Glass formation in hybrid metal halides via breaking molecular rotational order

Domain: neuroscience
Published: 2026-01-22
Editorial outcome: major_revision

Abstract
The critical progression of structural disorder, which governs the bulk glass-forming ability (GFA), can be elucidated as an ergodicity-breaking process. Understanding the atomic characteristics involved is imperative for establishing advanced glass design principles. However, conventional glasses present significant challenges due to their inherently complex and ambiguous disorder motifs, such as intricate and random atomic clusters or ring distributions. In this work, we synthesize a family of zero-dimensional hybrid metal halides with tunable short-to-medium-range structural arrangements to form glasses with diverse GFAs. Through altering molecular shape and surface electrostatic potential of organic cations, their rotational order is able to be broken in a controlled manner. This leads to distinct phase space partitions of molecular movements, allowing for tunable GFAs. Our findings provide a fundamental design approach for synthesizing property-oriented glasses by controlling molecular rotational order, which can be applicable to a wide range of molecular glasses and amorphous solids.

Introduction
Glasses, as non-periodic systems, possess inherent disorder and non-equilibrium states1–3, which are normally obtained through rapid cooling viscous melts, bypassing the crystallization process. During the liquid-glass transition, the atoms evolve from a non-localized state to a localized arrangement, while the disorder significantly remains4–9. From a perspective of dynamics, vitrification can be described as a process where atoms, experiencing any recurring states, are frozen to specific configurations. This is termed as the ergodicity breaking10, wherein structural disorder disperses across discrete phase space partitions, to allow the emergence of various localized motifs with similar energy11,12. Such a unique characteristic heavily depends on the formation dynamics, leading to elusive atomic arrangements in glasses and thus diverse properties13–18.

In the context of violating ergodicity, the sampling of adequate number of configurations of atoms and molecules, which determines the pathway of retarding nucleation and crystallization, would be frustrated. As this is strongly dependent on the motif of basic components and nature of atomic/molecular interactions19, how to design and manipulate the primary structural units is the key to engineer properties of glasses. However, the primitive ringed motifs in network-forming inorganic glasses have abundant varieties and are often intimately interwoven20–22. This complicates the confirmation of basic structural units and the possibility of modular control. In metallic glasses, the compositional clusters exhibit high diversity in both configurations and numbers of atoms23,24, so they normally only can be statistically described rather than quantitatively resolved25. In this context, selecting prototypical glass systems composed of definite components could provide insight into unravelling the structural and energetic evolution across ergodic-breaking, hence offering possibilities of engineering the formation abilities and properties of glasses.

Zero-dimensional (0D) hybrid metal halides, A2[MnBr4] (A= organic phosphonium cation), are a subclass of molecular solids, where the tetrahedral MnBr4 and pyramidal organic cations are associated via electrostatic interactions26–28. These materials form both crystals and glasses fairly easy, but with a wide range of temperatures both for melting and for the forming of the glass state on cooling the molten state (Tm and Tg respectively)29. In the crystalline phases, the length scales of [MnBr4]2− tetrahedra and the phosphonium cations are about 4.0 and 12.0–16.0 Å, respectively. The alternatively distributed [MnBr4]2− moieties show generally similar tetrahedra symmetry across all analogous compounds. The arrangement of the organic cations with distinct shape and polarity, spanning the short-range to medium-range order (MRO) scale within the phase space, is primarily responsible for the glass-forming ability (GFA, Fig. 1a). By thermally quenching the A2[MnBr4] melts, the fast flexing and rotating phosphonium cations are frozen, and settled at discrete energy positions in a random manner, which breaks the rotational ordering to form glass. Therefore, controlling the glass formation of A2[MnBr4] can be achieved by manipulating the ergodicity breaking of the organic cation.

In this work, nine A2[MnBr4] glasses were synthesized using the melt-quenched method (Fig. 1b, c and Supplementary Fig. 1). By applying molecular design principles, systems formed by different organic phosphonium cations show diverse GFAs. The organic cations, selected with different shapes and molecular electrostatic potential (ESP, describing the static distributions of charge around a molecule), give rise to distinct rotational disorder and broken ergodicity, hence versatile GFAs and properties. These glasses exhibit excellent processability, allowing for manufacturing in both the bulk (Fig. 1d and Supplementary Movie 1) and micron-sized fibers (Fig. 1e and Supplementary Fig. 2). Notably, the halide glasses are highly sensitive to X-ray radiation, making them promising scintillator materials with ease of manufacturing.

Results
Powder X-ray diffraction and pair distribution function (PDF) experiments were conducted before and after the melt-quenching to characterize the vitreous states of the formed glasses. In the case of [TPP]2[MnBr4] (TPP=tetraphenylphosphonium)30, where both the organic cations and MnBr4 anions are tetrahedral, the diffraction pattern of the melt-quenched sample closely resembles that of the parent phase, indicating no formation of glass (Supplementary Fig. 3). Conversely, other melt-quenched compounds, in which one phenyl group of TPP is substituted by aliphatic and benzyl side chains (denoted as Category I and II, Supplementary Data 1), show different behavior. Their diffraction patterns exhibit slight displacement and broadening upon heating (Supplementary Fig. 4), and do not show any significant Bragg peaks after quenching (Fig. 2a, Supplementary Fig. 3, and Supplementary Tables 1–3), indicating the absence of crystallinity. For the modified TPP derivatives, substituting one benzene ring with an aliphatic or benzyl group breaks the molecular symmetry. This modification introduces steric hindrance that prevents the structure from easily reordering into a crystalline phase during quenching. Although these side branches can rotate, their motion may be insufficient to restore the long-range translational symmetry, thereby suppressing the recrystallization process. This, in turn, facilitates the formation of a glassy phase. The observation is substantiated by the isotropic optical feature observed in the glassy samples under polarimetric imaging microscopy (Supplementary Fig. 5).

The PDF D(r) patterns of the crystalline and glassy samples are broadly similar below 5 Å, while all peaks in the range of 5–30 Å show significant flat feature for the melt-quenched counterparts (Fig. 2b and Supplementary Figs. 6 and 7; the glass form is denoted as a-A2[MnBr4]). Such phenomena reveal the breakdown of translational symmetry and corresponding loss of the MRO in the structure31. This implies that the disorder is attributed to the randomly-distributed organic cations resulting from the disruption of their freely-rotating molecular states. Additionally, reverse Monte Carlo (RMC) modeling based on experimental PDF data was conducted to elucidate the molecular arrangements of the phosphonium cations and [MnBr4]2− anions. The simulated and experimental D(r) and S(Q) are shown in Supplementary Figs. 8 and 9. The RMC models reveal that both the [MnBr4]2− and phosphonium cations maintain their molecular geometries, while displaying increased configuration and orientation diversity, indicative of the enhanced disorder upon vitrification (Fig. 2c and Supplementary Figs. 10 and 11). To quantify the rotational disorder, the orientational tensor Q was constructed from the RMC-derived models, and the maximum eigenvalue was extracted as the orientational order parameter Smax32:

Q = 3/2 <uuT> - 1/2 I (1)

where u is the unit vector along each P–C bond linking the phosphorus atom to the non-aromatic carbon atom, uT is the transpose of the orientation vector, and I is the identity matrix. Smax ranges from approximately 0.01 to 0.05, indicating pronounced rotational disorder (Supplementary Fig. 12). Lower Smax values, such as those of [c-PrMeTPP]2[MnBr4] and [BuTPP]2[MnBr4], correspond to broader orientational distributions and easier local reorientations. These features reflect weakened cooperative structural constraints, thus tending to reduce Tg while enhancing GFA. Conversely, higher Smax values (e.g., those of [BrBPP]2[MnBr4] and [MeTPP]2[MnBr4]) imply partial orientational alignment and stronger cation–anion interactions, leading to increased local rigidity, higher Tg, and reduced GFA.

The differential scanning calorimetry (DSC) results quantify the cation-dependent Tg and Tm of this family of halides (Fig. 2d, Supplementary Fig. 13, and Supplementary Table 4)33. For Category I halides, their Tg and Tm values lie in the range of 43.0–57.6 °C and 125.2–178.4 °C, respectively. The Tg/Tm ratios, which determine GFA according to the Kauzemann 2/3 law34, range from 0.705 for [EtTPP]2[MnBr4] (EtTPP=ethyltriphenylphosphonium) to 0.806 for [c-PrMeTPP]2[MnBr4] (c-PrMeTPP=cyclopropyl triphenyl phosphonium). Notably, these Tg/Tm ratios show an overall trend towards easier glass-formation, correlating to the length of the A-site cations. Compared with Category I, the Tg (77.6–96.9 °C) and Tm (218.3–271.1 °C) values of Category II are much higher, whereas their Tg/Tm values (0.680–0.716) are significantly lower. Interestingly, the GFAs show a strong dependence on the “push-pull electronic effect” of the benzyl side chains, as manifested by the larger Tg/Tm index for [MeBPP]2[MnBr4] (0.716, MeBPP=methylbenzyl phosphonium) but lower Tg/Tm values for [FBPP]2[MnBr4] (0.706, FBPP=6-fluorine benzyl phosphonium) and [BrBPP]2[MnBr4] (0.680, BrBPP=6-bromine benzyl phosphonium), compared with that of the original [BPP]2[MnBr4] (0.714), respectively. This suggests the push-pull substituent effect adjusts the electron density of the cations and hence modulates the strength of the interactions between inorganic and organic molecular motifs. These electronic variations lead to pronounced differences in GFAs. Furthermore, the activation energies (Ea) derived from the Moynihan and Kissinger analyses exhibit consistent trends (Supplementary Figs. 13–17 and Supplementary Table 5), quantifying the structural relaxation kinetics near Tg35–37. Compounds containing rigid or polar substituents exhibit markedly higher Ea values, indicative of slower structural relaxation and stronger resistance to molecular rearrangement. This enhanced rigidity contributes to the elevated Tg observed in these glass systems.

UV–Vis absorption spectra of the crystalline and glassy materials show similar absorption at 320–350 nm (Supplementary Fig. 18). Meanwhile, the Tauc plots analysis reveals direct bandgap transitions for both states (Supplementary Fig. 19). The photoluminescence (PL) and photoluminescence excitation (PLE) spectra at 80 K display broad green emissions at 500–550 nm and excitation bands at 350–450 nm (Supplementary Fig. 20 and Supplementary Table 6), typical of the 4T1 → 6A1 transitions in tetrahedrally coordinated Mn2+. Subsequent luminescence measurements on the nine halide glasses at room temperature demonstrate that they maintained a green luminescence, albeit with significant broadening and a redshift after vitrification (Fig. 3a and Supplementary Figs. 21). This redshift is attributed to the increased depth of the self-trapped exciton state, arising from the shortened Mn–Br distance and the disordered environment around [MnBr4]2− (Supplementary Figs. 22). The redshift behavior agrees with previous reported glasses29,38–42, which were attributed to disorder-induced effects. Notably, the luminescent lifetimes of the glasses are significantly lower than those of the crystalline phases (Fig. 3b and Supplementary Table 7), implying a large increase of non-radiative loss. Compared with the crystalline parents, the luminescent peak widths of the glasses are larger, by 22% for [BuTPP]2[MnBr4] to 33% for [BrBPP]2[MnBr4] (Supplementary Fig. 23 and Supplementary Table 8). This could arise from the small and large increases in the number of [MnBr4]2− configurations during vitrification for [BuTPP]2[MnBr4] and [BrBPP]2[MnBr4], respectively. X-ray excited luminescence and detection limit measurements reveal excellent X-ray response and low detection limits of the A2[MnBr4] glasses, surpassing some prototypical commercial materials. Among them, a- [MeBPP]2[MnBr4] exhibits an ultralow detection threshold of 23 nGy s−1, highlighting its high X-ray sensitivity (Supplementary Figs. 24 and 25 and Supplementary Table 9).

To comprehensively evaluate the scintillation properties of [c-PrMeTPP]2[MnBr4] and a- [c-PrMeTPP]2[MnBr4], a series of X-ray excited luminescence and kinetic tests were conducted (Supplementary Fig. 26). The emissions exhibit a linear dependence under dose rate of 2.94–366 mGyair s−1, suggesting stable X-ray responses. The detection limits, which are determined from a signal-to-noise of 3, are 131 and 110 nGyair s−1, respectively. Moreover, a- [c-PrMeTPP]2[MnBr4] retains 99% of its original intensity after 3000 s of continuous irradiation and 50 cycles, demonstrating excellent radiation stability. a- [c-PrMeTPP]2[MnBr4] also shows a spatial resolution of 12 lp mm−1, indicating its applicability for the X-ray imaging.

The glass transitions are confirmed by the Raman spectroscopy where several distinguishable peaks below 150 cm−1, corresponding to the vibrational modes of [MnBr4]2− tetrahedra, display a broad single peak after vitrification (Fig. 3c and Supplementary Fig. 27). FTIR analysis reveal that characteristic ν C–H and ν C=C (in the phenyl ring) vibration peaks roughly maintain their positions, while the C–H vibrations show significant broadening after vitrification (Supplementary Fig. 28). These results indicate the variations in chemical environments of the cations and emergence of disorder after the melt-quenching. Additional Raman peaks, for the symmetric and asymmetric C–H vibrations in the methylene and methyl groups, give similar results. To probe the evolution of molecular motion during vitrification, variable-temperature Raman spectra were analyzed for the Mn–Br stretching of [MnBr4]2− and the phenyl ring in-plane deformation of phosphonium cations (Supplementary Fig. 29). The peaks of Mn–Br stretching are located at 250–255 cm−1 (ν1) and 255–260 cm−1 (ν1’), while the vibration peak of the phenyl ring appears at 610–620 cm−1 (ν2) (Supplementary Fig. 30–37). The corresponding full widths at half maximum, fitted using the Lorentzian functions, are summarized in Supplementary Fig. 38. Both ν1 and ν2 bands exhibit gradual broadening with increasing temperature, and the spectra collected after quenching exhibit markedly broader features compared with those recorded before thermal annealing. Interestingly, the halide glasses with higher (or lower) GFAs give rise to less (or more) reduction of the lifetime as shown in the τglass/τcrystal plot (Fig. 3d). The low reduction in non-radiative decay of the high GFA glasses could arise from their approximate energy levels of the vibrational modes in their [MnBr4]2− configurations, which are relatively less altered compared with those in the melted phases. For the low GFA glasses, the [MnBr4]2− tetrahedra may experience subtle variations in their local environment after vitrification, leading to enhanced non-radiative decay. It is worth mentioning that the τglass/τcrystal curve is reminiscent of the trend of the Tg/Tm ratio. This implies the phase space distribution of molecular components would be more homogeneous in the high GFA glasses, and vice versa.

