MOF-based\nZr-PDI•– film 0.7 808 89 °C in 200 s 52.3\ncycles materials\nfour\nAg18 DMF 5.0 808 28 °C in 5 min NP nanoclusters\ncycles\nAg18 solid 0.35 808 337 °C in 4 s NP NP nanoclusters\nethylene 56.9 °C in 10\n(AgCu)31 1.0 532 67.6 NP nanoclusters\nglycol min cycles\naqueous about 46 °C in five\nIR-SS NPs 1.0 1064 77 small molecules\nsolution 5 min cycles\naqueous three\nPt@PDA-c 1.0 1064 27.5 71.3 nanoparticles\nsolution cycles\naqueous\nAu nanoshells 2.0 800 15 °C in 5 min 13 NP nanoparticles\ndispersion\naqueous\nAu nanorods 2.0 800 22 °C in 5 min 21 NP nanoparticles\ndispersion\naqueous\nCu2-xSe 2.0 800 22 °C in 5 min 22 NP nanoparticles\ndispersion\naqueous 15.1 °C in 10\nCu9S5 nanocrystals 0.51 980 25.7 NP nanoparticles\ndispersion min\naqueous 10.2 °C in 15\nCuS NPs NP 1280 93 NP nanodisks\ndispersion min\naqueous\nCuS nanoflakes NP 1064 NP 72 NP nanoflakes\nsolution\n29.3 °C in 3 three organic\nCPP film 2.33 808 42.5\nmin cycles materials\naqueous 33.6 °C in 500\nDpa-melanin CNSs 2.0 808 40 NP nanoparticles\nsolution s\nabout 23.5 °C\nCuO/Cu2O TNCs NP 0.3 808 73 NP nanocubes\nin 9 min\nabout 16 °C in\nCuO/Cu2O TNCs NP 0.3 1064 67 NP nanocubes\n9 min\nCuO/Cu2O TNCs NP 0.3 1550 about 25 °C in 78 NP nanocubes\n7\n9 min\naqueous 33.8 °C in 10 six\ndpGCS NCs 1.0 1064 71 nanocrystals\nsuspension min cycles\naqueous about 44 °C in five\nJanus-GCS NCs 1.0 1064 76.1 nanocrystals\nsolution 9 min cycles\naqueous 19.5 °C in 10 organic\nBPDI/(CB[7])2 1.0 808 31.6 NP\nsolutions min materials\naqueous 11.5 °C in 14 five MOF-based\nPMCS 2.0 808 33\ndispersion min cycles hybrid materials\nfree radical 34.1 °C in 17 six PDI-based\nPBI-[GD]2 1.0 808 59.5\nsolution min cycles radicals\nfree radical 27.7 °C in 22 six PDI-based\nPBI-[GY]2 1.0 808 49.1\nsolution min cycles radicals\n37 °C in 10 five organic\nDTC cocrystals 0.7 808 18.8\nmin cycles materials\naqueous five organic\ntfm-BDP NPs 0.3 808 54 °C in 5 min 88.3\ndispersion cycles nanoparticles\naqueous organic\nm-BDP 0.3 671 29 °C in 5 min 32 NP\ndispersion nanoparticles\naqueous organic\nH-BDP 0.3 671 20 °C in 5 min 50 NP\ndispersion nanoparticles\naqueous about 14.2 °C\nPd SAzyme 0.69 1064 33.9 NP nanoparticles\nsolution in 20 min\naqueous 35 °C in 15 six organic\nBAF4 NPs 0.75 1064 80\nsolution min cycles nanoparticles\nhexagonal\naqueous 20.7 °C in 10\npalladium 1.0 808 NP NP nanosheets\nsolution min\nnanosheets\naqueous 20.8 °C in 10\nSPNS 1.0 808 NP NP nanosheets\nsolution min\naqueous 23.2 °C in 10\nPNS–DOX 2.86 808 NP NP nanosheets\nsolution min\naqueous 35.3 °C in 10\nSPNS 1.0 808 52 NP nanosheets\nsolution min\naqueous 24.4 °C in 5 organic\nF-PANP 0.5 808 48.5 NP\nsolution min nanoparticles\naqueous 33.6 °C in 10 eight organic\nTPT–TT NPs 2.0 808 32\nsolution min cycles nanoparticles\naqueous 25 °C in 10 organic\nPPy NPs 1.0 808 44.7 NP\nsolution min nanoparticles\naqueous about 25 °C in organic\nPPY@PAA/fmSiO2 2.0 808 31.3 NP\nsolution 5 min nanoparticles\naqueous about 29 °C in twenty\nDA CNDs 1.5 808 35 nanodots\nsolution 5 min cycles\n8\naqueous 30.1 °C in 12\ncarbon dots 2.0 671 38.5 NP nanodots\ndispersion min\naqueous\nPEGylated Sb NPs 2.0 808 51 °C in 5 min 41 NP nanoparticles\nsolution\naqueous 18.5 °C in 5 five\nCys-CuS NPs 0.72 980 38 nanoparticles\nsolution min cycles\naqueous about 19 °C in six\nFe3O4@Cu2−xS 0.6 980 16 nanoparticles\ndispersion 10 min cycles\naqueous 19.9 °C in 13 ten\nGCNCs 0.5 808 40.4 nanocubes\ndispersion min cycles\naqueous 33.1 °C in five\nPt Spirals 1.2 1120 52.5 nanoparticles\nsolution 1000 s cycles\nPt/Te nano aqueous 33.4 °C in 8 five\n1.5 808 51.8 nanoparticles\nheterostructures solution min cycles\naqueous 30.0 °C in 10 five\nHA-Au@Pt 1.5 808 63.5 nanoparticles\nsolution min cycles\naqueous 38.2 °C in 30\nPorous Pt NPs 1.24 808 97.0 NP nanoparticles\nsolution min\naqueous 34.5 °C in 30\nPorous Pt NPs 1.24 980 89.9 NP nanoparticles\nsolution min\nBP/Pt-Ce6@PEG aqueous 19.8 °C in 10\n0.8 660 NP NP nanoparticles\nNSs solution min\nethylene 54.2 °C in 10 six\nPt23 1.0 532 68.4 nanoclusters\nglycol min cycles\ntoluene 32.8 °C in 7 eight inverse\nPd8‒S 0.5 808 73.3\nsolution min cycles palladocene\ntoluene\nPd8‒T 0.5 808 1.9 °C in 3 min 32.6 NP nanoclusters\nsolution\ninverse\nPd8‒P (this work) film 0.3 980 11.2 °C in 30 s 20.3 NP\npalladocene\ninverse\nPd8‒S (this work) film 0.3 980 11.6 °C in 30 s 24.1 NP\npalladocene\ninverse\nPd6 (this work) film 0.3 980 26.5 °C in 30 s 51.8 NP\npalladocene\ninverse\nPd5‒O (this work) film 0.3 980 37.5 °C in 30 s 68.1 NP\npalladocene\ninverse\nPd5‒C (this work) film 0.3 980 50.4 °C in 30 s 73.6\ncycles palladocene\ninverse\nPd5‒C (this work) film 0.3 1064 16.7 °C in 30 s 36.2 NP\npalladocene\ninverse\nPd5‒C (this work) film 0.3 1208 4.0 °C in 30 s 18.7 NP\npalladocene\nNP = Not Provided.\nconversion efficiency per basal-atom (η ) between various materials.\nbav\nWavelength\nSample η η\nbav\n(nm)\nAu (CHT) 650 30.3 0.82\n37 23\nAu (CHT) 650 42.9 0.89\n48 26\nTNMs 660 41.0 0.22\nZr-PDI•– 808 52.3 0.52\n(AgCu) 532 67.6 1.09\nCu S\n9 5\n980 25.7 1.84\nnanocrystals\nCPP 808 42.5 2.83\nBPDI/(CB[7]) 808 31.6 1.05\ntfm-BDP NPs 808 88.3 2.10\nm-BDP 671 32.0 0.82\nH-BDP 671 50.0 1.32\nBAF4 NPs 1064 80.0 1.11\nTPT–TT NPs 808 32.0 0.84\nPt 532 68.4 2.97\ncorrect for one less significant digit. PBE-D3/6-31G* is not appropriate for computing\nenergies (please add single points at higher level of theory).\nResponse: Thank the reviewer for the comments and constructive suggestions. We have\nfurther improved the reaction profile presentation to avoid possible confusion, and the\nbalanced stoichiometries were shown in revised Fig. 2a and Supplementary Fig. 2b. We\nhave also recalculated the energies by adding single points at higher level of theory:\nLANL2TZ (f) for Pd and 6-311G* for H, C, O, S, and P. However, the newly obtained\nresults showed minor differences compared with the previous ones, which have been\nshown below for the convenience of Editor and reviewers (Table R1). One less\nsignificant digit has been corrected for Gibbs free energies as shown in the revised Fig.\n10\n2b and the revised Supplementary Fig. 6.\nFig. 2a. The synthesis routes of Pd –P, Pd ‒O, and Pd –C.\n8 5 5\nSupplementary Figure 2. (a) The synthesis routes of Pd ‒P, Pd ‒O, and Pd ‒C as well\n8 5 5\n11\nas their reaction equations (b).\nTable R1. The comparison of single-point calculation results for inverse palladocenes.\nPd –C Pd ‒O Pd Pd –P Pd –S\n5 5 6 8 8\nainitial -3647.77 -3683.69 -4230.03 -5383.74 -5325.53\nsingle-point\nbhigher\n(Hartree) -3648.06 -3683.99 -4230.35 -5384.18 -5325.94\nlevel\nainitial: LANL2TZ basis set for Pd and 6-31G* for H, C, O, S, and P; bhigher level:\nLANL2TZ (f) for Pd and 6-311G* for H, C, O, S, and P.\nFig. 2b. DFT calculations of the Gibbs free energies during the transformation from\nPd to Pd ‒C.\n6 5\nSupplementary Figure 6 (previous 5). DFT calculation of the Gibbs free energies\nduring the transformation reactions from Pd ‒S to Pd –P inverse palladocenes.\n8 8\nPage 29\n…Based on the geometries optimized in the gas-phase, single-point calculations were\nfurther performed at the higher level of LANL2TZ (f)77 basis set for Pd atoms, and 6-\n311G*74,75 for the rest of atoms....\nbasis set exchange: An open, up-to-date resource for the molecular sciences\ncommunity. J. Chem. Inf. Model. 59, 4814-4820 (2019).\nQuestion 4: The depiction of the phosphinidene with an arrow is confusing. It is a 4-\nelectron donor (and not 2 electrons).\nResponse: Thank the reviewer for the comment. The arrow just indicated the electron\ndenoting direction, and it didn’t reflect the detailed electron count. We have changed it\nto dash arrow to avoid possible misunderstanding.\nQuestion 5: The TOC is overloaded for my taste.\nResponse: Thank the reviewer for the comment, and we have slightly simplified the\nTOC as shown below.\nThe previous TOC\nQuestion 6: Fig. 5: The assignment of transitions is not clear (it should specify as\nMLCT/LMCT, pi-pi, etc.). Transition difference densities would be much clearer. These\nseem NOT genuine HOMO→LUMO transitions (2.4 eV corresponds to 500 nm !)\nResponse: Thank the reviewer for the comment. Our transition assignments are based\non orbital contributions to excited states, a standard practice in the metal nanocluster\nfield (see Science 383, 326–330 (2024); Nat. Commun. 15, 7214 (2024); Nat. Chem. 15,\n940–947 (2023); J. Am. Chem. Soc. 144, 12381−12389 (2022). etc.).\nThe metal-to-ligand charge transfer (MLCT)/ligand-to-ligand charge transfer\n(LMCT) or π–π assignments are not very applicable to our nanocluster system due to\nits multiple metal centers and structural asymmetry. Taking Pd ‒C as an example,\n5\neffective (sole) MLCT/LMCT assignment failed as shown in the Supplementary Tables\n5 and 6. For the detail assignments, please see the Supplementary Discussion section in\nthe revised Supplementary Information, which are also copied below.\nPage S30\n...Transitions assignments of Pd ‒C by MLCT/LMCT\nwas applied to assign the transitions of Pd ‒C. As shown in Supplementary Table 5, we\n5\nfirst defined equivalent units within Pd ‒C for MLCT/LMCT analysis of the 945 nm\n5\nexcitation. However, effective MLCT/LMCT assignment failed. We then reclassified\nthe system into Pd , [S-Adm]–, [PPh]2–, and DPPM as integral fragments. As shown in\n5\ntransfer from fragment 1 to fragment 2 (0.17669 electron for MLCT and 0.20782\nelectron for LMCT). Additionally, intrafragment electron redistribution such as metal-\n14\ncentered (MC) and ligand-centered (LC) features significantly contribute to this\nexcitation (0.21122 electron for MC and 0.17385 electron for LC)....\nSupplementary Table 5. MLCT/LMCT analysis of Pd ‒C at 945 nm excitation (7\n5\nfragments were defined based on equivalent metals and ligands).\nelectron electron acceptor\ndonor 1 2 3 4 5 6 7\n1 0.00835 0.01584 0.01373 0.01603 0.01569 0.00005 0.00578\n2 0.03066 0.05819 0.05042 0.05887 0.05763 0.00019 0.02121\n3 0.00749 0.01422 0.01232 0.01438 0.01408 0.00005 0.00518\n4 0.02048 0.03887 0.03368 0.03932 0.03850 0.00013 0.01417\n5 0.02527 0.04796 0.04156 0.04852 0.04750 0.00016 0.01749\n6 0.00715 0.01358 0.01176 0.01373 0.01345 0.00004 0.00495\n7 0.00183 0.00348 0.00301 0.00352 0.00345 0.00001 0.00127\nSupplementary Table 6. MLCT/LMCT analysis of Pd ‒C at 945 nm excitation (4\n5\nfragments were defined based on metal and ligand types).\nElectron acceptor\nElectron donor\n1 2 3 4\n1 0.21122 0.17669 0.00029 0.03217\n2 0.20782 0.17385 0.00028 0.03166\n3 0.03249 0.02718 0.00004 0.00495\n4 0.00833 0.00697 0.00001 0.00127\nTo clearly elucidate the transition difference densities, we also carried out a charge\ndifference density analysis of the Pd ‒C during its transition from the ground state to\n5\nthe excited state. Details are shown in the Supplementary Discussion section of the\nrevised Supplementary Information, which are also copied below for the convenience\nof Editor and reviewers.\n...we carried out a charge difference density analysis of Pd ‒C during its transition from\n5\nthe ground state to the excited state as shown in Supplementary Fig. 33. The analysis\nreveals that during the excitation process, electron transfer mainly occurs within the\nmetallic Pd aromatic ring and partially involves those between Pd and the [SCH ]‒\n5 3\nligands....\nSupplementary Figure 33. Transition difference density analysis of Pd ‒C (electron\n5\ntransfer from ground state to excited state). Violet mesh indicates positive transition\ndifference density, while cyan mesh symbols negative transition difference density,\nisovalue = 0.002.\nThe relatively large HOMO-LUMO gap is probably caused by the use of PBE0\nfunctional (with 25% Hartree-Fock (HF) exchange, see Methods for calculation details).\nNote that, a higher HF fraction in the functional generally leads to a larger HOMO-\nLUMO gap. In the revised manuscript, we compared the calculation results obtained by\nseparately using PBE (0% HF) and PBE0 (25% HF) functionals for Pd ‒C.\nled to a deviated absorption spectra while an essentially decreased HOMO-LUMO gap of\n1.09 eV. To better reproduce the experimental spectra, we used PBE0 functional for\nTD‒DFT calculation in our manuscript.\n5\nnanocluster by separately using the PBE functional (with 0% Hartree-Fock (HF)\nexchange) and the PBE0 functional (with 25% HF exchange). (a) Comparison of NIR\nabsorptions of Pd ‒C separately reproduced by PBE and PBE0 functionals. (b)\ngaps for Pd ‒C separately derived from PBE and PBE0 functionals.\nResponse: Thank the reviewer for good suggestion, and we have added the information\nin the revised Supplementary Fig. 26 as shown below.\nSupplementary Figure 26. UV/Vis/NIR absorption spectra at different concentrations\n17\n(in toluene) and extinction coefficients of the main peaks for Pd ‒C (a), Pd ‒O (b), Pd\n8 5 6\n(c), and Pd ‒P (d), respectively.\nResponse: Thank the reviewer for good suggestion, and we have picked the peaks in\nthe mentioned spectra as shown below.\nFig. 2. (g–j) XPS analysis of Pd(3d) and NPA charge states of Pd for Pd –P, Pd , Pd ‒\n8 6 5\nO, and Pd ‒C, respectively.\nSupplementary Figure 9 (previous 7). XPS spectra of Pd –P. (a) Survey spectrum of\n8\n8 8\nrespectively.\nSupplementary Figure 10 (previous 8). XPS spectra of Pd . (a) Survey spectrum of\n6 6\nrespectively.\nSupplementary Figure 11 (previous 9). XPS spectra of Pd –O. (a) Survey spectrum\n5\nof Pd –O. (b–d) High-resolution XPS spectra of Pd –O for Pd(3d), S(2p), and P(2p),\n5 5\nrespectively.\n5\nof Pd ‒C. (b–d) High-resolution XPS spectra of Pd ‒C for Pd(3d), S(2p), and P(2p),\n5 5\nrespectively.\nSupplementary Figure 26. UV/Vis/NIR absorption spectra at different concentrations\n(in toluene) and extinction coefficients of the main peaks for Pd ‒C (a), Pd ‒O (b), Pd\n8 5 6\n(c), and Pd ‒P (d), respectively.\nResponse: Thank the reviewer for the suggestion, and we have further clarified the\nstructure-property relationships in the Conclusion section as shown below:\n...We introduced a new physical quantity, the nominal coplanar bond length standard\ndeviation (S ), to evaluate the conjugation degree of inverse palladocenes and\nncp\nrevealed conjugation‒photothermy correlation: the photothermal conversion\nefficiencies of inverse palladocenes increase with the conjugation degree increase. We\nalso found that the NIR absorption peak position and intensity positively correlate with\nconjugation degree for the series of inverse palladocenes....\nQuestion 10: I did not get the point of S .\nncp\nResponse: S is a newly introduced physical quantity to quantitatively assess the\nncp\nconjugated degree of the series of inverse palladocenes, given the consideration of co-\nplanarity. Taking Pd ‒C as an example, the nominal coplanar Pd–Pd bond length\n5\nstandard deviation (S\nncp\n) in Pd\n5\nstandard ring formed by projecting composed of Pd1a,\nPd2a, Pd3a, Pd4a and Pd5a (Supplementary Table 2) was calculated on the basis of the\nfollowing equation.\n∑ (𝑥 −𝑥̅)2\nS = √ 𝑖 𝑖\nncp 𝑁−1\nThe detail calculation process was shown below:\nSupplementary Table 2. The Pd–Pd bond lengths of original and standard Pd ring,\n5\nand the calculation of nominal coplanar Pd–Pd bond length standard deviations (S )\nncp\nfor Pd ‒C, Pd –O, Pd , Pd ‒S, and Pd –P, respectively.\n5 5 6 8 8\nDistance (Å)\nPd ‒S Pd ‒P\n8 8\nPd ‒C Pd ‒O Pd\n5 5 6\nPd (1) Pd (2) Pd (1) Pd (2)\n5 5 5 5\nPd1–Pd2 2.79 2.79 3.05 2.60 2.60 2.60 2.63\nPd2–Pd3 2.64 2.65 2.66 2.62 2.62 2.61 2.60\nPd3–Pd4 2.60 2.61 2.57 2.76 2.76 2.74 2.73\nPd4–Pd5 2.60 2.60 2.58 2.73 2.73 2.72 2.72\nPd5–Pd1 2.66 2.67 2.66 2.63 2.64 2.65 2.64\nPd1a–Pd2a 2.79 2.79 3.05 2.60 2.60 2.60 2.63\nPd2a–Pd3a 2.64 2.65 2.66 2.62 2.62 2.61 2.60\nPd3a–Pd4a 2.60 2.60 2.56 2.26 2.34 2.19 2.21\nPd4a–Pd5a 2.60 2.59 2.57 2.24 2.32 2.17 2.20\nPd5a–Pd1a 2.66 2.67 2.66 2.63 2.64 2.65 2.64\nncp\n∑ (𝑥 −𝑥̅)2\nS = √ 𝑖 𝑖\nncp 𝑁−1\nWhere 𝑥 is the Pd–Pd bond length of standard Pd ring, 𝑥̅ is the average Pd–Pd bond\n𝑖 5\nlength of original Pd ring, N is the number of the Pd–Pd bonds. The calculated 𝑥̅ of\n5 5 6 8 8\nrespectively, and the S of Pd ‒C, Pd –O, Pd , Pd ‒S, and Pd –P are accordingly 0.078,\nncp 5 5 6 8 8\n0.080, 0.201, 0.266, and 0.333, respectively, indicating the conjugation degree order of\nPd ‒C > Pd ‒O > Pd > Pd ‒S > Pd –P (from largest to smallest).