Subhash Bairagi

] Alaka

Nanda Pradhan

Dr Marie Cordier

Dr Thierry Roisnel

Sundargopal Ghosh
email: sghosh@iitm.ac.in

Ms Mr S A N Bairagi

Prof. Dr S Pradhan

Ghosh

Syntheses, Structures, and Electronic Properties of Mono-and Bimetallic Thiolato Complexes Containing Unusual Coordination Modes of Thiolato Ligands

Keywords: dithiol, paramagnetic, tantalum, thiolato, vanadium

Synthesis, bonding and chemistry of mono-and bimetallic complexes supported by chelating thiolato ligands have been established. Treatment of [Cp*VCl2]3 (1) with [LiBH4•THF] followed by the addition of ethane-1,2-dithiol led to the formation of an EPR active bimetallic vanadium thiolato complex [(Cp*V){μ-(SCH2CH2S)κ 2 S,S')2{V(SCH2CH2S-SH)}] (2). In complex 2, two ethane-1,2dithiolato ligands are symmetrically coordinated to two vanadium atoms through µ-S atoms. Interestingly, when similar reactions were carried out with heavier group 5 metal precursors, such as [Cp*NbCl4 ( ] 3a thiolato monometallic afforded it ), complex [Cp*Nb(SCH2CH2S)(SCH2CH2S-CH2S)] (4a). On the other hand, the Ta-analogue [Cp*TaCl4 ( ] 3b thiolato yielded ) species [Cp*Ta(SCH2CH2S)(SCH2CH2S-CH2S)] (4b) and [Cp*Ta(SCH2CH2S) (SCH2CH2S-S)] (5). In complexes 4a and 4b, one ethane-1,2dithiolato and one trithiolato ligand are coordinated to Nb and Ta centers, respectively. Whereas, in complex 5, one ethane-1,2dithiolato and one 2-disulfanylethanethiolato is coordinated to the Ta center. Moreover, the photolytic reaction of 5 with [Mo(CO)5•THF] yielded heterobimetallic thiolato complex [(Cp*Ta){μ-(SCH2CH2S)κ 2 S,S'}{μ-(SCH2CH2S-CH2(CH3)S)κ 2 S'':κ 1 S-'''':κ 1 S'''''}{Mo(CO)3}] (6). All the complexes have been characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction studies. Further, computational analyses were performed to provide an insight into the bonding of these complexes.

Introduction

The chemistry of sulfur-rich early transition metal (TM) thiolato complexes has received reasonable consideration over the years. 1 The polar metal-sulfur (M-S) bonded thiolato complexes are often found in living organisms where they play a crucial role in different biological processes. 2 The M-S bonds in metalloenzymes show a broad range of reactivities, such as the activation of small molecules. 3 Several sulfur-containing metalloenzymes are involved in thiolato/disulfide interconversion associated with the uptake or release of metal ions. 4 Vanadium has been identified as essential to growth in a myriad of living systems including green plants, seaweeds, marine microalgae, and higher animals. 5 In 1983, Christou group reported the first structurally characterized vanadium-thiolato complex [Ph4P]2[V2(SCH2CH2S)4] (A) (Figure 1), in which two vanadium atoms are quadruply bridged by four µ2-S-atoms of two dithiolato groups and each vanadium(III) atom is connected to a terminal dithiolato group. 6 Apart from these, the TM-complexes with thiolato ligands have emerged as a dynamic tool in the field of catalysis. For example, the transformation reactions, namely E-H (E = H, Si, and B) bond activation, chemo-selective reductions, dehydrogenative couplings (B-C, Si-C, Si-O, and Si-N), and hydrodefluorination reactions. 1b,7,8 In 2013, Duboc and coworkers synthesized a vanadium thiolato complex [VOL N2S2 ] (L N2S2 = 2,2′-(2,2′-bipyridine-6,6′-diyl)bis(1,1′-diphenyl ethanethiol)) (B) for efficient and selective sulfoxidation catalysis. 9 This complex displays a square-pyramidal geometry where the central vanadium atom is in +4 oxidation state, i.e., d 1 electronic configuration consistent with its EPR spectrum. In 2005, DuBois and co-worker showed that [(CpMo)2(μ-S)2(μ-η 2 -S2CH2)] (C) can react reversibly with olefins to form the corresponding dithiolato complex that acts as a hydrogenation catalyst for specific substrates. 10 In addition to biological and catalytic importance, the TM-thiolato complexes are useful in material science. The TM-thiolato complexes are suitable for the production of metal sulfide and organosulfur materials by metal-organic chemical vapor deposition (MOCVD) technique. 11 On the structural point of view, different types of TM-thiolato complexes with unusual coordination modes and geometries have been established over the years. In 1993, Duraj group reported the first group 4 thiolato complex [CpTi(S2CCH3)3] (D) having dithioacetate ligands. 12 This complex is an example of seven-coordinated distorted pentagonal bipyramidal species, in which the Ti atom coordinated to six sulfur atoms and one Cp ligand. In 1990, Tatsumi synthesized various bis-and trischelated dithiolato Nb(IV) and Ta(V) and tetrakis(arenethiolato) complexes of divalent transition metals. 13 The Nb(V) thiolato complex, [Nb(SCH2CH2S)3] ¯ was found to have a geometry intermediate between octahedral and trigonal prism which has been explained by twist angle. Recently, we have synthesized various bimetallic thiolato complexes, [(Cp*M)2(μ-S){μ-C(H)S3κ 2 S:κ 1 S′,S″}{μ-SC(H)S-κ 2 C:κ 1 S‴,S′′′′}] (M = Nb or Ta) (E) comprising methanetrithiolato (S3CH) and dithioformate (CHS2) 10.1002/ejic.202300060 ligands that lie practically orthogonal to each other. 14 One of the acute features of these molecules is the presence of an unusual penta-coordinated carbon in a square-pyramidal environment. Owing to these different coordinating natures, the TM-thiolato complexes also exhibit different magnetic behaviour. Although the TM-diamagnetic complexes are well documented, the paramagnetic ones are less discussed and, thus, become an exciting and active research field. For bimetallic thiolato complexes, the direct exchange through M-M bonds as well as superexchange via bridged thiolato ligands play crucial role for the magnetic behaviour. Recently, Rosenberg and co-worker isolated many thiolato complexes from the reaction of different metal carbonyls with dithiol ligands that led to the formation of bi and trimetallic thiolato complexes. The reaction of [M2(CO)10] (M = Mn and Re) with ethane-1,2-dithiol afforded a dinuclear complex [M2(CO)6(µ-ɳ 4 -(SCH2CH2S)2)] (M = Mn and Re), whereas 1,3-propanedithiol yielded an EPR active mixedvalence (I and IV) trimetallic manganese thiolato complex [Mn3(CO)6(SCH2CH2CH2S)3] (F). 15a Later, Zúñiga-Villarreal synthesized complex F from the reaction of 1,3-propanedithiol and [Mn(ɳ 5 -C5H7)(CO)3]. 15b In F, the central Mn-atom is coordinated to six S-atoms of three 1,3-propanedithiolato ligands in an octahedral fashion and three Mn atoms are almost linear having no metal-metal bonds. Our recent studies are focused on the coordination as well as magnetic behaviour of mono-and bimetallic TM-thiolato complexes. In our previous report, we have isolated metal-CS2 complexes [(Cp*M)(ɳ 2 -S2CH2)(ɳ 3 -S2CH)] (M = Mo or W) from the reaction of an intermediate generated from [Cp*MCl4] and [LiBH4•THF], followed by reaction with CS2. 16 [(Cp*V) complex trithiocarbonate paramagnetic 2(µ-CS3κ 2 S,S')(µ-H2CS2-κ 2 S'',S''')]. In case of the heavier metal precursor of group 5 [Cp*MCl4] (M = Nb and Ta), a bimetallic diamagnetic trithiolato and thiolato complexes have been isolated. 17 Therefore, to know the role of transition metals as well as thiolato ligands that determine the nature of thiolato complexes, we have varied the thiolato ligand from CS2 to ethane-1,2-dithiol. Although the biological importance of vanadium thiolato complexes is interesting, our main objective was to study the coordination of the thiol ligands with heavier group 5 elements along with electronic properties. In this study, the bidentate ethane-1,2-dithiol ligand has been mainly used because of its utility in thiolato chemistry. [18][19][20] This report provides a detailed account of the mono-and bimetallic thiolato complexes of group 5 transition metals.