To elucidate the critical motion behavior governing the phase space characteristics of the melts, classical and ab initio molecular dynamic (MD) simulations (Supplementary Figs. 39–46, Supplementary Note 1, and Supplementary Movie 2) were conducted43,44. The crystal phases were heated up to 800 K to reach fully melted states, and then quenched into glass phases at 500 K (Supplementary Fig. 47). The MSD of the terminal C atom in the side chain was extracted to compare the dynamics of organic cations in different halide glasses (Supplementary Figs. 48 and 49). The MSD values do not show an obvious correlation with the Tg/Tm ratios, thereby excluding their direct influence on GFA. This could be attributed to the fact that the MSD metric includes both the molecular translation and rotation, which is inadequate for characterizing the rotational disorder crucial for assessing glass-formation. Therefore, the rotational correlation function (RCF) (Fig. 4a), C(t), a statistical measure to quantify the rotational motion of molecular moieties over time, was adopted:

C(t) = 1/n ∫ Pn(cos(f(p(ξ), p(ξ+t)))dξ (2)

where ξ is the integration variable, representing the initial time point; t is the delay time, denoting the time elapsed from the initial time point ξ; p is the orientational vector defined from the central P atom to the terminal C atom in the side chain; Pn(x) is the nth order Legendre polynomial, and n is set to 1 for determining the rotational disorder. The RCF plots of the organic moieties in different glass systems show a pronounced correlation with Tg/Tm (Fig. 4a), where the RCF values decay more rapidly in systems with higher GFAs. The rotational correlation time (τc = ∫ 1 C(t)dt), derived from the RCF integration of the modified organic side chains in the glass state at 500 K also demonstrates a significant dependence on Tg/Tm. These results indicate the rotational energy landscape can provide an intuitive means to comprehend the features of phase space distribution affecting GFA. To capture the rotational energy landscape of phosphonium cations, metadynamics simulations based on angle and alphabeta CVs were employed, and the predominant characteristics of rotational phase space distribution were quantified45. The rotational potential wells in the phosphonium cations of [BuTPP]2[MnBr4], [BPP]2[MnBr4], and [BrBPP]2[MnBr4] glasses possess a gradually increasing depth, indicating an incremental hindrance to the cationic rotational behavior in these systems, as seen from the free-energy surfaces in Fig. 4b and Supplementary Fig. 50. The angles between primitive axes and the modified organic side chains are served as orientational indicators of phosphonium cations, and used as collective variables sx, sy and sz, for analyzing the energy landscape. Among the representative systems, [BuTPP]2[MnBr4] with a high GFA has a shallow potential well and a flat energy landscape, indicating a more uniform phase space distribution and pronounced disorder. In contrast, [BPP]2[MnBr4] and [BrBPP]2[MnBr4], as typical systems with higher Tg but lower GFAs, exhibits a substantially deeper potential well, which suggests the concentrated distribution in phase space and a reduced degree of disorder. The metadynamics simulations based on alphabeta CVs, featuring torsional indicator of the four side chains of the phosphonium cations, were also performed (Supplementary Fig. 51). The resulting free-energy profiles display the same trend as the angle-based CVs in these three glass systems, consistently confirming the distribution of energy landscapes.

Since molecular rotation depends on both shape and ESP surface of the organic moieties, the Spearman and Pearson correlation coefficients46–48, along with linear regression protocol, were employed to further quantify the molecular characteristics determining GFA (Fig. 4c and Supplementary Figs. 52–54; see formula in Supplementary Note 2). Three descriptors of phosphonium cations dominating GFA were obtained using the density functional theory (DFT) calculations49–51 and MD analysis, which are the rotational anisotropy descriptor (Iratio), the overall variance of ESP (σ2tot), and τc. Iratio was defined as:

Iratio = Imax / Imin (3)

where Imax and Imin are the maximum and minimum moments of inertia along the principal axes. This descriptor was derived from the moment of inertia in a homogeneous ellipsoid. σ2tot was defined as52:

σ2tot = 1/g ∑ (V+i - <V+>)2 + 1/h ∑ (V-j - <V->)2 (4)

where V+i and V-j are the positive and negative ESP values on the van der Waals surface, and g and h are the respective positive and negative grid points. The Iratio, σ2tot, and τc descriptors exhibit a significant positive correlation to Tg and Tm. Conversely, a negative correlation is observed with the Tg/Tm ratio, serving as efficient descriptors for assessing GFA. In addition, the orientational order parameter Smax, extracted from RMC modeling, exhibits a pronounced negative correlation with Tg/Tm, highlighting its reliability as an excellent indicator of GFA. These results demonstrate that the rotational disorder play a dominant role in governing glass formation. In terms of the molecular shape, it is noted that the mass distribution exerts a more pronounced influence in GFA than size alone. In addition, σ2tot, which quantifies the electrostatic and van der Waals interactions, was found to significantly affect GFA. To further illustrate these primary characteristics, a disorder model of the glass structures is proposed (Fig. 4d). According to the molecular shape and surface ESP of the phosphonium cations, the nine glasses can be divided into three types. In the first type, the organic component exhibits a significantly uniform distribution of rotation and a weakly polar (or non-polar) ESP surface. This leads to a significant number of allowed configurations and flat energy landscapes, hence enabling high GFA and low Tg and Tm as observed from [c-PrMeTPP]2[MnBr4], [BuTPP]2[MnBr4], and [PrTPP]2[MnBr4] glasses. For the second type, the non-uniform distribution of the molecular rotation promotes the ergodicity breaking, which reduces the number of sampled configurations and therefore results in lowered GFAs in [MeTPP]2[MnBr4], [MeBPP]2[MnBr4], [BPP]2[MnBr4], and [EtTPP]2[MnBr4]). The lower GFA of [BrBPP]2[MnBr4] compared to [MeBPP]2[MnBr4] is attributed to its greater molecular polarity, which strengthens intermolecular interactions and increases structural frustration in the glassy state. The phosphonium cations in the last type have increased non-uniform distribution of rotation and surface ESP polarity, which further narrows the distribution of rotational phase space and gives rise to low GFA and high Tg and Tm ([FBPP]2[MnBr4] and [BrBPP]2[MnBr4]). In brief, compact and symmetrical cations with weakly polar or aliphatic substituents tend to exhibit uniform ESP surfaces and higher rotational freedom. This facilitates orientational disorder of the structural motifs and produces relatively low intermolecular potential barriers, thereby enhancing the GFA. Whereas cations with elongated shapes or strong polar substituents display anisotropic charge distributions and stronger intermolecular interactions, which restrict molecular conformations, create pronounced potential energy extrema, and ultimately lead to reduced GFA.

In summary, through modifying the molecular components, a family of 0D hybrid metal halide glasses, with diverse GFAs, have been synthesized. Their tunable GFAs are attributed to the differences in molecular rotational disorder and associated energetic landscapes of the structural unit during the melt-quenching process. Specifically, a more uniform distribution of molecular rotation and reduced variance of surface ESP contributes to a greater number of permissible configurations, and flatter potential energy surfaces in these 0D hybrid halide glasses. This implies an evolution of rotational ordering and an expansion of the phase space distribution, ultimately resulting in enhanced GFA, lower Tg, and Tm. These findings offer a pathway towards understanding the origins of glass formation from a more general perspective of disorder, which is applicable to a broad realm of hybrid organic-inorganic solids through molecular design. Given the existence of small atomic clusters in metallic glasses, this approach might be generalized for these systems too.

Methods
Chemicals and materials
All chemicals were used as received without further purification. Manganese(II) bromide (MnBr2, 99.9%), tetraphenylphosphonium bromide (C24H20PBr, TPPBr, 99%), methyltriphenylphosphonium bromide (C19H18PBr, MeTPPBr, 98%), ethyltriphenylphosphonium bromide (C20H20PBr, EtTPPBr, 98%), propyltriphenylphosphonium bromide (C21H22PBr, PrTPPBr, 99%), methylenecyclopropyltriphenylphosphonium bromide (C22H22PBr, c-PrMeTPPBr, 98%), (n-butyl)triphenylphosphonium bromide (C22H24PBr, BuTPPBr, 98%), benzyltriphenylphosphonium bromide (C25H22PBr, BPPBr, 98%), (p-Xylyl)-triphenylphosphonium bromide (C26H24PBr, MeBPPBr, 98%), and (4-fluorobenzyl)triphenylphosphonium chloride (C25H21FPCl, FBPPCl, 98%), (4-bromobenzyl)triphenylphosphonium bromide (C25H21PBr2, BrBPPBr, 98%), were used for the synthesis of 0D hybrid metal halides. Ethanol (>99.5%), dichloromethane (>99.5%), hydrobromic acid (48%), and deionized water were used as solvents.

Synthesis of metal halide crystal
The crystals of [TPP]2[MnBr4], [MeTPP]2[MnBr4], and [EtTPP]2[MnBr4] were prepared according to the previous literatures26,53,54.
Synthesis of [PrTPP]2[MnBr4] crystal: PrTPPBr (0.7706 g, 2 mmol) and MnBr2 (0.2147 g, 1 mmol) were dissolved in an open-top 10 mL vial using ethanol (>99.5%, 4 mL), then the vial was placed into a 250 mL sealed container containing isopropanol. Pale green crystals were obtained after three days.
Synthesis of [BuTPP]2[MnBr4] crystal: The synthesis process of this compound is identical to that of [PrTPP]2[MnBr4], except that PrTPPBr was replaced by BuTPPBr (0.8026 g, 2 mmol), then the vial was transferred into a 250 mL sealed container containing isopropanol. Pale green crystals were obtained after three days.
Synthesis of [c-PrMeTPP]2[MnBr4] crystal: The synthesis process of this compound is the same as that of [PrTPP]2[MnBr4], except that PrTPPBr was replaced by c-PrMeTPPBr (0.7985 g, 2 mmol).
Synthesis of [MeBPP]2[MnBr4] crystal: The synthesis process is the same as that of [PrTPP]2[MnBr4], except that PrTPPBr was replaced by MeBPPBr (0.8966 g, 2 mmol).
Synthesis of [BPP]2[MnBr4] crystal: BPPBr (0.8666 g, 2 mmol) and MnBr2 (0.2147 g, 1 mmol) were dissolved in dichloromethane (>99.5%, 5 mL). After two weeks of allowing the mixture to settle undisturbed, the crystals were obtained.
Synthesis of [FBPP]2[MnBr4] crystal: FBPPCl (0.8136 g, 2 mmol) and MnBr2 (0.2147 g, 1 mmol) were dissolved in HBr (48%, 5 mL) upon heating and continuous stirring at 110 °C, and green crystals were obtained by slowly cooling the saturated solution to room temperature.
Synthesis of [BrBPP]2[MnBr4] crystal: The synthesis process of this compound is the same as that of [PrTPP]2[MnBr4], except that PrTPPBr was replaced by BrBPPBr (1.0244, 2 mmol). High-performance liquid chromatography analysis was performed using a SHIMADZU LC-20AD facility with commercial 5 µm, 4.6 × 150 mm columns, using a MeCN/H2O = 50/50 (v/v) at a flow rate of 1 mL min−1 and a detection wavelength of 254 nm. The results of BrBPPBr and [BrBPP]2[MnBr4] show that [BrBPP]2[MnBr4] possess two major peaks at retention times of 1.173 min and 3.526 min, corresponding to the organic cation and the inorganic species (Supplementary Fig. 55). Elemental analysis illustrates C and H contents of 47.94% and 3.47%, respectively, which is consistent with the theoretical values of 48.50% and 3.39%.

Synthesis of glasses
The synthesis of 0D metal halide glasses was performed on a Linkam LTS420 Heating and Freezing stage. The Category I crystalline samples were placed on the microscope slides and heated to 230 °C at a rate of 10 °C min−1 under N2 atmosphere. Glass samples were then obtained by cooling the halide melts to 30 °C at a rate of 10 °C min−1. The melt-quenching procedure of the Category II samples is similar to that described above, except that the target temperature was set to 260 °C for [BPP]2[MnBr4], [FBPP]2[MnBr4], and [MeBPP]2[MnBr4], and 280 °C for [BrBPP]2[MnBr4].

Synthesis of glass bulks and fibers
In the case of [BuTPP]2[MnBr4], for example, the crystal sample was placed in a silicone mold, heated to 190 °C in an oven until fully molten. Then the melt was cooled down naturally to form a glass bulk after removing mold. The fiber sample of [BPP]2[MnBr4] was synthesized using a homemade rotatable melting device.

Single crystal X-ray diffraction (SC-XRD) and Powder X-ray diffraction (PXRD) analysis
Single crystal X-ray diffraction experiments were performed on a Rigaku XtaLAB MM007 CCD facility using a mirror-monochromated Cu-Kα radiation (λ = 1.54178 Å) at 100 K. Data collection and reduction were processed using the Rigaku CrysAlisPro program. Structures were resolved with the ShelXT package using the intrinsic phasing and refined with the Olex255 and ShelXL refinement package using the least squares minimization. The crystal information files were deposited in the Cambridge Crystallographic Data Centre with reference numbers 2241752–2241754, 2284544–2284546, and 2370641. Powder XRD patterns were collected using a Rigaku MiniFlex 600 diffractometer at 40 kV, 100 mA with a Cu-target tube and a graphite monochromator. The 2θ varied between 5 and 50° with a step rate of 5° min−1.

X-ray total scattering analysis and reverse Monte Carlo (RMC) simulation
X-ray total scattering data (λ = 0.208566 Å, 59.45 KeV) were collected at the Beijing Synchrotron Radiation Facility. Data of the samples and background were collected in the region of 0.5 < Q < 24.7 Å−1. Data process and background corrections were performed using the pdfgetx2 program56. RMC simulations of [BPP]2[MnBr4] were processed using the RMCProfile package57. A 5 × 4 × 3 supercell structure of [BPP]2[MnBr4] crystal was used as the initial structure, and the experimental S(Q) data of crystalline and glassy samples were used for fitting. The S(Q) data of 0.5–20.5 Å−1 were used to exclude interference during experiments. Due to the lack of constraints in dihedral angle potentials in the simulation package, the phenyl rings showed distorted configurations.

