Article

# Bimetallic Perthiocarbonate Complexes of Cobalt: Synthesis, Structure and Bonding

Alaka Nanda Pradhan <fnref n="1" />,†, Shivankan Mishra <fnref n="1" />,†, Urminder Kaur <fnref n="1" />,†, Bikram Keshari Rout <fnref n="1" />, Jean-François Halet <fnref n="2" />,* †,‡ and Sundargopal Ghosh <fnref n="1" />,* ‡,§

**Abstract:** The syntheses and structural elucidation of bimetallic thiolate complexes of early and late transition metals are described. Thermolysis of the bimetallic hydridoborate species [((Cp\*CoPh)(\μ-TePh){\μ-TeBH₃-κ²Te,H})((Cp\*Co)] (Cp\* = η⁵-C₅Me₅) (1) in the presence of CS₂ afforded the bimetallic perthiocarbonate complex [((Cp\*Co)₂(μ-CS₄-κ¹S:κ²S'))(μ-S₂-κ²S'':κ¹S''')] (2) and the dithiolene complex [((Cp\*Co)(μ-C₃S₅-κ¹S,S')] (3). Complex 2 contains a four-membered metallaheterocycle (Co₂S₂) comprising a perthiocarbonate [CS₄]<fnref n="2" />⁻ unit and a disulfide [S₂]<fnref n="2" />⁻ unit, attached opposite to each other. Complex 2 was characterized by employing different multinuclear NMR, infrared spectroscopy, mass spectrometry, and single-crystal X-ray diffraction studies. Preliminary studies show that [Cp\*VCl₂]₃ (4) with an intermediate generated from CS₂ and [LiBH₄·THF] yielded thiolate species, albeit different from the cobalt system. Furthermore, a computational analysis was performed to provide insight into the bonding of this bimetallic perthiocarbonate complex.

**Keywords:** chalcogen; cobalt; perthiocarbonate; sulfur; trithiocarbonate; vanadium

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**Citation:** Pradhan, A.N.; Mishra, S.; Kaur, U.; Rout, B.K.; Halet, J.-F.; Ghosh, S. Bimetallic Perthiocarbonate Complexes of Cobalt: Synthesis, Structure and Bonding. *Molecules* **2024**, *29*, 2688. https://doi.org/10.3390/molecules29112688

Academic Editors: Andrea Bencini and Vito Lippolis

Received: 3 May 2024

Revised: 23 May 2024

Accepted: 2 June 2024

Published: 6 June 2024

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**Copyright:** © 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## 1. Introduction

The efficiency of metal sulfides as heterogeneous catalysts and the activity of metalloproteins in enzyme-mediated catalysis are generally significantly impacted by the nature of the metal-sulfur entities. An intriguing and unusual structural chemistry became apparent via a systematic search for metal-sulfur types of compounds given the variety of coordination possibilities that sulfur ligands can provide [1,2]. Indeed, CS₂ ligands have been shown to be versatile synthetic reagents ever since the first transition metal-CS₂ complexes were synthesized in 1967 [3] due to their electron donating and electron accepting properties, yielding an array of binding modes with one or more transition metal atoms [4–6].

In this context, Jagirdar's group demonstrated the insertion of CS₂ into one of the Ir-H bonds in [Ir(H)₅(PCy₃)₂] to afford the dihydrido dithioformate complex cis-[Ir(H)₂(η<fnref n="2" />-S₂CH)(PCy₃)₂] (A), accompanied by the elimination of H₂ [7]. Similarly, the cyclometalated ruthenium complex [Ru(S₂C(H)PMe₂CH₂-κ³S,S,C)(PMe₃)₃] was shown to react with an excess of CS₂, which undergoes a second insertion into a Ru-S bond to yield [Ru(SC(=S)SCH(-S)PMe₂CH₂-κ³S,S,C)(PMe₃)₃] (B) [8]. Wang and coworkers reported the disproportionation of CS₂ when reacted with the Me₂C and Me₂Si doubly bridged bis(cyclopentadienyl) dinuclear molybdenum carbonyl complex (Me₂C)(Me₂Si)[(η⁵-C₅H₃)Mo(CO)₃]₂, which led to the formation of complex C [9]. Likewise, in 2021, Fischer's group showcased that the nucleophilicity of the monodithiolene species [Mo(CO)₂(dt)(dppe)] (dt: cydt = cyclohex-1-ene-1,2-dithiol or tpydt = 5,6-dihydro-2H-thiopyran-3,4-dithiol, dppe = 1,2-bis(diphenylphosphino)