Results and Discussion

Reactivity of [Cp*VCl2]3 (1) with [HS(CH2)2SH]

Low-temperature reaction of [Cp*VCl2]3 (1) with [LiBH4•THF] formed an unstable and sensitive intermediate which, on treatment with ethane-1,2-dithiol at elevated temperature yielded a green solid 2 (31% yield, Rf = 0.46 in n-hexane/CH2Cl2 (40:60 v/v)) (Scheme 1). This complex is characterized by various spectroscopic means and single-crystal X-ray analysis. Surprisingly, the 1 H NMR spectrum of 2 did not show any important signal. The mass spectrometry of complex 2 shows an isotopic pattern (ESI + mode) at m/z = 544.9019 [M-H] + that corresponds to the molecular formula C16H27S7V2. The removal of one H-atom may be due to the S-H bond cleavage in 2, which is quite common in metal thiolato complexes containing a terminal S-H bond. Moreover, the presence of a terminal S-H proton was confirmed by infrared spectroscopy. All these spectroscopic data were not adequate to predict the structure of 2 until a single-crystal X-ray diffraction analysis was carried out.

Scheme 1. Synthesis of bimetallic thiolato complex of vanadium, 2.

The solid-state X-ray analysis of 2, shown in Figure 2a, shows that it is a bimetallic thiolato complex [(Cp*V){μ-(SCH2CH2S)-κ 2 S,S')2{V(SCH2CH2S-SH)}] in which two ethane-1,2-dithiolato ligands are symmetrically coordinated to two vanadium atoms through four µ-S atoms (S1, S2, S3 and S4), to form a quadruply bridged vanadium bimetallic complex. A similar bonding situation has also been observed in [V2(SCH2CH2S)4] 6 , [CpVSC2H4S]2 21 , and bis(dithiolato)-bridged complexes of molybdenum 22 . Additionally, one of the vanadium atoms in 2 is attached to the Cp* ligand, whereas the other vanadium atom is coordinated to a thiol group [SCH2CH2S-SH] in η 3 -fashion, which is very unusual. Herein, one of the five electron donor Cp* ligands attached to vanadium is replaced by a five electrons donor [SCH2CH2S-SH] ligand, which may be due to the higher chelating effect of [SCH2CH2S-SH] compared to Cp* ligand. The formation of [SCH2CH2S-SH] ¯ ligand indicates sulfur elimination from ethane-1,2-dithiol ligand during the progress of the reaction. Overall, the presence of two different types of ligands around the vanadium centers makes this molecule an unsymmetric one which is interesting. The [SCH2CH2S-SH] ligand in 2 binds with the metal center through three sulfur atoms by forming one 10.1002/ejic.202300060

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European Journal of Inorganic Chemistry covalent (V2-S6) and two coordinate covalent bonds (V2-S5 and V2-S7). The presence of various types of S-S bonds in transition metal thiolato complexes are established in literature, for example, [Nb(C6H4S2)2(C6H4S3)] 23a , and [(MeCpMo)2(SCH2S) (SCH2S2)] 23b . Moreover, the S5-S7 bond length of 2.025(4) Å in [SCH2CH2S-SH] ligand in 2 is comparable with the S-S bond length in vanadium-sulfido complexes, such as [Cp*2VS2] 24a (2.053(3) Å) and [Cp*VS5] 24b (2.038-2.055 Å). Besides, S5-S7 is bonded to metal only through coordinative covalent bond which is rare. The coordinate covalent bonds (V2-S5 2.419(3) and V2-S7 2.406(3) Å) are significantly longer as compared to the covalent bond length (V2-S6 2.296(3) Å). The bond lengths and bond angles in the V2S4 core of 2 are also very similar to those observed in bimetallic thiolato complexes of vanadium and molybdenum. 6,22,[START_REF] Miller | Proceedings of the 4th International Conference on the Chemistry and Uses of Molybdenum[END_REF] Nevertheless, all the V-S-V bridges are unsymmetric to some extent (V1-S1 2.390(3), V2-S1 2.424(3), V1-S2 2.500(3), V2-S2 2.427(3) Å). The metal-metal bond lengths in this type of thiolato complexes are largely determined by the oppositely coordinated two dithiolato ligands as well as the formal oxidation state variation of the metal atoms. The oxidation states of both the vanadium atoms are +3. However, the V(III)-V(III) single bond length of 2.607(2) Å in 2 is comparable with [V2(SCH2CH2S)4] 2-(A) 6 (2.600(2) Å) but longer than [CpVSC2H4S)2] 21 (2.541(1) Å) and [(Cp*V)2(μ-CS3-κ 2 S,S')(μ-H2CS2-κ 2 S'',S''')] 17 (2.5548(7) Å). All the V-S-V bond angles ranging from 64.39-65.31° are comparable to the other reported bimetallic thiolato complexes of vanadium. 17 9), S7-H7 1.201(5), S5-S7 2.025(4), S6-C16 1.814 (13), C11-C12 1.512 (13), C15-C16 1.528 (18), V1-S1-V2 64.39(8), S2-V2-S3 69.38 (9), V1-S3-V2 65.31(8), S5-S7-V2 65.51 (11), C15-C16-S6 111.7(8); (b) EPR spectrum of the solid sample of complex 2 recorded at 77 K with microwave frequency of 9.179 GHz.