\nReviewer 2:\nMetallocenes with layered structures have had a significant impact on the development\nof organometallic chemistry. In particular, metallocenes with high catalytic activity and\nelectrochemical redox ability play a very important role in their applications. This paper\nproposes a new group of compounds called “Inverse palladocenes”, which are different\nfrom the general “palladocenes”, which are metallocenes based on palladium. These\ngroups of materials have a high degree of novelty in the fields of metal organic\nchemistry and cluster chemistry. Furthermore, these researches have already been\ninvestigated at a high level.\nMinor comments are shown below.\nResponse: We thank the reviewer for highly positive comments.\nQuestion 1: What is the essential difference between Reference 15 (Angew. Chem. Int.\nEd. 63, e202313491 (2024).) and this study?\nResponse: Thank the reviewer for the question. We did synthesize the\nPd (PPh) (PPh ) (S-Adm) (Pd –S for short) nanocluster previously (Angew. Chem. Int.\n8 2 3 2 6 8\nEd. 63, e202313491 (2024)), which might indicate the emergence of a novel type of\nmaterial: inverse metallocene. However, we didn’t propose the concept “inverse\nmetallocene” in that work since additional instances are required to validate a single\ncase report. In particular, at that time it remained uncertain whether metal five-\nmembered ring structures analogous to the cyclopentadienyl anion (Cp) structure exist.\nHere we proposed the concept “inverse metallocene” and demonstrate that the five-\nmembered aromatic metal ring is a fundamental metal building block for inverse\nmetallocene by developing synthesis methods and synthesizing a series of new\ncompounds. Therefore, one point of this work is that it declares the birth of a novel type\nof materials with fundamental study values and great application potentials. There are\nsome other essential differences between the two works as summarized below:\ni) the longest laser irradiation wavelength was extended from the previous 808 nm\nto 1208 nm, which is nontrivial for practical applications, and the high\nphotothermal conversion efficiency (PCE) of 14.7% per metal atom was\nachieved in this work, which considerably outperforms that for Pd ‒S and other\n8\nreported materials as displayed in Fig. 6c and supplementary Table 9;\n22\nii) a novel physical quantity—nominal coplanar bond length standard deviation\n(S ) was introduced to evaluate the conjugation degree of inverse palladocenes\nncp\nand the conjugation-correlated photothermy was revealed in this work; it is also\nfound that the NIR absorption peak position and intensity positively correlate\nwith conjugation degree for the series of inverse palladocenes;\niii) the application of photothermy was greatly extended to a large range of fields\nincluding laser shielding, high-temperature degradation, ignition and\ntemperature control in this work, demonstrating great potentials of inverse\npalladocenes for practical applications;\niv) the nonmetal-aromatic ring to metallo-aromatic-ring weak interaction was\nfound in the crystal structure of Pd ‒C, which was not previously reported;\n5\n...\nIn short, we have made great advances in the synthesis, structure, property and\nstructure-property correlation study of a novel type of materials, and we have further\nexpanded the application fields of this type of materials. Therefore, this work is\nessentially different from the previous work, and its novelty, significance and impact\nare nontrivial.\nQuestion 2: There is a lack of information on the synthesis mechanism. What results\nwould you get if the authors used a different thiolate? It is better to provide experimental\nevidence of the origin of (Ph P) O.\n2 2\nResponse: Thank the reviewer for the comment and questions. Basing on our results\nand the previous reports (Chem. Rev. 85, 171‒185 (1985); Inorg. Chem. 32, 1662‒1670\n(1993)), we have proposed a plausible mechanism for the direct synthesis of Pd ‒C\n5\nusing DPPM and Adm-SH as ligands (see the Supplementary Discussion section of the\nrevised Supplementary Information), which are also copied below for the convenience\nof the Editor and the reviewers.\nPage S28\n…Proposed mechanism for the Pd ‒C Formation1,2\n5 2\n[Pd(DPPM)(OAc) ] (1). Next, [BH₄]⁻ from NaBH₄ replaces [AcO]⁻ in the intermediate\n2 n\n1, generating intermediate 2. Activated B-bound hydrogens then cleave the P‒C bond,\nreleasing benzene and forming intermediate 3. Additional reaction of 3 with [BH₄]⁻\nleads to another [AcO]⁻ substitution to yield 4. Subsequently, six-membered ring P–C\nactivation in 4 triggers the departure of Ph PCH , producing intermediate 5, which\n2 3\ncontains [PhP]2‒—a critical species for inverse palladocene nanocluster formation.\nConcurrently, [Adm-S-B(OH) ]‒Na+ (derived from Adm-SH + NaBH₄) reacts with 1 to\n3\nform intermediate 6, which further interacts with 5 to yield the Pd ‒C precursor,\n5\nfollowed by a size-focusing to provide Pd –C finally.…\n5\nits relevance to homogeneous catalyst deactivation. Chem. Rev. 85, 171-185\n(1985).\npotential models for M X (010) and M (100) surfaces. Synthesis and\n2 4\nspectroscopic and structural characterization of M (CO) (μ -PPh) (M =\n4 13 3\nruthenium, osmium). Pyramidal clusters with M P square faces. Inorg. Chem.\n3\n32, 1662-1670 (1993).\nThe transformation mechanisms from Pd ‒S to Pd ‒P and from Pd to Pd ‒O have\n8 8 6 5\nbeen detailed in the Supplementary Figs. 3 and 4, respectively, as shown below:\n8 8\nP.\nSupplementary Figure 4. A plausible pathway for the transformation of Pd to Pd –O\n6 5\nand Pd ‒C.\nin the revised manuscript as shown below:\nPage 5\n…The thiolate type influences the final products due to the space and electronic effects.\nAmong the investigated thiolates, only 1-adamantanethiol led to the production of Pd –\nSupplementary Fig. 5.…\nSupplementary Figure 5. The product illustration on the PTLC plates when various\nthiols were used in the synthesis of Pd –C: (a) 1-adamantanethiol; (b)\n5\ntriphenylmethanethiol, 2-phenylethanethiol, benzenemethanethiol, cyclohexanethiol,\n4-tert-butylphenylthiol, or 2,4-dimethylbenzenethiol.\n(Ph P) O is volatile and difficulty to be isolated, but its existence and protecting\n2 2\nrole for Pd –O can be verified by an indirect experiment. We have added “Metal salt\n5\nreduction method for the synthesis of Pd ‒O” section in the revised Supplementary\nPages S28-29\n... Metal salt reduction method for the synthesis of Pd ‒O\n5\n26\nyield via using Ph PH(=O) and Ph PCl as P ligand precursors (which can react and\n2 2\nproduce the protecting (Ph P) O ligand3). Specifically, Pd(CH COO) (50.0 mg, 0.223\n2 2 3 2\nmmol) and Ph PH(=O) (50.0 mg, 0.247 mmol) were co-dissolved in 8 mL of THF in a\n2\nthree-necked flask with continuous stirring for 5 min. Then Ph PCl (60.0 mg, 0.272\n2\nmmol) and Et N (25 mg, 0.247 mmol) were added, accompanied with a solution color\n3\nchange from yellow to red. 10 min later, a cold water solution containing NaBH (100.0\n4\nmg, 2.643 mmol)and Adm-SH (150.0 mg, 0.891 mmol) was immediately added all at\nonce under vigorous stirring. 30 min later, multi-sized Pd nanoclusters were\nprecipitated out and washed with excess methanol. The precipitates were redissolved\nin toluene (10 mL) and water (5 mL) mixed solution and heated at 80 °C for 12 h. After\nthis two-phase reaction was completed, the dark yellow organic solution was washed\nwith methanol for three times. Pd ‒Owas isolated from the crude product by PTLC in\n5\n10% yield....\nSupplementary Figure 45. Synthesis of Pd ‒O with different P precursors. (a) Images\n5\nof the reaction solution and PTLC plates with Ph PH(=O) and Ph PCl (1), or (Ph P=O)\n2 2 2 2\n(2) as the P precursor. (b) Detailed reaction routes in the above mentioned two cases.\nNote: “X” on the arrow indicates that the reaction is inhibited.\n2 2\nat the 30% probability level. Orange denotes P, gray denotes C, light gray denotes H.\nSupplementary Figure 50. 1H NMR spectrum of as-synthesized (Ph P=O) (400 MHz,\n2 2\nCDCl , 25 oC). δ [ppm] 7.39 (t, J = 7.6 Hz, 8H, H-Ar), 7.49 (t, J = 7.4 Hz, 4H, H-Ar),\n3\n7.92 (q, J = 6.3 Hz, 8H, H-Ar).\n2 2\nCDCl , 25 oC). δ [ppm] 128.7 (t, J = 5.9 Hz), 129.7 (t, J = 51.3 Hz), 131.9 (t, J = 5.3\nSupplementary Figure 52. 31P NMR spectrum of as-synthesized (Ph P=O) (100 MHz,\n2 2\nCDCl , 25 oC). δ [ppm] 24.2 (s, 2P).\n3\nIt is better to measure DPV or SWV.\nResponse: Thank the reviewer for the suggestion, and following the reviewer’s\nsuggestion we have provided the DPV data and discussion in the revised manuscript as\nshown below.\nPages 12-13\n…The use of PBE functional (with the basis set as PBE0) led to a deviated absorption\nspectra while an essentially decreased HOMO-LUMO gap of 1.09 eV (Supplementary\nFig. 31), which is consistent with the measured electrochemical gap of 1.60 V (taking\nPd ‒C as an example). Of note, the series of inverse palladocenes have close DPV\n5\nprofiles and electrochemical gaps with 1.63, 1.59, 1.69 and 1.68 V for Pd ‒O, Pd ‒S,\n5 8\nPd and Pd ‒P, respectively (Supplementary Fig. 32), providing further support for the\n6 8\nexistence of metal building block — five-membered aromatic metal ring, which plays\nthe functional group-like53 role.…\nPages 27-28\n...A conventional three-electrode system was used for differential pulse voltammetry\n(DPV) measurement. The saturated calomel electrode (SCE) (with saturated KCl\nsolution) and carbon rods are used as a reference (RE) and counter electrode (CE),\nrespectively. A Pt disk electrode (1 mm diameter) was used as working electrode (WE).\nThe electrode potentials were controlled by a potentiostat (Zahner, Germen). The\ninverse palladocenes were dissolved in CH Cl /0.1 M Bu NPF that was constantly\n2 2 4 6\npurged by N (99.99% Nanjing Special Gas Corp.) during the experiments. All\n2\nelectrochemical experiments were carried out at room temperature (ca. 25 oC)....\nReference\n57, 15450-15454 (2018).\n5 5 6 8 8\nin degassed CH Cl containing 0.1 M Bu NPF with 1 mm diameter Pt working, SCE\n2 2 4 6\nreference, and carbon rod counter electrodes.\nQuestion 4: The number of vibration intensities reproduced in the theoretical\ncalculation for Fig. 5 seems to be too few. It would be better to try a more accurate\ncalculation.\nResponse: Thank the reviewer for the suggestion. We initially employed 200\nexcitations for reproduction of absorption spectra. Following the reviewer’s suggestion,\nwe have improved the excitation number from 200 to 600, updated the data in Fig. 5a\n(Pd ‒C), Supplementary Figs. 28a (Pd ‒O, the previous Supplementary Fig. 21a), 29a\n5 5\n(Pd , the previous Supplementary Fig. 22a), and 30a (Pd ‒P, the previous\n6 8\nSupplementary Fig. 23a), and made corresponding adjustments to the “Computational\ndetails” section in the revised manuscript. Additionally, the reproduced spectra\ncomparison under 200 vs. 600 excitations was provided in the revised Supplementary\nFig. 47, which reveals that the additional excitations predominantly contribute to\nspectral reproduction below 260 nm (purple region) as shown below.\n5\n‒\nC (a), Pd –O (b), Pd (c), and Pd ‒P (d) using various excitations (200 vs. 600). Note:\n5 6 8\nthe green regions correspond to spectra reproduced with 200 excitations, while the\npurple regions highlight the absorption increment reproduced by additional 400\nexcitations.\nQuestion 5: The experimental method is not explained enough. In particular, the reader\ndoes not know how the photothermal measurement was performed. Were inverse\npalladocenes supported on TiO used? Were inverse palladocenes mixed with\n2\npolystyrene used?\nResponse: Thank the reviewer for the criticism and questions. We did many\nphotothermal measurements under various conditions (including the use of TiO or\n2\npolystyrene for support or dispersion of inverse palladocenes in some cases). We are\nsorry for bringing confusion to the reviewer. We further clarified them or provided more\n32\ndetails in the revised manuscript as shown below.\nPage 26\n…To measure the PCE of Pd nanoclusters, the as-prepared Pd nanoclusters/PS films\nwere shaped into 1 cm2 circular discs with a thickness of 0.20‒0.26 mm (detailed\ncalculation procedures are provided in the “Photothermal effects and efficiency\ncalculation” section of the Supplementary Information).…\nPages 39-40\nFig. 6. Photothermal conversion performance of inverse palladocenes. (a) Time-\ndependent images of Pd ‒C, Pd ‒O, Pd , and Pd –P solutions (80 μg/mL, 0.5 mL of\n5 5 6 8\ntoluene) upon laser irradiation (980 nm, 0.5 W/cm2) followed by a cooling period. (b)\nPCEs of different materials upon 980 nm laser irradiation. (c) Average PCE per Pd atom\nfor Pd ‒C, Pd ‒O, Pd , and Pd –P. (d) Peak temperatures of Pd ‒C solutions (0.5 mL,\n5 5 6 8 5\ntoluene) with different concentrations upon laser irradiation (980 nm, 0.5 W/cm2). (e)\nEight photothermal conversion cycles of Pd ‒C solution upon laser irradiation (980 nm,\n5\n0.5 W/cm2) with different concentrations (40 and 80 μg/mL, 0.5 mL of toluene). (f)\nTemperature change of Pd ‒C solution (80 μg/mL, 0.5 mL of toluene) upon 0.5 W/cm2\n5\nlaser irradiation with different wavelengths (980, 1064, and 1208 nm)....\nPage S24\nSupplementary Figure 38 (previous 28). UV/Vis/NIR absorption spectra of Pd ‒C\n5\nsolution (80 μg/mL, toluene) upon laser irradiation (980 nm, 0.5 W/cm2) before and\nafter eight photothermal conversion cycles.\nPage S25\nSupplementary Figure 39 (previous 29). Time-dependent temperature changes of\nPd ‒C solution (0.5 mL, toluene) in different concentrations at 1064 nm (a) and 1208\n5\nnm (b) laser irradiation (0.5 W/cm2).\nQuestion 6: Is it possible to experimentally clarify the orientation dependence in the\nphotothermal measurement using inverse palladocenes with a flat shape?\nResponse: Thank the reviewer for the question. So far we didn’t achieve success in\nexperimentally clarifying the orientation dependence in the photothermal measurement\nof planar inverse palladocenes due to both measurement and handling difficulty at such\na small size scale.\nQuestion 7: It is better to add the results of the comparison with reference materials in\nthe calculation of PCE. How much PCE can be obtained with only polystyrene, only\nligands, or only Pd precursors?\nResponse: Thank the reviewer for the suggestion, and we have provided the data in the\nrevised Supplementary Information as shown below.\nSupplementary Table 7. The PCE comparison between inverse palladocenes and some\n33\nassociated substances.\nsample Wavelength m T T η\ni surr max\nIntensity (a.u.) lnθ\n(nm) (mg) (oC) (oC) (%)\n980 25.5 0.74576 20.1 70.5 11.07 73.6\nPd ‒C 1064 25.5 0.36835 19.7 36.4 7.63 36.2\n5\n1208 25.5 0.13736 19.4 23.4 7.47 18.7\nPd ‒O 980 23.4 0.38041 21.4 58.9 8.20 68.1\nAdm-SH 980 24.1 0.00310 20.4 20.6 ‒ ‒\nDPPM 980 25.8 0.00552 20.1 20.4 ‒ ‒\nPd(OAc) 980 26.1 0.03117 20.6 21.0 ‒ ‒\nuniformly (1% wt) with the basal area of 1 cm2 and thickness of 0.20‒0.26 mm, which\nis placed in the air and fixed by a needle for the measurement. Power density = 0.3\nW/cm2.\nQuestion 8: The shapes of the spectra in Fig. 5a and Supplementary Fig. 28 seem to be\nvery different. Why does this difference occur? Is Pd ‒C stable by light?\nattributed to the inconsistence of wavelength and absorbance ranges in the two figures,\nwhich was confirmed by the restructuring as shown in Fig. R2. Pd ‒C is stable under\n5\nthe light, and we have provided additional information in the revised manuscript as\nshown below.\nPage 10\n…The series of compounds not only show environmental stability (water- and oxygen-\nresistant during the synthesis and use), but also exhibit rather thermostability and\nphotostability (Supplementary Figs. 19 and 20), providing experimental support for\ntheir aromaticity....