<footnote n="1">¹ Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India; salupradhan7@gmail.com (A.N.P.); shivankan1994@gmail.com (S.M.); urminderkaur27@gmail.com (U.K.); bikramrout44@gmail.com (B.K.R.)</footnote>

<footnote n="2">² Univ Rennes, CNRS, École Nationale Supérieure de Chimie de Rennes, Institut des Sciences Chimiques de Rennes (ISCR)—UMR 6226, F-35000 Rennes, France</footnote>

<footnote>* Correspondence: jean-francois.halet@univ-rennes.fr (J.-F.H.); sghosh@iitm.ac.in (S.G.); Tel.: +91-44-225-742-30 (S.G.)</footnote>
ethane) can be switched on by reduction with 2 eq. of [Co(Cp*)₂] in a mixture of DCM and ACN, which leads to the isomorphic complexes [Mo(CO)₂(CH₂-dt)(dppe)] (dt = cydt (D); dt = tpydt (D'))), with molybdenum formally in the zero oxidation state [10]. In addition, Bianchini's group showcased the nucleophilic nature of η²-CS₃, where the trithiocarbonate complex of cobalt [Co(tppme)(S₂CS)] (tppme = 1.1.1-tris(diphenylphosphinomethyl)ethane) was reacted with [Cr(CO)₅·THF], resulting in the formation of E [11]. Recently, our group has reported the reaction of *arachno*-ruthenaborane [(Cp*Ru)(CO)₂(µ-CO)₂(µ₃-CH₂S₂-κ²S':κ²S'')}{M(CO)₂}] (M = Mo and W) (F) [12] (Chart 1).

<figure><img src="image_3.png" /><figcaption>**Chart 1.** Different binding modes of CS₂-based ligands (A–F) in transition metal complexes.</figcaption></figure>

Over the last few decades, we and others have synthesized interesting polyhedral clusters, both single-cage and fused, employing early and late transition metals [13–18]. Despite being largely uncontrolled, the isolation of numerous unique metallaheteroboranes demonstrating novel coordination modes prompted us to investigate this area more meticulously. In this context, our group utilized three distinct strategies: (i) pentamethylcyclopentadienyl-based metal halides with chalcogen-based borate ligands such as [LiBH₂E₃], [LiBH₃EPh] (E = S, Se, Te), [LiBH₄ + CS₂], or [NaBH₄ + CS₂] [19–21]; (ii) preformed metallaboranes with the above chalcogen-based borate ligands [21]; and (iii) preformed metallaboranes with CS₂ or CS₂-based ligands such as [CS₂·PPh₃] [22,23]. In our earlier reports, the classical diborane [B₂H₅]⁻ was stabilized by the reaction of [Cp*TaCl₄] with [LiBH₄·THF], followed by the addition of excess [S₂C·PPh₃] adduct [23]. Also, these chalcogen-based borate ligands have been utilized for cluster expansion reactions. The reactivity of *nido-[[Cp*M]*₂B₆H₁₀] (M = Co and Rh) with the chalcogen-based borate Li[BH₂E₃] (E = S, Se, or Te) afforded 10-vertex *nido*-dimetallaheteroborane clusters [21]. By using a different chalcogen-based ligand (intermediate generated from CS₂ and [LiBH₄·THF]) with *nido-[[Cp*M]*₂B₆H₁₀] (M = Co and Rh), unique dimetalladecaborane(14) analogues containing di(thioboralane)-thione {B₂CS₃} and di(thioborolane) {B₂S₂CH₂} moieties were isolated [21]. Very recently, the reactivity of a borate ligand derived from CS₂ with κ²-N,S-chelated ruthenium borate complexes, [Ph₃P(κ²-N,S-L)Ru{κ³-H,S,S'-H₂B(L)₂}] (L = C₇H₄NS₂, C₅H₄NS), has been investigated [24]. Therefore, we pursued this chemistry, reacting the cobalt borate complex [{Cp*CoPh}{µ-TePh}{µ-TeBH₃-κ²Te,H}{Cp*Co}] (1) [19] with CS₂. Although the objective of obtaining transition metal complexes containing boron content was not achieved, interesting cobalt and vanadium thiolate complexes were isolated.
## 2. Results and Discussion