Density functional theory (DFT) studies at the B3LYP/def2-TZVP level were carried out to understand the electronic structure and bonding nature of 2. The structural parameters of the optimized structure are in well agreement with the X-ray crystallographic data. The molecular orbital (MO) analysis of 2 shows the HOMO-LUMO energy gap of 2.800 eV, suggesting a thermodynamic stable complex. Further, the V-V bonding interaction of 2 is depicted in α-SOMO-1, in which dz 2 orbitals of both the vanadium centers are delocalized (Figure 3a). A higher Wiberg bond index (WBI) of 0.8603 for V-V bond also suggests the presence of a strong metal-metal interaction which is further confirmed by the contour line diagram of 2 (Figure 3d). The contour line map perpendicular to the V-V bond is showing the coordination scenario of two dithiol ligands opposite to one another (Figure 3e). On the other hand, the α-SOMO-14 shows the d-p orbital interaction in V2-S5 and V2-S7 coordinated covalent bonds (Figure 3b). While the α-SOMO-24 is showing the S5-S7 end-to-end overlap that confirms the presence of S-S single bond in [SCH2CH2S-SH] ligand of 2 (Figure 3c). Moreover, the natural bonding orbital (NBO) analysis of 2 also shows these bonding interactions. The NBO analysis shows negative natural charge on metal atoms and positive natural charge on sulfur atoms that indicates the electron donation from sulfur to metal centers in 2. This is further supported by the natural valence populations on V and S atoms (Table S3). Vanadium complexes show various oxidation states from -1 to +5 among which +2, +3, and +4 oxidation states are paramagnetic in nature. 26 It is observed that vanadium(III) thiolato complexes are stable in physiological conditions. 27 Thus, the investigation of the electronic properties of vanadium thiolato complexes has become of interest. Therefore, we have performed an EPR experiment of the solid sample of 2 at 77K that displays a signal with the g value of 1.982 (Figure 2b). The nuclear spin of vanadium is I = 7/2; hence, hyperfine splitting is expected to be observed. 26a However, complex 2 did not show any hyperfine splitting; instead, a broad signal is observed. This may be due to the small values of the hyperfine splitting parameters {A} and relatively large width of the EPR line. A similar type EPR has been reported for mixed-valence vanadium cluster, [V IV 4V V 2O7(OCH3)12], where six vanadium atoms four paramagnetic vanadium (IV) and two diamagnetic vanadium (V)) surrounded an oxo anion, forming a slightly distorted octahedron. 28 Note that the typical range of g values for V(III) complexes is 1.72-2. 10. 26 The molecular orbitals housing the two unpaired electrons indicate non-orthogonality of the d orbitals of vanadium in the  and  subspaces (Figure S21). It is expected that the electrons on two vanadium centers would interact with each other. However, the dxy orbitals do not overlap mainly due to the small V-S-V angle while dz 2 orbitals are 10.1002/ejic.202300060

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delocalized to form V-V bonding. As a result, these weakly interacting electrons in the dxy orbitals on each vanadium center give rise to the EPR signal.

Reactivity of [Cp*MCl4] (M = Nb (3a) and Ta (3b)) with [HS(CH2)2SH]

To synthesize the dithiolato complexes of heavier analogue of vanadium, we have performed the reaction of [Cp*MCl4] (M = Nb (3a) and Ta (3b)) with ethane-1,2-dithiol in a similar approach described for complex 2 (Scheme 2). In the case of [Cp*NbCl4], the reaction at elevated temperature yielded red solid 4a (35% yield, Rf = 0. Monometallic thiolato complexes 4a and 4b. Complexes 4a and 4b were isolated in 35% and 19% yields, respectively. The 1 H NMR spectra of 4a and 4b show one type of Cp* environment at δ = 2.10 and 2.24 ppm, respectively, along with the peaks for CH2 protons (δ = 2.96 to 5.22 ppm). The 13 C{ 1 H} NMR of 4a and 4b also exhibit the peaks corresponding to Cp* carbons as well as CH2 carbons. The mass spectrum of complex 4a shows an isotopic pattern (ESI + mode) at m/z = 472.9860 that corresponds to [M+CH3] + , whereas 4b shows at m/z = 547.0121 that corresponds to [M+H] + . All these spectroscopic data were not enough to reveal the structure of 4a and 4b. Therefore, we have performed solid-state X-ray analyses on suitable crystals of 4a and 4b. Scheme 2. Synthesis of monometallic thiolato complexes 4a, 4b, and 5. The X-ray diffraction studies established complex 4a as [Cp*Nb(SCH2CH2S)(SCH2CH2S-CH2S)] and complex 4b as [Cp*Ta(SCH2CH2S)(SCH2CH2S-CH2S)] (Figure 4). Both the complexes 4a and 4b exist as six coordinated molecules in the crystalline state. The coordination geometry around the central Nb(V)/Ta(V) atom is a distorted octahedron. A η 5 -Cp* ring occupies one axial position, and one bidentate ethane-1,2dithiolato occupies two equatorial sites. Whereas the remaining two equatorial and one axial position are occupied by ɳ 3 -[SCH2CH2S-CH2S] ligand. Note that thiolate chemistry is very complex that mostly deals with the fragmentation of starting materials in harsh conditions. Although we are not sure about the mechanism, we believe that the fragmentation or decompositions of ethane-1,2-dithiol under harsh reaction conditions might have arrested in the coordination sphere of these thiolato complexes. Therefore, we can assume that both in complexes 4a and 4b, one ethane-1,2-dithiol ligand might have coupled with a [CH2SH] to generate tridentate [SCH2CH2S-CH2S] moiety followed by doubly deprotonation. The four equatorial sulfur atoms (S1, S2, S3, and S5 for 4a; S11, S13, S14, and S15 for 4b) are covalently bonded to metal centers (Nb-S: 2.412-2.532 Å and Ta-S: 2.422-2.496 Å) that are shorter as compared to the axial coordinate covalent M-S bonds (2.612 Å of 4a and 2.641 Å of 4b). Similar types of bonds along with comparable bonding parameters are observed in the Nb-complexes (C8H20N) [Nb(C6H4S2)2(C6H4S3)] 23a and [(η 5 -C5H5)Nb(η 2 -S2)(S2CC6H5)2] 12 Ta and -[(Cp*Ta) complexes 2(μ-S){μ-C(H)S3-κ 2 S:κ 1 S′,S″}{μ-SC(H)S-κ 2 C:κ 1 S‴,S′′′′}] 14 [(Cp*Ta) and 2(μ-S)(μ-S2CH2CHS2κ 2 S:κ 1 S',S'')(μ-H)(μ-S2CH2κ 1 S''',S'''')] 17 . On the other hand, the four equatorial sulfur atoms of 4a and 4b are not located in the same plane which is reflected in the average Seq-M-Seq bond angles (4a: 86.35°; 4b: 85.05°). In particular, the S5-Nb-S3 angle (102.08(8)°) of 4a and S11-Ta2-S15 angle (99.40(7)°) of 4b are largely deviated from that of ideal square planar geometry (90°). This Seq-M-Seq angle deviation may be resulted due to the steric crowding originated by [SCH2CH2S-CH2S] ligand. In this connection, more steric hindrance is expected to be experienced in 4a than 4b due to the higher atomic radii of Ta than Nb, which is exactly reflected in their respective Seq-M-Seq angle. In addition, the oxidation states of niobium and tantalum in 4a and 4b are +5, which is common in most of the niobium and tantalum thiolato complexes. 12,17,23a Selected bond lengths (Å) and bond angles (°); 4a: Nb1-S1 2.532(2), Nb1-S4 2.612(2), S4-C15 1.845( 12), S3-C13 1.803( 9), C13-C14 1.544( 16), S3-Nb1-S4 79.21(8), C14-S4-C15 105.3(5), 4b: Ta2-S13 2.4960( 18), Ta2-S15 2.4599( 19), S12-C35 1.772( 9), C33-C34 1.473( 13), S12-C35-S15 103.3(4), C35-S15-Ta2 97.2(3).