Thermogravimetric (TGA) and differential scanning calorimetry (DSC) analysis
Thermogravimetric curves were collected using a Rigaku ThermoPlus EVO2 analyzer under a constant airflow (20 mL min−1). Approximately 5 mg powder sample was heated from room temperature to 800 °C in an alumina crucible at a rate of 10 °C min−1. The TGA data were used to determine the decomposition temperatures (Td).
Differential scanning calorimetry (DSC) measurements were performed on a TA DSC25 facility with the heating/cooling rates of 10 °C min−1 under N2 protection. For each measurement, approximately 5 mg sample was sealed into an aluminum crucible. It took two up-scans to determine the melting points (Tm) and glass transition temperatures (Tg). Tm was determined from the onset of the endothermic peak in the first heating run of the DSC curve, and Tg was determined from the midpoint of the step change in heat flow in the second heating run. To quantify the kinetic behavior of the system, DSC measurements were conducted at diverse heating and cooling rates. Owing to the absence of distinct crystallization peaks in the compounds, the activation energies associated with the glass transition were estimated using the Moynihan and Kissinger methods. The corresponding formulas are as follows:

d(lnβ) / d(1/Tg) = -Ea / R

ln(β / Tg2) = -Ea / RTg + K

where β is the heating or cooling rate, Ea is the activation energy related to the structural relaxation.

Photoluminescence (PL) and X-ray scintillation properties measurements
PL and time-resolved luminescence spectra were measured on a FS5 spectrofluorometer with a monochromatized Xe lamp. X-ray emission spectra were measured on a FS5 spectrofluorometer with a radiation source (40 kV, 150 μA). X-ray imaging was performed using a homemade X-ray imaging system. The object and scintillator glass were placed under X-ray radiation, and a camera was used to take pictures of the object.

Fourier transform infrared spectrometer (FTIR) and Raman measurements
FTIR spectra were recorded using a Thermo Scientific Nicolet iS20 facility in the range of 400–4000 cm−1. All the samples were fully dried, mixed with KBr, and then pressed into pellets approximately 1 mm thick. Raman spectra at room temperature were measured on a HORIBA Scientific LabRAM HR Evolution spectrometer. All samples were excited with a 785 nm laser beam. Three cycles of data collection were implemented to reduce the effect of background noise. Variable temperature Raman spectra were measured on an Edinburgh RMS1000 spectrometer and the samples were excited with a 625 nm laser beam.

Density functional theory (DFT) calculations
DFT calculations were performed using the ORCA 5.0.3 package to obtain geometry information and surface ESP information50,51. The geometry optimization of phosphonium cations and [MnBr4]2− anions was performed using a PBE0 functional58 and def2-TZVP basis sets59 with the Grimme’s DFT-D3(BJ) dispersion corrections60,61, following with frequency calculations. The optimized structures were used for calculating molecular descriptors with the Multiwfn package49. The dipole moments were calculated using the ma-def2-TZVP basis sets62. As a comparison, the molecular descriptors of phosphonium cations based on geometries in the crystal structures were calculated using the same methodology mentioned above. The heavy atoms were fixed and the positions of hydrogen atoms were optimized.

Classical molecular dynamics (MD) simulations
To investigate the behaviors of phosphonium cations and [MnBr4]2− tetrahedra in the solid and liquid phases, and elucidate the difference between different halide glasses, classical MD simulations were carried out using the GROMACS 2022 package44. The geometries of phosphonium cations and [MnBr4]2− anions was obtained from DFT calculations, and the full systems were built using PACKMOL, including 400 cations and 200 anions63. The topology files were generated using the Sobtop package64. The Generalized Amber Force Field (GAFF) was used as the initial parameters to the simulation system, with Mn and Br atoms assigned Universal Force Field atomic types. Bond and angle parameters were derived from DFT frequency calculations using the modified Seminario method (ORCA), and the remaining parameters were taken from GAFF65,66. The atomic charges were calculated with the Multiwfn using the restrained ESP method. During the production simulations, we used a leap-frog Verlet integrator with a 0.5 fs time interval, a Velocity-Rescale thermostat, and a Parrinello-Rahman barostat. To improve the performance, the bonds with H atoms were constrained. Since [MnBr4]2− anions in [MeTPP]2[MnBr4] and [EtTPP]2[MnBr4] models inclined to dimerize due to the small cation size, we modified the atomic charge distribution of [MnBr4]2− in these two models to prevent dimerization. Energy minimization and equilibration were performed under isothermal-isobaric ensembles (NPT), that is, the number of particles, the temperature and pressure are fixed, for 1 ns and 100 ns at 800 K, respectively. Then, the whole systems were annealed from 600 to 300 K to determine the Tg. The constant temperature simulations were performed at 500, 600, and 800 K for 40 ns, and the last 10 ns of the trajectories was used to calculate the root mean square deviation, mean square displacement (MSD), radial distribution function, and root mean square fluctuation. In addition, for the calculations of RCF, the simulations were conducted at 500 K for 100~300 ns. All trajectories were analyzed and drawn in the Visual Molecular Dynamics67.