### 2.1. Reactivity of 1 with CS₂

Transition metal–chalcogen complexes are well documented in the literature. Recently, we have shown that the reaction of [Cp\*Ru(μ-Cl)Cl]₂ with Na[BH₃(SCHS)] led to the formation of several bimetallic dithioformato ruthenium complexes, where the dithioformate ligand (CH₂S₂) shows diverse binding modes with the metal center(s) [20]. In addition, the reaction of [1,2-(Cp\*Ru)₂(μ-H)₂B₃H₇] with CS₂ yielded the *arachno*-ruthenaborane [(Cp\*Ru)₂(B₃H₈)(CS₂H)], with a dithioformato ligand attached to it by the metal-assisted hydroboration [22]. Thus, investigation of the CS₂ ligand with transition metal boron species became of interest. With this background, we reacted **1** with CS₂ under thermolytic condition. Thus the reaction of **1** with CS₂ under thermolytic conditions. The reaction of **1** with CS₂ in toluene at 70 °C for 6 h led to the formation of an air-stable complex, the brown solid **2** (18% yield, R<sub>f</sub> = 0.46), and the known green dithiolene complex [(Cp\*Co)(μ-C₃S₅-κ¹S:κ¹S')] **3** [25] (12% yield, R<sub>f</sub> = 0.58) (Scheme 1). The identification of complex **2** was confirmed by combined ¹H, ¹³C{¹H} NMR, IR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction studies. The detailed characterization of complex **2** is discussed below.

<figure><img src="image_4.png" /><figcaption>**Scheme 1.** Synthesis of the perthiocarbonate (2) and dithiolene (3) complexes of cobalt.</figcaption></figure>

The ¹¹B NMR of complex **2** shows no chemical shifts, and the ¹H NMR spectrum shows no upfield region peaks, which rules out the possibility of the formation of a boron-containing complex. Indeed, complex **2** is formed by the release of BH₃ from complex **1**. We confirmed the release of the [BH₃·PPh₃] adduct by trapping it with PPh₃. The ¹¹B{¹H} and ³¹P{¹H} NMR spectra (Figures S7 and S8) of the reaction mixture show resonances at δ = -39.3 and 20.8 ppm, respectively. The ¹H NMR spectrum displays two resonances at δ = 1.38 and 1.63 ppm at a 1:1 ratio, corresponding to Cp\* ligands. The presence of two different Cp\* ligands is also supported by the ¹³C{¹H} NMR spectrum. In addition to Cp\* peaks, the ¹³C{¹H} NMR shows resonance at δ = 252.7 ppm, which indicates the presence of a C=S moiety. The infrared spectrum shows a peak at 1020 cm⁻¹ that confirms the presence of this C=S double bond. Further, the mass spectrometric analysis of **2** shows an isotopic pattern (ESI⁺ mode) at *m/z* = 592.9376, which corresponds to the molecular formula C₂₁H₃₁Co₂S₆. Although all the spectroscopic and mass spectrometric data point toward the formation of a thiolate complex, the solid-state framework of **2** was confirmed by single-crystal X-ray diffraction studies. The crystals were grown by slow evaporation of an *n*-hexane/CH₂Cl₂ (30:70) solution at 5 °C.

The solid-state X-ray structure of complex **2** shows the bimetallic perthiocarbonate complex [(Cp\*Co)₂(μ-CS₄-κ¹S:κ²S')*(μ-S₂-κ²S'':κ¹S''')] (Figure 1). Note that there are two molecules in the asymmetric unit. To the best of our knowledge, complex **2** is the first structurally characterized perthiocarbonate complex of cobalt. It consists of a four-membered metallaheterocycle (Co₂S₂) comprising a rare perthiocarbonate [CS₄]²⁻ unit and a disulfide [S₂]²⁻ unit, attached opposite to each other. The bidentate [CS₄]²⁻ fragment bridges two {CoCp\*} moieties in a μ₂-η² fashion. Complex **2** represents, in turn, a novel type of structure having both perthiocarbonate anion [CS₄]²⁻ and disulfide [S₂]²⁻ units, with 18-electron
cobalt (III) centers. Note that Adams' group previously showed that the disulfur unit is a potential candidate for disulfur/dithiolate conversion [26,27].