\n5\nsupplementary Fig. 39 (b) with the same axis range.\nSupplementary Figure 38 (previous 28). UV/Vis/NIR absorption spectra of Pd ‒C\n5\nsolution (80 μg/mL, toluene) upon laser irradiation (980 nm, 0.5 W/cm2) before and\nafter eight photothermal conversion cycles.\nSupplementary Figure 20. UV/Vis/NIR spectra monitors the stability of Pd ‒C under\n5\nthe sunlight (dissolved in toluene).\n5 6\nand Pd ‒S are stable up to about 280 oC. However, looking at the results of the time-\n8\ndependent temperature changes shown in Supplementary Fig. 31, the temperature rises\nto a temperature higher than their decomposition temperatures. Can inverse\npalladocenes maintain their structure at such high temperatures?\nResponse: Thank the reviewer for the question. No, inverse palladocenes can NOT\nmaintain their complete structure at such high temperatures. However, they might\nmaintain the Pd P or Pd P framework structures with almost unchanged photothermal\n5 8 2\nperformances, evidenced by the accurate evaluation of their mass losses in TG\nexperiments (see the previous Supplementary Fig. 25) as well as the photothermal\ninvestigation after the ligand removal (see the previous Supplementary Fig. 26). In\nanother word, these inverse palladocenes can almost maintain their photothermal\nperformance even if the ligands were removed.\nSupplementary Figure 35 (previous 25). TGA of Pd ‒C, Pd , and Pd ‒S. Note: based\n5 6 8\non the weight loss, it is concluded that Pd P or Pd P might be the final product after\n5 8 2\nheated to over 400 oC.\nof Pd ‒C/TiO (1.0 mg of powder, 20% wt of Pd ‒C) composites with and without\n5 2 5\nligand removal of Pd ‒C under 980 nm laser irradiation. (a, b) SEM image of ligand\n5\nremoved Pd ‒C/TiO composite (the inset of B is atomic percentages of Ti, Pd, P, and\n5 2\nS elements). (c‒e) EDS mapping of ligand-removed Pd ‒C/TiO composite. HADDF‒\n5 2\nTEM images of Pd ‒C (f) and ligand-removed Pd ‒C (g) revealed the sizes of Pd ‒C\n5 5 5\nwere maintained after ligands removal. (h) The photothermal conversion performances\nof Pd ‒C/TiO and ligand-removed Pd ‒C/TiO composites. (i) The 10 photothermal\n5 2 5 2\nconversion cycles of ligand-removed Pd ‒C/TiO composites under 0.30 and 0.25\n5 2\nW/cm2 laser irradiation. Note: the Pd ‒C/TiO composite were heated at 400 oC for\n5 2\nthree hours under N atmosphere to prepare ligand-removed Pd ‒C/TiO composite.\n2 5 2\nThis manuscript presents a comprehensive study on the synthesis, characterization, and\nphotothermal properties of a novel class of Pd-based nanoclusters “inverse\npalladocenes”. The work is highly original and addresses an under-explored area in\norganometallic chemistry involving “nonmetal-to-metal” coordination and Pd\naromaticity. The inverse palladocenes demonstrate rigorous structural/electronic\ncharacterization and promising applications, particularly in photothermal conversion\nand laser shielding.\nThe study is in general well-organized and the major conclusions are supported by the\nresults, which is suitable for the audience of Nature Communications. However, there\nare a few issues should be addressed:\nResponse: Thank the reviewer for highly positive comments.\nQuestion 1: In Fig. 4f, the RDG plot appears with many jagged edges, making it\ndifficult to fully observe the π-π stacking interaction. We kindly suggest considering an\nincrease in the number of grid points to improve the visualization.\nResponse: We thank the reviewer for this helpful suggestion, and we have improved\nthe figure quality as shown below.\n5\npalladocene. (a) Nonmetal-to-metallo-aromatic-ring coordination and nonmetal-\naromatic-ring to metallo-aromatic-ring π…π-like interactions. (b) Three 6c–2e AdNDP\norbitals and the corresponding orbital compositions (isovalue = 0.04). (c) The ELF map\non the Pd pentagon plane. (d) Calculated ICSSs of Pd ‒C and the comparison of\n5 5\nsimulated [Pd ]6+ with aromatic [C H ]‒ (green and purple regions correspond to\n5 5 5\nchemical shielding and de-shielding areas, respectively. ICSS isosurface = ±0.18). (e)\nOne-dimensional assembly via intermolecular nonmetal-aromatic-ring to metallo-\naromatic-ring π…π like interactions. (f) The RDG representations of the interactions\nbetween the Ph ligand and the five-membered Pd ring. (g) The oppositely directional\nassembly mode of adjacent Pd ‒C in the unit cell.\nDPPM ligand and the nearby metal five-membered ring? We kindly suggest calculating\n39\nthe orbital distribution based on the crystal structure to analyze the orbital or\nhole-electron distribution within the aggregate. Additionally, it may be helpful to calculate\nthe electrostatic potential of inverse palladocycles for further analysis.\nResponse: Thank the reviewer for the kind suggestion, and we have provided additional\ndata and discussion in the revised manuscript following the reviewer’s good suggestion,\nwhich are also copied below for the convenience of Editor and reviewers.\nPage 10\n…Decomposition analysis (EDA) calculation on a simplified (Pd ‒C) dimer based on\n5 2\nthe crystal structure (Supplementary Table 3), reveals that electrostatic attraction\nbetween the phenyl group of the DPPM ligand and the nearby metal five-membered\nring dominates, rather than orbital interactions induced by the electron transfer\n(accounting for 69.7% vs 30.3%), which is further confirmed by the electrostatic\npotential distribution within the dimer. As shown in Supplementary Fig. 21, the plot of\nelectrostatic potential surfaces suggests that the electrostatic potential is asymmetrically\ndistributed among the Pd ‒C: the palladium five-membered ring is more negatively\n5\ncharged while the phenyl group of the DPPM ligand is relatively positive, facilitating\ntheir electrostatic attraction between the two moieties....\nSupplementary Table 3. The EDA results of (Pd ‒C) dimer with two Pd ‒C fragments,\n5 2 5\nwhich was calculated by using ADF 2019.304 at PBE level (The TZP and DZP basis\nsets were applied for Pd and other atoms, respectively)\nTerms Energy (kcal/mol)\nE -7.22\nint\nE 17.30\nPauli\nE -17.09 (69.7%)\nelstat\nE -7.43 (30.3%)\norb\nSupplementary Figure 21. The electrostatic potential surfaces of the simplified Pd ‒\nisovalue is 0.0004.)\nQuestion 3: Should the authors provide more details about the testing conditions for\nthe absorption spectra of inverse palladocenes? For instance, are the samples in the form\n40\nof powder, thin films, or solutions? If the samples are in solution, it would be interesting\nto explore how different polarities of solvents affect their absorption spectra. On the\nother hand, if the samples are in the form of powder or thin films, the author could\ninvestigate any differences in their absorption spectra under various conditions.\nResponse: Thank the reviewer for the suggestion, and we have provided additional data\nand discussion following the reviewer’s suggestion in the revised manuscript as shown\nbelow.\nPage 11\n…Note that, the absorptions of inverse palladocenes are solvent dependent. However,\nnot only absorption intensities but also absorption maximum wavelengths don’t\npositively correlate with the solvent polarity as shown in Supplementary Fig. 27…\nSupplementary Figure 27. UV/Vis/NIR absorption spectra of inverse palladocenes in\nsolvents with different polarities (CHCl , toluene, CH Cl , THF, and acetone).\n3 2 2\nQuestion 4: The inverse palladocences synthesized by the author show diverse\nphotothermal conversion capabilities. Referring to the Jablonski energy level diagram,\nmight a structure with relatively lower photothermal conversion efficiency exhibit\nphotoluminescence? If this material features near-infrared luminescence properties,\nits potential application could be greatly broadened.\nResponse: Thank the reviewer for the comment and question. Unfortunately, the\nnotable photoluminescence of inverse palladocences was not found yet, and we have\nadded the information in the revised manuscript as shown below.\nPage 15\n…Referring to the Jablonski energy level diagram (which indicates that a structure with\n41\nrelatively lower PCE might exhibit photoluminescence), we also attempted to\ninvestigate the photoluminescence properties of inverse palladocenes under different\nexcitation wavelengths. Unfortunately, no notable photoluminescence of inverse\npalladocenes was observed so far, as shown in Supplementary Fig. 33.…\nSupplementary Figure 40. PL spectra of inverse palladocenes upon excitation at 530\n(a) and 870 nm (b).\nQuestion 5: The author noted that the photothermal conversion originates from the\nconjugation of the five-membered palladium aromatic ring of inverse palladocences.\nHowever, we also observe five-membered palladium aromatic rings in Pd and Pd .\n8 6\nWhy Pd and Pd don’t demonstrate sufficiently strong photothermal conversion\n8 6\ncapabilities?\nResponse: Thank the reviewer for the question. As discussed in the manuscript, the\nphotothermal conversion efficiencies (PCE) of inverse palladocenes are positively\ncorrelated with their conjugation degrees. Although both Pd and Pd contain five-\n8 6\nmembered palladium aromatic rings, they exhibit relatively weak photothermal\nconversion capabilities due to that the conjugation degrees of their five-membered\npalladium aromatic rings are lower than that of Pd .\n5\nencapsulated in polystyrene assist in the degradation of polystyrene at 368 oC. However,\nin Supplementary Fig. 25, the Pd ‒C decomposed at ~300 oC and reached a mass loss\n5\nof 60% by ~350 °C. Considering this information, why the reaction might specifically\noccur at 368 °C?\nResponse: Thank the reviewer for the question. Although Pd\n5\n‒C decomposed at ~300\noC and reached a mass loss of 60% by ~350 °C, it might maintain the Pd P framework\n5\nstructure for over 400 °C with almost unchanged photothermal performances,\nevidenced by the accurate evaluation of their mass losses in TG experiments (see the\nprevious Supplementary Fig. 25) as well as the photothermal investigation after the\nligand removal (see the previous Supplementary Fig. 26). Anyway, Pd ‒C can maintain\n5\nits photothermal performance for over 400 °C, and its temperature can be lifted to ~368\noC after laser irradiation (980 nm, 0.8 W/cm2; see the previous Supplementary Fig. 31).\nSupplementary Figure 35 (previous 25). TGA of Pd ‒C, Pd , and Pd ‒S. Note: based\n5 6 8\non the weight loss, it is concluded that Pd P or Pd P might be the final product after\n5 8 2\nheated to over 400 oC.\nof Pd ‒C/TiO (1.0 mg of powder, 20% wt of Pd ‒C) composites with and without\n5 2 5\nligand removal of Pd ‒C under 980 nm laser irradiation. (a, b) SEM image of ligand\n5\nremoved Pd ‒C/TiO composite (the inset of B is atomic percentages of Ti, Pd, P, and\n5 2\nS elements). (c‒e) EDS mapping of ligand-removed Pd ‒C/TiO composite. HADDF‒\n5 2\nTEM images of Pd ‒C (f) and ligand-removed Pd ‒C (g) revealed the sizes of Pd ‒C\n5 5 5\nwere maintained after ligands removal. (h) The photothermal conversion performances\nof Pd ‒C/TiO and ligand-removed Pd ‒C/TiO composites. (i) The 10 photothermal\n5 2 5 2\nconversion cycles of ligand-removed Pd ‒C/TiO composites under 0.30 and 0.25\n5 2\nW/cm2 laser irradiation. Note: the Pd ‒C/TiO composite were heated at 400 oC for\n5 2\nthree hours under N atmosphere to prepare ligand-removed Pd ‒C/TiO composite.\n2 5 2\nPd ‒C/polystyrene composites under 980 nm, 0.8 W/cm2 laser irradiation (inset is the\n5\nselected IR images).\nQuestion 7: It is suggested to present the values involved in the PCE calculation in a\ntable format for better clarity and organization.\nResponse: Thank the reviewer for the suggestion, and we have presented the values\ninvolved in the PCE calculation in a table format following the reviewer’s suggestion\nin the revised Supplementary Information, as shown below.\nSupplementary Table 7. The PCE comparison between inverse palladocenes and some\n45\nassociated substances.\nsample Wavelength m T T η\ni surr max\nIntensity (a.u.) lnθ\n(nm) (mg) (oC) (oC) (%)\n980 25.5 0.74576 20.1 70.5 11.07 73.6\nPd ‒C 1064 25.5 0.36835 19.7 36.4 7.63 36.2\n5\n1208 25.5 0.13736 19.4 23.4 7.47 18.7\nPd ‒O 980 23.4 0.38041 21.4 58.9 8.20 68.1\nAdm-SH 980 24.1 0.00310 20.4 20.6 ‒ ‒\nDPPM 980 25.8 0.00552 20.1 20.4 ‒ ‒\nPd(OAc) 980 26.1 0.03117 20.6 21.0 ‒ ‒\n2\nuniformly (1% wt) with the basal area of 1 cm2 and thickness of 0.20‒0.26 mm, which\nis placed in the air and fixed by a needle for measurements. Power density = 0.3 W/cm2.\nQuestion 8: In which solution was the photothermal conversion tested (Fig. 6a), water\nor toluene?\nResponse: Thank the reviewer for the question. We used the solvent toluene and have\nadded the information in the caption of the revised Fig. 6 as shown below.\nFig. 6. Photothermal conversion performance of inverse palladocenes. (a) Time-\ndependent images of Pd ‒C, Pd ‒O, Pd , and Pd –P solutions (80 μg/mL, 0.5 mL of\n5 5 6 8\ntoluene) upon laser irradiation (980 nm, 0.5 W/cm2) followed by a cooling period. (b)\nPCEs of different materials upon 980 nm laser irradiation. (c) Average PCE per Pd atom\nfor Pd ‒C, Pd ‒O, Pd , and Pd –P. (d) Peak temperatures of Pd ‒C solutions (0.5 mL,\n5 5 6 8 5\ntoluene) with different concentrations upon laser irradiation (980 nm, 0.5 W/cm2). (e)\nEight photothermal conversion cycles of Pd ‒C solution upon laser irradiation (980 nm,\n5\n0.5 W/cm2) with different concentrations (40 and 80 μg/mL, 0.5 mL of toluene). (f)\nTemperature change of Pd ‒C solution (80 μg/mL, 0.5 mL of toluene) upon 0.5 W/cm2\n5\nlaser irradiation with different wavelengths (980, 1064, and 1208 nm). (g) Laser\nshielding performance of Pd ‒C solution (0.5 mL, toluene) with different\n5\nconcentrations (50–2000 μg/mL). (h) Laser shielding performance comparison of Pd ‒\n5 6 8\n2000 μg/mL) under 980 nm laser irradiation. (i) Laser shielding performances of Pd ‒\n1064, or 1208 nm laser irradiation. (j) Pd ‒C-assisted polystyrene (25 mg, 1 wt% of\n5 5\nC-assisted cotton (0.5 mg of Pd ‒C was loaded on the ~100 mg cotton surface ) ignition\n5\nunder laser irradiation (980 nm, 0.8 W/cm2). (l) Photothermal stability and time-\ndependent images of Pd ‒C/polyurethane composites (30 mg, 1 wt% of Pd –C, 0.2 mm\n5 5\nthickness) under continuous laser irradiation (0.4 W/cm², 980 nm).\n46"}, {"round": 2, "reviewer_comments": {"reviewer_1": "Whereas I have been initially undecided (if not tentatively supportive) relating to the match between Nat. Commun and this manuscript, the author’s rebuttal has flipped my assessment strongly in disfavor, as many – if not most – of my remarks are not properly addressed despite of the rebuttal’s 21 pages referring to my review. Some of the author's replies are factually incorrect. Overall, the rebuttal casts serious doubts whether the overall manuscript has been composed with appropriate care/honesty to be published in a top-journal:\n1.) Being a synthetic chemist, I mentioned that I do not find the synthesis on its own impressive, and that I consider the overall manuscript quite similar to the previous ACIE manuscript, hence limiting to some extent novelty. I understand that others might judge this point differently. Yet, the authors’ reply “this is in strong contrast to the other two reviewers’ comments (see below)” is not ok: None of the other reviewers has assessed the novelty of the underlying synthesis; in fact, reviewer 2 specifically asks: “Question 1: What is the essential difference between Reference 15 (Angew. Chem. Int. Ed. 63, e202313491 (2024).) and this study?”\n2.) The authors correct my statement of “photothermal conversion in the NIR (850 nm)” with “the longest laser irradiation wavelength was extended from the previous 808 (not 850!) nm to 1208 nm”. However, Fig. 3, blue trace in Angew. Chem. Int. Ed. 63, e202313491 (2024) clearly indicates that the absorption band is centered way beyond 826 nm. I understand, the authors refer to the laser, yet I was referring to the band… This is not a major issue on its own, yet tentatively suggests that the rebuttal has not been composed with appropriate care and reflection.