Ab initio molecular dynamics (AIMD) and metadynamics simulations
To probe the dynamics of A2[MnBr4] at different temperatures, AIMD simulations at 300, 600, and 800 K were performed using the CP2K program43. In these simulations, the PBE functional68 and Grimme’s DFT-D3(BJ) dispersion corrections were used in combination with the DZVP-MOLOPT-SR-GTH basis sets and Goedecker-Teter-Hutter pseudopotentials69. The CUTOFF and REL_CUTOFF were set to 600 Ry and 40 Ry, respectively, and the Canonical Sampling through Velocity Rescaling thermostat and Martyna–Tobias–Klein barostat were used. All AIMD models were pre-equilibrated and run for 10 ps with a time interval of 0.5 fs in the NPT ensemble. In addition, a frequency calculation was performed to confirm the IR/Raman peak contributions using CP2K.
The metadynamics simulations based on angle and alphabeta CVs were performed using the CP2K program70. The angle CVs are defined using the angles between the primitive vectors a, b, c, and directional vectors defined by modified organic side chains. Note that only 2 of 3 collective variables (sx and sy) were used to plot the free-energy landscapes for clarity. The alphabeta CVs are defined as:
sAB = 1/2 ∑ (1+cos(ϕi - ϕRefi))
where sAB is the alphabeta CV value, ϕi is the instantaneous torsional angle, ϕRefi is the corresponding reference torsion angle. Four torsional angles between the principle axes and each of the four side chains of the phosphonium cation are combined into a single alphabeta CV, ranging from 0 to 4. Note that the angle CVs used GFN1-xTB method with CP2K built-in kernel, while the alphabeta CVs used density-functional tight binding method with Plumed package71,72,73.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this communication, the authors investigate the bulk glass-forming ability (GFA) of zero-dimensional (0D) hybrid metal halides, focusing on the role of an ergodicity-breaking process achieved by controlling molecular rotational order. The vitrification process, achieved through melt-quenching, enables glass formation with adjustable local structures and properties. While macroscopic observation of phase transitions provides a direct understanding of glass formation, a detailed examination of local structures is necessary to elucidate structure-property relationships and establish design rules for glass formation.\n\nThe authors synthesized a family of 0D hybrid metal halides by varying the size, shape, and surface electrostatic potential of organic cations. These modifications allow for the study and comparison of distinct phase-space partitions of molecular movements and GFAs. While the manuscript effectively demonstrates the synthesis aspects, the experimental characterization of short-range interactions within the glasses remains limited. This leads to incomplete conclusions about the interrelation between structure and properties. The following comments may help addressing gaps in the characterization and interpretation of glass-forming mechanisms and properties.\n\n1. Mechanism of Glass Formation: The powder XRD analysis of melt-quenched [TPP]₂[MnBr₄] reveals retention of the parental crystalline motif, whereas melt-quenching of modified TPP derivatives with aliphatic and benzyl side chains results in glass phases. Given the similar bulkiness and expected identical rotational degrees of freedom of these moieties, the underlying mechanism driving glass formation in the latter case is unclear and requires explanation.\n\n2. Importance of Local Structural Analysis: A defining feature of glasses is their local structure, which includes the degree of order or disorder at various length scales and local dynamics, such as the rotations of specific functional groups. While the authors employ pair distribution function analysis, Raman spectroscopy, and molecular dynamics simulations to explore these aspects, the study lacks a critical technique for investigating the local nature of glasses: solid-state NMR spectroscopy. Recent work by Mitzi is an example (Journal of the American Chemical Society, 2024, 146, 37, 25656–25668), which demonstrates its utility in addressing these questions.\n\n3. Variable-Temperature Experiments: Changes in rotational degrees of freedom can be further elucidated using variable-temperature (VT) experiments such as Raman spectroscopy, NMR, or PXRD measurements. These techniques can provide insights into activation energies and rotational correlation times, which are crucial for understanding the dynamics of molecular rotations in glasses.\n\n4. Impact of Rotational Heterogeneity: The effect of a non-uniform distribution of rotations within phosphonium cations on glass transition temperature (T₈) and GFA is not clearly addressed in the manuscript. A more thorough discussion of this aspect from the perspective of structural chemistry would be valuable.\n\n5. Figure 2 (GFAs): The substantial difference in GFA between BrBPP and MeBPP, despite their structural similarity and the presence of free-to-rotate phenyl rings in both cases, is intriguing. The manuscript should provide a more detailed explanation of this phenomenon.", "reviewer_2": "The authors reported a study on how structural disorder governs the bulk glass-forming ability by synthesizing a family of zero-dimensional hybrid metal halides with tunable short- to medium range structural arrangements to form glasses with diverse GFAs. They found the rotational order is able to be broken in a controlled manner, leading to distinct phase space partitions of molecular movements, allowing for tunable GFAs.This work affords new ideas on glass materials.\nIt could be accepted after some revisions are made.\nIt is important to indicate how to extract the values of Tg and Tm from the DSC curves. Note: Peak values are unreasonable.\nIt is said that, in the caption of Fig 2, [BrBPP]2[MnBr4] exhibits the highest Tg (96.9 °C) and Tm (271.1 °C). But it seems [TPP]2[MnBr4] exhibits the highest Tm.\nFig 1abc and 4d illustrate three configurations of molecular motifs. In my opinion, the last two, nonspherical and polar ESP surface, are same. In fact, except for TPP, all the others are polar ellipsoids. Please consider this point.\nBesides the AIMD, is there any experimental test to reveal the dynamic disorders?", "reviewer_3": "In this work, the authors have presented the synthesis of zero-dimensional Mn-based hybrid metal halides with tunable structural arrangements to achieve glasses with diverse glass-forming abilities (GFAs). Further, authors have claimed that by altering the molecular shape and surface electrostatic potential of organic cations, the rotational order of these molecules is controllably disrupted, creating distinct phase space partitions for molecular motion and enabling tunable GFAs thereby providing some physical insight into the design principle of glasses from 0D Metal halide hybrids (in contrast to inorganic/metallic glasses)\nThe work may be considered for publication after major revision. I would like to be invited to review the revised manuscript.\nThe following issues must be addressed:\n1. Authors have performed a detailed structural and theoretical study on the materials to elucidate the relation between GFA and the size, shape and electrostatic nature of organic cations. Not much efforts have been given to optical characterisation on these materials. Absorption measurements, Tauc plots (band gaps), PL/PLE at low temperatures should be provided for comprehensive optical property assessment\n2. Further, X-ray scintillation properties has been shown for materials other than the best glass forming material [c-PrMeTPP]2[MnBr4]. For, [c-PrMeTPP]2[MnBr4] scintillation property characterisation should be provided.\n3. No Data has been given for scintillation performance of the glass materials (such as X-ray response with variable dose rates, X-ray detection limit etc.). These data would strengthen the potential of application of such materials.\n4. Many supporting figures are there without any comment and discussion in the main manuscript (such as Supplementary Fig. 14 etc). Please provide an excerpt on what these figure convey in words.\n5. Authors have given a thorough theoretical understanding of the rotational freedom of organic cations and its relation with glass forming ability. Authors have analysed 9 different glasses and provide an ESP based chemical design principle for glasses with high GFA. It will be prudent and impactful if the authors can provide simpler chemical insight/physical picture to gauge the structure of the organic cations and its relation to ESP and spherecity. Design principles driven by chemical intuition (based on the structure of the organic cation) without performing calculations to get to extent of spherecity and surface ESP will be impactful. Please add a discussion on this.\n6. Please measure the kinetics of the glass formation for the systems and provide correlations to their GFAs\n7. Different glasses on Mn-Halides show lightly redshifted emission although PDF analysis shows not much change in the local Metal – halide environment. How do you rationalize the observed changes in the electronic properties of the Mn-X (that causes PL peak position shift) for these glassy systems that are dominated by rotational disorder/freezing. Comment\n8. Authors must take reported examples of glasses that show substantial PL peak position change from crystalline to glassy phase and demonstrate that effect of local structural changes in the M-X geometry and showcase that rotational disorder is one of the criteria for forming glasses. The primary criteria being changes in the local structure. PDF analysis of such materials that show changes in PL peak position (changes in local structure), their rotational disorder quantification, and their relative weightages can provide detailed understanding of the GFAs of variety of glasses for demonstrating generality. Experiments and discussions on these will be useful for the work.", "reviewer_4": "In this paper, the authors report a series of Mn-based hybrid metal halides with different GFAs. The authors conducted a multi-faceted investigation into the relationship between cationic species and GFA in this emerging glass material system. A more uniform distribution of molecular rotation and reduced variance of surface ESP ultimately are suggested to lead to reduced Tg and Tm, which could offer valuable guidance for the rational design of hybrid metal halide glass. Several significant issues should be addressed before considering it for this journal.\n1. Is the force field used in the simulation (GAFF) appropriate for describing manganese halide systems? The authors should provide a detailed explanation of how manganese and bromine are treated in the classical molecular dynamics section. For the potential dimerization issue of [MnBr4]2- ions, specific modifications to the charge distribution should be proposed. It is recommended to supplement the discussion with an analysis of how well the force field parameters match experimental or high-precision computational data. Additionally, providing the simulation input files would be beneficial for reproducibility.\n2. How does the \"push-pull electronic effect\" specifically influence Tg/Tm? Additionally, have the authors synthesized and analyzed materials with Cl substituents to evaluate its properties?\n3. Is any experimental or theoretical evidence to support the statement that \"the [MnBr4]2- tetrahedra in the low GFA glasses exhibit vibrational modes with more non-equivalent energies\"?\n4. Supplementary Fig. 9 lacks sufficient labeling, making it difficult to interpret. Specifically, the direction of heat flow and the correspondence between the two heating cycles are not clearly indicated. In Supplementary Fig. 9d, [PrBPP]2[MnBr4] exhibits two peaks. How was the Tm determined in this case? In Supplementary Fig. 9e, why does the cold crystallization peak of [BrBPP]2[MnBr4] indicate its poor glass-forming ability? Could this peak be attributed to the presence of impurities, leading to cold crystallization and subsequent melting? Additionally, the significant difference between melting peaks of the first and second up-scan raises concerns about the sample purity and the origin of the cold crystallization behavior. Clarifying these points and improving the figure annotations would greatly enhance the interpretability of the data.\n5. Using only angles as collective variables may not fully capture the energy landscape. The referee recommend that the authors discuss the appropriateness of their chosen CVs or supplement the analysis with additional variables."}, "author_response": "We sincerely thank the reviewer for the thoughtful evaluation of our manuscript. We have carefully addressed the reviewer’s concerns, and the following are our point-to-point responses to the comments. We hope that the analysis and mechanisms presented in this study are now more comprehensive, thereby enhancing the credibility of the rationale.\n\n1. Mechanism of Glass Formation: The powder XRD analysis of melt-quenched [TPP]₂[MnBr₄] reveals retention of the parental crystalline motif, whereas melt-quenching of modified TPP derivatives with aliphatic and benzyl side chains results in glass phases. Given the similar bulkiness and expected identical rotational degrees of freedom of these moieties, the underlying mechanism driving glass formation in the latter case is unclear and requires explanation.\n\nResponse:\nWe sincerely thank the reviewer for the insightful suggestion regarding the mechanism of glass formation. We have added a detailed explanation comparing [TPP] [MnBr ] with its derivatives. 2 4 While TPP and its derivatives share comparable size, charge, and intermolecular interactions, their markedly different glass forming abilities arise predominantly from differences in molecular shape and polarity, which plays a critical role in both vitrification and crystallization.\n\nIn [TPP] [MnBr ], the TPP cations display a high degree of tetrahedral symmetry, with four 2 4 phenyl rings arranged in nearly equivalent positions. In the molten state, these geometrically equivalent phenyl rings can readily align during motion. Consequently, during crystallization upon cooling, the rearrangement of TPP cations does not require a full 360° rotation; instead, a small angular adjustment is sufficient to reach one of the symmetry-equivalent, crystal-compatible configurations. In contrast, substituting a phenyl ring with an aliphatic or benzyl group disrupts the rotational symmetry of the modified TPP derivatives. The resulting steric hindrance hampers the efficient arrangement of the system into a crystalline lattice during quenching. In particular, the rotational motion of these asymmetric substituents leads to configurations that deviate from translational symmetry, thereby impeding recrystallization and favoring the formation of a glassy phase.\n\nWe apologize for the initial oversight in not including this explanation in our manuscript. In the revised version, we have incorporated the detailed explanation for the discrepancy of [TPP] [MnBr ] and the other compounds. 2 4\n\nRevised text:\n“For the modified TPP derivatives, substituting one benzene ring with an aliphatic or benzyl group breaks the molecular symmetry. This modification introduces steric hindrance that prevents the structure from easily reordering into a crystalline phase during quenching. Although these side branches can rotate, their motion may be insufficient to restore the long-range translational symmetry, thereby suppressing the recrystallization process. This, in turn, facilitates the formation of a glassy phase.”\n\n2. Importance of Local Structural Analysis: A defining feature of glasses is their local structure, which includes the degree of order or disorder at various length scales and local dynamics, such as the rotations of specific functional groups. While the authors employ pair distribution function analysis, Raman spectroscopy, and molecular dynamics simulations to explore these aspects, the study lacks a critical technique for investigating the local nature of glasses: solid-state NMR spectroscopy. Recent work by Mitzi is an example (Journal of the American Chemical Society, 2024, 146, 37, 25656–25668), which demonstrates its utility in addressing these questions.\n\nResponse:\nWe sincerely thank the reviewer for the insightful suggestion for highlighting the importance of local structure characterization. We fully agree that elucidating the local structure is crucial for understanding the microscopic structural evolution in glassy materials, as demonstrated by the work of Mitzi et al. However, in our Mn-based metal halide system, solid-state NMR spectroscopy is challenging to apply due to the paramagnetic nature of Mn2+ ions (S = 5/2). This leads to line broadening and signal attenuation with NMR signals, making it difficult to extract reliable information about the variation of local structures and intermolecular interactions.\n\nAs an alternative, we performed the Reverse Monte Carlo (RMC) modeling based on the experimental pair distribution function (PDF) data to reconstruct the glass structure at a molecular level. This method provides a quantitative description into the local structure, including short- and medium-range ordering, which allows us to investigate the structural features that are typically addressed by NMR. The RMC-derived glass models reveal that the molecular structures of both cations and anions remain largely unchanged upon vitrification, and the Mn2+ ions retain the tetrahedral coordination environment with Br-. The major structural change after vitrification lies in the reorganization of the molecular components, featuring disordered orientation of the phosphonium cations and thus the broken translational symmetry. These results confirm that the structural disorder in these 0D hybrid metal halide glasses primarily originate from the orientational disorder of the organic cations. Such insights from the PDF and RMC analyses can provide microscopic evidence for understanding and further tuning the GFAs of 0D hybrid metal halide glasses. The corresponding discussion has been updated in the revised manuscript.