Asymmetric by Design: Heteroleptic Coordination Compounds with Redox-Active Dithiolene and 1,2,4,5-Tetrakis(isopropylthio)benzene Ligands

The 1,2,4,5-tetrakis(alkylthio)benzenes are redox-active organosulfur molecules that support oxidation to a stable radical cation. Their utility as ligands for the assembly of multimetal complexes with tailored functionality/property is unexamined. Here, 1,2,4,5-tetrakis(isopropylthio)benzene (tptbz, 1) is shown to bind PdCl2 at either one end, leaving the other open, or at both ends to form centrosymmetric [Cl2Pd(tptbz)PdCl2], 4. Ligand metathesis between Na2[(N≡C)2C2S2] (Na2mnt) and [Cl2M(tptbz)] (M = Pd, 2; M = Pt, 3) yields [(mnt)M(tptbz)] (M = Pd, 5; M = Pt, 6), but an alternative route involving transmetalation with [(mnt)SnMe2] delivers substantially greater yield. The mixed dithiolene-dithioether compound [(Ph2C2S2)Pt(tptbz)] (8) is formed by a similar transmetalation protocol using [(Ph2C2S2)SnnBu2]. Compounds 5, 6, and 8 are the first such heteroleptic complexes prepared by deliberate synthesis. The cyclic voltammetry of 8 reveals anodic waves at +0.14 and +0.97 V vs Fc+/Fc, which are attributed to successive dithiolene oxidation processes. While oxidized at +0.73 V as a free ligand, the redox-active MO of tptbz is pushed to a higher potential upon coordination to Pt2+ and is inaccessible. Calculations of the structures of [8]+ and of [((Cl2-3,5-C6H3)2C2S2)Pt(tptbz)]+ show that, in the latter, the dithiolene MOs are drawn down in energy into proximity with the tptbz MOs.


■ INTRODUCTION
In a series of recent reports, 1−4 we have described the utility of 1,2,4,5-tetrakis(diphenylphosphino)benzene (tpbz; Figure 1) as a rigid connector between redox-active metallodithiolene groups, which can be reversibly oxidized to access the radical monoanionic form of the dithiolene ligand ((b) in Scheme 1).The tpbz ligand is an effective electronic insulator that permits only weak dipolar coupling between the peripheral ligand radicals, thereby enabling the creation of a coherent quantum state that in principle could function as a qubit in quantum computing or memory applications.Improvement of coherence lifetimes in qubit candidates based upon electron-spins can be accomplished by minimizing the presence of spin-active nuclei in the vicinity, 5 the effect of which is to induce decoherence in the entangled state.In this regard, 31 P with I = 1/2 at 100% natural abundance is a less desirable nuclide for incorporation into a molecule-based qubit than is 32 S, with I = 0 at 95% natural abundance, because its nuclear spin contributes to the decohering magnetic background "noise".
Quite apart from the removal of spin-active nuclei that undercut coherent quantum state lifetimes, substitution of the tpbz connector for a tetrathioarene bridge creates altogether new possibilities for qubit engineering in that it, just as the dithiolene ligand opposite it in a heteroleptic complex, can , where n is the number of reflections and p is the total number of parameters refined.
sustain reversible oxidation to a spin-delocalized radical.Indeed, the cations that are accessible from 1,2,4,5tetrathioarenes have been the subject of spectroscopic study, first by Pedulli and co-workers, 6 and later by Chen and associates, 7 who also reported solid-state conductivity measurements and the first instances of structural characterization of such radical cationic salts by X-ray crystallography.Thus, if amenable to the formation of heteroleptic complexes with dithiolene ligands, tetrathioarenes might enable the formation of multiqubit systems whose component spins reside in chemically distinctive environments and thus might be separately addressable.