<figure><img src="image_5.png" /><figcaption>**Figure 1.** Molecular structure and labeling diagram of 2. Selected bond lengths (Å) and bond angles (°): Co1–S4 2.200(3), Co1–S3 2.264(4), S5–S6 2.043(14), Co2–S5 2.202(4), Co2–S6 2.258(15), Co1···Co2 3.332, C41–S1 1.663(10), C41–S2 1.724(12), C41–S3 1.722(10), S2–S4 2.080(4), S3–C41–S2 119.3(6), Co1–S4–Co2 95.97(12), S4–Co1–S5 83.08(13), S5–Co2–S6 54.5(4), Co2–S5–Co1 96.91(13), S5–S6–Co2 61.4(4).</figcaption></figure>

The average Co–S bond length of 2.242 Å is comparable to that in cobalt–thiolate complexes [28,29], and the average bridged Co–S distance of 2.233 Å is slightly shorter than the unbridged Co–S bonds (2.261 Å). Further, the Co···Co distance of 3.332 Å clearly suggests the absence of any metal–metal (Co–Co) bond, making it a coordinatively saturated 18-electron species. Transition metal–perthiocarbonate complexes are well documented in the literature, in which the [CE₄]²⁻ ion (E = S, Se) acts as a 1,1'-dithiolate ligand. Some examples of such complexes are listed in Table 1 [30–33], which describe the different bonding modes, structural parameters, and spectroscopic data of complexes with [CE₄]²⁻ units.

Generally, the perthiocarbonate anion, [CS₄]²⁻, is obtained by the reaction of CS₂ with disulfide or polysulfide dianions. Perthiocarbonate complexes can be synthesized from trithiolate complexes [M(CS₃)₂]²⁻ by I₂ oxidation or the addition of sulfur [34]. Shieh and co-workers reported the first example of [CE₄]²⁻ incorporated into transition metal–carbonyl complexes, [(CE₄)₂Mn₂(CO)₆]²⁻ (E = S, Se) (Table 1) [32], where two [CE₄]²⁻ fragments were connected to two {Mn(CO)₃} units symmetrically. In the case of complex 2, only one [CS₄]²⁻ unit is present. In this [CS₄]²⁻ unit, the bond distance C41–S1 (1.663(10) Å) is a bit shorter than C41–S3 (1.722(10) Å) and C41–S2 (1.724(12) Å) and indicates a double-bond character. In 3, the double-bond character of C=S (1.657(7) Å) is slightly more pronounced than in 2 (1.663(10) Å). On the other hand, the four-electron donor disulfide ligand is coordinated to two cobalt centers in η¹,η²-S₂ mode, similar to [(Cp*Co)₂(η¹,η²-S₂)₂] [35], [(Cp*Ru)₂(η¹,η²-S₂)(η¹,η¹,η¹-S₃)] [36], and [(triphos)₂Rh₂(η¹,η²-Se₂)₂][PPh₄]₂ (triphos = H₃CC(CH₂PPh₂)₃) [37]. The S–S distance of 2.043(14) Å in 2 is comparable to the S–S distances measured in [(Cp*Co)₂(η¹,η²-S₂)₂] (2.062(6) Å) [35] and [(Cp*Ru)₂(η¹,η²-S₂)(η¹,η¹,η¹-S₃)] (1.907(5) Å) [36].
<figure><img src="image_6.png" /><figcaption>**Figure 2.** (a) HOMO-12, (b) HOMO-17, and (c) HOMO-26 of 2. Contour isodensity values for isosurface are ±0.045 (e/bohr³)¹/². (d,e), Laplacian maps of the electron density distribution computed for 2 in the Co2–S5–S6 plane and the S1–S2–S3 plane, respectively.</figcaption></figure>