Monometallic thiolato complex 5. Complex 5 was isolated as yellow solid in 24% yield. The 1 H NMR spectrum of 5 displays a single peak for Cp* protons (δ = 2.34 ppm), along with the peaks for CH2 protons (δ = 2.39-4.64). The 13 C{ 1 H} NMR also confirms the presence of Cp* along with CH2 carbons. The mass spectrum of complex 5 shows an isotopic pattern (ESI + mode) at m/z = 532.9945, which is 14 units more than 4b. These observations led us to envisage complex 5 is similar to 4b with an extra CH2 group. All the spectroscopic data were not adequate to predict the identity of 5. A clear explanation eluded us until the solid-state X-ray structure analysis of 5 was carried out.

The single crystal X-ray diffraction study establishes complex 5 as [Cp*Ta(SCH2CH2S)(SCH2CH2S-S)] (Figure 5). Similar to 4a and 4b, in complex 5, the central tantalum atom is six-coordinated and with distorted octahedral geometry. The ɳ 3 -2-disulfanyl-ethanethiolato ligand has replaced an ɳ 3 -[SCH2CH2S-S] ligand of complex 4b to generate 5. The ɳ 3 -[SCH2CH2S-S] ligand of 5 might have generated by sulfur 10.1002/ejic.202300060

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European Journal of Inorganic Chemistry elimination from ethane-1,2-dithiol ligand. A similar type of sulfur extraction from a benzene-1,2-dithiolate ligand has been observed in an Nb thiolato complex (Et4N)[Nb(C6H4S2)2 (C6H4S3)]. 23a Similar to complexes 4a and 4b, the equatorial sulfur atoms of 5 are not in the same plane with Ta center. The central Ta atom is 0.737 Å above the mean S4 least-square plane. The equatorial covalent Ta-S bond lengths (2.426-2.507 Å) and axial coordinate covalent Ta-S bond lengths (2.620 Å) of 5 are comparable with that of 4b. 14,17 Also, the disulfur (S3-S5) bond length of 2.056(2) Å in 5 is comparable with monometallic disulfur complex (Et4N) [Nb(C6H4S2)2(C6H4S3)] 23a (2.0561(9) Å). Whereas, S-Ta-S angle is decreased (4a: S11-Ta2-S15 99.40(7)°; 5: S4-Ta1-S5 93.84(6)°) with the loss of CH2 group in 5. In order to understand the electronic structure and bonding situation in monometallic thiolato complexes 4a, 4b, 5 and [Cp* V(SCH2CH2S)(SCH2CH2S-CH2S)]

(proposed vanadium analogue of 4a and 4b), we have performed the DFT analysis at B3LYP/def2-TZVP level of theory. Having a series of group 5 mono-metallic thiolato complexes, we have compared their HOMO-LUMO energy gaps that show the gradual increase of energy gaps with the change of metals from V to Nb to Ta. The smaller HOMO-LUMO gap and energetically higher-lying HOMO of the vanadium analogue of 4a and 4b may be the reason behind the unsuccessful attempt to isolate the vanadium analogue. The HOMOs of all these molecules are largely localized on the sulfur atoms (p-orbital) of the thiol ligands (Figure 6). On the other hand, the HOMO-8 of 5 shows the d-p orbital interaction of both the Ta1-S3 and Ta1-S5 coordinated covalent and covalent bonds, respectively (Figure S22b). Similar bonding interactions were also depicted in the MOs of 4a and 4b. Further, the HOMO-15 shows the S3-S5 end-to-end p-p orbital overlap that confirms the presence of S-S single bond of 2disulfanylethane thiolato group in 5 (Figure S22c). This is also validated by the contour line map in the Ta1-S3-S5 plane shown in Figure S22d. The NBO analyses of 4a, 4b and 5 also show negative natural charges on the metal center and positive natural charges on sulfur atoms (Table S3). This indirectly indicates the electron donation from the sulfur atoms towards the metal center. This is further supported by the natural valence populations on metal (Ta, Nb, and V) and S atoms.

Reactivity of 5 with [Mo(CO)5•THF]

In terms of bonding, complex 5 is an interesting monometallic thiolato species of tantalum. The MO analysis of 5 revealed a HOMO-LUMO energy gap of 3.19 eV in which the HOMO is largely localized on the sulfur atom (p-orbital) of the dithiol ligand along with little contribution of other sulfur atoms (Figure 6). This suggests a reactive nature or donating ability of the sulfur atoms. As a result, to examine the coordinating ability of these S atoms, we have treated 5 with [Mo(CO)5•THF] in photolytic conditions that yielded green solid 6 (27% yield, Rf = 0.42 in n-hexane/CH2Cl2 (40:60 v/v) (Scheme 3). The 1 H NMR spectrum of 6 shows a single Cp* proton peak along with the peaks due to CH2 protons (δ = 2.45 to 4.79 ppm). The 13 C{ 1 H} NMR spectrum also confirms the presence of a single type of Cp* carbon along with CH and CH2 carbons. The mass spectrum shows an isotopic pattern (ESI + mode) peak at m/z = 741.9142 that corresponds to [M+H] + along with other peaks analogous to CO fragmentations (Figure S16). This data suggest the formation of a tantalum thiolato complex containing Mo(CO)3 moiety. Nonetheless, we could not predict the structure of complex 6 based on these spectroscopic data. Therefore, we have performed the single crystal X-ray analysis on a suitable single crystal of 6 grown by the slow evaporation of a solution of n-hexane/dichloromethane (50:50) at 5 °C.

Scheme 3. Synthesis of heterobimetallic thiolato complex 6.