\n\nSupplementary Fig. 10 | RMC simulation derived glass models of the A [MnBr ] glasses. 2 4\n\nRevised text:\n“Additionally, reverse Monte Carlo (RMC) modeling based on experimental PDF data was conducted to elucidate the molecular arrangements of the phosphonium cations and [MnBr ]2- 4 anions. The simulated and experimental D(r) and S(Q) are shown in Supplementary Figs. 8 and 9. The RMC models reveal that both the [MnBr ]2- and phosphonium cations maintain their molecular 4 geometries, while displaying increased configuration and orientation diversity, indicative of the enhanced disorder upon vitrification (Fig. 2c and Supplementary Figs. 10 and 11).”\n\n3. Variable-Temperature Experiments: Changes in rotational degrees of freedom can be further elucidated using variable-temperature (VT) experiments such as Raman spectroscopy, NMR, or PXRD measurements. These techniques can provide insights into activation energies and rotational correlation times, which are crucial for understanding the dynamics of molecular rotations in glasses.\n\nResponse:\nWe sincerely appreciate the reviewer’s valuable suggestion considering variable-temperature experiments. We have conducted variable-temperature Raman and PXRD measurements to monitor the variation of molecular arrangement during thermal treatments. Due to the strong paramagnetic nature of Mn2+ center, NMR measurements are difficult to capture the alteration of microenvironments because of the line broadening and rapid signal quenching behaviors. The variable-temperature PXRD patterns show slight shift and widening as the temperature increases, suggesting gradual lattice expansion and enhanced structural disorder upon heating (Supplementary Fig. 4).\n\nTo elucidate the evolution of molecular motion and rotational degrees of freedom, we analyzed the variable-temperature Raman spectra obtained during the melt-quenching process. Two representative peaks from the Mn–Br stretching and phenyl ring in-plane deformation were selected for detailed analysis (Supplementary Fig. 29). The peaks of Mn–Br stretching are located at 250–255 cm-1 (ν ) and 255–260 cm-1 (ν ’), which are partially overlapped, while the organic vibration 1 1 appears at 610–620 cm-1 (ν ). Four representative temperatures were selected for comparison and 2 are shown in Supplementary Figs. 30–37, corresponding to 25 °C before and after the melt-quenching process, 105 °C (between T and T ), and 245 °C (above most of the T except for g m m [BrBPP] [MnBr ]). All spectra were fitted using the Lorentzian functions, and the corresponding 2 4 full widths at half maximum (FWHM) are summarized in Supplementary Fig. 38. Both ν and ν 1 2 progressively broaden with increasing temperature, and the peaks collected after quenching exhibit markedly broader features compared with those recorded before thermal annealing. These results provide direct evidence of local environment variations surrounding the [MnBr ]2- anions and 4 phosphonium cations, thereby supporting the occurrence of molecular rearrangement during melt-quenching process. The corresponding results have been added in the discussion section and methods in the revised manuscript.\n\nRevised text:\n“Their diffraction patterns exhibit slight displacement and broadening upon heating (Supplementary Fig. 4), and do not show any significant Bragg peaks after quenching (Fig. 2a, Supplementary Fig. 3 and Supplementary Tables 1–3), indicating the absence of crystallinity.”\n\n“To probe the evolution of molecular motion during vitrification, variable-temperature Raman spectra were analyzed for the Mn–Br stretching of [MnBr ]2- and the phenyl ring in-plane 4 deformation of phosphonium cations (Supplementary Fig. 29). The peaks of Mn–Br stretching are located at 250–255 cm-1 (ν ) and 255–260 cm-1 (ν ’), while the vibration peak of the phenyl ring 1 1 appears at 610–620 cm-1 (ν ) (Supplementary Fig. 30–37). The corresponding full widths at half 2 maximum (FWHM), fitted using the Lorentzian functions are summarized in Supplementary Fig. 38. Both ν and ν bands exhibit gradual broadening with increasing temperature, and the spectra 1 2 collected after quenching exhibit markedly broader features compared with those recorded before thermal annealing.”\n\nSupplementary Fig. 4 | Variable temperature PXRD patterns of the A [MnBr ] compounds. 2 4\n\nSupplementary Fig. 30 | Variable-temperature Raman spectra showing the Mn–Br stretching peaks (ν and ν ’, 250–260 cm-1) recorded at 25 °C before melt-quenching for the A [MnBr ] 1 1 2 4 compounds.\n\nSupplementary Fig. 31 | Variable-temperature Raman spectra showing the Mn–Br stretching peaks (ν and ν ’, 250–260 cm-1) recorded at 25 °C after melt-quenching for the A [MnBr ] 1 1 2 4 compounds.\n\nSupplementary Fig. 32 | Variable-temperature Raman spectra showing the Mn–Br stretching peaks (ν and ν ’, 250–260 cm-1) recorded at 105 °C during melt-quenching for the A [MnBr ] 1 1 2 4 compounds.\n\nSupplementary Fig. 33 | Variable-temperature Raman spectra showing the Mn–Br stretching peaks (ν and ν ’, 250–260 cm-1) recorded at 245 °C during melt-quenching for the A [MnBr ] 1 1 2 4 compounds.\n\nSupplementary Fig. 34 | Variable-temperature Raman spectra showing the in-plane deformation of the phenyl rings (ν , 610–620 cm-1) recorded at 25 °C before melt-quenching 2 for the A [MnBr ] compounds. 2 4\n\nSupplementary Fig. 35 | Variable-temperature Raman spectra showing the in-plane deformation of the phenyl rings (ν , 610–620 cm-1) recorded at 25 °C after melt-quenching for 2 the A [MnBr ] compounds. 2 4\n\nSupplementary Fig. 36 | Variable-temperature Raman spectra showing the in-plane deformation of the phenyl rings (ν , 610–620 cm-1) recorded at 105 °C during melt-quenching 2 for the A [MnBr ] compounds. 2 4\n\nSupplementary Fig. 37 | Variable-temperature Raman spectra showing the in-plane deformation of the phenyl rings (ν , 610–620 cm-1) recorded at 245 °C during melt-quenching 2 for the A [MnBr ] compounds. 2 4\n\nSupplementary Fig. 38 | Temperature-dependent FWHMs of the representative Raman peaks ν , ν ’ and ν for the A [MnBr ] compounds. The stars indicate the FWHM values of corresponding 1 1 2 2 4 peaks measured after quenching.\n\n4. Impact of Rotational Heterogeneity: The effect of a non-uniform distribution of rotations within phosphonium cations on glass transition temperature (T₈) and GFA is not clearly addressed in the manuscript. A more thorough discussion of this aspect from the perspective of structural chemistry would be valuable.\n\nResponse:\nWe sincerely thank the reviewer for the insightful suggestion. To clarify the structural–property relationship between the rotational heterogeneity within phosphonium cations and T /GFA, we g constructed the glass structures using the RMC method and extracted the orientation vector and order parameter of the phosphonium cations. The orientation vector u, defined as the unit vector along each P–C bond linking the phosphorus atom to the non-aromatic carbon atom (Supplementary Figs. 11 and 12), serves as a local descriptor of the rotational orientation of the cations. From these vectors, we built the Q tensor and extracted its maximum eigenvalue as the orientational order parameter S , according to the following equation (J. V. Selinger, Introduction to the theory of soft max matter: From ideal gases to liquid crystals Ch. 5, Springer, 2016):\n\n3 1 𝐐= 〈𝐮𝐮T〉− 𝐈 2 2\n\nwhere uT is the transpose of the orientation vector and I is the identity matrix. The case that S ≈ max 1 corresponds to highly aligned cations, while values close to 0 indicate a highly disordered and isotropic orientational distribution. For the studied phosphonium series, S ranges from max approximately 0.01 to 0.05, indicating pronounced rotational disorder. [c-PrMeTPP] [MnBr ] and 2 4 [BuTPP] [MnBr ] exhibit lower S values, reflecting broader orientational distributions and easier 2 4 max local reorientations, which weaken cooperative structural constraints, thus tending to reduce T g while enhancing GFA by hindering the translational/rotational symmetry required for crystallization. Conversely, [BrBPP] [MnBr ] and [EtTPP] [MnBr ] exhibit higher S values, implying partial 2 4 2 4 max orientational alignment and stronger cation–anion coordination shells, increasing local rigidity and elevating T but potentially reducing GFA. The RMC-derived order parameter provides a practical g quantitative means to clarify the effects of “rotational heterogeneity” and “chemical composition” in analyzing the T –GFA relationship. We have updated the discussion in the revised text:\n\n“To quantify the rotational disorder, the orientational tensor Q was constructed from the RMC-derived models, and the maximum eigenvalue was extracted as the orientational order parameter S 32:\n\nmax\n\n𝐐= 3 〈𝐮𝐮T〉− 1 𝐈 (1) 2 2\n\nwhere u is the unit vector along each P–C bond linking the phosphorus atom to the non-aromatic carbon atom, uT is the transpose of the orientation vector and I is the identity matrix. S ranges max from approximately 0.01 to 0.05, indicating pronounced rotational disorder (Supplementary Fig. 12). Lower S values, such as those of [c-PrMeTPP] [MnBr ] and [BuTPP] [MnBr ], correspond max 2 4 2 4 to broader orientational distributions and easier local reorientations. These features reflect weakened cooperative structural constraints, thus tending to reduce T while enhancing GFA. Conversely, g higher S values (e.g., those of [BrBPP] [MnBr ] and [MeTPP] [MnBr ]) imply partial max 2 4 2 4 orientational alignment and stronger cation–anion interactions, leading to increased local rigidity, higher T , and reduced GFA.” g\n\n32. Selinger, J. V. Introduction to the Theory of Soft Matter: From Ideal Gases to Liquid Crystals, Ch. 5 (Springer, 2016).\n\nSupplementary Fig. 11 | The scheme of orientation disorder in the RMC glass models for different A [MnBr ] glasses. The arrows reflect the of vector u of each phosphonium cations, 2 4 defined as the unit vector along the P–C bond linking the phosphorus atom to the non-aromatic carbon atom.\n\nSupplementary Fig. 12 | The orientational order parameter of different A [MnBr ] glasses. 2 4\n\n5. Figure 2 (GFAs): The substantial difference in GFA between BrBPP and MeBPP, despite their structural similarity and the presence of free-to-rotate phenyl rings in both cases, is intriguing. The manuscript should provide a more detailed explanation of this phenomenon.\n\nResponse:\nWe thank the reviewer for the constructive comment, and we have expanded the discussion to explain the GFA difference between [BrBPP] [MnBr ] and [MeBPP] [MnBr ] based on molecular 2 4 2 4 polarity and intermolecular interactions. As discussed in the extracted descriptor, the glass-forming ability in this type of system is influenced by factors such as molecular shape and surface electrostatic potential. Although the molecular shapes of BrBPP and MeBPP are similar, the substitution of Br- for CH - significantly alters the molecular polarity and intermolecular 3 interactions. The stronger and more directional interactions in BrBPP restrict molecular mobility and reduce configurational freedom during melt quenching, leading to a localized phase space distribution and a deeper potential well, which facilitates recrystallization and thus limits glass formation. The corresponding description of the mechanism has been supplemented in the revised text.\n\n“The lower GFA of [BrBPP] [MnBr ] compared to [MeBPP] [MnBr ] is attributed to its 2 4 2 4 greater molecular polarity, which strengthens intermolecular interactions and increases structural frustration in the glassy state.”\n\nReviewer #2 (Remarks to the Author):\nThe authors reported a study on how structural disorder governs the bulk glass-forming ability by synthesizing a family of zero-dimensional hybrid metal halides with tunable short- to medium range structural arrangements to form glasses with diverse GFAs. They found the rotational order is able to be broken in a controlled manner, leading to distinct phase space partitions of molecular movements, allowing for tunable GFAs. This work affords new ideas on glass materials. It could be accepted after some revisions are made.\n\nResponse:\nWe thank the reviewer for the positive comments on our work. We have carefully addressed the reviewer’s questions as detailed below.\n\n1. It is important to indicate how to extract the values of T and T from the DSC curves. Note: Peak g m values are unreasonable.\n\nResponse:\nWe thank the reviewer for this careful attention of the definition, and we have revised the data extraction procedure accordingly. The T values were identified from the midpoint of the heat-flow g step in the second run of the DSC curve, which is consistent with standard DSC analysis. The T m values have now been refined by using the onset of the endothermic peak in the first heating run of the DSC curve. The updated values have been provided in the revised manuscript, and Fig. 2(d) has been updated accordingly.\n\n“Fig. 2. d, T , T and GFAs of A [MnBr ] glasses extracted from DSC results. The T /T values of g m 2 4 g m [BuTPP] [MnBr ], [BPP] [MnBr ] and [BrBPP] [MnBr ] increase sequentially. [c- 2 4 2 4 2 4 PrMeTPP] [MnBr ] has the highest T /T of 0.811 and [BrBPP] [MnBr ] exhibits the highest T 2 4 g m 2 4 g (96.9 °C) and T (269.4 °C) among the glass-forming compounds. For detailed information, please m see Supplementary Table 4.”\n\nMethods:\nThermogravimetric (TGA) and differential scanning calorimetry (DSC) analysis\n“T was determined from the onset of the endothermic peak in the first heating run of the DSC m curve, and T was determined from the midpoint of the step change in heat flow in the second heating g run.”\n\nSupplementary Table 4 | Summary of the thermal parameters of A [MnBr ] samples using 2 4 TGA and DSC measurements.\n\nTd (°C) Tg (°C) Tm (°C) Tg/Tm\n[MeTPP]2[MnBr4] 280 (Ref. 44) 57.64 177.07 0.735\n[EtTPP]2[MnBr4] 250 (Ref. 45) 43.03 173.22 0 . 7 0 8\n[PrTPP]2[MnBr4] 300.9 47.48 160.67 0.739\n[BuTPP]2[MnBr4] 266.9 46.12 135.69 0.781\n[c-PrMeTPP]2[MnBr4] 280.3 47.85 122.55 0.811\n[BPP]2[MnBr4] 270.4 77.55 216.76 0.716\n[MeBPP]2[MnBr4] 262.0 81.55 220.18 0.719\n[FBPP]2[MnBr4] 263.1 82.84 228.84 0.709\n[BrBPP]2[MnBr4] 287.0 96.85 269.38 0.682\n\n2. It is said that, in the caption of Figure 2, [BrBPP] [MnBr ] exhibits the highest T (96.9 °C) and 2 4 g T (271.1 °C). But it seems [TPP] [MnBr ] exhibits the highest T . m 2 4 m\n\nResponse:\nWe apologize for the lack of clarity in our previous discussion. In this work, [BrBPP] [MnBr ] 2 4 exhibits the highest T among the compounds that can form stable glasses. We have revised the m description in the caption of Fig. 2 to avoid ambiguity.\n\nFig. 2. Structural and thermal properties of A [MnBr ] glasses. ……Among the glass-forming 2 4 compounds, [c-PrMeTPP] [MnBr ] has the highest T /T of 0.811 and [BrBPP] [MnBr ] exhibits 2 4 g m 2 4 the highest T (96.9 °C) and T (269.4 °C). …… g m\n\n3. Figure 1abc and 4d illustrate three configurations of molecular motifs. In my opinion, the last two, nonspherical and polar ESP surface, are same. In fact, except for TPP, all the others are polar ellipsoids. Please consider this point.\n\nResponse:\nWe sincerely thank the reviewer for the insightful comment and for pointing out this issue. We apologize for the inappropriate use of terminology and agree that the “nonspherical” and “polar ESP surface” features are interrelated. In our revised version, we have clarified the polar configurations of molecular motifs except for TPP. To better describe this point, we have unified the terminology and revised the description of \"non-polarity\" to \"weak polarity\" throughout the manuscript to better reflect the actual molecular characteristics. The gradient color of Fig. 1 and Fig. 4 has also been revised correspondingly.\n\nFig. 1. Design and synthesis of hybrid A [MnBr ] glasses. a, Schematic patterns of the design 2 4 strategy. Silver ball: organic components; Yellow ball: inorganic components. In the enlarged diagram, the molecular shape and surface are represented as the core and shell of the ellipsoid, respectively. b, Diagram of glass formation through the melt-quenching process. The insets show the rotational order breaking behavior of molecular components during liquid-glass transition. The inorganic components are omitted for clarity. c, Structural models for A [MnBr ] glasses with 2 4 diverse glass properties attributed to different molecular ergodicity breaking pathways. d, Photographs of bulk [BuTPP] [MnBr ] glass under sunlight and X-ray radiation. e, SEM (top) and 2 4 microscopic (bottom) images under UV light of [BPP] [MnBr ] fibers. 2 4\n\nFig. 4. Correlations between molecular structures and glass-forming properties. a, RCF of phosphonium cations in the nine different glass models simulated at 500 K. b, The free-energy surfaces obtained from metadynamics simulations. The depth of the 3D map indicates the system energy with different molecular orientation. The contour map is the projection of the 3D map, which indicates the energy distribution. c, Correlation matrix of glass properties and molecular descriptors. The descriptors include I , 𝜎2 , S and . See the formula in Supplementary Note 2 and the ratio tot max c full correlation matrix in Supplementary Figs. 53 and 54. d, Schematic illustrations of the relationship between three representative structural motifs and glass properties with incremental ergodicity breaking characteristics. The ellipsoid with arrows denotes the possible configuration of molecular motifs, and the curve represents the rotational energy landscapes.\n\n4. Besides the AIMD, is there any experimental test to reveal the dynamic disorders?