\n3.) I mentioned that the manuscript would benefit from carving out structure (i.e. Pd5/ligand) – property (i.e. PCE properties) relationships. This question was answered with the Sncp, although I mentioned the Sncp only later, i.e. it seems also this part of my assessment was not read carefully and/or ignored…\n4.) I questioned the usefulness of Sncp beyond more established descriptors (such as these reviewed/developed by the Sola group). I am still not convinced that it is superior to these descriptors, as the authors just repeated its definition; I am certainly not convinced that it deserves to be specifically highlighted…\n5.) I pointed out that the assignment as a simple HOMO-LUMO transition is inappropriate, as the transitions >950 nm (E <1.3 eV) have a very different energy to the computed HOMO/LUMO gap (E = 2.4 eV = 500 nm), almost a factor of 2. The authors replied, this is due to commonly known dependend on the amount of exact exchange, yet it is (of course) due to orbital mixing, i.e. this reply tentatively suggests a general lack of understanding…\n6.) I pointed out that simply plotting canonical orbitals / partial charges do not allow to specify overall oxidation states, and that \"charge state\" is imprecise language. However, I see that the authors still claim “Molecular orbital (MO) analysis verified the charge state of Pd in various inverse palladocenes.” I note massive orbital mixing with the ligand…\n7.) The authors claim in the letter that “Pd8(PAr) clusters, planar Pd7 clusters, and Pd4 clusters are sensitive to air atmosphere and require strict anhydrous- and oxygen-free conditions for synthesis. Due to the exceptional stability of the inverse palladocenes, these novel materials provide great potentials for practical applications in common (aqueous-, oxygen-containing) conditions.” This statement is incorrect, the first example is air stable and water-stable in boiling solvent. Generally, I would not consider this oversight a major issue, yet given all the other inaccuracies, this seems troublesome.\n8.) I mentioned it would be interesting to also include/mention/compare the P-signal in the XPS analysis (which usually is obtained along the way of the Pd-measurement). This comment has not been addressed; also this is on its own not a major issue, yet again casts doubt about how carefully the rebuttal/manuscript has been composed\n9.) The authors added Supplementary Table 8 to underscore the exceling PCE properties. However, I note that this table seems to compare apples with pears (solution vs. film), and that the properties of quite a bit of reference compounds seem still quite similar…", "reviewer_2": "The authors have addressed all my comments. Thus, I'd like to recommend its publication in the present form.", "reviewer_3": "The author has thoroughly addressed all the questions raised by the reviewers and provided clear and detailed responses.\nWe believe the article is now ready for publication.", "reviewer_4": "The authors did a thorough job in addressing the questions raised by the different reviewers. The manuscript is written well and the complexes have been thorough investigated and analyzed. So the methodology is sound and most claims are supported by experimental findings.\nI agree with referee 1 that the current manuscript is an extension to the authors’ previous work reported in Angewandte Chemie. However, the current contribution contains novel aspects and also shows that this seems to be a novel class of compounds for which different derivatives can be prepared. Hence, I would argue that there is enough novelty to argue for Nature Communications.\nHowever, I would request some revisions and changes:\n1) The yields are in some cases rather poor. Can the authors please explicitly specify how much material (in mg) was actually isolated in each case. The reported isolated yield is based on which starting material?\n2) What happens if the synthesis is actually performed under strictly anaerobic/anahydrous conditions would these materials be then isolate at all?\n3) Please be more specific with the comment: “The thiolate type influences the final products due to the space and electronic effects.” This is a rather general comment. What is more important sterics or electronics?\n4) Include in the SI the d-electron counts per palladium atom. In their reply to referee 1 the authors state: “Given that Pd has a d10 electron configuration, the d-electron counts of Pd8–S, Pd8–P, Pd6, Pd5‒O, and Pd5–C are concluded to be 70, 70, 64, 44 and 44, respectively, on the basis of the charge state of Pd.” What do the authors mean with the numbers: 70, 70, 64, 44 and 44??\n5) Supplementary Figure 2 (b): Replace “=” by proper arrows.\n6) Is it reasonable to compare in the TOC contrast the interaction between the Pd5 fragment and an arene fragment to that of Cp5- and an arene ring? Have the authors directly compared these interactions?\n7) Figure S32: Can the authors please label/assign the individual redox events? Some of them seem to be not very reversible.\n8) One issue I have with the current manuscript is the authors’ insistence on classifying the metal atom in a classic metallocene complex as electron acceptor, but there is a also delta-backdonation from the metal to the empty orbitals of the Cp- or arene ring. This interaction is completely ignored in the interest of stressing differences. From the bonding analysis I would argue that these systems as the “classic” d-transition metal metallocenes share the feature of strongly covalent covalent molecules."}, "author_response": "Manuscript number: NCOMMS-25-38974A-Z\nMS Type: Research Article\nTitle: “Inverse palladocenes”\nCorrespondence Author: Prof. Zhikun Wu\nWe thank Editor Eren Peterson and all the reviewers for their reading of the manuscript\nand helpful suggestions. Below our point-by-point response (or the words from the\nprevious manuscript) is in blue, revisions (except for figures) are in red, and the page\nnumber mentioned in the manuscript is referred to the version with revision marked.\nResponse to reviewer 1’ comments: pages 1-11\nResponse to reviewer 2’ comments: page 11\nResponse to reviewer 3’ comments: page 11\nResponse to reviewer 4’ comments: pages 11-21\nReviewers’ comments:\nReviewer 1:\nWhereas I have been initially undecided (if not tentatively supportive) relating to the\nmatch between Nat. Commun and this manuscript, the author’s rebuttal has flipped my\nassessment strongly in disfavor, as many – if not most – of my remarks are not properly\naddressed despite of the rebuttal’s 21 pages referring to my review. Some of the author's\nreplies are factually incorrect. Overall, the rebuttal casts serious doubts whether the\noverall manuscript has been composed with appropriate care/honesty to be published\nin a top-journal:\nResponse: Thank the reviewer for clarifying the previous assessment. We have to\nprovide a long rebuttal due to that Editor made a decision majorly basing on the\nreviewer’s evaluation. Thank the reviewer for understanding, and we apologize for any\npossible misunderstanding.\n1.) Being a synthetic chemist, I mentioned that I do not find the synthesis on its own\nimpressive, and that I consider the overall manuscript quite similar to the previous\nACIE manuscript, hence limiting to some extent novelty. I understand that others might\njudge this point differently. Yet, the authors’ reply “this is in strong contrast to the other\ntwo reviewers’ comments (see below)” is not ok: None of the other reviewers has\nassessed the novelty of the underlying synthesis; in fact, reviewer 2 specifically asks:\n“Question 1: What is the essential difference between Reference 15 (Angew. Chem. Int.\nEd. 63, e202313491 (2024).) and this study?”\nResponse: Thank the reviewer for the comments. We are sorry for the\npreviously\nimproper expression in response to reviewer 1’s evaluation of the synthetic aspects of\nour work. For question 1 raised by reviewer 2, we had clearly illustrated the essential\ndifferences between Reference 15 (Angew. Chem. Int. Ed. 63, e202313491 (2024).) and\n1\nthis study, which have been agreed by reviewer 2.\n2.) The authors correct my statement of “photothermal conversion in the NIR (850 nm)”\nwith “the longest laser irradiation wavelength was extended from the previous 808 (not\n850!) nm to 1208 nm”. However, Fig. 3, blue trace in Angew. Chem. Int. Ed. 63,\ne202313491 (2024) clearly indicates that the absorption band is centered way beyond\n826 nm. I understand, the authors refer to the laser, yet I was referring to the band…\nThis is not a major issue on its own, yet tentatively suggests that the rebuttal has not\nbeen composed with appropriate care and reflection.\nResponse: Thank the reviewer for the comments. The correction of the reviewer’s\nstatement was not the major care of the rebuttal, but rather to clarify the laser\nwavelength used in our work for better understanding. We apologize for any possible\nmisunderstanding.\n3.) I mentioned that the manuscript would benefit from carving out structure (i.e.\nPd /ligand) – property (i.e. PCE properties) relationships. This question was answered\n5\nwith the Sncp, although I mentioned the Sncp only later, i.e. it seems also this part of\nmy assessment was not read carefully and/or ignored…\nResponse: Thank the reviewer for the comments. We agree with the reviewer’s\ncomment that the manuscript would benefit from carving out structure (i.e. Pd /ligand)\n5\n– property (i.e. PCE properties) relationships, and we apologize for any possible\nmisunderstanding concerning this. We have further elaborated on the structure-property\nrelationship in the revised manuscript, as detailed below:\nPage 14\n...Specifically, Pd aromatic ring is the primary contributor of the NIR absorption and\n5\nthus strong conjugation within the Pd ring leads to intensive NIR absorption, enabling\n5\nenhanced photothermal conversion in the NIR-II window....\n4.) I questioned the usefulness of Sncp beyond more established descriptors (such as\nthese reviewed/developed by the Sola group). I am still not convinced that it is superior\nto these descriptors, as the authors just repeated its definition; I am certainly not\nconvinced that it deserves to be specifically highlighted…\nResponse: Thank the reviewer for the comments. The introduced Sncp was given the\nconsideration to both metal‒metal bond length uniformity and coplanarity, and can be\nused to evaluate the conjugation degrees of the Pd ring in various inverse palladocenes,\n5\nwhich interprets the photothermal conversion efficiency sequence of as-obtained\ninverse palladocenes well in this work, thus it is usefull. We don’t mean that it is\nsuperior to established descriptors, including these reviewed/developed by the Solà\ngroup (J. Phys. Chem. A 115, 13104–13113 (2011), but rather to mention that it is an\nalternative (supplement) to these established descriptors. Note that, one advantage of\nsuch a metric is that its value can be calculated based on experimental crystal data.\n5.) I pointed out that the assignment as a simple HOMO-LUMO transition is\n2\ninappropriate, as the transitions >950 nm (E <1.3 eV) have a very different energy to\nthe computed HOMO/LUMO gap (E = 2.4 eV = 500 nm), almost a factor of 2. The\nauthors replied, this is due to commonly known dependend on the amount of exact\nexchange, yet it is (of course) due to orbital mixing, i.e. this reply tentatively suggests\na general lack of understanding…\nResponse: Thank the reviewer for the comments. In the previous response, we have\nmentioned that the PBE0 functional can well reproduce the absorption spectra, but\nfailed to accurately predict the HOMO–LUMO gaps in our systems. To avoid possible\nargument, we now have replaced all PBE0-derived results with the alternative PBE-\ncalculated ones in the revised Fig. 5 and Supplementary Figs. 30-32, which are also\ncopied below for the convenience of the Editor and the reviewers. The PBE-calculated\nHOMO–LUMO gaps for Pd –C, Pd –O, Pd , and Pd –P are 1.09, 1.09, 1.21, and 1.16\n5 5 6 8\neV, respectively, which are in close agreement with their experimental optical gaps (see\nSupplementary Fig. 27 in the revised manuscript, as shown below).\nFig. 5. Optical property interpreting of Pd ‒C. (a) Experimental and simulated\nDisassembling the UV/Vis/NIR absorptions along three axial directions. (d)\nRelationship between the wavelengths and transition dipole moments along three axial\ndirections. (e) The selected frontier MO distributions.\nDisassembling the UV/Vis/NIR absorptions along three axial directions. (d)\nRelationship between the wavelength and transition dipole moments along three axial\ndirections. (e) The selected frontier MO distributions.\nSupplementary Figure 31. Optical property interpreting of Pd . (a) Simulated\nDisassembling the UV/Vis/NIR absorptions along three axial directions. (d)\nRelationship between the wavelength and transition dipole moments along three axial\ndirections. (e) The selected frontier MO distributions.\nDisassembling the UV/Vis/NIR absorptions along three axial directions. (d)\nRelationship between the wavelength and transition dipole moments along three axial\ndirections. (e) The selected frontier MO distributions.\nSupplementary Figure 27. Optical gap analysis of Pd ‒C, Pd –O, Pd , and Pd –P\n5 5 6 8\n(dissolved in toluene).\n6.) I pointed out that simply plotting canonical orbitals / partial charges do not allow to\nspecify overall oxidation states, and that \"charge state\" is imprecise language. However,\nI see that the authors still claim “Molecular orbital (MO) analysis verified the charge\nstate of Pd in various inverse palladocenes.” I note massive orbital mixing with the\nligand…\n“charge state”, which have been modified to “formal oxidation state” in the revised\nmanuscript, as copied below, since the oxidation state (OS) of an atom is the charge of\nthis atom after ionic approximation of its heteronuclear bonds (see “oxidation state” in\nIUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure\nand Applied Chemistry; 2025. Online version 5.0.0, 2025.\nhttps://doi.org/10.1351/goldbook.O04365). We agree that significant metal-ligand\norbital mixing occurs in these inverse palladocenes, but the formal oxidation states of\nthe constituent atoms in the ligands are determined based on their valence electron\nconfiguration. Specifically, the formal oxidation states of S-Adm, PPh , and PPh\n3\nligands are assigned to –1, 0, and –2, respectively. For the formal oxidation states of the\nPd metal units, they are calculated based on the charge-neutrality of the whole\nn\ncompounds. Taking Pd (PPh)(S-Adm) [(Ph P) CH ] (Pd –C) as an example, the formal\n5 4 2 2 2 5\noxidation state of the Pd unit is calculated to be +6 = 0 – (–2)  1 – (–1)  4 – 0  3.\n...Given the exact compositions and the recognized formal oxidation states (OSs) of\nligands [S-Adm]−, [PPh]2−, [Ph P=O]−, and PPh (−1, −2, −1, and 0, respectively; Note:\n2 3\nthe detailed analysis of the OS of phosphorus in inverse palladocenes is provided in the\n“Analysis of the OS of phosphorus in inverse palladocenes” section of the\nSupplementary Information), the average OSs of Pd in Pd –P, Pd , Pd ‒O, and Pd –C\n8 6 5 5\nwere calculated to be +1.25, +1.33, +1.2, and +1.2, respectively, indicating the low OSs\nof Pd across all these nanoclusters38. Molecular orbital (MO) analysis verified the OSs\nof Pd in various inverse palladocenes. Taking Pd –C as an example, the revealed three\n5\nempty MOs is consistent with the total OS of its five Pd atoms (+6) (Supplementary\nFig. 8). The low OSs of Pd were further authenticated using X-ray photoelectron\nspectroscopy (XPS) and natural population analysis (NPA) charge, as shown in Fig. 2g‒\nj and Supplementary Figs. 9‒12....