In the recent past, we isolated and structurally characterized paramagnetic thiocarbonate complexes from the reaction of Na₅[B(CH₂S₂)₄] and [Cp*VCl₂]₃ (4) [38]. Thus, with the objective of isolating similar types of thiolate complexes to that of complex 2, we explored the reactivity of [Cp*VCl₂]₃ (4) with an intermediate generated from CS₂ and [LiBH₄·THF] under different reaction conditions, which yielded the inseparable yellow solids 5 and 6 (Scheme S1). Although we do not have detailed characterizations of these inseparable complexes, preliminary studies (X-ray diffraction analysis) show that 5 and 6 are binuclear vanadium trithiocarbonate [(Cp*V)₂(μ-CS₃-κ²S,S')₂] and (disulfaneyl)methanethiolate [(Cp*V)₂(μ-SCH₂S₂-κ²S,S')₂] complexes, respectively (Figures S1 and S2).

## 2.2. UV-vis Study of 2

The absorption patterns of the colored complex 2 may be of interest due to the presence of different chalcogen fragments. Therefore, the UV-vis absorption spectrum of 2 was measured in the range of 280–800 nm in CH₂Cl₂ solution at 298 K (Figure 3). In fact, the most intense peaks in the higher-energy regions (280–320 nm) are due to the spin-allowed π-π* transition of the Cp* ligands present in these complexes [39]. Comparatively low-intensity peaks at a lower energy around 320–550 nm may be due to the charge transfer bands. In order to obtain more detail, time-dependent DFT calculations were carried out on 2. In complex 2, the high-intensity absorption band near 326 nm is due to the HOMO-6→LUMO electronic transition. The HOMO-6 is mostly from metal-based *d* orbitals, while the LUMO has both metal (*d* orbital) and disulfide [*S*]²⁻ (*p* orbital on S atoms) orbital characters (Figure S10). Therefore, these absorption bands can be assigned as metal-to-ligand charge transfer (MLCT) transitions. In the low-energy wavelength region, 2 shows a low-intensity absorption band at 570 nm, which could be due to the intramolecular LMCT transitions.
<figure><img src="image_7.png" /><figcaption>**Figure 3.** UV-vis spectrum of **2** in CH<sub>2</sub>Cl<sub>2</sub>.</figcaption></figure>

## 2.3. *Electrochemical Study of 2*

The redox properties of complex **2** dissolved in DMF were examined using cyclic voltammetry (Figure 4). The DMF solution displays two irreversible responses at *E*<sub>pc</sub> = -1.47 V and -0.86 V vs. Fc/Fc<sup>+</sup>. They may originate from the reduction of the disulfide or metal-centered reduction based on the reported literature. The two irreversible anodic responses at *E*<sub>pa</sub> = 0.11 V and 0.27 V vs. Fc/Fc<sup>+</sup> are most likely due to the oxidation of the thiolate ligand [40–44].

<figure><img src="image_8.png" /><figcaption>**Figure 4.** Cyclic voltammogram (CV) recorded for complex **2** in DMF at 298 K.</figcaption></figure>

# 3. Materials and Methods

## 3.1. *General Procedures and Instrumentation*

All the experimental procedures were performed in an argon atmosphere by using standard Schlenk line techniques and a glove box. All the solvents, *n*-hexane, DCM (dichloromethane), toluene, and THF (tetrahydrofuran), were distilled under an argon atmosphere prior to use. All the chemicals, such as Ph<sub>2</sub>Te<sub>2</sub> (diphenyl ditelluride) (Sigma Aldrich, Bangalore, India) and CS<sub>2</sub> (Loba Chemie Pvt. Ltd., Mumbai, India), were purchased and used as received. The complexes [{Cp\*CoPh}{μ-TePh}{μ-TeBH<sub>3</sub>-κ<sup>2</sup>Te,H}{Cp\*Co}] (1) [19] and [Cp\*VCl<sub>2</sub>]₃ (4) [45] were prepared according to the methods from the literature. Dialuminum-supported TLC plates (MERCK TLC plates, Bangalore, India) were used for the separation of the reaction mixtures. All the NMR spectra for the synthesized complexes were obtained on 500 MHz Bruker FT-NMR spectrometers, Billerica, MA, USA. The
residual solvent protons (CDCl₃, δ = 7.26 ppm) and carbons (CDCl₃, δ = 77.1 ppm) were employed as references for the ¹H and ¹³C{¹H} NMR spectra, respectively. The mass data of all the synthesized complexes were recorded on Q-Tof Micro YA263 HRMS, Milford, MA, USA and 6545 Q-Tof LC/MS instruments, Santa Clara, CA, USA. The IR spectrum of **2** was recorded in dichloromethane solvent with a JASCO FT/IR-1400 spectrometer, Easton, MD, USA. The UV-vis spectrum was recorded on a JASCO V-650 spectrometer, Tokyo, Japan. The cyclic voltammetry measurement was performed on an OrigaLys potentiostat, Rillieux-la-Pape, France in a standard three-electrode system (glassy carbon working electrode, platinum wire counter electrode, and Ag/Ag⁺ as pseudo reference electrode). For deoxygenation, argon was bubbled into the electrolyte medium for 10 min. The cyclic voltammograms were recorded at a scan rate of 50 mVs⁻¹.