\n\nResponse:\nWe appreciate the reviewer’s insightful question. In addition to the AIMD and MD simulations, we have performed variable-temperature Raman spectroscopy (Supplementary Figs. S29). The Raman spectra during the melt-quenching process reveal the evolution of the local microenvironment and capture the feature of dynamic disorder. We have identified representative peaks corresponding to the Mn–Br stretching (ν at 250–255 cm-1 and ν ’ at 255–260 cm-1), and 1 1 phenyl ring in-plane deformation (ν at 610–620 cm-1). These modes correspond to vibrations of the 2 inorganic [MnBr ]2- anions and the phosphonium cations, respectively. As shown in Supplementary 4 Fig. S38, these peaks show progressive broadening with increasing temperature. Notably, the melt-quenched samples measured at 25 °C display broader peaks than those in the pristine crystalline state at the same temperature. This broadening indicates significantly variation of local environment and dynamic disorders, supporting the presence of rotational disorder in the molecular components. The corresponding description and results have been added to the revised manuscript.\n\n“To probe the evolution of molecular motion during vitrification, variable-temperature Raman spectra were analyzed for the Mn–Br stretching of [MnBr ]2- and the phenyl ring in-plane 4 deformation of phosphonium cations (Supplementary Fig. 29). The peaks of Mn–Br stretching are located at 250–255 cm-1 (ν ) and 255–260 cm-1 (ν ’), while the vibration peak of the phenyl ring 1 1 appears at 610–620 cm-1 (ν ) (Supplementary Fig. 30–37). The corresponding full widths at half 2 maximum (FWHM), fitted using the Lorentzian functions are summarized in Supplementary Fig. 38. Both ν and ν bands exhibit gradual broadening with increasing temperature, and the spectra 1 2 collected after quenching exhibit markedly broader features compared with those recorded before thermal annealing.”\n\nSupplementary Fig. 38 | Temperature-dependent FWHMs of the representative Raman peaks ν , ν ’ and ν for the A [MnBr ] compounds. The stars indicate the FWHM values of corresponding 1 1 2 2 4 peaks measured after quenching.\n\nReviewer #3 (Remarks to the Author):\nIn this work, the authors have presented the synthesis of zero-dimensional Mn-based hybrid metal halides with tunable structural arrangements to achieve glasses with diverse glass-forming abilities (GFAs). Further, authors have claimed that by altering the molecular shape and surface electrostatic potential of organic cations, the rotational order of these molecules is controllably disrupted, creating distinct phase space partitions for molecular motion and enabling tunable GFAs thereby providing some physical insight into the design principle of glasses from 0D Metal halide hybrids (in contrast to inorganic/metallic glasses)\nThe work may be considered for publication after major revision. I would like to be invited to review the revised manuscript. The following issues must be addressed:\n\nResponse:\nWe sincerely thank the reviewer for the valuable feedback. We have carefully addressed all the reviewer’s concerns, and the detailed responses can be found below.\n\n1. Authors have performed a detailed structural and theoretical study on the materials to elucidate the relation between GFA and the size, shape and electrostatic nature of organic cations. Not much efforts have been given to optical characterization on these materials. Absorption measurements, Tauc plots (band gaps), PL/PLE at low temperatures should be provided for comprehensive optical property assessment.\n\nResponse:\nWe greatly appreciate the reviewer for this constructive comment to include more comprehensive optical characterizations. In response, we have conducted comprehensive optical measurements, including UV–Vis absorption, Tauc analysis, and low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy for both the crystalline and glassy phases. The results of these optical characterizations are shown in Supplementary Figs. 18–20.\n\nDue to the pronounced fluorescence interference in the system, UV-Vis absorption measurements were conducted using non-polarized mode in the circular dichroism (CD) spectrometer. Tauc plots derived from the experimental data indicate that these compounds exhibit a direct electronic transition, with estimated bandgaps ranging from 3.64 to 4.24 eV. The close similarity in absorption edges and E values between different compounds indicates that their g fundamental optical transitions remain consistent across the series. The PL and PLE spectra at 80 K display broad emissions at 500–550 nm and excitations at 350–450 nm, which correspond to the d-d transition of the Mn2+ in [MnBr ]2- tetrahedra Minor variations in the spectral features can be 4 attributed to the differences in the local coordination environments and electrostatic fields surrounding [MnBr ]2-. Overall, the optical properties of the system primarily originate from the 4 intrinsic d-d transition of Mn2+, which is affected by the surrounding environment. The corresponding spectra and detailed description have been added to the main text and supplementary information.\n\n“UV-Vis absorption spectra of the crystalline and glassy materials show similar absorption at 320–350 nm (Supplementary Fig. 18). Meanwhile, the Tauc plots analysis reveals direct bandgap transitions for both states (Supplementary Fig. 19). The photoluminescence (PL) and photoluminescence excitation (PLE) spectra at 80 K display broad green emissions at 500–550 nm and excitation bands at 350–450 nm (Supplementary Fig. 20 and Supplementary Table 6), typical of the 4T →6A transitions in tetrahedrally coordinated Mn2+.” 1 1\n\nSupplementary Fig. 18 | UV-Vis spectra of the crystalline and glassy A [MnBr ] compounds. 2 4\n\nSupplementary Fig. 19 | Tauc plots of the crystalline and glassy A [MnBr ] compounds. 2 4\n\nSupplementary Fig. 20 | Photoluminescence emission and excitation spectra of the crystalline and glassy A [MnBr ] compounds at 80 K. 2 4\n\n2. Further, X-ray scintillation properties has been shown for materials other than the best glass forming material [c-PrMeTPP] [MnBr ]. For, [c-PrMeTPP] [MnBr ] scintillation property 2 4 2 4 characterisation should be provided.\n\nResponse:\nWe sincerely thank the reviewer for the insightful suggestion to include the X-ray scintillation property characterization of [c-PrMeTPP] [MnBr ]. We have performed comprehensive X-ray 2 4 response measurements, including variable dose rates, X-ray detection limits, and cycling stability. As shown in Supplementary Fig. 26, the X-ray induced luminescence spectra indicate that both [c-PrMeTPP] [MnBr ] and a -[c-PrMeTPP] [MnBr ] exhibit a clear response under dose rate of 2.94– 2 4 g 2 4 366 mGy /s radiation. The detection limits are calculated to be 133 nGyair/s for [c- air PrMeTPP] [MnBr ] and 110 nGyair/s for a -[c-PrMeTPP] [MnBr ]. Cycling experiments show 2 4 g 2 4 good radiation stability for a -[c-PrMeTPP] [MnBr ] under a dose rate of 67.3 mGyair/s. In addition, g 2 4 the spatial resolution of a -[c-PrMeTPP] [MnBr ] is 12 lp/mm, which reveals the excellent g 2 4 scintillation imaging property. These results, along with a detailed discussion, have been added to the revised manuscript.\n\n“To comprehensively evaluate the scintillation properties of [c-PrMeTPP] [MnBr ] and a -[c- 2 4 g PrMeTPP] [MnBr ], a series of X-ray excited luminescence and kinetic tests were conducted 2 4 (Supplementary Fig. 26). The emissions exhibit a linear dependence under dose rate of 2.94–366 mGy s-1, suggesting stable X-ray responses. The detection limits, which are determined from a air signal-to-noise of 3, are 131 and 110 nGyair s-1, respectively. Moreover, a -[c-PrMeTPP] [MnBr ] g 2 4 retains 99% of its original intensity after 3000 s of continuous irradiation and 50 cycles, demonstrating excellent radiation stability. a -[c-PrMeTPP] [MnBr ] also shows a spatial resolution g 2 4 of 12 lp mm-1, indicating its applicability for the X-ray imaging.”\n\nSupplementary Fig. 26 | The scintillator properties of [c-PrMeTPP] [MnBr ] and a -[c- 2 4 g PrMeTPP] [MnBr ]. a, The radioluminescence spectra, b, The detection limit, c, The cyclic stability 2 4 of a -[c-PrMeTPP] [MnBr ] under a dose rate of 67.3 mGy /s. d, Photographs of a -[c- g 2 4 air g PrMeTPP] [MnBr ] and its imaging application. 2 4\n\n3. No Data has been given for scintillation performance of the glass materials (such as X-ray response with variable dose rates, X-ray detection limit etc.). These data would strengthen the potential of application of such materials.\n\nResponse:\nWe sincerely thank the reviewer’s suggestions to further evaluate the X-ray scintillation performance of the glass materials. Following the review’s suggestion, we have conducted the corresponding measurements of the X-ray excited luminescence with variable dose rates and X-ray detection limit for the glass materials. As shown in Supplementary Figs. 24 and 25-x, all glass materials exhibit a clear response to X-ray irradiation, and the luminescence intensity increases linearly with the dose rate. Moreover, the detection limit evaluation demonstrates that the glass materials possess high sensitivity to low-dose X-ray, indicating their potential for efficient X-ray detection applications. The corresponding spectra and quantitative results have been added to the revised manuscript.\n\n“X-ray excited luminescence and detection limit measurements reveal excellent X-ray response and low detection limits of the A [MnBr ] glasses, surpassing some prototypical 2 4 commercial materials. Among them, a -[MeBPP] [MnBr ] exhibits an ultralow detection threshold g 2 4 of 23 nGy air s-1, highlighting its high X-ray sensitivity (Supplementary Figs. 24 and 25, and Supplementary Table 9).”\n\nSupplementary Fig. 24 | Radioluminescence spectra of the A [MnBr ] glasses under 2.94–366 2 4 mGy /s doses. air\n\nSupplementary Fig. 25 | The radiation dose rate dependence measurements and detection limit of the A [MnBr ] glasses. 2 4\n\nSupplementary Table 9 | Summary of the detection limit of a -A [MnBr ]. g 2 4\n\nFitting equation Detection limit (nGyair/s)\nag-[MeTPP]2[MnBr4] y=352.6x+20.9 194\nag- [EtTPP]2[MnBr4] y=572.7x+35.7 134\nag-[PrTPP]2[MnBr4] y=962.1x+66.2 66\nag-[BuTPP]2[MnBr4] y=810.7x+77.9 95\nag-[c-PrMeTPP]2[MnBr4] y=634.72x+77.8 110\nag-[BPP]2[MnBr4] y=2244.5x+126.1 31\nag-[MeBPP]2[MnBr4] y=2844.1+199.4 23\nag-[FBPP]2[MnBr4] y=1661.3x+110.3 42\nag-[BrBPP]2[MnBr4] y=554.6x+28.8 139\n\n4. Many supporting figures are there without any comment and discussion in the main manuscript (such as Supplementary Fig. 14 etc). Please provide an excerpt on what these figure convey in words.\n\nResponse:\nWe sincerely thank the reviewer for the critical comment. We have carefully reviewed the manuscript and supplementary text and have now added detailed descriptions for the Supplementary figures, including the Supplementary Figs. 27 and 28 (original Supplementary Figs. 14 and 15). The revised texts are as follows:\n\n“The glass transitions are confirmed by the Raman spectroscopy where several distinguishable peaks below 150 cm-1, corresponding to the vibrational modes of [MnBr ]2- tetrahedra, display a 4 broad single peak after vitrification (Fig. 3c, and Supplementary Fig. 27).”\n\n“FTIR analysis reveal that characteristic ν and ν (in the phenyl ring) vibration peaks C–H C=C roughly maintain their positions, while the C–H vibrations show significant broadening after vitrification (Supplementary Fig. 28). These results indicate the variations in chemical environments of the cations and emergence of disorder after the melt-quenching. Additional Raman peaks, for the symmetric and asymmetric C–H vibrations in the methylene and methyl groups, give similar results.”\n\n5. Authors have given a thorough theoretical understanding of the rotational freedom of organic cations and its relation with glass forming ability. Authors have analysed 9 different glasses and provide an ESP based chemical design principle for glasses with high GFA. It will be prudent and impactful if the authors can provide simpler chemical insight/physical picture to gauge the structure of the organic cations and its relation to ESP and sphericity. Design principles driven by chemical intuition (based on the structure of the organic cation) without performing calculations to get to extent of spherecity and surface ESP will be impactful. Please add a discussion on this.\n\nResponse:\nWe are very grateful for the reviewer’s insightful comment. We have revised the discussion of the electrostatic potential (ESP) and sphericity descriptor to provide a simpler chemical insight. These parameters serve as intuitive indicators of the influence of weak intermolecular interactions (reflected by the ESP distribution) and steric effects (represented by the sphericity), which together govern the degree of orientational disorder and hence the GFA. The relevant sections in the manuscript have been revised to clarify the conceptual relationships and better highlight their underlying physical meaning.\n\n“In brief, compact and symmetrical cations with weakly polar or aliphatic substituents tend to exhibit uniform ESP surfaces and higher rotational freedom. This facilitates orientational disorder of the structural motifs and produces relatively low intermolecular potential barriers, thereby enhancing the GFA. Whereas cations with elongated shapes or strong polar substituents display anisotropic charge distributions and stronger intermolecular interactions, which restrict molecular conformations, create pronounced potential energy extrema, and ultimately lead to reduced GFA.”\n\n6. Please measure the kinetics of the glass formation for the systems and provide correlations to their GFAs.\n\nResponse:\nWe thank the reviewer for the valuable suggestion. DSC measurements were performed under various heating and cooling rates to probe the glass-forming kinetics. Since no distinct crystallization peaks are observed in the system, the kinetic measurement of crystallization activation energy becomes impractical. Consequently, we focused on evaluating the glass transition temperatures at varying heating rates to estimate the activation energy of the glass transition (E ). g Both the Moynihan and Kissinger methods were employed to determine the corresponding values. As shown in Supplementary Figs. 14–17 and Table 5, the E values derived from the Moynihan and g Kissinger analyses fall within the range of 210–480 kJ/mol and exhibit consistent trends. Compounds containing rigid or polar substituents exhibit higher E values, reflecting slower g structural relaxation and greater resistance to molecular rearrangement, which together contribute to their relatively higher T values. g\n\nAlthough the E values provide insight into the local relaxation kinetics near T , they do not g g show linear correlations with GFAs. This is not only consistent with the distinct physical origins of E and GFA, but also a reflectance of the diverse core factors derived from the molecular motifs. g GFA is primarily influenced by the competition between vitrification and crystallization during the melt-quenching process, which are governed by the mobility, size, and polarity of the structural motifs. In contrast, the activation energy is primarily influenced by the strength of intermolecular interactions and the distribution of free volume during glassy state transited to the viscous state. Overall, E describes local relaxation barriers of the glass, and GFA reflects the tendency of the g system to avoid crystallization. These observations suggest that the distinct dynamic behaviors and interaction mechanisms of the structural motifs, which are controlled by both molecular rigidity and orientation effects, collectively account for the variations in T and GFA observed in these g compounds. The corresponding characterizations and descriptions have been added to the revised manuscript:\n\nRevised text:\n“Furthermore, the activation energies (E ) derived from the Moynihan and Kissinger analyses g exhibit consistent trends (Supplementary Figs. 13–17 and Supplementary Table 5), quantifying the structural-relaxation kinetics near T 35–37. Compounds containing rigid or polar substituents exhibit g markedly higher E values, indicative of slower structural relaxation and stronger resistance to g molecular rearrangement. This enhanced rigidity contributes to the elevated T observed in these g glass systems.”\n\n“Thermogravimetric (TGA) and differential scanning calorimetry (DSC) analysis” section:\nTo quantify the kinetic behavior of the system, DSC measurements were conducted at diverse heating and cooling rates. Owing to the absence of distinct crystallization peaks in the compounds, the activation energies associated with the glass transition were estimated using the Moynihan and Kissinger methods. The corresponding formulas are as follows:\n\n𝑑(ln𝛽) 𝐸 a =− 𝑑(1/𝑇 ) 𝑅 g\n\n𝛽 𝐸 a ln( )=− +𝐾 𝑇 2 𝑅𝑇 g g\n\nwhere β is the heating or cooling rate, E is the activation energy related to the structural relaxation. a\n\nSupplementary Fig. 14 | DSC curves of A [MnBr ] glasses at different heating and cooling 2 4 rates.\n\nSupplementary Fig. 15 | Kinetic analysis of glass transition by the Kissinger method for A [MnBr ] glasses. Linear relationships were fitted following the Kissinger formula. 2 4\n\nSupplementary Fig. 16 | Determination of the activation energy of glass transition by Moynihan method for A [MnBr ] glasses. Linear relationships were fitted following the 2 4 Moynihan formula.\n\nSupplementary Fig. 17 | Correlation between the activation energies obtained from the Moynihan and Kissinger methods and the thermal parameters of A [MnBr ] glasses. 2 4\n\nSupplementary Table 5 | Summary of the kinetic parameters of A [MnBr ] glasses using DSC 2 4 measurements.\n\nEg (Moynihan) Eg (Kissinger)\n[MeTPP]2[MnBr4] 411.4 390.0\n[EtTPP]2[MnBr4] 320.5 302.5\n[PrTPP]2[MnBr4] 241.5 215.5\n[BuTPP]2[MnBr4] 329.7 302.2\n[c-PrMeTPP]2[MnBr4] 379.4 366.2\n[BPP]2[MnBr4] 406.1 386.0\n[MeBPP]2[MnBr4] 394.7 367.8\n[FBPP]2[MnBr4] 434.4 408.4\n[BrBPP]2[MnBr4] 471.5 451.4\n\n7. Different glasses on Mn-Halides show lightly redshifted emission although PDF analysis shows not much change in the local Metal – halide environment. How do you rationalize the observed changes in the electronic properties of the Mn-X (that causes PL peak position shift) for these glassy systems that are dominated by rotational disorder/freezing.