\n7.) The authors claim in the letter that “Pd (PAr) clusters, planar Pd clusters, and Pd\n8 6 7 4\nclusters are sensitive to air atmosphere and require strict anhydrous- and oxygen-free\nconditions for synthesis. Due to the exceptional stability of the inverse palladocenes,\nthese novel materials provide great potentials for practical applications in common\n(aqueous-, oxygen-containing) conditions.” This statement is incorrect, the first\nexample is air stable and water-stable in boiling solvent. Generally, I would not consider\nthis oversight a major issue, yet given all the other inaccuracies, this seems troublesome.\nResponse: Thank the reviewer for pointing that out. We have checked the literature,\nand found that although Pd (PAr) was synthesized under strict anhydrous and\n8 6\nanaerobic conditions, it is indeed rather stable in air and water. However, the statement\nis correct for most of the reported Pd clusters. Therefore, we have modified the\nstatement in the revised manuscript as shown below. We apologize for the previously\nimprudent statement.\nPages 26-27\n6\n…Note that, inverse palladocenes with planar aromatic Pd ring unit and unanticipated\n5\nnonmental-to-metal aromatic Pd ring coordination are synthesized under aqueous-,\n5\noxygen-containing conditions and demonstrate remarkable stability in air atmosphere,\ndistinctly differing from reported Pd clusters such as cubic Pd (PAr) clusters56, planar\n8 6\nPd clusters57 and Pd clusters58 (which require strict anhydrous- and oxygen-free\n7 4\nconditions for synthesis and most of them are sensitive to air atmosphere).…\n8.) I mentioned it would be interesting to also include/mention/compare the P-signal in\nthe XPS analysis (which usually is obtained along the way of the Pd-measurement).\nThis comment has not been addressed; also this is on its own not a major issue, yet\nagain casts doubt about how carefully the rebuttal/manuscript has been composed.\nResponse: Thank the reviewer for pointing that out, and we apologize for the overlook.\nWe have added the information in the revised manuscript as shown below:\nPages S33-34\n...Analysis of the OS of phosphorus in inverse palladocenes\nXPS analysis revealed that the P(2p) signals for Pd ‒C, Pd –O, and Pd in the range of\n5 5 6\n130.95–131.33 eV (Supplementary Figs. 10–12) are consistent with those observed in\nphosphorus (III) compounds5 such as PdCl (PPh ) (131.5 eV) and PPh (130.9 eV),\n2 3 2 3\nbut they slightly differ from that in the Pd (PDip) cluster (130.2 eV) due to the OS\n8 6\ndifference (–3 vs –1)6. The OS of the dianionic [PPh]2‒ group is not only evidenced by\nthe aforementioned XPS analyses, but also supported by the repeated reports involving\nin related organometallic complexes (e.g. [LSc(μ-PAr)] (L = (MeC(NDIPP)CHC(Me)-\n2\n(NCH CH N(iPr) )), DIPP = 2,6-(iPr) C H ; Ar = 2,6-Me C H ), where [PAr]2‒ has an\n2 2 2 2 6 3 2 6 3\nOS of –27)...\nReferences (Supplementary Information)\nDatabase Number 20, National Institute of Standards and Technology,\nGaithersburg MD, 20899 (2000), DOI: https://dx.doi.org/10.18434/T4T88K,\n(accessed: 20.11.2023).\n8 6\n2400699 (2024).\ncomplex: Reduction, addition, and CO activation reactions. J. Am. Chem. Soc.\n135, 14784-14796 (2013).\n9.) The authors added Supplementary Table 8 to underscore the exceling PCE properties.\nHowever, I note that this table seems to compare apples with pears (solution vs. film),\nand that the properties of quite a bit of reference compounds seem still quite similar…\nResponse: Thank the reviewer for the comment. It is worth noting that the PCE\ncalculation adopt a standardized method, independent of sample states (J. Phys. Chem.\nsample states presentation in the revised Supplementary Information, which is also\ncopied below for the convenience of the Editor and the reviewers. As shown in the\nrevised Supplementary Table 9, Pd ‒C shows excellent photothermal performance in\n5\nterms of comprehensive irradiation power, response wavelength, temperature change,\nphotothermal conversion efficiency, and stability. Especially, given the consideration\nof the average PCE per metal atom (see Fig. 6c), it is much higher than that of most of\nthe reported photothermy materials.\nSupplementary Table 9. Comparison of the photothermal efficiency (η) between\nvarious materials\nLaser power Wavelength Temperature η\nSample Cycle Category\n(W/cm2) (nm) changes (T) (%)\nAu NPs 2.4 514 2 °C in 6 min <10 NP nanoparticles\nabout 33 °C in 30 six\nAu PBs 1.0 808 88.6 plasmonic\nmin cycles\nabout 31.5 °C in 30 six\nAu PBs 1.0 1064 80.8 plasmonic\nmin cycles\nabout 26 °C in 5 five\nAu NDs 0.4 1064 84.9 nanodumbbells\nmin cycles\nabout 34.5 °C in 5 five\nAuNCs@SiO2 0.5 1064 82.2 nanochains\nmin cycles\nAu/TiO2 0.5 532 11.5 °C NP NP nanoparticles\nSi-GO 4.0 532 40 °C in 10 min NP NP nanoparticles\nNS-40 0.32 532 12 °C in 6 min 42.8 NP nanoparticles\nNS-60 0.32 532 9 °C in 6 min 30.6 NP nanoparticles\nAu NPs 0.34 532 52 °C in 10 min 62.9 NP nanoparticles\nabout 17.5 °C in 10 six\nGA-CuFeSe2 0.27 532 79.6 nanoparticles\nmin cycles\nAu NP-Packed\n0.15 532 220 °C in 2 s NP NP nanoparticles\nSpheres\nAuNP–mTHPC\n0.015 532 0.3 °C in 2 min NP NP nanoparticles\ncomplex\nACA 1.3 532 10 °C in 6 min NP NP nanoparticles\nthree\nGO 1.3 532 17 oC in 30 s NP\ncycles inorganic materials\nAu37(CHT)23 0.25 650 12 oC in 5 min 30.3 NP nanoclusters\nAu48(CHT)26 0.25 650 17.2 oC in 5 min 42.9 NP nanoclusters\n15−36.8 °C in 10 three\nTNMs 1.0 660 41.0 organic materials\nmin. cycles\nsix\nAg155 0.1 660 39.1 °C in 6 min NP nanoclusters\ncycles\nAu42 1.0 808 27 °C in 5 min. NP NP nanoclusters\nUiO-66@PAN 1.5 808 21.6\n10 min cycles materials\nfive MOF-based\nZr-PDI•– 0.7 808 89 °C in 200 s 52.3\ncycles materials\nfour\nAg18 5.0 808 28 °C in 5 min NP nanoclusters\ncycles\nAg18 0.35 808 337 °C in 4 s NP NP nanoclusters\n(AgCu)31 1.0 532 56.9 °C in 10 min 67.6 NP nanoclusters\nabout 46 °C in 5 five\nIR-SS NPs 1.0 1064 77 small molecules\nmin cycles\nthree\nPt@PDA-c 1.0 1064 27.5 71.3 nanoparticles\nsolution cycles\nAu nanoshells 2.0 800 15 °C in 5 min 13 NP nanoparticles\nAu nanorods 2.0 800 22 °C in 5 min 21 NP nanoparticles\nCu2-xSe 2.0 800 22 °C in 5 min 22 NP nanoparticles\nCu9S5 nanocrystals 0.51 980 15.1 °C in 10 min 25.7 NP nanoparticles\nCuS NPs NP 1280 10.2 °C in 15 min 93 NP nanodisks\nCuS nanoflakes NP 1064 NP 72 NP nanoflakes\nthree\nCPP 2.33 808 29.3 °C in 3 min 42.5 organic materials\ncycles\nDpa-melanin CNSs 2.0 808 33.6 °C in 500 s 40 NP nanoparticles\nabout 23.5 °C in 9\nCuO/Cu2O TNCs 0.3 808 73 NP nanocubes\nmin\nabout 16 °C in 9\nCuO/Cu2O TNCs 0.3 1064 67 NP nanocubes\nmin\nabout 25 °C in 9\nCuO/Cu2O TNCs 0.3 1550 78 NP nanocubes\nmin\nsix\ndpGCS NCs 1.0 1064 33.8 °C in 10 min 71 nanocrystals\ncycles\nabout 44 °C in 9 five\nJanus-GCS NCs 1.0 1064 76.1 nanocrystals\nmin cycles\nBPDI/(CB[7])2 1.0 808 19.5 °C in 10 min 31.6 NP organic materials\nfive MOF-based hybrid\nPMCS 2.0 808 11.5 °C in 14 min 33\ncycles materials\nsix\nPBI-[GD]2 1.0 808 34.1 °C in 17 min 59.5 PDI-based radicals\ncycles\nsix\nPBI-[GY]2 1.0 808 27.7 °C in 22 min 49.1 PDI-based radicals\ncycles\nfive\nDTC 0.7 808 37 °C in 10 min 18.8 organic materials\ncycles\nfive organic\ntfm-BDP NPs 0.3 808 54 °C in 5 min 88.3\ndispersion cycles nanoparticles\norganic\nm-BDP 0.3 671 29 °C in 5 min 32 NP\nnanoparticles\n9\norganic\nH-BDP 0.3 671 20 °C in 5 min 50 NP\nnanoparticles\nabout 14.2 °C in 20\nPd SAzyme 0.69 1064 33.9 NP nanoparticles\nsolution in 20 min\nsix organic\nBAF4 NPs 0.75 1064 35 °C in 15 min 80\ncycles nanoparticles\nhexagonal\npalladium 1.0 808 20.7 °C in 10 min NP NP nanosheets\nsolution min\nnanosheets\nSPNS 1.0 808 20.8 °C in 10 min NP NP nanosheets\nPNS–DOX 2.86 808 23.2 °C in 10 min NP NP nanosheets\nSPNS 1.0 808 35.3 °C in 10 min 52 NP nanosheets\norganic\nF-PANP 0.5 808 24.4 °C in 5 min 48.5 NP\nnanoparticles\neight organic\nTPT–TT NPs 2.0 808 33.6 °C in 10 min 32\ncycles nanoparticles\norganic\nPPy NPs 1.0 808 25 °C in 10 min 44.7 NP\nnanoparticles\nabout 25 °C in 5 organic\nPPY@PAA/fmSiO2 2.0 808 31.3 NP\nmin nanoparticles\nabout 29 °C in 5 twenty\nDA CNDs 1.5 808 35 nanodots\nmin cycles\ncarbon dots 2.0 671 30.1 °C in 12 min 38.5 NP nanodots\nPEGylated Sb NPs 2.0 808 51 °C in 5 min 41 NP nanoparticles\nfive\nCys-CuS NPs 0.72 980 18.5 °C in 5 min 38 nanoparticles\ncycles\nabout 19 °C in 10 six\nFe3O4@Cu2−xS 0.6 980 16 nanoparticles\ndispersion 10 min cycles\nten\nGCNCs 0.5 808 19.9 °C in 13 min 40.4 nanocubes\ncycles\nfive\nPt Spirals 1.2 1120 33.1 °C in 1000 s 52.5 nanoparticles\ncycles\nPt/Te nano five\n1.5 808 33.4 °C in 8 min 51.8 nanoparticles\nheterostructures cycles\nfive\nHA-Au@Pt 1.5 808 30.0 °C in 10 min 63.5 nanoparticles\nsolution cycles\nPorous Pt NPs 1.24 808 38.2 °C in 30 min 97.0 NP nanoparticles\nPorous Pt NPs 1.24 980 34.5 °C in 30 min 89.9 NP nanoparticles\nBP/Pt-Ce6@PEG\n0.8 660 19.8 °C in 10 min NP NP nanoparticles\nNSs\nsix\nPt23 1.0 532 54.2 °C in 10 min 68.4 nanoclusters\ncycles\neight\nPd8‒S 0.5 808 32.8 °C in 7 min 73.3 inverse palladocene\ncycles\nPd8‒P (this work) 0.3 980 11.2 °C in 30 s 20.3 NP inverse palladocene\nPd8‒S (this work) 0.3 980 11.6 °C in 30 s 24.1 NP inverse palladocene\nPd6 (this work) 0.3 980 26.5 °C in 30 s 51.8 NP inverse palladocene\nPd5‒O (this work) 0.3 980 37.5 °C in 30 s 68.1 NP inverse palladocene\neight\nPd5‒C (this work) 0.3 980 50.4 °C in 30 s 73.6 inverse palladocene\ncycles\nPd5‒C (this work) 0.3 1064 16.7 °C in 30 s 36.2 NP inverse palladocene\nPd5‒C (this work) 0.3 1208 4.0 °C in 30 s 18.7 NP inverse palladocene\nReviewer 2:\nThe authors have addressed all my comments. Thus, I'd like to recommend its\npublication in the present form.\nResponse: Thank the reviewer for recommending the publication of this work in the\npresent form.\nReviewer 3:\nThe author has thoroughly addressed all the questions raised by the reviewers and\nprovided clear and detailed responses. We believe the article is now ready for\npublication.\nResponse: Thank the reviewer for highly positive comments.\nReviewer 4:\nThe authors did a thorough job in addressing the questions raised by the different\nreviewers. The manuscript is written well and the complexes have been thorough\ninvestigated and analyzed. So the methodology is sound and most claims are supported\nby experimental findings.\nI agree with referee 1 that the current manuscript is an extension to the authors’ previous\nwork reported in Angewandte Chemie. However, the current contribution contains\nnovel aspects and also shows that this seems to be a novel class of compounds for which\ndifferent derivatives can be prepared. Hence, I would argue that there is enough novelty\nto argue for Nature Communications.\nHowever, I would request some revisions and changes:\nResponse: Thank the reviewer for highly positive comments.\n1.) The yields are in some cases rather poor. Can the authors please explicitly specify\nhow much material (in mg) was actually isolated in each case. The reported isolated\nyield is based on which starting material?\nResponse: Thank the reviewer for the suggestion and question, and we have provided\nthe information in the revised manuscript as shown below:\n... Pd\n8\n‒P was isolated from the crude product of 20 combined reaction batches by\npreparative thin-layer chromatography (PTLC) in 1.2 mg (yield: 2%, based on the\nstarting material Pd ‒S)....\n... Pd\n6\nwas isolated from the crude product by PTLC in 22.4 mg (yield: 30%, based on\nthe starting material Pd(CH COO) )....\n3 2\nPage 26\n... Pd\n5\n‒O was isolated from the crude product of 20 combined reaction batches by PTLC\nin 1.5 mg (yield: 3%, based on the starting material Pd\n6\n)....\nPage 26\n... Pd\n5\n‒C was isolated from the crude product by PTLC in 9.8 mg (yield: 13%, based on\nthe starting material Pd(CH COO) )....\n3 2\nPage S33\n... Pd ‒Owas isolated from the crude product by PTLC in 7.6 mg (yield: 10%, based\n5\non the starting material Pd(CH COO) )....\n3 2\n2.) What happens if the synthesis is actually performed under strictly\nanaerobic/anahydrous conditions? Would these materials be then isolated at all?\nResponse: Thank the reviewer for the good question. Following the reviewer’s\nsuggestion, we tried the synthesis of Pd ‒C under strictly anaerobic/anahydrous\n5\nconditions; however, this effort did not yield the target product. To elucidate the role of\nwater and oxygen in the formation of inverse palladocenes, we conducted controlled\nexperiments. The investigations revealed that the presence of water is essential for\ngenerating the target product, whereas O offers no assistance to the reaction. The\n2\ndetails are provided in the “Water/oxygen regulation on the synthesis of Pd ‒C” section\n5\nof the revised Supplementary Information as shown below:\nPages S30-32\n…Water/oxygen regulation on the synthesis of Pd ‒C\npalladocenes, we carried out a study on water/oxygen regulation during the synthesis\nof Pd ‒C (Supplementary Figure 47). The specific procedure is as follows:\n5\n(1) Synthesis attempt of Pd ‒C under strictly anaerobic/anahydrous conditions\n5\n(Supplementary Figure 47c): under a N atmosphere, Pd(CH COO) (50.0 mg, 0.223\n2 3 2\nmmol) and DPPM (100.0 mg, 0.260 mmol) were co-dissolved in 8 mL of THF in a\nSchlenk tube with continuous stirring for 5 min, accompanied by a solution color\nchange from yellow to red. Then, a MeOH/THF mixed solvent (1:9; 1 mL) containing\nNaBH (100.0 mg, 2.643 mmol) and Adm-SH (150.0 mg, 0.891 mmol) was\n4\nimmediately added all at once under vigorous stirring, resulting in the solution color\n12\nchanging from red to dark (note: without the participation of MeOH, NaBH is difficult\n4\nto dissolve and participate in the reaction, leading only to [Pd(S-Adm) ] complexes3,\n2 n\nsee Supplementary Figure 47b). After 30 min.’s reaction, the THF solution was\nevaporated to dryness under vacuum, and the residue was re-dissolved in toluene (10\nmL) and heated at 80 oC for 24 h. Then the black organic layer was washed with\nmethanol three times. The crude product was isolated using PTLC, without Pd ‒C\n5\nobserved. Subsequent UV-Vis spectral analysis of the crude product revealed the\nmaximum absorption at 440 nm, indicating the presence of multi-disperse Pd\nnanoparticles.\n(2) Synthesis attempt of Pd ‒C under an oxygen atmosphere (Supplementary Figure\n5\n47c): following the synthesis protocols described above, after the immediate addition\nof a MeOH/THF mixed solvent (1:9; 1 mL) containing NaBH (100.0 mg, 2.643 mmol)\n4\nand Adm-SH (150.0 mg, 0.891 mmol), the N atmosphere was replaced with O , and\n2 2\nthe subsequent operations were conducted as per those of process (1). After the reaction\nwas completed, PTLC and UV-Vis spectral analysis revealed that the as-obtained\nproducts were similar to those synthesized under strictly anaerobic/anhydrous\nconditions.\n(3) Synthesis attempt of Pd ‒C under a water-containing atmosphere (Supplementary\nimmediate addition of a MeOH/THF mixed solvent (1:9; 1 mL) containing NaBH\n4\n(100.0 mg, 2.643 mmol) and Adm-SH (150.0 mg, 0.891 mmol), 1 mL of water was\nadded, and the subsequent operations were conducted as per those of the process (1).\nAfter the reaction was completed, Pd ‒C was isolated from the crude product by PTLC\n5\nin 31.7 mg (yield: 42%, based on the starting material Pd(CH COO) ).…\n3 2\nSupplementary Figure 47. Water/oxygen regulation on the synthesis of Pd ‒C.\nconditions: [Pd(S-Adm) ] complexes (b), multi-disperse Pd nanoparticles (c), and\n2 n\nPd ‒C (d).\n5\n3. Chen, J. et al. Synthesis and properties evolution of a family of tiara-like\nphenylethanethiolated palladium nanoclusters. Sci. Rep. 5, 16628 (2015).\n3.) Please be more specific with the comment: “The thiolate type influences the final\nproducts due to the space and electronic effects.” This is a rather general comment.\nWhat is more important sterics or electronics?\nResponse: Thank the reviewer for the criticism, and we specified the comment\nfollowing the reviewer’s suggestion in the revised manuscript as shown below.