As shown in Figure 7, the solid-state X-ray structure of 6 reveals that this is distinctive heterobimetallic thiolato complex of 10.1002/ejic.202300060

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Ta and Mo, [(Cp*Ta){μ-(SCH2CH2S)-κ 2 S,S'}{μ-(SCH2CH2S-CH2(CH3)S)-κ 2 S'':κ 1 S'''':κ 1 S'''''}{Mo(CO)3}], where one ethane-1,2dithiolato ligand is symmetrically coordinated to Ta and Mo atoms through two µ-S atoms (S4 and S5). Other thiolato group [SCH2CH2S-CH2(CH3)S] is unsymmetrically coordinated to the Ta and Mo atoms through three S atoms (S1, S2 and S3) in κ 1 and κ 2 fashion. The vacant coordination sites of [Mo(CO)3] fragment in 6 are stabilized by the coordination of thiolato ligands present in the complex. Note that bimetallic complexes of early transition metals are quite interesting in various reactions such as formation of µ-acyl complex as well as halogen substitution reactions at metal centers. 29 11), S3-Ta1 2.4573( 10), Mo2-S4 2.5212( 11), Mo2-S3 2.5197( 10), C12-C13 1.526( 7), C11-C16 1.504( 6), S4-Mo2-S3 75.27(4), S3-Mo2-S5 105.12(3), Ta1-S3-Mo2 72.56(3), S3-Ta1-S1 139.67(4), C16 -C11-S1 115.0(4).

The oxidation state of tantalum remained unaffected (+5), whereas the oxidation state of molybdenum stayed zero. The Ta1-Mo2 bond length in 6 of 2.9455(4) Å is significantly shorter as compared to the Ta-Mo bond distance in [{(Cp*Ta)(CH2 S2)}2(B2H5)(H){Mo(CO)3}] 30 (3.245(3) Å). The molybdenum tricarbonyl fragment is coordinated to the tantalum thiolato part through three sulfur atoms and the corresponding Ta-S bond length (avg. 2.5148 Å) increases as compared to complex 5 (avg. 2.4688 Å). The Ta1-S1 bond length of 2.5321 (11) Å is elongated whereas, the Ta1-S2 got reduced (2.5342( 11) Å) as compared to the Ta-S bond distances in 5 (Ta1-S5 2.4532( 16) Å and Ta1-S3 2.6205( 16) Å). The average Mo-S bond length of 2.5281 Å is comparable with that of Mo-S bonds in [{(Cp*Ta)(CH2S2)}2 (B2H5)(H){Mo(CO)3}] 30 (2.542( 9) Å and 2.565 (9) Å). However, this is significantly longer as observed in complexes, [CpMoSC2H4S]2 22 (2.352(2)-2.479(2) Å) and [Mn3(CO)6 (SCH2CH2CH2S)3] 15a (2.3111(9)-2.3975(9) Å).

To understand the electronic structure and bonding situation of 6, DFT calculations have been carried out. The MO analysis of 6 revealed that the HOMO-LUMO energy gap of 2.84 eV is smaller than that of 5 (3.19 eV). Moreover, the MO analysis shows that the HOMO-2 is delocalized over Ta(dz 2 )-Mo(dz 2 ) orbital suggesting the Ta-Mo bonding interaction (Figure 8a). A lower WBI of 0.5356 for the Ta-Mo bond also suggests the presence of a weak metal-metal bonding interaction which has also been reflected in the contour line diagram along the Ta1-S3-Mo2 plane (Figure 8d). The HOMO-10 and HOMO-11 of 6 depict the Mo-S and Ta-S boding interactions, respectively (Figures 8b and8c). Also, the NBO analysis of 6 shows negative natural charge on Mo atom (-1.721) and positive natural charges on S atoms (0.317, 0.208, 0.336) that suggest the donating nature of S and the accepting nature of Mo. The above observations have also been supported by natural valence populations on S and Mo atoms (Table S3). UV-visible studies. The TM-thiolato complexes 2, 4a, 4b, 5 and 6 with two or three numbers of ethane-1,2-dithiolato moieties have one or two metal centers at their cores. Hence, the absorption pattern of these coloured complexes became of interest. The UV-vis absorption spectroscopy helped to measure the optical properties of complexes 2, 4a, 4b, 5 and 6. The UVvis spectra of all the complexes were measured in CH2Cl2 medium and mainly three absorption bands have been observed in the range of 280-800 nm (Figure 9). The most intense peaks at higher energy regions 280-300 nm are due to the spin allowed Π-Π* transition of the Cp* ligands present in all the complexes. 31 The comparatively low intense peaks at higher wavelength regions 320-656 nm may be due to the charge transfer bands. 16,32 Unlike other group 5 metal thiolato complexes, in complex 2, a relatively low energy absorption band has been observed at 656 nm.

In order to reproduce the UV-vis spectrum and get some idea about the electronic transitions, Time-Dependent DFT formalism was used. The studies show that the possible number of electronic transitions are more in bimetallic complexes 2 and 6 compared to the monometallic thiolato complexes 4a, 4b, and 5 (Tables S5-S9, Figures S23-S27). Moreover, owing to the paramagnetic nature, complex 2 shows the transitions having  and  subspaces. The molecular orbitals of 2, 4a, 4b, 5 and 6, exhibiting the most intense electronic transitions, are shown in Figures S23-S27. In complex 2, the high-intensity absorption bands near 301 nm may be assigned as an intramolecular MLCT transition, whereas the low-intensity absorption bands near 367 and 656 nm could be the intramolecular LMCT transition. The weak adsorption band at 656 nm corresponds to -SOMO-1-LUMO and -SOMO-1-LUMO+3 transitions. The absorptions in 320-470 nm region for complexes 4a, 4b, and 5 are mainly due to the intramolecular LMCT transitions. A 10.1002/ejic.202300060

Accepted Manuscript

comparison among the low-intensity absorption bands of these group 5 monometallic thiolato complexes 4a, 4b, and 5, shows a blue shift from 4a to 5 to 4b, which are in good accord with their HOMO-LUMO energy gaps. On the other hand, the absorption bands at 332 and 444 nm for 6 are due to MLCT transitions, whereas the LMCT transitions dominate in 5. Due to the formation of 6 from 5, the HOMO-LUMO energy gap has been decreased that caused a red shift from 410 (5) to 444 nm (6).

Conclusion

The present work details a new synthetic procedure for the formation of various thiolato complexes of group 5 transition metals having uncommon coordination. The chemistry of group 5 metal precursors, for example, 1, 3a, and 3b, with ethane-1,2dithiol appear to be very resourceful. These thiolato complexes have either two or three ethane-1,2-dithiolato moieties associated to metal centers that show unique structural and electronic properties. In complex 2, the presence of a V-V bond resulted the paramagnetic properties of this complex. Thiolato complexes 4a, 4b, and 5 have distorted octahedron geometry around metal centers M(V) (M = Nb or Ta). Treatment of [Mo(CO)5•THF] with 5 afforded a heterobimetallic thiolato complex 6. Although the reaction of V precursor (1) with CS2, reported earlier; 14,17 resulted a bimetallic paramagnetic and a monometallic diamagnetic thiolato complex, a bimetallic paramagnetic thiolato complex (2) was observed with ethane-1,2-dithiol. On the other hand, the reactions of CS2 with heavier Nb (3a) and Ta (3b) congeners resulted various bimetallic diamagnetic thiolato complexes. 14,17 However, the monometallic diamagnetic complexes (4a, 4b and 5) are yielded in the case of ethane-1,2-dithiol These results evidently demonstrate the influence of both metal and dithiolato ligands in the formation of these thiolato complexes. Investigations to evaluate the scope for other early transition metal thiolato complexes specially with heavier chalcogen atoms are underway.