\n\nResponse:\nWe sincerely thank the reviewer for the valuable comment. The emission of the compounds originates from the spin-forbidden 4T –6A transition of Mn2+ in the [MnBr ]2- anion. The observed 1 1 4 redshifted emission can be attributed to the increased depth of self-trapped excitons upon vitrification, which strongly depends on the ligand field strength and the surrounding environment of [MnBr ]2-. 4\n\nTo understand this effect, the Mn–Br coordination environment was analyzed based on the PDF g(r) data. The Mn–Br bond length shortens by approximately 0.01–0.02 Å after vitrification (Supplementary Fig. 22). This small change suggests a slightly increased ligand field splitting of Mn2+ (Phys. Rev. B, 2009, 80, 085115), which could contribute to the redshift emission. Besides, the emission peak position and bandwidth of Mn2+ can be tuned by varying organic cations, showing that the external cationic environment significantly affects the radiative transition of [MnBr ]2- 4 (Chem. Mater., 2019, 31, 10161). After vitrification, the disordered orientation and distribution of the organic cations can lead to spatial fluctuations in the polarization environment. This broadens the energy distribution of the 4T state and deepens the self-trapped exciton potential. Both effects 1 modify the self-trapped exciton state and give rise to the observed redshift emission.\n\nWe have added the discussion to the luminescence measurements section of the revised manuscript:\n\n“This redshift is attributed to the increased depth of the self-trapped exciton state, arising from the shortened Mn–Br distance and the disordered environment around [MnBr ]2- (Supplementary 4 Figs. 22).”\n\nSupplementary Fig. 22 | The changes in Mn–Br bond length before and after glass formation.\n\n8. Authors must take reported examples of glasses that show substantial PL peak position change from crystalline to glassy phase and demonstrate that effect of local structural changes in the M-X geometry and showcase that rotational disorder is one of the criteria for forming glasses. The primary criteria being changes in the local structure. PDF analysis of such materials that show changes in PL peak position (changes in local structure), their rotational disorder quantification, and their relative weightages can provide detailed understanding of the GFAs of variety of glasses for demonstrating generality. Experiments and discussions on these will be useful for the work.\n\n(1) Authors must take reported examples of glasses that show substantial PL peak position change from crystalline to glassy phase and demonstrate that effect of local structural changes in the M-X geometry.\n\nResponse:\nWe sincerely thank the reviewer’s valuable suggestions. In response, we have summarized representative literatures on similar organic-inorganic metal halide glasses, which show photoluminescence peak shift after vitrification. In Mn-based halide systems, the crystalline and glassy phases exhibit consistent short-range ordering, with preserved [MnBr ]2- and cations. In the 4 reported works, the PL changes observed after vitrification are mainly manifested as red-shifted emission peaks, reduced intensity, and shortened lifetimes. These studies generally attribute the red-shift and other effects to the differences in the degree of molecular disorder (ACS Nano 2024, 18, 16715), the non-radiative recombination and defect states induced by disorder (Sci. Adv., 2025, 11, eadu1982; Adv. Optical Mater., 2024, 12, 2302434), the excited-state stabilization energy perturbated by structural deformation differences (J. Am. Chem. Soc., 2024, 146, 7373), and new self-trapped excitons with lower energy level (Chem. Commun., 2023, 59, 11361).The studies emphasize the importance of the introduced disorder and structural deformation for the emission, which significantly alter the excited-state energy. In our study, the slight shift of the emission peaks was also observed, which is consistent with the previous reports. PDF and RMC analysis have shown the preserved structural motifs after vitrification, except for the orientational disorder and shortened Mn–Br distance. The corresponding references have been added to the revised manuscript to support the discussion:\n\nRevised text:\n“The redshift behavior agrees with previous reported glasses29, 38–42, which were attributed to disorder-induced effects.”\n\n38. Yin M., et al. Crystal–glass phase transition enabling reversible fluorescence switching in zero-dimensional antimony halides. Chem. Commun. 59, 11361–11364 (2023).\n39. Zhang Z.-Z., et al. Organic–inorganic hybrid Mn-based transparent glass for curved X-ray scintillation imaging. Adv. Optical Mater. 12, 2302434 (2024).\n40. Dong C. et al. Organic–inorganic hybrid glasses of atomically precise nanoclusters. J. Am. Chem. Soc. 146, 7373–7385 (2024).\n41. Feng T., et al. Large-area transparent antimony-based perovskite glass for high-resolution X-ray imaging. ACS Nano 18, 16715–16725 (2024).\n42. He Z.-L., et al. A universal strategy toward two-component organic–inorganic metal-halide luminescent glasses and glass–crystal composites. Sci. Adv. 11, eadu1982 (2025).\n\nSupplementary Table 6 | Summary of the representative literature of the glass samples with PL position shift compared with their crystals.\n\nCompound PL peak shift (crystal to glass) Reference\n[HTPP]2[MnBr4]29 9 nm Angew. Chem. Int. Ed. 2023, 62, e202216504\n(MEP/ETP/BUP/BTP)2[SbCl5]38 47, 36, 28, 69 nm Chem. Commun., 2023, 59, 11361\n[CH3Ph3P]2[MnBr4]39 4 nm Adv. Optical Mater. 2024, 12, 2302434\n[PPh2Et]4[Cu4I4]40 25 nm J. Am. Chem. Soc. 2024, 146, 7373\n[C20H20P]2[SbCl5]41 25 nm ACS Nano 2024, 18, 16715\n[TPG]2[MnBr4]42 14 nm Sci. Adv. 2025, 11, eadu1982\n\n(2) Showcase that rotational disorder is one of the criteria for forming glasses. The primary criteria being changes in the local structure. PDF analysis of such materials that show changes in PL peak position (changes in local structure), their rotational disorder quantification, and their relative weightages can provide detailed understanding of the GFAs of variety of glasses for demonstrating generality. Experiments and discussions on these will be useful for the work.\n\nResponse:\nWe sincerely appreciate the reviewer’s comment that the local structural variations are the core factors influencing the disorder in these glasses. In response to the reviewer’s question, additional PDF analyses and RMC modeling based on the experimental PDF data were performed, yielding microscopic structural models of the glass states (Supplementary Fig. 11). Using these models, the rotational disorder and its correlation with GFA were quantitatively examined.\n\nTo describe the orientational disorder in these glasses, we defined the orientational vector u from the using the P–C bond vectors. The orientational order parameter S was then derived from max the maximum eigenvalue of the Q tensor:𝐐= 3 〈𝐮𝐮T〉− 1 𝐈 , where uT is the transpose of the 2 2 orientation vector, and I is the identity matrix (J. V. Selinger, Introduction to the theory of soft matter: From ideal gases to liquid crystals Ch. 5, Springer, 2016). The case that S ≈ 1 corresponds to max highly aligned cations, while values close to 0 indicate a highly disordered and isotropic orientational distribution. As shown in Supplementary Fig. 12, the calculated S values range from max 0.01 to 0.05 among the system. [BrBPP] [MnBr ] and [c-PrMeTPP] [MnBr ] display the value of 2 4 2 4 0.048 and 0.016, respectively. The correlation between S and glass properties was further max examined (Supplementary Figs. 53 and 54). The Pearson and Spearman correlation coefficients between S and T /T were calculated to be -0.76 and -0.85, respectively, indicating a strong max g m negative correlation and hence a strong linkage between orientational disorder and GFA. These results provide direct and quantitative support for the intrinsic connection between the rotational disorder and GFAs in these 0D hybrid metal halide glasses.\n\nRevised text:\n“The I , 𝜎2 and t descriptors exhibit a significant positive correlation to T and T . ratio tot c g m Conversely, a negative correlation is observed with the T /T ratio, serving as efficient descriptors g m for assessing GFA. In addition, the orientational order parameter S , extracted from RMC max modeling, exhibits a pronounced negative correlation with T /T , highlighting its reliability as an g m excellent indicator of GFA. These results demonstrate that the rotational disorder play a dominant role in governing glass formation.”\n\nSupplementary Fig. 53 | The correlation matrix (a) and linear and quadratic fitting curves (b) of GFAs and A-site descriptors calculated using DFT optimized structures. The filled areas represent 95% confidence intervals. The descriptors include R (radius of cations), m (molecular mass), I (moment ratio of inertia along the shortest and longest principal axis), V (molecular ratio volume), S (orientational order parameter),  (dipole moment),  (average deviation of ESP on max the molecular surface), 𝜎2 (overall variance of ESP on the molecular surface), and  (rotational tot c correlation time at 500 K).\n\nSupplementary Fig. 54 | The correlation matrix (a) and linear and quadratic fitting curves (b) of GFAs and molecular descriptors based on the configurations of phosphonium cations in A [MnBr ] crystals. The filled areas represent 95% confidence intervals. 2 4\n\nReviewer #4 (Remarks to the Author):\nIn this paper, the authors report a series of Mn-based hybrid metal halides with different GFAs. The authors conducted a multi-faceted investigation into the relationship between cationic species and GFA in this emerging glass material system. A more uniform distribution of molecular rotation and reduced variance of surface ESP ultimately are suggested to lead to reduced Tg and Tm, which could offer valuable guidance for the rational design of hybrid metal halide glass. Several significant issues should be addressed before considering it for this journal.\n\nResponse:\nWe sincerely thank the reviewer for the careful evaluation of our work. We have carefully addressed the comments and revised the manuscript accordingly.\n\n1. Is the force field used in the simulation (GAFF) appropriate for describing manganese halide systems? The authors should provide a detailed explanation of how manganese and bromine are treated in the classical molecular dynamics section. For the potential dimerization issue of [MnBr4]2- ions, specific modifications to the charge distribution should be proposed. It is recommended to supplement the discussion with an analysis of how well the force field parameters match experimental or high-precision computational data. Additionally, providing the simulation input files would be beneficial for reproducibility.\n\n(1) Is the force field used in the simulation (GAFF) appropriate for describing manganese halide systems? The authors should provide a detailed explanation of how manganese and bromine are treated in the classical molecular dynamics section.\n\nResponse:\nWe sincerely appreciate the valuable comments and have added detailed computational methods to the Methods section. In this work, the carbon, hydrogen, nitrogen, and phosphorus atoms were assigned GAFF atomic types, while manganese and bromine atoms were assigned UFF atomic types. Bond and angle parameters were derived from DFT frequency calculations using the modified Seminario method (J. Chem. Theory Comput. 2018, 14, 274), whereas proper and improper dihedral terms were taken from the GAFF force field.\n\nGAFF is primarily developed for organic systems, while it has been successfully applied to predict the thermodynamic and transport properties of ionic liquids (J. Phys. Chem. B 2015, 119, 5882) and to describe the motion behavior and melting processes of tetraphenylphosphonium and related salts (J. Phys. Chem. B 2018, 122, 4006; Phys. Chem. Chem. Phys. 2020, 22, 12301). These studies support the applicability of GAFF in modeling phosphonium metal halide systems as in our work. The combination of GAFF with force field parameters derived via the modified Seminario method has also been adopted in recent studies of organic–inorganic hybrid systems (Carbon 2025, 236, 120102; Sci. China Chem. 2023, 66, 228). The detailed parameterization procedure has been fully described in the revised Methods section:\n\nRevised text:\n“The Generalized Amber Force Field (GAFF) was used as the initial parameters to the simulation system, with Mn and Br atoms assigned Universal Force Field (UFF) atomic types. Bond and angle parameters were derived from DFT frequency calculations using the modified Seminario method (ORCA), and the remaining parameters were taken from GAFF65,66.”\n\n(2) For the potential dimerization issue of [MnBr ]2- ions, specific modifications to the charge 4 distribution should be proposed. It is recommended to supplement the discussion with an analysis of how well the force field parameters match experimental or high-precision computational data.\n\nResponse:\nWe have provided detailed description of the charge modification procedure. During the initial setup of the MD simulations, the atomic charges were obtained from DFT calculation using the restrained electrostatic potential (RESP) fitting method. However, during the production run of the melting system of [MeTPP] [MnBr ] and [EtTPP] [MnBr ], an unexpected dimerization of 2 4 2 4 [MnBr ]2- to [Mn Br ]4- was observed. To mitigate this issue, we adjusted the atomic charge 4 2 8 distribution of [MnBr ]2- ions while keeping the total charge unchanged. The atomic charges in 4 different systems are listed in Table R1. A weaker modification with the charge of Mn setting to 0.56 and 0.26 has also been tested, while the dimerization phenomenon persisted.\n\nIn addition, the electronic continuum correction (ECC) approach (J. Chem. Theory Comput. 2010, 6, 1498) and the implicit solvent models of ionic liquid (J. Phys. Chem. B, 2012, 116, 9122) during DFT calculation were also attempted to correct the electrostatics, while these two methods failed to solve the dimerization problem and maintaining the comparability of the motion behavior of phosphonium cations. The Hirshfeld-I charge averaged from the equivalent position of the crystal charge calculation was also tried, but it failed to preserve the comparability of the cationic motion.\n\nTable R1. The atomic charges of [MnBr ]2- in different simulation systems. 4\n\nAtomic Charge [MeTPP]2[MnBr4] and [EtTPP]2[MnBr4] Other systems\nMn 0.06161052 1.06161052\nBr -0.51469751 -0.76469751\nBr -0.51613329 -0.76613329\nBr -0.51544224 -0.76544224\nBr -0.51533748 -0.76533748\n\nTo further confirm the effectiveness of the MD simulations, the bond lengths and angles at 800 K were extracted and compared from the AIMD simulation, the original MD simulation, and the MD simulation with modified charge of [BPP] [MnBr ]. As shown in Fig. R41, the average values 2 4 of the Mn–Br, P–C, and C–C bond lengths and angles were found to be consistent across the three simulations. Regarding the distributions, the Mn–Br bond lengths and Br–Mn–Br bond angles in the inorganic component exhibit slightly broader distributions, and the distribution for P–C and C– C bonds in the phosphonium cations were observed to closely resemble those from the AIMD simulation. Given that the primary focus of this study lies in the mean square displacement (MSD) and rotational correlation function (RCF) of the organic components, it can be concluded that the current MD simulations and the implemented charge modification method are both reliable and appropriate for the studied glass systems. The corresponding discussion has been added to the Supplementary Note 1:\n\n“Due to the dimerization issue in [MeTPP] [MnBr ] and [EtTPP] [MnBr ], the charge of 2 4 2 4 [MnBr ]2- was slightly adjusted while keeping the total charge constant. The charge of Mn and Br 4 were changed from 1.062 and -0.765 to 0.0616 and -0.515, respectively. The influences in the bond lengths and angles are listed in Supplementary Fig. 41.”\n\nSupplementary Fig. 41 | The comparison of the bond lengths and bond angles obtained from the AIMD and MD simulations (original and charge-modified) of [BPP] [MnBr ] at 800 K. 2 4\n\n(3) Additionally, providing the simulation input files would be beneficial for reproducibility.\n\nResponse:\nThe detailed input files have been uploaded to the supplementary materials in a zip file.\n\n2. How does the \"push-pull electronic effect\" specifically influence Tg/Tm? Additionally, have the authors synthesized and analyzed materials with Cl substituents to evaluate its properties?\n\n(1) How does the \"push-pull electronic effect\" specifically influence Tg/Tm?\n\nResponse:\nThe push-pull electronic effects of the benzyl side chains play a crucial role in tuning the polarity of the phosphonium cations. Since the molecular interactions in these glasses are primarily governed by electrostatic and van der Waals forces, the variations in the electronic properties of the benzyl side groups adjust the electron density around the phosphonium cations, which modifies the interactions between [ZnBr ]2- and phosphonium cations. These variations in molecular interactions 4 give rise to the observed differences in thermal properties, including T and T . g m\n\nRevised text:\n“This suggests the push-pull substituent effect adjusts the electron density of the cations and hence modulates the strength of the interactions between inorganic and organic molecular motifs. These electronic variations lead to pronounced differences in GFAs.”\n\n(2) Additionally, have the authors synthesized and analyzed materials with Cl substituents to evaluate its properties?