\nPage 5\n…The thiolate type influences the final products due to the space and electronic effects,\nwhich influence the formation kinetics and thermodynamics of the products. In our case,\nthe space effect looks more prominent than the electronic effect since only very bulky\n1-adamantanethiol led to the production of Pd –C among the investigated thiolates. For\n5\nthe other thiol (including those with close electronic effects), they led to Pd\nnanoparticles or complexes as shown in the Supplementary Fig. 5.…\n4.) Include in the SI the d-electron counts per palladium atom. In their reply to referee\n1 the authors state: “Given that Pd has a d10 electron configuration, the d-electron\ncounts of Pd –S, Pd –P, Pd , Pd ‒O, and Pd –C are concluded to be 70, 70, 64, 44 and\n8 8 6 5 5\n44, respectively, on the basis of the charge state of Pd.” What do the authors mean with\nthe numbers: 70, 70, 64, 44 and 44?\nResponse: Thank the reviewer for the suggestion and the question, and we further\ninterpreted the d-electron counts and added the information in the revised manuscript\nas shown below:\nPages S35-36\n...d-Electron counts of inverse palladocenes\nGiven the strong metal–ligand and metal–metal interactions, along with significant\norbital mixing within multi-metal nanocluster systems, we assigned the formal\noxidation states of Pd basing on the IUPAC definition9. For Pd (PPh) (PPh ) (S-Adm) (Pd –S),\n8 2 3 2 6 8\nthe total ligand charge contribution is calculated as: (–2) × 2 + (0) × 2 + (–1)\n× 6 = –10 based on the facts that PPh group is dianionic, PPh /(Ph P) O/(Ph P) CH\n3 2 2 2 2 2\ngroup is neutral, and S-Adm/Ph₂P=O group is monoanionic. Therefore, the Pd metal\n8\nunit carries a formal charge of +10 to maintain charge neutrality. Given that every free\nPd atom has 10 d-electrons (d10 configuration), the total d-electron count for the Pd\n8\nunit in Pd –S is 10 × 8 – 10 = 70, corresponding to an average of 70/8 = 8.75 d-electrons\n8\nper Pd atom. Similarly, for Pd (PPh) (PPh ) (Ph P=O)(S-Adm) (Pd –P), the total\n8 2 3 2 2 5 8\nligand charge contribution is: (–2) × 2 + (0) × 2 + (–1) × 1 + (–1) × 5 = –10, and the\nPd metal unit carries a formal charge of +10, resulting in a total d-electron count of 10\n8\n× 8 – 10 = 70 and an average of 70/8 = 8.75 d-electrons per Pd atom; for\nPd (PPh)(PPh )(S-Adm) (Pd ), the total ligand charge contribution is: (–2) × 1 + (0) ×\n6 3 6 6\n1 + (–1) × 6 = –8, thus the Pd metal unit carries a formal charge of +8, resulting in a\n6\n14\ntotal d-electron counts of 10 × 6 – 8 = 52 and an average of 52/6 = 8.67 d-electrons per\nPd atom; for Pd (PPh)(S-Adm) [(Ph P) O] (Pd –O), the total ligand charge\n5 4 2 2 5\ncontribution is: (–2) × 1 + (–1) × 4 + (0) × 1 = –6, thus the Pd metal unit carries a\n5\nformal charge of +6, resulting in a total d-electron counts of 10 × 5 – 6 = 44 and an\naverage of 44/5 = 8.80 d-electrons per Pd atom; for Pd (PPh)(S-Adm) [(Ph P) CH ]\n5 4 2 2 2\n(Pd –C), the total ligand charge contribution is: (–2) × 1 + (–1) × 4 + (0) × 1 = –6, thus\n5\nthe Pd metal unit carries a formal charge of +6, resulting in a total d-electron count of\n5\n10 × 5 – 6 = 44 and an average of 44/5 = 8.80 d-electrons per Pd atom....\nReference (Supplementary Information)\n9 'oxidation state' in IUPAC Compendium of Chemical Terminology, 5th ed.\nInternational Union of Pure and Applied Chemistry; 2025. Online version 5.0.0,\n(2025). DOI: 10.1351/goldbook.O04365.\n5.) Supplementary Fig. 2b: Replace “=” by proper arrows.\nResponse: Thank the reviewer for pointing that out, and we have replaced the “=” in\nSupplementary Fig. 2b with arrows as suggested.\nSupplementary Figure 2. (a) The synthesis routes of Pd ‒P, Pd ‒O, and Pd ‒C as well\n8 5 5\nas their reaction routes (b).\n6.) Is it reasonable to compare in the TOC contrast the interaction between the Pd\n5\nfragment and an arene fragment to that of Cp– and an arene ring? Have the authors\ndirectly compared these interactions?\nResponse: We thank the reviewer for the question. For comparison, we now provide\n15\nthe reduced density gradient (RDG) calculations for Cp–...arene ring interaction, which\nis described in the revised manuscript as shown below:\nPages 10-11\n...An intriguing finding in the crystal structure was that one phenyl (Ph) motif of the\nDPPM ligand in the Pd ‒C was pseudo-parallel to the metallic pentagon unit of the\n5\nadjacent Pd ‒C (face to face), separated by an inter-ring distance of 3.7 Å. This is\n5\nformally similar to π…π stacking between organic aromatic rings (e.g. between Ph and\nCp), indicating possible π…π-like interactions36 (Fig. 4a and 4e). Reduced density\ngradient (RDG) calculations revealed that the similar major van der Waals (vdW)\ninteraction between Ph and Pd ring (Fig. 4f), and between Ph and Cp45 (Supplementary\nbased on Hirshfeld partition (IGMH) analysis (Supplementary Fig. 22), which\npreviously disclosed the unreported nonmetal-aromatic ring to metallo-aromatic-ring\ninteractions23,46-50. Taken together, these results demonstrated that the metal-aromatic\nring was comparable to the nonmetal-aromatic ring....\nReference\nSoc. 112, 5525-5534 (1990).\nSupplementary Figure 21. The RDG representations of the interactions (left) between\nthe Ph ligand and the five-membered Pd ring and (right) between the C H (Ph) and the\n6 6\nC H ‒ (Cp) ring.\n5 5\nligand and the five-membered Pd ring (left) and between C H (Ph) and the C H ‒ (Cp)\n6 6 5 5\nring (right). isosurfaces of δginter function with isovalue of 0.004 a.u. colored by\nsign(λ )ρ according to the color bar are also shown.\n2\n7.) Figure S32: Can the authors please label/assign the individual redox events? Some\nof them seem to be not very reversible.\nResponse: Thank the reviewer for careful reading and good suggestion. Some\nasymmetrical peaks in the previous DPV curves were caused by the interferences from\ncontinuous N flow during DPV measurements. we optimized the experimental\n2\nprotocols by pausing N purging between anodic and cathodic scans and got symmetric\n2\nredox peaks as shown in the revised Supplementary Fig. 34 (which is also copied below\nfor the convenience of the Editor and the reviewers), displaying the electrochemical\nreversibility for these compounds. In the refined DPV curves, we have labelled the\noxidation (O1 and O2) and reduction(R1) states as shown below following the\nreviewer’s suggestion.\n5 5 6 8 8\nin degassed CH Cl containing 0.1 M Bu NPF with 1 mm diameter Pt working, SCE\n2 2 4 6\nreference, and carbon rod counter electrodes. Note: “O1”, “O2”, and “R1” denote the\nfirst oxidation, second oxidation, and first reduction, respectively.\n8.) One issue I have with the current manuscript is the authors’ insistence on classifying\nthe metal atom in a classic metallocene complex as electron acceptor, but there is an\nalso delta-backdonation from the metal to the empty orbitals of the Cp– or arene ring.\nThis interaction is completely ignored in the interest of stressing differences. From the\nbonding analysis I would argue that these systems as the “classic” d-transition metal\nmetallocenes share the feature of strongly covalent covalent molecules.\nResponse: Thank the reviewer for pointing that out. We agree that there is an also delta-\nbackdonation from the metal to the empty orbitals of the Cp– or arene ring in a classic\nmetallocene complex, but the similar interaction does not exist in our compounds (see\nadded “EDA-NOCV analysis of inverse palladocenes” section of the Supplementary\nInformation). We have added the information in the revised manuscript and stressed\nthis in the illustrations shown below. Furthermore, in all figures containing metallocene\nstructures, arrows have been replaced with solid lines to denote covalent interactions.\nPage 9\n...Unlike “classic” d-transition metal metallocenes, wherein the interaction between Cp\n(or its analogues) and the metal atom involves strong covalent bonding with both Cp\n(and its analogues)-to-metal atom electron donation and metal atom-to-empty orbitals\n18\nof Cp (and its analogues) -backdonation, inverse palladocenes have major orbital\ninteractions comprising of ligand-to-metal atom coordination, where the Pd aromatic\n5\nring served as electron acceptor (Supplementary Fig. 16a; the energy decomposition\nanalysis with natural orbitals for chemical valence (EDA-NOCV) of both metallocenes\nand inverse palladocenes are provided in the “EDA-NOCV analysis of inverse\npalladocenes” section of the Supplementary Information)....\nPages S34-35\nEDA-NOCV analysis of inverse palladocenes\nThe EDA-NOCV analysis uses charged fragments as the references8 according to their\nformal OSs in the complexes. A large charge flow in the direction [PH]2– →\n[Pd (SH) (H P) CH ]2+ (from red to blue in Supplementary Figure 49) is shown in\n5 4 2 2 2\nPd (PH)(SH) ((H P) CH ). In MnC H , there are two charge flow directions\n5 4 2 2 2 5 5\n(Supplementary Figure 49b), which come from the -donation and -backdonation,\nrespectively; after comparing their strength, it is found that the -donation is dominant\n(–112.80 kcal/mol) relative to the -backdonation (–77.17 kcal/mol), thus, the net\ncharge flow occurs in the direction of [C H ]1– → Mn1+ in MnC H .\n5 5 5 5\nSupplementary Table 5. The EDA-NOCV results on Pd (PH)(SH) ((H P) CH ) with\n5 4 2 2 2\ntwo fragments of [PH]2– and [Pd (SH) (H P) CH ]2+, and on MnC H with two\n5 4 2 2 2 5 5\nfragments of [C H ]1– and Mn1+. The energy unit is kcal/mol.\n5 5\nEnergy Terms Pd (PH)(SH) ((H P) CH ) MnC H\n5 4 2 2 2 5 5\nE -676.21 -278.93\nint\nE 1088.25 267.13\nPauli\nE -1393.51 -310.70\nelstat\nE -370.96 -235.36\norb\nE -112.54 -112.80\norb(1)\nE -100.42 -77.17\norb(2)\nE -80.15\norb(3)\nSupplementary Fig. 49. The contour line plots of the deformation densities, which are\nconnected to the pairwise interactions from E to E in (a)\norb(1) orb(3)\nPd (PH)(SH) ((H P) CH ) and from E to E in (b) MnC H molecules. The\n5 4 2 2 2 orb(1) orb(2) 5 5\ndirection of the charge flow is from red to blue in term of color denote.\nazide-bridged dicerium Complex. J. Am. Chem. Soc. 146, 7088-7096 (2024).\nFig. 4. Coordination and interaction mode of Pd pentagon unit in Pd ‒C inverse\n5\npalladocene. (a) Nonmetal-to-metallo-aromatic-ring coordination and nonmetal-\naromatic-ring to metallo-aromatic-ring π…π-like interactions.\nSupplementary Figure 1. The pentalene (C ) versus inverse metallocene-like structure\n8\nof Pd ‒S.\n8\nmetallocenes and metallocenes (together with their analogues). (b) The reported\naromatic Cr pentagons in large main group metal cages. (c) The reported main group\n5\nmetal aromatic ring to metal atom coordination. Note: the -backdonation from metal\natom to empty orbitals of Cp within metallocenes (and their analogues) is not marked\nin the figure.\nGraphical abstract\n21"}, {"round": 3, "reviewer_comments": {"reviewer_4": "In my opinion the authors addressed the comments raised by the referees in sufficient detail, and this has certainly improved the quality of the manuscript. From my perspective all relevant concerns were addresed and hence I would recommend acceptance of the manuscript."}, "author_response": "Manuscript number: NCOMMS-25-38974A-Z\nMS Type: Research Article\nTitle: “Inverse palladocenes”\nCorrespondence Author: Prof. Zhikun Wu\nWe thank Editor Eren Peterson and all the reviewers for their reading of the manuscript\nand helpful suggestions. Below our point-by-point response (or the words from the\nprevious manuscript) is in blue, revisions (except for figures) are in red, and the page\nnumber mentioned in the manuscript is referred to the version with revision marked.\nResponse to reviewer 1’ comments: pages 1-11\nResponse to reviewer 2’ comments: page 11\nResponse to reviewer 3’ comments: page 11\nResponse to reviewer 4’ comments: pages 11-21\nReviewers’ comments:\nReviewer 1:\nWhereas I have been initially undecided (if not tentatively supportive) relating to the\nmatch between Nat. Commun and this manuscript, the author’s rebuttal has flipped my\nassessment strongly in disfavor, as many – if not most – of my remarks are not properly\naddressed despite of the rebuttal’s 21 pages referring to my review. Some of the author's\nreplies are factually incorrect. Overall, the rebuttal casts serious doubts whether the\noverall manuscript has been composed with appropriate care/honesty to be published\nin a top-journal:\nResponse: Thank the reviewer for clarifying the previous assessment. We have to\nprovide a long rebuttal due to that Editor made a decision majorly basing on the\nreviewer’s evaluation. Thank the reviewer for understanding, and we apologize for any\npossible misunderstanding.\n1.) Being a synthetic chemist, I mentioned that I do not find the synthesis on its own\nimpressive, and that I consider the overall manuscript quite similar to the previous\nACIE manuscript, hence limiting to some extent novelty. I understand that others might\njudge this point differently. Yet, the authors’ reply “this is in strong contrast to the other\ntwo reviewers’ comments (see below)” is not ok: None of the other reviewers has\nassessed the novelty of the underlying synthesis; in fact, reviewer 2 specifically asks:\n“Question 1: What is the essential difference between Reference 15 (Angew. Chem. Int.\nEd. 63, e202313491 (2024).) and this study?”\nResponse: Thank the reviewer for the comments. We are sorry for the\npreviously\nimproper expression in response to reviewer 1’s evaluation of the synthetic aspects of\nour work. For question 1 raised by reviewer 2, we had clearly illustrated the essential\ndifferences between Reference 15 (Angew. Chem. Int. Ed. 63, e202313491 (2024).) and\n1\nthis study, which have been agreed by reviewer 2.\n2.) The authors correct my statement of “photothermal conversion in the NIR (850 nm)”\nwith “the longest laser irradiation wavelength was extended from the previous 808 (not\n850!) nm to 1208 nm”. However, Fig. 3, blue trace in Angew. Chem. Int. Ed. 63,\ne202313491 (2024) clearly indicates that the absorption band is centered way beyond\n826 nm. I understand, the authors refer to the laser, yet I was referring to the band…\nThis is not a major issue on its own, yet tentatively suggests that the rebuttal has not\nbeen composed with appropriate care and reflection.\nResponse: Thank the reviewer for the comments. The correction of the reviewer’s\nstatement was not the major care of the rebuttal, but rather to clarify the laser\nwavelength used in our work for better understanding. We apologize for any possible\nmisunderstanding.\n3.) I mentioned that the manuscript would benefit from carving out structure (i.e.\nPd /ligand) – property (i.e. PCE properties) relationships. This question was answered\n5\nwith the Sncp, although I mentioned the Sncp only later, i.e. it seems also this part of\nmy assessment was not read carefully and/or ignored…\nResponse: Thank the reviewer for the comments. We agree with the reviewer’s\ncomment that the manuscript would benefit from carving out structure (i.e. Pd /ligand)\n5\n– property (i.e. PCE properties) relationships, and we apologize for any possible\nmisunderstanding concerning this. We have further elaborated on the structure-property\nrelationship in the revised manuscript, as detailed below:\nPage 14\n...Specifically, Pd aromatic ring is the primary contributor of the NIR absorption and\n5\nthus strong conjugation within the Pd ring leads to intensive NIR absorption, enabling\n5\nenhanced photothermal conversion in the NIR-II window....\n4.) I questioned the usefulness of Sncp beyond more established descriptors (such as\nthese reviewed/developed by the Sola group). I am still not convinced that it is superior\nto these descriptors, as the authors just repeated its definition; I am certainly not\nconvinced that it deserves to be specifically highlighted…\nResponse: Thank the reviewer for the comments. The introduced Sncp was given the\nconsideration to both metal‒metal bond length uniformity and coplanarity, and can be\nused to evaluate the conjugation degrees of the Pd ring in various inverse palladocenes,\n5\nwhich interprets the photothermal conversion efficiency sequence of as-obtained\ninverse palladocenes well in this work, thus it is usefull. We don’t mean that it is\nsuperior to established descriptors, including these reviewed/developed by the Solà\ngroup (J. Phys. Chem. A 115, 13104–13113 (2011), but rather to mention that it is an\nalternative (supplement) to these established descriptors. Note that, one advantage of\nsuch a metric is that its value can be calculated based on experimental crystal data.