**Synthesis of 2.** In a pre-dried Schlenk tube, **1** (0.10 g, 0.123 mmol) was suspended in 10 mL of toluene. Under the atmosphere of argon, CS₂ (4 mL) was added slowly using a syringe at room temperature to the green solution of complex **1**. Then, the reaction mixture was kept at 70 °C (temperature of oil bath) for 6 h with continuous stirring under an atmosphere of argon. The solvent was removed by vacuum, and the remaining residue was separated and purified using the TLC method on silica gel TLC plates. Elution with n-hexane/CH₂Cl₂ (30:70 v/v) yielded the brown complex **2** (0.014 g, 18%) and the known green complex [(Cp\*Co)(µ-C₃S₅-κ¹S:κ¹S')**3** (0.012 g, 12%) [25].

**2:** MS (ESI⁺) calcd. for C₂₁H₃₁Co₂S₆⁺ [M+H]⁺ m/z 592.9414, found 592.9376; ¹H NMR (CDCl₃, 500 MHz, 22 °C): δ = 1.38 (s, 15H; 1 × Cp*), 1.63 ppm (s, 15H; 1 × Cp*); ¹³C{¹H} NMR (CDCl₃, 125 MHz, 22 °C): δ = 9.1, 10.0 (s, C₅Me₅), 92.4, 94.9 (s, C₅Me₅), 252.7 (C=S) ppm; IR (CH₂Cl₂): ν̃ = 1020 cm⁻¹ (C=S); UV-vis [CH₂Cl₂, λ, nm]: 326, 384, and 570.

## 3.2. Single Crystal X-ray Diffraction Analysis

Suitable X-ray-quality crystals of **2** and **5/6** were grown by slow diffusion of an *n*-hexane/CH₂Cl₂ solution at 5 °C. The crystal data were collected and integrated using a Bruker D8 VENTURE diffractometer (Billerica, MA, USA) with a PHOTON 100 CMOS detector (Tokyo, Japan) for **2** and a Bruker AXS Kappa APEX2 CCD diffractometer (Billerica, MA, USA) for **5** and **6** with graphite monochromated Mo-Kα (λ = 0.71073 Å) radiation at 293(2) K. The structures of these complexes were solved by heavy atom methods using SHELXS-97 [46] and SHELXT-2014 and refined using SHELXL-2014, SHELXL-2017, and SHELXL-2018 [47]. All the molecular structures were drawn using Olex2 [48]. Note that complexes **5** and **6** co-crystallize in the same crystallographic unit with disorder mainly over the sulfur and carbon atoms, with 0.56 and 0.44 occupancies, respectively. The crystal structure of **6** is further disordered over two components with a site occupancy ratio of 0.31:0.13. The crystallographic data were deposited with the Cambridge Crystallographic Data Centre as supplementary publication, nos. CCDC-2111767 (**2**) and 2349360 (**5** and **6**). These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif access on 18 April 2024.

Crystal data for **2**: C₂₁H₃₀Co₂S₆, *M*<sub>r</sub> = 592.67, monoclinic, space group *P*2₁/*n*, unit cell, *a* = 10.4689(14) Å, *b* = 32.997(5) Å, *c* = 14.971(2) Å, *α* = 90°, *β* = 99.029(10)°, *γ* = 90°, *Z* = 8, *V* = 5107.6(12) Å³, *μ* = 14.806 mm⁻¹, *F*(000) = 2448, *ρ*<sub>cacld</sub> = 1.541 g/cm³, *R*₁ = 0.0883, *wR*₂ = 0.2689, 8461 independent reflections [2*θ* ≤ 64.999°] and 672 parameters.