Experimental Section

General procedures and instrumentation. All the experiments were done under an argon atmosphere using standard Schlenk-technique or glove box techniques. Solvents were dried over sodium/benzophenone ketyl and distilled under an argon atmosphere prior to use. Chloroform-d was purchased from SyNmr chemicals and dried over 4 Å molecular sieves. Other commercial chemicals, [LiBH4•THF], and ethane-1,2-dithiol were purchased from sigma Aldrich and used as received. The starting materials [Cp*VCl2]3 (1), 33 [Cp*NbCl4] (3a), 34 and [Cp*TaCl4] (3b), 35 were prepared by following the reported literature. The chromatographic workup was done using 250 mm dialuminuim supported silica gel TLC plates. NMR spectra of synthesized complexes were recorded on 500 and 400 MHz Bruker FT-NMR spectrometers. Chemical shifts are reported with reference to the residual solvent proton (δ = 7.26 ppm, CDCl3 and 7.16 ppm, C6D6) and carbon (δ = 77.16 ppm, CDCl3 and 128.06 ppm, C6D6) for the 1 H and 13 C{ 1 H} NMR spectra, respectively. Mass spectrometric data were obtained on Qtof Micro YA263 HRMS and 6545 Qtof LC/MS instrument. JEOL Model JES FA200 instrument was used for the measurement of the electron paramagnetic resonance spectra. UV-vis spectra were recorded on a JASCO V-650 spectrometer. A JASCO 400 FT-IR spectrometer was used to record the IR spectra. The light source for the photolysis reaction described in this work was Oriel Instrument with a 500 W Hg/Xe arc lamp equipped with liquid and coloured glass filters, irradiating 280-780 nm.

Synthesis of 2.

In a clean and flame-dried Schlenk tube, [(Cp*VCl2)3] (0.200 g, 0.26 mmol) was suspended in toluene (20 mL) with a magnetic bar. The brownish suspension was cooled to -78 °C and 6 equivalents 2M solution of [LiBH4·THF] was added dropwise through a syringe. Then, the reaction mixture was allowed to come to room temperature over 1 h under stirring conditions and no such drastic colour change was observed. After 1 h, ethane-1,2-dithiol (0.1 mL, 1.06 mmol) was added to the reaction mixture and continued the reaction at 85 °C for 24 h. The solution colour remained dark brown upon heating. After that, the solvent was evaporated under vacuum and the residue was passed through 3 cm of celite using n-hexane/CH2Cl2 (40:60 v/v). After evaporation of solvents, the residue was subjected to chromatographic workup and eluted with an n-hexane/ CH2Cl2 (40:60 v/v) which afforded green 2 (0.029 g, 31%).

2: MS (ESI + ) calcd. for C16H26V2S7 + [M-H] + m/z 544.9036, found 544.9019; Well-grounded solid powder of complex 2 (~10 mg) was loaded into a sample holder under argon atmosphere, and the X-band EPR spectrum was recorded at 77 K using the following parameters. Microwave frequency = 9179.728 MHz, microwave power = 0.99800 mW, modulation frequency = 100.00 kHz, modulation amplitude CH1= 2.5, CH2 = 2.0, field center = 400 mT, time constant CH1 = 0.03 s, CH2 = 0.03 s and sweep time = 30 s; IR (dichloromethane): ̃ = 2550 cm -1 (S-H); UV-vis [CH2Cl2, , nm]: 301, 367, 656.

Synthesis of 4a, 4b, and 5. In a flame-dried Schlenk tube, the deep brown toluene suspension (20 mL) of [Cp*NbCl4] (0.200 g, 0.54 mmol) was treated with 4 equivalents 2M solution of [LiBH4·THF] at -78 °C. After 1 h of continuous stirring, the solution colour changes from deep brown to deep orange. Then 0.1 mL ethane-1,2-dithiol (1.06 mmol) was added to this purple intermediate which turned the colour of the solution from purple to dark brown and the reaction mixture was allowed to stir at 85 °C for 24 h. The solution colour remained dark brown upon heating. The solvent was removed by vacuum. The residue was extracted through a glass frit containing celite using n-hexane/CH2Cl2 (40:60 v/v). After removing the volatiles from the filtrate, a chromatographic work-up was carried out on TLC plates. Elution using an n-hexane/CH2Cl2 (40:60 v/v) yielded red solid 4a (0.087 g, 35%). Under similar conditions, the reaction of [Cp*TaCl4] (0.200 g, 0.44 mmol) with 4 equivalents 2M solution of [LiBH4·THF] yielded a deep blue intermediate. Then 0.1 mL ethane-1,2dithiol (1.06 mmol) was added to this intermediate which turned the colour of the solution from deep blue to dark brown and the reaction mixture was allowed to stir at 85 °C for 24 h. The solution colour remained dark brown upon heating. After that, we executed the above- 4b: MS (ESI + ) calcd. for C15H27S5Ta + [M+H] + m/z 547.0118, found 547.0121; 1 H NMR (CDCl3, 500 MHz, 22 °C): δ = 2.24 (s, 15H; 1×Cp*), 3.00 (m, 2H), 3.48 (dt, 2 J = 13.6, 3 J = 2.7 Hz, 2H), 3.64 (m, 1H), 3.73 (m, 1H), 3.79 (m, 1H), 3.90 (d, 2 J = 11.0 Hz, 1H), 4.36 (d, 2 J = 12.4 Hz, 1H), 5.22 (q, 3 J = 7.2 Hz, 1H) ppm; 13 C{ 1 H} NMR (CDCl3, 125 MHz, 22 °C): δ = 12.5 (s, C5Me5), 38.9, 39.0, 41.6, 42.6 (s, CH2) J = 13.9, 3 J = 4.2 Hz, 1H), 2.69 (dt, 2 J = 12.2, 3 J = 3.9 Hz, 1H), 3.81 (dt, 2 J = 12.1, 3 J = 4.0 Hz, 1H), 3.89 (m, 1H), 4.06 (m, 2H), 4.38 (m, 1H), 4.64 (dt, 2 J = 14.0, 3 J = 4.5 Hz, 1H) ppm; 13 C{ 1 H} NMR (CDCl3, 125 MHz, 22 °C): δ = 12.7 (s, C5Me5), 42.4, 42.7, 44.5, 48.5 (s, CH2), 121.6 (s, C5Me5) ppm; UV-vis [CH2Cl2, , nm]: 410, 461.