\n5.) I pointed out that the assignment as a simple HOMO-LUMO transition is\n2\ninappropriate, as the transitions >950 nm (E <1.3 eV) have a very different energy to\nthe computed HOMO/LUMO gap (E = 2.4 eV = 500 nm), almost a factor of 2. The\nauthors replied, this is due to commonly known dependend on the amount of exact\nexchange, yet it is (of course) due to orbital mixing, i.e. this reply tentatively suggests\na general lack of understanding…\nResponse: Thank the reviewer for the comments. In the previous response, we have\nmentioned that the PBE0 functional can well reproduce the absorption spectra, but\nfailed to accurately predict the HOMO–LUMO gaps in our systems. To avoid possible\nargument, we now have replaced all PBE0-derived results with the alternative PBE-\ncalculated ones in the revised Fig. 5 and Supplementary Figs. 30-32, which are also\ncopied below for the convenience of the Editor and the reviewers. The PBE-calculated\nHOMO–LUMO gaps for Pd –C, Pd –O, Pd , and Pd –P are 1.09, 1.09, 1.21, and 1.16\n5 5 6 8\neV, respectively, which are in close agreement with their experimental optical gaps (see\nSupplementary Fig. 27 in the revised manuscript, as shown below).\nFig. 5. Optical property interpreting of Pd ‒C. (a) Experimental and simulated\nDisassembling the UV/Vis/NIR absorptions along three axial directions. (d)\nRelationship between the wavelengths and transition dipole moments along three axial\ndirections. (e) The selected frontier MO distributions.\nDisassembling the UV/Vis/NIR absorptions along three axial directions. (d)\nRelationship between the wavelength and transition dipole moments along three axial\ndirections. (e) The selected frontier MO distributions.\nSupplementary Figure 31. Optical property interpreting of Pd . (a) Simulated\nDisassembling the UV/Vis/NIR absorptions along three axial directions. (d)\nRelationship between the wavelength and transition dipole moments along three axial\ndirections. (e) The selected frontier MO distributions.\nDisassembling the UV/Vis/NIR absorptions along three axial directions. (d)\nRelationship between the wavelength and transition dipole moments along three axial\ndirections. (e) The selected frontier MO distributions.\nSupplementary Figure 27. Optical gap analysis of Pd ‒C, Pd –O, Pd , and Pd –P\n5 5 6 8\n(dissolved in toluene).\n6.) I pointed out that simply plotting canonical orbitals / partial charges do not allow to\nspecify overall oxidation states, and that \"charge state\" is imprecise language. However,\nI see that the authors still claim “Molecular orbital (MO) analysis verified the charge\nstate of Pd in various inverse palladocenes.” I note massive orbital mixing with the\nligand…\n“charge state”, which have been modified to “formal oxidation state” in the revised\nmanuscript, as copied below, since the oxidation state (OS) of an atom is the charge of\nthis atom after ionic approximation of its heteronuclear bonds (see “oxidation state” in\nIUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure\nand Applied Chemistry; 2025. Online version 5.0.0, 2025.\nhttps://doi.org/10.1351/goldbook.O04365). We agree that significant metal-ligand\norbital mixing occurs in these inverse palladocenes, but the formal oxidation states of\nthe constituent atoms in the ligands are determined based on their valence electron\nconfiguration. Specifically, the formal oxidation states of S-Adm, PPh , and PPh\n3\nligands are assigned to –1, 0, and –2, respectively. For the formal oxidation states of the\nPd metal units, they are calculated based on the charge-neutrality of the whole\nn\ncompounds. Taking Pd (PPh)(S-Adm) [(Ph P) CH ] (Pd –C) as an example, the formal\n5 4 2 2 2 5\noxidation state of the Pd unit is calculated to be +6 = 0 – (–2)  1 – (–1)  4 – 0  3.\n...Given the exact compositions and the recognized formal oxidation states (OSs) of\nligands [S-Adm]−, [PPh]2−, [Ph P=O]−, and PPh (−1, −2, −1, and 0, respectively; Note:\n2 3\nthe detailed analysis of the OS of phosphorus in inverse palladocenes is provided in the\n“Analysis of the OS of phosphorus in inverse palladocenes” section of the\nSupplementary Information), the average OSs of Pd in Pd –P, Pd , Pd ‒O, and Pd –C\n8 6 5 5\nwere calculated to be +1.25, +1.33, +1.2, and +1.2, respectively, indicating the low OSs\nof Pd across all these nanoclusters38. Molecular orbital (MO) analysis verified the OSs\nof Pd in various inverse palladocenes. Taking Pd –C as an example, the revealed three\n5\nempty MOs is consistent with the total OS of its five Pd atoms (+6) (Supplementary\nFig. 8). The low OSs of Pd were further authenticated using X-ray photoelectron\nspectroscopy (XPS) and natural population analysis (NPA) charge, as shown in Fig. 2g‒\nj and Supplementary Figs. 9‒12....\n7.) The authors claim in the letter that “Pd (PAr) clusters, planar Pd clusters, and Pd\n8 6 7 4\nclusters are sensitive to air atmosphere and require strict anhydrous- and oxygen-free\nconditions for synthesis. Due to the exceptional stability of the inverse palladocenes,\nthese novel materials provide great potentials for practical applications in common\n(aqueous-, oxygen-containing) conditions.” This statement is incorrect, the first\nexample is air stable and water-stable in boiling solvent. Generally, I would not consider\nthis oversight a major issue, yet given all the other inaccuracies, this seems troublesome.\nResponse: Thank the reviewer for pointing that out. We have checked the literature,\nand found that although Pd (PAr) was synthesized under strict anhydrous and\n8 6\nanaerobic conditions, it is indeed rather stable in air and water. However, the statement\nis correct for most of the reported Pd clusters. Therefore, we have modified the\nstatement in the revised manuscript as shown below. We apologize for the previously\nimprudent statement.\nPages 26-27\n6\n…Note that, inverse palladocenes with planar aromatic Pd ring unit and unanticipated\n5\nnonmental-to-metal aromatic Pd ring coordination are synthesized under aqueous-,\n5\noxygen-containing conditions and demonstrate remarkable stability in air atmosphere,\ndistinctly differing from reported Pd clusters such as cubic Pd (PAr) clusters56, planar\n8 6\nPd clusters57 and Pd clusters58 (which require strict anhydrous- and oxygen-free\n7 4\nconditions for synthesis and most of them are sensitive to air atmosphere).…\n8.) I mentioned it would be interesting to also include/mention/compare the P-signal in\nthe XPS analysis (which usually is obtained along the way of the Pd-measurement).\nThis comment has not been addressed; also this is on its own not a major issue, yet\nagain casts doubt about how carefully the rebuttal/manuscript has been composed.\nResponse: Thank the reviewer for pointing that out, and we apologize for the overlook.\nWe have added the information in the revised manuscript as shown below:\nPages S33-34\n...Analysis of the OS of phosphorus in inverse palladocenes\nXPS analysis revealed that the P(2p) signals for Pd ‒C, Pd –O, and Pd in the range of\n5 5 6\n130.95–131.33 eV (Supplementary Figs. 10–12) are consistent with those observed in\nphosphorus (III) compounds5 such as PdCl (PPh ) (131.5 eV) and PPh (130.9 eV),\n2 3 2 3\nbut they slightly differ from that in the Pd (PDip) cluster (130.2 eV) due to the OS\n8 6\ndifference (–3 vs –1)6. The OS of the dianionic [PPh]2‒ group is not only evidenced by\nthe aforementioned XPS analyses, but also supported by the repeated reports involving\nin related organometallic complexes (e.g. [LSc(μ-PAr)] (L = (MeC(NDIPP)CHC(Me)-\n2\n(NCH CH N(iPr) )), DIPP = 2,6-(iPr) C H ; Ar = 2,6-Me C H ), where [PAr]2‒ has an\n2 2 2 2 6 3 2 6 3\nOS of –27)...\nReferences (Supplementary Information)\nDatabase Number 20, National Institute of Standards and Technology,\nGaithersburg MD, 20899 (2000), DOI: https://dx.doi.org/10.18434/T4T88K,\n(accessed: 20.11.2023).\n8 6\n2400699 (2024).\ncomplex: Reduction, addition, and CO activation reactions. J. Am. Chem. Soc.\n135, 14784-14796 (2013).\n9.) The authors added Supplementary Table 8 to underscore the exceling PCE properties.\nHowever, I note that this table seems to compare apples with pears (solution vs. film),\nand that the properties of quite a bit of reference compounds seem still quite similar…\nResponse: Thank the reviewer for the comment. It is worth noting that the PCE\ncalculation adopt a standardized method, independent of sample states (J. Phys. Chem.\nsample states presentation in the revised Supplementary Information, which is also\ncopied below for the convenience of the Editor and the reviewers. As shown in the\nrevised Supplementary Table 9, Pd ‒C shows excellent photothermal performance in\n5\nterms of comprehensive irradiation power, response wavelength, temperature change,\nphotothermal conversion efficiency, and stability. Especially, given the consideration\nof the average PCE per metal atom (see Fig. 6c), it is much higher than that of most of\nthe reported photothermy materials.\nSupplementary Table 9. Comparison of the photothermal efficiency (η) between\nvarious materials\nLaser power Wavelength Temperature η\nSample Cycle Category\n(W/cm2) (nm) changes (T) (%)\nAu NPs 2.4 514 2 °C in 6 min <10 NP nanoparticles\nabout 33 °C in 30 six\nAu PBs 1.0 808 88.6 plasmonic\nmin cycles\nabout 31.5 °C in 30 six\nAu PBs 1.0 1064 80.8 plasmonic\nmin cycles\nabout 26 °C in 5 five\nAu NDs 0.4 1064 84.9 nanodumbbells\nmin cycles\nabout 34.5 °C in 5 five\nAuNCs@SiO2 0.5 1064 82.2 nanochains\nmin cycles\nAu/TiO2 0.5 532 11.5 °C NP NP nanoparticles\nSi-GO 4.0 532 40 °C in 10 min NP NP nanoparticles\nNS-40 0.32 532 12 °C in 6 min 42.8 NP nanoparticles\nNS-60 0.32 532 9 °C in 6 min 30.6 NP nanoparticles\nAu NPs 0.34 532 52 °C in 10 min 62.9 NP nanoparticles\nabout 17.5 °C in 10 six\nGA-CuFeSe2 0.27 532 79.6 nanoparticles\nmin cycles\nAu NP-Packed\n0.15 532 220 °C in 2 s NP NP nanoparticles\nSpheres\nAuNP–mTHPC\n0.015 532 0.3 °C in 2 min NP NP nanoparticles\ncomplex\nACA 1.3 532 10 °C in 6 min NP NP nanoparticles\nthree\nGO 1.3 532 17 oC in 30 s NP\ncycles inorganic materials\nAu37(CHT)23 0.25 650 12 oC in 5 min 30.3 NP nanoclusters\nAu48(CHT)26 0.25 650 17.2 oC in 5 min 42.9 NP nanoclusters\n15−36.8 °C in 10 three\nTNMs 1.0 660 41.0 organic materials\nmin. cycles\nsix\nAg155 0.1 660 39.1 °C in 6 min NP nanoclusters\ncycles\nAu42 1.0 808 27 °C in 5 min. NP NP nanoclusters\nUiO-66@PAN 1.5 808 21.6\n10 min cycles materials\nfive MOF-based\nZr-PDI•– 0.7 808 89 °C in 200 s 52.3\ncycles materials\nfour\nAg18 5.0 808 28 °C in 5 min NP nanoclusters\ncycles\nAg18 0.35 808 337 °C in 4 s NP NP nanoclusters\n(AgCu)31 1.0 532 56.9 °C in 10 min 67.6 NP nanoclusters\nabout 46 °C in 5 five\nIR-SS NPs 1.0 1064 77 small molecules\nmin cycles\nthree\nPt@PDA-c 1.0 1064 27.5 71.3 nanoparticles\nsolution cycles\nAu nanoshells 2.0 800 15 °C in 5 min 13 NP nanoparticles\nAu nanorods 2.0 800 22 °C in 5 min 21 NP nanoparticles\nCu2-xSe 2.0 800 22 °C in 5 min 22 NP nanoparticles\nCu9S5 nanocrystals 0.51 980 15.1 °C in 10 min 25.7 NP nanoparticles\nCuS NPs NP 1280 10.2 °C in 15 min 93 NP nanodisks\nCuS nanoflakes NP 1064 NP 72 NP nanoflakes\nthree\nCPP 2.33 808 29.3 °C in 3 min 42.5 organic materials\ncycles\nDpa-melanin CNSs 2.0 808 33.6 °C in 500 s 40 NP nanoparticles\nabout 23.5 °C in 9\nCuO/Cu2O TNCs 0.3 808 73 NP nanocubes\nmin\nabout 16 °C in 9\nCuO/Cu2O TNCs 0.3 1064 67 NP nanocubes\nmin\nabout 25 °C in 9\nCuO/Cu2O TNCs 0.3 1550 78 NP nanocubes\nmin\nsix\ndpGCS NCs 1.0 1064 33.8 °C in 10 min 71 nanocrystals\ncycles\nabout 44 °C in 9 five\nJanus-GCS NCs 1.0 1064 76.1 nanocrystals\nmin cycles\nBPDI/(CB[7])2 1.0 808 19.5 °C in 10 min 31.6 NP organic materials\nfive MOF-based hybrid\nPMCS 2.0 808 11.5 °C in 14 min 33\ncycles materials\nsix\nPBI-[GD]2 1.0 808 34.1 °C in 17 min 59.5 PDI-based radicals\ncycles\nsix\nPBI-[GY]2 1.0 808 27.7 °C in 22 min 49.1 PDI-based radicals\ncycles\nfive\nDTC 0.7 808 37 °C in 10 min 18.8 organic materials\ncycles\nfive organic\ntfm-BDP NPs 0.3 808 54 °C in 5 min 88.3\ndispersion cycles nanoparticles\norganic\nm-BDP 0.3 671 29 °C in 5 min 32 NP\nnanoparticles\n9\norganic\nH-BDP 0.3 671 20 °C in 5 min 50 NP\nnanoparticles\nabout 14.2 °C in 20\nPd SAzyme 0.69 1064 33.9 NP nanoparticles\nsolution in 20 min\nsix organic\nBAF4 NPs 0.75 1064 35 °C in 15 min 80\ncycles nanoparticles\nhexagonal\npalladium 1.0 808 20.7 °C in 10 min NP NP nanosheets\nsolution min\nnanosheets\nSPNS 1.0 808 20.8 °C in 10 min NP NP nanosheets\nPNS–DOX 2.86 808 23.2 °C in 10 min NP NP nanosheets\nSPNS 1.0 808 35.3 °C in 10 min 52 NP nanosheets\norganic\nF-PANP 0.5 808 24.4 °C in 5 min 48.5 NP\nnanoparticles\neight organic\nTPT–TT NPs 2.0 808 33.6 °C in 10 min 32\ncycles nanoparticles\norganic\nPPy NPs 1.0 808 25 °C in 10 min 44.7 NP\nnanoparticles\nabout 25 °C in 5 organic\nPPY@PAA/fmSiO2 2.0 808 31.3 NP\nmin nanoparticles\nabout 29 °C in 5 twenty\nDA CNDs 1.5 808 35 nanodots\nmin cycles\ncarbon dots 2.0 671 30.1 °C in 12 min 38.5 NP nanodots\nPEGylated Sb NPs 2.0 808 51 °C in 5 min 41 NP nanoparticles\nfive\nCys-CuS NPs 0.72 980 18.5 °C in 5 min 38 nanoparticles\ncycles\nabout 19 °C in 10 six\nFe3O4@Cu2−xS 0.6 980 16 nanoparticles\ndispersion 10 min cycles\nten\nGCNCs 0.5 808 19.9 °C in 13 min 40.4 nanocubes\ncycles\nfive\nPt Spirals 1.2 1120 33.1 °C in 1000 s 52.5 nanoparticles\ncycles\nPt/Te nano five\n1.5 808 33.4 °C in 8 min 51.8 nanoparticles\nheterostructures cycles\nfive\nHA-Au@Pt 1.5 808 30.0 °C in 10 min 63.5 nanoparticles\nsolution cycles\nPorous Pt NPs 1.24 808 38.2 °C in 30 min 97.0 NP nanoparticles\nPorous Pt NPs 1.24 980 34.5 °C in 30 min 89.9 NP nanoparticles\nBP/Pt-Ce6@PEG\n0.8 660 19.8 °C in 10 min NP NP nanoparticles\nNSs\nsix\nPt23 1.0 532 54.2 °C in 10 min 68.4 nanoclusters\ncycles\neight\nPd8‒S 0.5 808 32.8 °C in 7 min 73.3 inverse palladocene\ncycles\nPd8‒P (this work) 0.3 980 11.2 °C in 30 s 20.3 NP inverse palladocene\nPd8‒S (this work) 0.3 980 11.6 °C in 30 s 24.1 NP inverse palladocene\nPd6 (this work) 0.3 980 26.5 °C in 30 s 51.8 NP inverse palladocene\nPd5‒O (this work) 0.3 980 37.5 °C in 30 s 68.1 NP inverse palladocene\neight\nPd5‒C (this work) 0.3 980 50.4 °C in 30 s 73.6 inverse palladocene\ncycles\nPd5‒C (this work) 0.3 1064 16.7 °C in 30 s 36.2 NP inverse palladocene\nPd5‒C (this work) 0.3 1208 4.0 °C in 30 s 18.7 NP inverse palladocene\nReviewer 2:\nThe authors have addressed all my comments. Thus, I'd like to recommend its\npublication in the present form.\nResponse: Thank the reviewer for recommending the publication of this work in the\npresent form.\nReviewer 3:\nThe author has thoroughly addressed all the questions raised by the reviewers and\nprovided clear and detailed responses. We believe the article is now ready for\npublication.\nResponse: Thank the reviewer for highly positive comments.\nReviewer 4:\nThe authors did a thorough job in addressing the questions raised by the different\nreviewers. The manuscript is written well and the complexes have been thorough\ninvestigated and analyzed. So the methodology is sound and most claims are supported\nby experimental findings.\nI agree with referee 1 that the current manuscript is an extension to the authors’ previous\nwork reported in Angewandte Chemie. However, the current contribution contains\nnovel aspects and also shows that this seems to be a novel class of compounds for which\ndifferent derivatives can be prepared. Hence, I would argue that there is enough novelty\nto argue for Nature Communications.\nHowever, I would request some revisions and changes:\nResponse: Thank the reviewer for highly positive comments.