Crystal data for **5** and **6**: 0.56 (C₂₂H₃₀S₆V₂) + 0.44 (C₂₂H₄S₆V₂), *M*<sub>r</sub> = 590.42, monoclinic, space group *C*2/*c*, unit cell, *a* = 18.6613(7) Å, *b* = 9.5327(4) Å, *c* = 16.0532(6) Å, *α* = 90°, *β* = 114.511(10)°, *γ* = 90°, *Z* = 4, *V* = 2598.39(18) Å³, *μ* = 1.211 mm⁻¹, *F*(000) = 1223, *ρ*<sub>cacld</sub> = 1.509 g/cm³, *R*₁ = 0.0392, *wR*₂ = 0.1066, 11180 independent reflections [2*θ* ≤ 54.218°] and 217 parameters.

## 3.3. Computational Details

Density functional theory (DFT) optimization of complex **2** was carried out using the Gaussian 16 program [49] with the B3LYP functional [50] and the def2-TZVP [51,52] basis set from the EMSL (Environmental Molecular Sciences Laboratory) Basis Set Exchange
Library. Complex **2** was thoroughly optimized without any solvent effect in the gaseous state, starting from its X-ray crystallographic structure. Frequency calculations were carried out to check the nature of the stationary state of **2** to confirm the absence of any imaginary frequency to confirm that it was an energy minimum on the potential energy hypersurface. A natural bonding analysis (NBO) was carried out with the NBO partitioning scheme [53–56], and Wiberg bond indexes [57] were obtained from it. A QTAIM [58–60] analysis was performed utilizing the *Multiwfn V.3.6* package [61]. The optimized structure and orbital graphics were produced using the *GaussView* (Version 3.09) [62] and *Chemcraft* (Version 1.8) [63] software.

**4. Conclusions**

In summary, we have isolated and structurally characterized a couple of bimetallic thiolate complexes of early and late transition metals featuring both partial and full reduction of the CS₂ moiety. One is a bimetallic cobalt thiolate complex which contains a perthiocarbonate group, as well as a disulfide group connected to two Co atoms in a µ<sub>2</sub>-η<sup>2</sup> fashion. This complex displays an interesting coordination environment around the two homometallic centers. Investigations to evaluate the possibility of other early and late transition metal thiolate complexes with rare coordination modes are underway.

**Supplementary Materials:** The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/molecules29112688/s1. It contains ¹H, ¹³C{¹H}, ¹¹B{¹H}, ³¹P{¹H} NMR, IR, and mass spectra (Figures S3–S8), X-ray analysis details, and CIF and checkCIF files, as well as the xyz coordinates of the DFT-optimized cluster **2**, calculated HOMO and LUMO energy levels and HOMO-LUMO gaps, selected bond parameters, and Wiberg bond indices (WBI) for cluster **2** (Figures S10 and S11). All pulse sequences are available in a commercial Bruker spectrometer. ¹H decoupled ¹¹B spectra were processed with backward linear prediction algorithm to remove broad ¹¹B background signal from NMR probe and NMR tube. References [38,64–66] are cited in the supplementary materials.

**Author Contributions:** A.N.P. and U.K. formulated and planned the experiments; A.N.P., S.M., U.K. and B.K.R. carried out the synthesis and spectroscopic analyses and discussed the results with S.G. and J.-F.H.; A.N.P., S.M. and U.K. organized the manuscript with guidance from S.G. and J.-F.H.; S.G., supervision; S.G. and J.-F.H., project administration. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by SERB, New Delhi, India, grant no. CRG/2023/000189.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.

**Acknowledgments:** A.N.P. thanks UGC, India, for the research fellowship. S.M. and U.K. thank IIT Madras for the research fellowships. We thank Babu Varghese, P. K. Sudhadevi Antharjanam, and SAIF, IIT Madras, for the single-crystal X-ray data collection and structure analyses. The computational facilities of IIT Madras are gratefully acknowledged.

**Conflicts of Interest:** The authors declare no conflicts of interest.

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