Synthesis of 6.

In a flame-dried Schlenk tube complex 5 (0.030 g, 0.041 mmol) was taken in 10 mL THF. To it, a freshly prepared [Mo(CO)5·THF] (0.05 g, 0.189 mmol) was added and irradiated for 1 h. After the removal of the solvent, the residue was subjected to chromatographic workup. Elution with n-hexane/CH2Cl2 (40:60 v/v) yielded green solid 6 (0.012 g, 27%). 33.7, 39.3, 42.1, 48.1 (s, CH2 ), 62.1 (s, CH), 113.5 (s, C5Me5) ppm; IR (dichloromethane): ̃ = 1957, 1895, 1829 cm -1 (CO); UV-Vis [CH2Cl2, , nm]: 332, 444.

Computational Details. All the molecular geometry optimization and electronic structures calculations were performed using the hybrid Becke-Lee-Yang-Parr (B3LYP) functional 36 in conjunction with the triple-ζ quality basis set def2-TZVP 37 using the Gaussian 16 program 38 . The hybrid functional B3LYP has proven to be an accurate method for reproducing metal-ligand bond lengths or metal-metal bond lengths; hence, its selection is here. 39 In complex 2, both the vanadium centers are in +3 oxidation state, which suggests the possibility of having both the low spin paramagnetic state and high spin diamagnetic state. Calculation shows that the high spin triplet state (multiplicity = 3; E = -5302.6291741 a.u.) is energetically more stable by 0.037776 a.u. compared to the low spin singlet state (multiplicity = 1; E = -5302.5914005 a.u.). Note that during optimization V2S7 distant was frozen and optimized. For other group 5 thiolato complexes, metals are in +5 oxidation states having d 0 electronic configuration, leaving the only possibility of having low spin diamagnetic states. For the optimization of all the molecules except 2, multiplicity = 1 is considered as all the molecules are diamagnetic in nature, and optimization was done in gaseous state using their X-ray crystallographic coordinates. The vibrational analysis shows the absence of any imaginary frequency, which confirms the presence of all the structural minima on the potential energy hypersurface. To study the NMR chemical shifts, the gauge including atomic orbital (GIAO) 40 method was employed, and TMS (SiMe4) has been taken as the internal standard (shielding constant 31.92 ppm). The natural bonding analysis (NBO) was carried out with the NBO partitioning scheme 41 and Wiberg bond indexes 42 were obtained from it. QTAIM 43 analysis was performed utilizing the Multiwfn, V.3.6, package 44 . All the optimized structures and orbital graphics were produced using the Gaussview 45 and Chemcraft [START_REF]ChemCraft -Graphical software for visualization of quantum chemistry computations[END_REF] .

Single-Crystal X-ray diffraction analyses. Suitable X-ray quality crystals of 2, 4a, 4b, 5, and 6 were grown by slow diffusion of an nhexane/CH2Cl2 solution at 5 °C. The crystal data were collected and integrated using a D8 VENTURE Bruker AXS diffractometer for 2, 4a, and 4b, Bruker D8 VENTURE diffractometer with PHOTON 100 CMOS detector for 5, and Bruker AXS Kappa APEXII CCD diffractometer for 6 with graphite monochromated Mo-Kα (λ = 0.71073 Å) radiation at 150(2) K (2, 4a and 4b), 293(2) K (5) and 296(2) K (for 6). Note that the crystal data of 4b was obtained from the X-ray analysis of a co-crystal of 4b and 5. The structures of these complexes were solved by heavy atom methods using SHELXS-97, 47 SHELXT-2014 and refined using SHELXL-2014, SHELXL-2017, SHELXL-2018. [START_REF] Sheldrick | [END_REF] Using Olex2 49 all the molecular structures were drawn. Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no CCDC -2162881 (2), 2162916 (4a), 2162989 (4b), 2162927 (5) and 2162953 (6). These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Figure 1 .

 1 Figure 1. Transition metal thiolato complexes showing different coordination modes of thiolato ligands.

Figure 2 .

 2 Figure 2. (a) Molecular structure and labelling diagram of 2. Selected bond lengths (Å) and bond angles (°); V1-V2 2.607(2), V1-S1 2.390(3), V2-S2 2.427(3), V1-S3 2.371(3), V2-S5 2.419(3), S1-C11 1.838(9), S7-H7 1.201(5), S5-S7 2.025(4), S6-C16 1.814(13), C11-C12 1.512(13), C15-C16 1.528(18), V1-S1-V2 64.39(8), S2-V2-S3 69.38(9), V1-S3-V2 65.31(8), S5-S7-V2 65.51(11), C15-C16-S6 111.7(8); (b) EPR spectrum of the solid sample of complex 2 recorded at 77 K with microwave frequency of 9.179 GHz.

Figure 3 .

 3 Figure 3. (a) α-SOMO-1, (b) α-SOMO-14 and (c) α-SOMO-24 of 2. Contour values for isosurface are ±0.045 (e/bohr 3 ) 1/2 . (d) and (e) Laplacian map of the electron density distribution computed for 2 in the V1-V2-S6 plane and the perpendicular plane with respect to V-V bond, respectively. Dashed crimson lines indicate areas of charge concentration (∇2ρ(r) < 0), while dotted dark green lines indicate areas of charge depletion (∇2ρ(r) > 0). Solid brown lines connecting the atomic nuclei are the bond paths. The thick blue lines indicate the zero-flux surfaces crossing the molecular plane. Blue and orange dots indicate BCPs (bond critical points) and RCPs (ring critical points), respectively.

  38 in n-hexane/CH2Cl2 (40:60 v/v)). While the reaction of [Cp*TaCl4] afforded yellow solid 4b (19% yield, Rf = 0.38 in n-hexane/CH2Cl2 (40:60 v/v)) and yellow solid 5 (24% yield, Rf = 0.47 in n-hexane/CH2Cl2 (40:60 v/v)). The detailed characterizations of these thiolato complexes are discussed below.

Figure 4 .

 4 Figure 4. Molecular structures and labelling diagrams of 4a (left) and 4b (right).Selected bond lengths (Å) and bond angles (°); 4a: Nb1-S1 2.532(2), Nb1-S4 2.612(2), S4-C15 1.845(12), S3-C13 1.803(9), C13-C14 1.544(16), S3-Nb1-S4 79.21(8), C14-S4-C15 105.3(5), 4b: Ta2-S13 2.4960(18), Ta2-S15 2.4599(19), S12-C35 1.772(9), C33-C34 1.473(13), S12-C35-S15 103.3(4), C35-S15-Ta2 97.2(3).

Figure 5 .