\n1.) The yields are in some cases rather poor. Can the authors please explicitly specify\nhow much material (in mg) was actually isolated in each case. The reported isolated\nyield is based on which starting material?\nResponse: Thank the reviewer for the suggestion and question, and we have provided\nthe information in the revised manuscript as shown below:\n... Pd\n8\n‒P was isolated from the crude product of 20 combined reaction batches by\npreparative thin-layer chromatography (PTLC) in 1.2 mg (yield: 2%, based on the\nstarting material Pd ‒S)....\n... Pd\n6\nwas isolated from the crude product by PTLC in 22.4 mg (yield: 30%, based on\nthe starting material Pd(CH COO) )....\n3 2\nPage 26\n... Pd\n5\n‒O was isolated from the crude product of 20 combined reaction batches by PTLC\nin 1.5 mg (yield: 3%, based on the starting material Pd\n6\n)....\nPage 26\n... Pd\n5\n‒C was isolated from the crude product by PTLC in 9.8 mg (yield: 13%, based on\nthe starting material Pd(CH COO) )....\n3 2\nPage S33\n... Pd ‒Owas isolated from the crude product by PTLC in 7.6 mg (yield: 10%, based\n5\non the starting material Pd(CH COO) )....\n3 2\n2.) What happens if the synthesis is actually performed under strictly\nanaerobic/anahydrous conditions? Would these materials be then isolated at all?\nResponse: Thank the reviewer for the good question. Following the reviewer’s\nsuggestion, we tried the synthesis of Pd ‒C under strictly anaerobic/anahydrous\n5\nconditions; however, this effort did not yield the target product. To elucidate the role of\nwater and oxygen in the formation of inverse palladocenes, we conducted controlled\nexperiments. The investigations revealed that the presence of water is essential for\ngenerating the target product, whereas O offers no assistance to the reaction. The\n2\ndetails are provided in the “Water/oxygen regulation on the synthesis of Pd ‒C” section\n5\nof the revised Supplementary Information as shown below:\nPages S30-32\n…Water/oxygen regulation on the synthesis of Pd ‒C\npalladocenes, we carried out a study on water/oxygen regulation during the synthesis\nof Pd ‒C (Supplementary Figure 47). The specific procedure is as follows:\n5\n(1) Synthesis attempt of Pd ‒C under strictly anaerobic/anahydrous conditions\n5\n(Supplementary Figure 47c): under a N atmosphere, Pd(CH COO) (50.0 mg, 0.223\n2 3 2\nmmol) and DPPM (100.0 mg, 0.260 mmol) were co-dissolved in 8 mL of THF in a\nSchlenk tube with continuous stirring for 5 min, accompanied by a solution color\nchange from yellow to red. Then, a MeOH/THF mixed solvent (1:9; 1 mL) containing\nNaBH (100.0 mg, 2.643 mmol) and Adm-SH (150.0 mg, 0.891 mmol) was\n4\nimmediately added all at once under vigorous stirring, resulting in the solution color\n12\nchanging from red to dark (note: without the participation of MeOH, NaBH is difficult\n4\nto dissolve and participate in the reaction, leading only to [Pd(S-Adm) ] complexes3,\n2 n\nsee Supplementary Figure 47b). After 30 min.’s reaction, the THF solution was\nevaporated to dryness under vacuum, and the residue was re-dissolved in toluene (10\nmL) and heated at 80 oC for 24 h. Then the black organic layer was washed with\nmethanol three times. The crude product was isolated using PTLC, without Pd ‒C\n5\nobserved. Subsequent UV-Vis spectral analysis of the crude product revealed the\nmaximum absorption at 440 nm, indicating the presence of multi-disperse Pd\nnanoparticles.\n(2) Synthesis attempt of Pd ‒C under an oxygen atmosphere (Supplementary Figure\n5\n47c): following the synthesis protocols described above, after the immediate addition\nof a MeOH/THF mixed solvent (1:9; 1 mL) containing NaBH (100.0 mg, 2.643 mmol)\n4\nand Adm-SH (150.0 mg, 0.891 mmol), the N atmosphere was replaced with O , and\n2 2\nthe subsequent operations were conducted as per those of process (1). After the reaction\nwas completed, PTLC and UV-Vis spectral analysis revealed that the as-obtained\nproducts were similar to those synthesized under strictly anaerobic/anhydrous\nconditions.\n(3) Synthesis attempt of Pd ‒C under a water-containing atmosphere (Supplementary\nimmediate addition of a MeOH/THF mixed solvent (1:9; 1 mL) containing NaBH\n4\n(100.0 mg, 2.643 mmol) and Adm-SH (150.0 mg, 0.891 mmol), 1 mL of water was\nadded, and the subsequent operations were conducted as per those of the process (1).\nAfter the reaction was completed, Pd ‒C was isolated from the crude product by PTLC\n5\nin 31.7 mg (yield: 42%, based on the starting material Pd(CH COO) ).…\n3 2\nSupplementary Figure 47. Water/oxygen regulation on the synthesis of Pd ‒C.\nconditions: [Pd(S-Adm) ] complexes (b), multi-disperse Pd nanoparticles (c), and\n2 n\nPd ‒C (d).\n5\n3. Chen, J. et al. Synthesis and properties evolution of a family of tiara-like\nphenylethanethiolated palladium nanoclusters. Sci. Rep. 5, 16628 (2015).\n3.) Please be more specific with the comment: “The thiolate type influences the final\nproducts due to the space and electronic effects.” This is a rather general comment.\nWhat is more important sterics or electronics?\nResponse: Thank the reviewer for the criticism, and we specified the comment\nfollowing the reviewer’s suggestion in the revised manuscript as shown below.\nPage 5\n…The thiolate type influences the final products due to the space and electronic effects,\nwhich influence the formation kinetics and thermodynamics of the products. In our case,\nthe space effect looks more prominent than the electronic effect since only very bulky\n1-adamantanethiol led to the production of Pd –C among the investigated thiolates. For\n5\nthe other thiol (including those with close electronic effects), they led to Pd\nnanoparticles or complexes as shown in the Supplementary Fig. 5.…\n4.) Include in the SI the d-electron counts per palladium atom. In their reply to referee\n1 the authors state: “Given that Pd has a d10 electron configuration, the d-electron\ncounts of Pd –S, Pd –P, Pd , Pd ‒O, and Pd –C are concluded to be 70, 70, 64, 44 and\n8 8 6 5 5\n44, respectively, on the basis of the charge state of Pd.” What do the authors mean with\nthe numbers: 70, 70, 64, 44 and 44?\nResponse: Thank the reviewer for the suggestion and the question, and we further\ninterpreted the d-electron counts and added the information in the revised manuscript\nas shown below:\nPages S35-36\n...d-Electron counts of inverse palladocenes\nGiven the strong metal–ligand and metal–metal interactions, along with significant\norbital mixing within multi-metal nanocluster systems, we assigned the formal\noxidation states of Pd basing on the IUPAC definition9. For Pd (PPh) (PPh ) (S-Adm) (Pd –S),\n8 2 3 2 6 8\nthe total ligand charge contribution is calculated as: (–2) × 2 + (0) × 2 + (–1)\n× 6 = –10 based on the facts that PPh group is dianionic, PPh /(Ph P) O/(Ph P) CH\n3 2 2 2 2 2\ngroup is neutral, and S-Adm/Ph₂P=O group is monoanionic. Therefore, the Pd metal\n8\nunit carries a formal charge of +10 to maintain charge neutrality. Given that every free\nPd atom has 10 d-electrons (d10 configuration), the total d-electron count for the Pd\n8\nunit in Pd –S is 10 × 8 – 10 = 70, corresponding to an average of 70/8 = 8.75 d-electrons\n8\nper Pd atom. Similarly, for Pd (PPh) (PPh ) (Ph P=O)(S-Adm) (Pd –P), the total\n8 2 3 2 2 5 8\nligand charge contribution is: (–2) × 2 + (0) × 2 + (–1) × 1 + (–1) × 5 = –10, and the\nPd metal unit carries a formal charge of +10, resulting in a total d-electron count of 10\n8\n× 8 – 10 = 70 and an average of 70/8 = 8.75 d-electrons per Pd atom; for\nPd (PPh)(PPh )(S-Adm) (Pd ), the total ligand charge contribution is: (–2) × 1 + (0) ×\n6 3 6 6\n1 + (–1) × 6 = –8, thus the Pd metal unit carries a formal charge of +8, resulting in a\n6\n14\ntotal d-electron counts of 10 × 6 – 8 = 52 and an average of 52/6 = 8.67 d-electrons per\nPd atom; for Pd (PPh)(S-Adm) [(Ph P) O] (Pd –O), the total ligand charge\n5 4 2 2 5\ncontribution is: (–2) × 1 + (–1) × 4 + (0) × 1 = –6, thus the Pd metal unit carries a\n5\nformal charge of +6, resulting in a total d-electron counts of 10 × 5 – 6 = 44 and an\naverage of 44/5 = 8.80 d-electrons per Pd atom; for Pd (PPh)(S-Adm) [(Ph P) CH ]\n5 4 2 2 2\n(Pd –C), the total ligand charge contribution is: (–2) × 1 + (–1) × 4 + (0) × 1 = –6, thus\n5\nthe Pd metal unit carries a formal charge of +6, resulting in a total d-electron count of\n5\n10 × 5 – 6 = 44 and an average of 44/5 = 8.80 d-electrons per Pd atom....\nReference (Supplementary Information)\n9 'oxidation state' in IUPAC Compendium of Chemical Terminology, 5th ed.\nInternational Union of Pure and Applied Chemistry; 2025. Online version 5.0.0,\n(2025). DOI: 10.1351/goldbook.O04365.\n5.) Supplementary Fig. 2b: Replace “=” by proper arrows.\nResponse: Thank the reviewer for pointing that out, and we have replaced the “=” in\nSupplementary Fig. 2b with arrows as suggested.\nSupplementary Figure 2. (a) The synthesis routes of Pd ‒P, Pd ‒O, and Pd ‒C as well\n8 5 5\nas their reaction routes (b).\n6.) Is it reasonable to compare in the TOC contrast the interaction between the Pd\n5\nfragment and an arene fragment to that of Cp– and an arene ring? Have the authors\ndirectly compared these interactions?\nResponse: We thank the reviewer for the question. For comparison, we now provide\n15\nthe reduced density gradient (RDG) calculations for Cp–...arene ring interaction, which\nis described in the revised manuscript as shown below:\nPages 10-11\n...An intriguing finding in the crystal structure was that one phenyl (Ph) motif of the\nDPPM ligand in the Pd ‒C was pseudo-parallel to the metallic pentagon unit of the\n5\nadjacent Pd ‒C (face to face), separated by an inter-ring distance of 3.7 Å. This is\n5\nformally similar to π…π stacking between organic aromatic rings (e.g. between Ph and\nCp), indicating possible π…π-like interactions36 (Fig. 4a and 4e). Reduced density\ngradient (RDG) calculations revealed that the similar major van der Waals (vdW)\ninteraction between Ph and Pd ring (Fig. 4f), and between Ph and Cp45 (Supplementary\nbased on Hirshfeld partition (IGMH) analysis (Supplementary Fig. 22), which\npreviously disclosed the unreported nonmetal-aromatic ring to metallo-aromatic-ring\ninteractions23,46-50. Taken together, these results demonstrated that the metal-aromatic\nring was comparable to the nonmetal-aromatic ring....\nReference\nSoc. 112, 5525-5534 (1990).\nSupplementary Figure 21. The RDG representations of the interactions (left) between\nthe Ph ligand and the five-membered Pd ring and (right) between the C H (Ph) and the\n6 6\nC H ‒ (Cp) ring.\n5 5\nligand and the five-membered Pd ring (left) and between C H (Ph) and the C H ‒ (Cp)\n6 6 5 5\nring (right). isosurfaces of δginter function with isovalue of 0.004 a.u. colored by\nsign(λ )ρ according to the color bar are also shown.\n2\n7.) Figure S32: Can the authors please label/assign the individual redox events? Some\nof them seem to be not very reversible.\nResponse: Thank the reviewer for careful reading and good suggestion. Some\nasymmetrical peaks in the previous DPV curves were caused by the interferences from\ncontinuous N flow during DPV measurements. we optimized the experimental\n2\nprotocols by pausing N purging between anodic and cathodic scans and got symmetric\n2\nredox peaks as shown in the revised Supplementary Fig. 34 (which is also copied below\nfor the convenience of the Editor and the reviewers), displaying the electrochemical\nreversibility for these compounds. In the refined DPV curves, we have labelled the\noxidation (O1 and O2) and reduction(R1) states as shown below following the\nreviewer’s suggestion.\n5 5 6 8 8\nin degassed CH Cl containing 0.1 M Bu NPF with 1 mm diameter Pt working, SCE\n2 2 4 6\nreference, and carbon rod counter electrodes. Note: “O1”, “O2”, and “R1” denote the\nfirst oxidation, second oxidation, and first reduction, respectively.\n8.) One issue I have with the current manuscript is the authors’ insistence on classifying\nthe metal atom in a classic metallocene complex as electron acceptor, but there is an\nalso delta-backdonation from the metal to the empty orbitals of the Cp– or arene ring.\nThis interaction is completely ignored in the interest of stressing differences. From the\nbonding analysis I would argue that these systems as the “classic” d-transition metal\nmetallocenes share the feature of strongly covalent covalent molecules.\nResponse: Thank the reviewer for pointing that out. We agree that there is an also delta-\nbackdonation from the metal to the empty orbitals of the Cp– or arene ring in a classic\nmetallocene complex, but the similar interaction does not exist in our compounds (see\nadded “EDA-NOCV analysis of inverse palladocenes” section of the Supplementary\nInformation). We have added the information in the revised manuscript and stressed\nthis in the illustrations shown below. Furthermore, in all figures containing metallocene\nstructures, arrows have been replaced with solid lines to denote covalent interactions.\nPage 9\n...Unlike “classic” d-transition metal metallocenes, wherein the interaction between Cp\n(or its analogues) and the metal atom involves strong covalent bonding with both Cp\n(and its analogues)-to-metal atom electron donation and metal atom-to-empty orbitals\n18\nof Cp (and its analogues) -backdonation, inverse palladocenes have major orbital\ninteractions comprising of ligand-to-metal atom coordination, where the Pd aromatic\n5\nring served as electron acceptor (Supplementary Fig. 16a; the energy decomposition\nanalysis with natural orbitals for chemical valence (EDA-NOCV) of both metallocenes\nand inverse palladocenes are provided in the “EDA-NOCV analysis of inverse\npalladocenes” section of the Supplementary Information)....\nPages S34-35\nEDA-NOCV analysis of inverse palladocenes\nThe EDA-NOCV analysis uses charged fragments as the references8 according to their\nformal OSs in the complexes. A large charge flow in the direction [PH]2– →\n[Pd (SH) (H P) CH ]2+ (from red to blue in Supplementary Figure 49) is shown in\n5 4 2 2 2\nPd (PH)(SH) ((H P) CH ). In MnC H , there are two charge flow directions\n5 4 2 2 2 5 5\n(Supplementary Figure 49b), which come from the -donation and -backdonation,\nrespectively; after comparing their strength, it is found that the -donation is dominant\n(–112.80 kcal/mol) relative to the -backdonation (–77.17 kcal/mol), thus, the net\ncharge flow occurs in the direction of [C H ]1– → Mn1+ in MnC H .\n5 5 5 5\nSupplementary Table 5. The EDA-NOCV results on Pd (PH)(SH) ((H P) CH ) with\n5 4 2 2 2\ntwo fragments of [PH]2– and [Pd (SH) (H P) CH ]2+, and on MnC H with two\n5 4 2 2 2 5 5\nfragments of [C H ]1– and Mn1+. The energy unit is kcal/mol.\n5 5\nEnergy Terms Pd (PH)(SH) ((H P) CH ) MnC H\n5 4 2 2 2 5 5\nE -676.21 -278.93\nint\nE 1088.25 267.13\nPauli\nE -1393.51 -310.70\nelstat\nE -370.96 -235.36\norb\nE -112.54 -112.80\norb(1)\nE -100.42 -77.17\norb(2)\nE -80.15\norb(3)\nSupplementary Fig. 49. The contour line plots of the deformation densities, which are\nconnected to the pairwise interactions from E to E in (a)\norb(1) orb(3)\nPd (PH)(SH) ((H P) CH ) and from E to E in (b) MnC H molecules. The\n5 4 2 2 2 orb(1) orb(2) 5 5\ndirection of the charge flow is from red to blue in term of color denote.\nazide-bridged dicerium Complex. J. Am. Chem. Soc. 146, 7088-7096 (2024).\nFig. 4. Coordination and interaction mode of Pd pentagon unit in Pd ‒C inverse\n5\npalladocene. (a) Nonmetal-to-metallo-aromatic-ring coordination and nonmetal-\naromatic-ring to metallo-aromatic-ring π…π-like interactions.\nSupplementary Figure 1. The pentalene (C ) versus inverse metallocene-like structure\n8\nof Pd ‒S.\n8\nmetallocenes and metallocenes (together with their analogues). (b) The reported\naromatic Cr pentagons in large main group metal cages. (c) The reported main group\n5\nmetal aromatic ring to metal atom coordination. Note: the -backdonation from metal\natom to empty orbitals of Cp within metallocenes (and their analogues) is not marked\nin the figure.\nGraphical abstract\n21"}]

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