\n\nResponse:\nWe sincerely thank the reviewer for the insightful comment. Following the suggestion, we synthesized [ClBPP] [MnBr ] and characterized its glass formation properties. As shown in Fig. R1, 2 4 [ClBPP] [MnBr ] can form a glass via the melt-quenching process, denoted as a -[ClBPP] [MnBr ]. 2 4 g 2 4 The T and T are 90.74 and 227.00 °C, respectively, yielding a T /T ratio of 0.727. The T of g m g m g [ClBPP] [MnBr ] is close to that of [BrBPP] [MnBr ] (96.85 °C), while its T matches that of 2 4 2 4 m [FBPP] [MnBr ] (228.84 °C). The T /T ratio is slightly higher than those of [BrBPP] [MnBr ] and 2 4 g m 2 4 [FBPP] [MnBr ] (0.682 and 0.709, respectively). After the melt-quenching process, the a - 2 4 g [ClBPP] [MnBr ] retains strong luminescence emission originating from [MnBr ]2-. The UV-vis 2 4 4 absorption and fitted Tauc plots indicate the band gaps of [ClBPP] [MnBr ] and a -[ClBPP] [MnBr ] 2 4 g 2 4 are 3.72 and 3.77 eV, respectively. X-ray excited luminescence spectra measured under varying dose rates confirm that both samples exhibit efficient scintillation properties, with detection limits of 82 and 95 nGy s-1 for the crystalline and the glassy states, respectively.\n\nFig. R1 Fundamental characterizations and optical properties of [ClBPP] [MnBr ] and a - 2 4 g [ClBPP] [MnBr ]. a, PXRD spectra of [ClBPP] [MnBr ] and melt-quenched sample. b, DSC curves 2 4 2 4 of [ClBPP] [MnBr ]. c, PL and PLE spectra of a -[ClBPP] [MnBr ]. d, UV-vis spectra of 2 4 g 2 4 [ClBPP] [MnBr ] and a -[ClBPP] [MnBr ]. e–f, Tauc plots. g–h, X-ray excited emission spectra 2 4 g 2 4 under dose rate of 2.94–366 mGy /s. i, The detection limit of [ClBPP] [MnBr ] and a - air 2 4 g [ClBPP] [MnBr ]. 2 4\n\n3. Is there any experimental or theoretical evidence to support the statement that \"the [MnBr4]2- tetrahedra in the low GFA glasses exhibit vibrational modes with more non-equivalent energies\"?\n\nResponse:\nWe sincerely appreciate the reviewer’s insightful comment, and have revised the corresponding discussion to improve the reliability. The distortion of the [MnBr ]2- tetrahedra could affect trap 4 states and lead to additional nonradiative decay channel (Angew. Chem. Int. Ed. 2020, 132, 17533; Adv. Mater. 2025, 10.1002/adma.202514522). The tetrahedral quadratic elongation parameter 〈𝜆 〉 of [MnBr ]2- based on the RMC models was extracted, which is defined as (Science, 1971, tet 4 172, 567):\n\n1 4 𝑙 2 𝑖 〈𝜆 〉= ∑( ) tet 4 𝑙̅ 𝑖=1\n\nwhere 𝑙 is the length of the ith bond. The Pearson and Spearman correlation coefficients between 𝑖 distortion and GFAs are -0.41 and -0.65, respectively, showcasing weak negative correlation. The results indicate that the [MnBr ]2- units in the glasses with lower GFA may exhibit slightly higher 4 structural distortion. However, the direct evidence from Raman spectra is absent due to the signal overlap and the severe broadening after melt-quenching process. As an alternative, we have revised the description in the manuscript to better illustrate the corresponding properties, emphasizing the local environmental changes instead of the vibrational energies.\n\nFig. R2 | The scattering plot of the distance distortion and T /T of the A [MnBr ] glasses. g m 2 4\n\nRevised text:\n“For the low GFA glasses, the [MnBr ]2- tetrahedra may experience subtle variations in their 4 local environment after vitrification, leading to enhanced non-radiative decay.”\n\n4. Supplementary Fig. 9 lacks sufficient labeling, making it difficult to interpret. Specifically, the direction of heat flow and the correspondence between the two heating cycles are not clearly indicated. In Supplementary Fig. 9d, [PrBPP]2[MnBr4] exhibits two peaks. How was the Tm determined in this case? In Supplementary Fig. 9e, why does the cold crystallization peak of [BrBPP]2[MnBr4] indicate its poor glass-forming ability? Could this peak be attributed to the presence of impurities, leading to cold crystallization and subsequent melting? Additionally, the significant difference between melting peaks of the first and second up-scan raises concerns about the sample purity and the origin of the cold crystallization behavior. Clarifying these points and improving the Fig. annotations would greatly enhance the interpretability of the data.\n\n(1) Supplementary Fig. 9 lacks sufficient labeling, making it difficult to interpret. Specifically, the direction of heat flow and the correspondence between the two heating cycles are not clearly indicated.\n\nResponse:\nWe sincerely thank the reviewers for this critical comment. We have modified the figure label in the Supplementary Fig. 9 to improve its readability and added arrows to specify the heat flow in the two heating cycles.\n\nSupplementary Fig. 13 | TGA and DSC curves of A [MnBr ] compounds. a, TGA profiles of 2 4 the Category I halides, showing the decomposition temperatures at 401.2 °C for [TPP] [MnBr ], 2 4 300.9 °C for [PrTPP] [MnBr ], 266.9 °C for [BuTPP] [MnBr ], and 280.3 °C for [c- 2 4 2 4 PrMeTPP] [MnBr ], respectively. b, TGA profiles of the Category II halides, showing the 2 4 decomposition temperatures at 287.0 °C for [BrBPP] [MnBr ]), 270.4 °C for [BPP] [MnBr ], 2 4 2 4 263.1 °C for [FBPP] [MnBr ], and 262.0 °C for [MeBPP] [MnBr ], respectively. c, DSC curves of 2 4 2 4 [TPP] [MnBr ]. d–e, DSC curves of Category I (d) and Category II (e) halides. The up-scan curve 2 4 of [BrBPP] [MnBr ] shows a recrystallization peak, which indicates its poor glass-forming ability 2 4 compared to other systems. All the temperature ramping rates were set as 10 °C min-1.\n\n(2) In Supplementary Fig. 9d, [PrBPP] [MnBr ] exhibits two peaks. How was the T determined in 2 4 m this case?\n\nResponse:\nWe sincerely thank the reviewers for the valuable comment. The first endothermic peak observed during heating is attributed to the loss of solvents, as each unit cell of [PrTPP] [MnBr ] 2 4 contains one acetonitrile molecule.\n\nAs the temperature increases, the solvent is released prior to melting, leading to the appearance of an endothermic peak. The loss of the solvent is also evident from the thermogravimetric (TG) curve of [PrTPP] [MnBr ]. Furthermore, we conducted DSC measurement for [PrTPP] [MnBr ] 2 4 2 4 after heat treatment by 110 °C for 24 h to verify the peak assignment, in which only the second peak remained (Fig. R3). This observation confirms that the T is determined by the second peak. m\n\nFig. R3 | TG plot of [BrBPP] [MnBr ] and DSC curves of the [BrBPP] [MnBr ] treated by 110 °C. 2 4 2 4\n\n(3) In Supplementary Fig. 9e, why does the cold crystallization peak of [BrBPP] [MnBr ] indicate 2 4 its poor glass-forming ability? Could this peak be attributed to the presence of impurities, leading to cold crystallization and subsequent melting? Additionally, the significant difference between melting peaks of the first and second up-scan raises concerns about the sample purity and the origin of the cold crystallization behavior. Clarifying these points and improving the Fig. annotations would greatly enhance the interpretability of the data.\n\nResponse:\nWe sincerely thank the reviewer for the valuable suggestion to clarify the origin of the cold crystallization peak of [BrBPP] [MnBr ]. The cold crystallization peak mainly arises from the 2 4 structural rearrangement and recrystallization of the glassy phase upon heating, which reflects the metastable feature of a -[BrBPP] [MnBr ] and is typically observed in materials with weak GFA. g 2 4\n\nTo verify the observed cold crystallization behavior, we conducted repeated DSC measurements using powders obtained from bulk single crystals (Fig. R4). The DSC results consistently show significant cold crystallization peaks in a -[BrBPP] [MnBr ] during the g 2 4 secondary heating process, regardless of whether the heating and cooling rate were 10 or 30 °C min- 1. The persistence of the cold crystallization peak even at a faster cooling rate of 30 °C/min confirms the strong tendency of the system to recrystallize during thermal treatment, indicating its poor GFA. Additionally, high-performance liquid chromatography measurements and elemental analysis of [BrBPP] [MnBr ] were also conducted to clarify the composition and purity of the sample. The 2 4 High-performance liquid chromatography results revealed that the reference compound BrBPPBr exhibits a single peak at t1=1.164 min and [BrBPP] [MnBr ] contained two peaks of organic cations 2 4 and [MnBr ]2- tetrahedra at t =1.173 min and t =3.536 min. The first peak exhibits consistent 4 1 2 retention time with the reference cation, confirming the presence of the organic component, while the second minor peak is mainly attributed to the inorganic species under the condition. Elemental analysis shows that the content of C and H of [BrBPP] [MnBr ] is 47.94% and 3.47%, respectively, 2 4 which agree well with the theoretical values (48.50% and 3.39%). These results collectively confirm the good phase purity of [BrBPP] [MnBr ] and demonstrate that the observed peak arises from the 2 4 recrystallization by the thermal treatment. The detailed description and corresponding discussion have been added to the revised manuscript.\n\nFig. R4 | DSC curves of the powder sample ground from the bulk single crystals of [BrBPP] [MnBr ] 2 4\n\nMethods:\n“High-performance liquid chromatography analysis was performed using a SHIMADZU LC-20AD facility with commercial 5 µm, 4.6×150 mm columns, using a MeCN/H O = 50/50 (v/v) at a 2 flow rate of 1 mL min-1 and a detection wavelength of 254 nm. The results of BrBPPBr and [BrBPP] [MnBr ] show that [BrBPP] [MnBr ] possess two major peaks at retention times of 1.173 2 4 2 4 min and 3.526 min, corresponding to the organic cation and the inorganic species. Elemental analysis illustrates C and H contents of 47.94% and 3.47%, respectively, which is consistent with the theoretical values of 48.50% and 3.39%.”\n\nSupplementary Fig. 55 | High-performance liquid chromatography spectra of BrBPPBr and [BrBPP] [MnBr ]. 2 4\n\n5. Using only angles as collective variables may not fully capture the energy landscape. The referee recommend that the authors discuss the appropriateness of their chosen CVs or supplement the analysis with additional variables.\n\nResponse:\nWe thank the reviewer for the helpful suggestions. In response, we have supplemented our study with additional metadynamics simulations using the alphabeta collective variable (CV) to comprehensively capture the free-energy landscape.\n\nIn the initial manuscript, we used the angles between the principle axes and the aliphatic or benzyl chains as CVs to characterize the orientational dynamics of the cations. These angle-based CVs can effectively describe the orientational fluctuations of the aliphatic and benzyl moieties. However, we agree with the reviewer that these CVs may not fully represent the entire energy landscape, especially the coupled motions and collective rearrangements of the whole cations that contribute to the free-energy barriers.\n\nTo address this limitation, additional metadynamics simulations were performed using the alphabeta CV, defined as:\n\n1 𝑠 = ∑[1+cos(𝜙 −𝜙Ref)] AB 2 𝑖 𝑖 𝑖\n\nwhere s is the alphabeta CV value, ϕ is the instantaneous torsional angle, ϕRef is the corresponding AB i i reference torsion angle. In our case, four torsional angles between the principle axis and each of the four side chains of the phosphonium cation are combined into a single alphabeta CV. Subsequently, a three-dimensional metadynamics simulation was conducted using three alphabeta CVs to thoroughly explore the energy landscape. The ϕRef was set to the initial value of the torsional angle. i Due to the limited support for complex CVs in the native CP2K metadynamics module, these additional simulations were performed using the PLUMED software and density functional tight binding (DFTB) method. The results are shown in Supplementary Fig. 51.\n\nNotably, the resulting free-energy profiles based on the s CVs clearly reveal the distinct AB rotational energy landscape among the three representative systems. The free-energy surface of [BuTPP] [MnBr ] exhibits relatively shallow and smooth potential wells, indicating a more uniform 2 4 distribution of rotational energy distribution. In contrast, [BPP] [MnBr ] shows pronounced barriers 2 4 separating different conformational basins, while the potential well of [BrBPP] [MnBr ] is 2 4 significantly deeper than the other systems, signifying a strongly hindered rotational motion and highly localized configurations. These results are highly consistent with the angle CVs-based metadynamics analysis, and support the interpretation that the rotational disordering drives ergodicity breaking and governs the GFAs in these halide glasses. We have accordingly revised the metadynamics analysis section and Methods part to incorporate the additional simulations:\n\nRevised text:\n“To capture the rotational energy landscape of phosphonium cations, metadynamics simulations based on angle and alphabeta CVs were employed, and the predominant characteristics of rotational phase space distribution were quantified. …… The metadynamics simulations based on alphabeta CVs, featuring torsional indicator of the four side chains of the phosphonium cations, were also performed (Supplementary Fig. 51). The resulting free-energy profiles display the same trend as the angle-based CVs in these three glass systems, consistently confirming the distribution of energy landscapes.”\n\nMethods:\n“The metadynamics simulations based on angle and alphabeta CVs were performed using the CP2K program.”\n\n“The alphabeta CVs are defined as:\n\n1 𝑠 = ∑[1+cos(𝜙 −𝜙Ref)] AB 2 𝑖 𝑖 𝑖\n\nwhere s is the alphabeta CV value, ϕ is the instantaneous torsional angle, ϕRef is the corresponding AB i i reference torsion angle. Four torsional angles between the principle axes and each of the four side chains of the phosphonium cation are combined into a single alphabeta CV, ranging from 0 to 4. Note that the angle CVs used GFN1-xTB method with CP2K built-in kernel, while the alphabeta CVs used density-functional tight binding (DFTB) method with Plumed package71–74.”\n\nSupplementary Fig. 51 | 1D free energy profiles of [BuTPP] [MnBr ] (a), [BPP] [MnBr ] (b) 2 4 2 4 and [BrBPP] [MnBr ] (c) as a function of the alphabeta CV. The CVs s (a), s (b) and s (c) 2 4 AB AB AB represent the α-β torsional CVs between the four side-chain vectors of the phosphonium cations, and the a, b and c axis, respectively, ranging from 0 to 4.\n\n71. Elstner M. et al. Self‐consistent‐charge density‐functional tight-binding method for simulations of complex materials properties. Phys. Rev. B 58, 7260–7268 (1998).\n72. Cui, M., Reuter, K. & Margraf, J. T. Obtaining robust density functional tight-binding parameters for solids across the periodic table. J. Chem. Theory Comput. 20, 5276–5290 (2024).\n73. Grimme, S., Bannwarth, C. & Shushkov, P. A robust and accurate tight-binding quantum chemical method for structures, vibrational frequencies, and noncovalent interactions of large molecular systems parametrized for all spd-block elements (Z = 1–86). J. Chem. Theory Comput. 13, 1989–2009 (2017).\n74. Bonomi M. et al. PLUMED: a portable plugin for free-energy calculations with molecular dynamics. Comput. Phys. Commun. 180, 1961–1972 (2009)"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have adequately addressed my comments. In doing so, they have conducted additional experiments including variable temperature XRD, and Raman spectroscopy, and molecular dynamics simulations to reveals new insights into glass formation. These results further support the proposed relationship between molecular rotational order and glassy behavior in hybrid metal halides. They have also acknowledged the limitations of solid-state NMR spectroscopy, particularly the peak broadening caused by Mn2+ ions. With these additions and clarifications, the manuscript is now more suitable for publication in Nature Communications", "reviewer_2": "The manuxcript has been adequately revised. It can be accepted.", "reviewer_3": "The manuscript presents a compelling study on the critical progression of structural disorder governing bulk glass-forming ability (GFA), framed through the lens of ergodicity breaking. The authors address a longstanding challenge in establishing structure–property relationships in conventional glasses, which is hindered by their highly complex and ambiguous disorder motifs, such as random atomic clusters and broad ring-size distributions. In this work, the authors successfully synthesize a family of zero-dimensional hybrid metal halides that offer tunable short- to medium-range structural arrangements, enabling the formation of glasses with distinctly different GFAs. By systematically modifying the molecular shape and surface electrostatic potential of the organic cations, they demonstrate controlled breaking of rotational order. This, in turn, leads to well-defined phase-space partitioning of molecular motions, providing a clear and rational pathway for tuning GFA.\nThe authors have addressed all reviewer comments thoroughly and revised the manuscript appropriately. The responses are satisfactory, and the revised version has improved in clarity and quality. I recommend that the manuscript be accepted in its current form.", "reviewer_4": "The authors addressed most of the issues following the reviewers' previous comments. The current version is potentially publishable for this journal."}, "author_response": "We greatly appreciate Reviewer 1’s recognition of our manuscript. The insightful comments provided by Reviewer 1 have been invaluable in further clarifying the structure characteristics and glass formation mechanisms, which offer important guidance for our work.\n\nWe sincerely thank Reviewer 2 for the constructive feedback and for recognizing the improvements made in the revised version of our manuscript.\n\nWe are grateful for Reviewer 3’s positive evaluation of the manuscript. The comments from Reviewer 3 have significantly helped in the material characterization, and improve the overall data completeness of the manuscript."}]

Decision letter