 5 Figure 5. Molecular structure and labelling diagram of 5. Selected bond lengths (Å) and bond angles (°); Ta1-S1 2.4726(15), Ta1-S3 2.6205(16), Ta1-S4 2.4264(15), Ta1-S5 2.4532(16), S3-S5 2.056(2), C11-C12 1.498(10), S3-Ta1-S5 47.67(5), S1-Ta1-S4 148.53(6), S2-Ta1-S4 77.32(6), S3-S5-Ta1 70.43(7).

  Figure 6. Comparison of frontier molecular orbitals of [Cp*V(SCH2CH2S)(SCH2CH2S-CH2S)], 4a, 4b, and 5; respectively. Contour values for isosurface are ±0.045 (e/bohr 3 ) 1/2 .

Figure 7 .

 7 Figure 7. Molecular structures and labelling diagrams of 6. Selected bond lengths (Å) and bond angles (°); Mo2-Ta1 2.9455(4), S1-Ta1 2.5321(11), S3-Ta1 2.4573(10), Mo2-S4 2.5212(11), Mo2-S3 2.5197(10), C12-C13 1.526(7), C11-C16 1.504(6), S4-Mo2-S3 75.27(4), S3-Mo2-S5 105.12(3), Ta1-S3-Mo2 72.56(3), S3-Ta1-S1 139.67(4), C16 -C11-S1 115.0(4).

Figure 8 .

 8 Figure 8. (a) HOMO-2, (b) HOMO-10 and (c) HOMO-11 of 6. Contour values for isosurface are ±0.045 (e/bohr 3 ) 1/2 . (d) Laplacian map of the electron density distribution computed for 6 in the Ta1-S3-Mo2 plane.

Figure 9 .

 9 Figure 9. Combined UV-vis spectra of 2, 4a, 4b, 5 and 6 in CH2Cl2.

  10.1002/ejic.202300060 Accepted Manuscript described work-up process which yielded yellow solid 4b (0.045 g, 19%) and yellow solid 5 (0.055 g, 24%). 4a: MS (ESI + ) calcd. for C16H29S5Nb + [M+CH3] + m/z 472.9858, found 472.9860; 1 H NMR (CDCl3, 500 MHz, 22 °C): δ = 2.10 (s, 15H; 1×Cp*), 2.96 (m, 3H), 3.46 (m, 1H), 3.62 (m, 2H), 3.78 (m, 2H), 3.90 (m, 1H), 5.19 (m, 1H) ppm; 13 C{ 1 H} NMR (CDCl3, 125 MHz, 22 °C): δ = 12.8 (s, C5Me5), 39.4, 40.5, 42.2, 43.9 (s, CH2), 123.5 (s, C5Me5) ppm; UV-Vis [CH2Cl2, , nm]: 320, 468.

6 :

 6 MS (ESI + ) calcd. for C19H28O3S5MoTa + [M+H] + m/z 742.9177, found 742.9142; 1 H NMR (CDCl3, 500 MHz, 22 °C): δ = 1.11 ppm (s, 3H; CH3), 1.96 ppm (s, 15H; Cp*), 2.45 (m, 1H), 2.84 (m, 1H), 3.16 (m, 1H), 3.35 (m, 2H), 3.47 (m, 2H), 3.65 (m, 1H), 3.96 (m, 1H), 4.79 (q, 3 J = 6.5 Hz, 1H) ppm; 13 C{ 1 H} NMR (CDCl3, 125 MHz, 22 °C): δ = 11.8 (s, C5Me5),

2:

  C16H28S7V2, Mr = 546.68, Monoclinic, space group P21, unit cell, a = 11.4026(9) Å, b = 29.239(2) Å, c = 13.3489(12) Å, α = 90°, β = 91.543(3)°, γ = 90°, Z = 8, V = 4448.9(6) Å 3 , µ = 1.497 mm -1 , F(000) = 2256.0, ρcacld = 1.632 g/cm 3 , R1 = 0.0534, wR2 = 0.1073, 17272 independent reflections [2θ ≤ 54.986°] and 911 parameters.

4a: 6 :

 6 C15H25S5Nb, Mr = 458.56, Triclinic, space group P-1, unit cell, a = 9.3536(17) Å, b = 13.975(2) Å, c = 16.078(3) Å, α = 67.835(6)°, β = 89.831(7)°, γ = 89.811(6)°, Z = 4, V = 1946.4(6) Å 3 , µ = 1.146 mm -1 , F(000) = 944.0, ρcacld = 1.565 g/cm 3 , R1 = 0.0580, wR2 = 0.1453, 8875 independent reflections [2θ ≤ 54.9284°] and 387 parameters. 4b: C15H25S5Ta, Mr = 546.63, Triclinic, space group P-1, unit cell, a = 8.4203(15) Å, b = 14.314(3) Å, c = 15.424(3) Å, α = 85.636(7)°, β = 76.390(7)°, γ = 86.098(7)°, Z = 2, V = 1799.1(6) Å 3 , µ = 6.679 mm -1 , F(000) = 1056.0, ρcacld = 1.992 g/cm 3 , R1 = 0.0398, wR2 = 0.0889, 8145 independent reflections [2θ ≤ 55.054°] and 343 parameters. 5: C14H23S5Ta, Mr = 532.37, Monoclinic, space group P21/n, unit cell, a = 8.49000(10) Å, b = 24.6775(4) Å, c = 8.8551(2) Å, α = 90°, β = 103.237(2)°, γ = 90°, Z = 4, V = 1805.96(6) Å 3 , µ = 6.653 mm -1 , F(000) = 1040.0, ρcacld = 1.959 g/cm 3 , R1 = 0.0418, wR2 = 0.1011, 5444 independent reflections [2θ ≤ 61.054°] and 182 parameters. C19H27MoO3S5Ta, Mr = 740.59, Monoclinic, space group P21/n, unit cell, a = 9.3964(3) Å, b = 15.6738(5) Å, c = 16.7308(5) Å, α = 90°, β = 105.9879(12) °, γ = 90°, Z = 4, V = 2368.76(13) Å 3 , µ = 5.605 mm -1 , F(000) = 1440.0, ρcacld = 2.077 g/cm 3 , R1 = 0.0199, wR2 = 0.0471, 4170 independent reflections [2θ ≤ 49.996°] and 268 parameters.

European Journal of Inorganic Chemistry

Acknowledgements

We acknowledge the support of SERB, New Delhi, India, Grant No. CRG/2019/001280. S.B thanks IIT Madras and A.N.P. thanks UGC for research fellowships. We express our gratitude to P.K. Sudhadevi Antharjanam, V. Ramkumar, and SAIF, IIT Madras for single-crystal X-ray data collection as well as structure analyses. IIT Madras is gratefully acknowledged for the computational facility. 10.1002/ejic.202300060 Accepted Manuscript

Entry for the Table of Contents

A series of mono-and bimetallic thiolato complexes have been synthesized and structurally characterized by NMR, UV-vis, EPR spectroscopy and mass spectrometry (see picture). 10.1002/ejic.202300060 Accepted Manuscript