The foregoing considerations motivated us to examine the feasibility of substituting the tpbz connector with the 1,2,4,5tetrakis(isopropylthioether)benzene (tptbz) platform.Like tpbz, this tetrathioether has the virtues of amenability to scaled synthesis and stability in air, but it enjoys the further advantage that the alkyl groups of the thioether groups can be readily varied for effect upon solubility and steric profile.However, thioethers are generally weak ligands with a decided binding preference for soft, later transition metals of the second and third rows.Nonetheless, the potential advantages offered by tptbz in contrast to tpbz in supporting ligand-based coherent quantum states are sufficient to justify efforts to synthesize mono-and dimetallic compounds of the forms In this report, we present the leading results of this exploratory synthetic foray.
■ EXPERIMENTAL SECTION Physical Methods.All 1 H spectra were recorded at 25 °C with a Bruker Avance spectrometer operating at 300.13 MHz and referenced to the protonated solvent residual.Mass spectra (ESI + ) were obtained with a Bruker micrOTOF II mass spectrometer with an Agilent Technologies 1200 Series LC.The UV−vis spectra were acquired on a Hewlett-Packard 8752A diode array spectrometer.Elemental analyses were performed by Galbraith Laboratories, Inc. of Nashville, TN, or by Kolbe Microanalytical Laboratory in Oberhausen, Germany.Electrochemical measurements were performed using a CHI 620C electrochemical analyzer workstation with a Ag/AgCl reference electrode, glassy carbon working electrode, Pt wire as the auxiliary electrode, and [ n Bu 4 N][PF 6 ] as the supporting electrolyte.Under these conditions, the Cp 2 Fe + /Cp 2 Fe couple consistently occurred at +0.50 V. Spectroelectrochemical measurements were made with an Ocean Optics HR2000 spectrophotometer along with a Pine Research Instruments platinum honeycomb working electrode and a Ag/AgCl reference electrode.Procedural details regarding crystal growth, X-ray diffraction data collection, data processing, and structure solution and refinement are deferred to the Supporting Information (SI).Unit cell data and selected refinement statistics for the compounds that have been structurally identified are presented in Table 1; more complete crystallographic data are summarized in Table S1.
General Considerations.Literature methods were implemented for the syntheses of the tptbz ligand, 1, 8 disodium maleonitriledithiolate(2−), 9 [(mnt)SnMe 2 ], 10 and 4,5-diphenyl-1,3-dithiol-2-one. 11ll other reagents were purchased from commercial sources and used as received.Solvents were either dried with a system of drying columns from the Glass Contour Company (CH 2 Cl 2 , Et 2 O) or freshly distilled according to standard procedures (MeOH, CH 3 CN). 12All reactions described below were conducted under an atmosphere of N 2 , where mnt = maleonitriledithiolate ( Syntheses.C 6 (S i Pr) 6 .The following procedure is a modification of a published preparation of C 6 (S i Pr) 6.
[Cl 2 Pd(tptbz)], 2. To a 25 mL Schlenk flask charged with a stirring bar and PdCl 2 (0.248 g, 1.41 mmol), 20 mL of MeCN were added under an active N 2 flow.The mixture was heated to ∼70 °C until most of the solids dissolved.To this mixture was then added solid tptbz (0.528 g, 1.40 mmol), and the mixture was left to stir at ambient temperature overnight.All volatiles were removed from the reaction mixture under reduced pressure, and the orange solid residue was washed with Et 2 O (2 × 20 mL) and collected by filtration.Yield: 0.651 g, 1.18 mmol, 85%. 1  [Cl 2 Pt(tptbz)], 3. A 50 mL Schlenk flask with PtCl 2 (0.241 g, 0.906 mmol) was charged with MeCN (15 mL) via a syringe, and the mixture was heated at ∼70 °C until most of the solids dissolved and a yellow solution was formed.To this mixture was added solid tptbz (0.345 g, 0.921 mmol) under an outward flow of N 2 , and the mixture was left to stir at ambient temperature overnight.All volatiles were then removed in vacuo.The solid residue was redissolved in 2 mL of CH 2 Cl 2 and then precipitated by the addition of 50 mL of Et 2 O.The resulting pale yellow solid was isolated by cannula filtration, washed with an additional portion of Et 2 O (25 mL), and then dried under vacuum.Yield: 0.348 g, 60% yield. 1  [Cl 2 Pd(tptbz)PdCl 2 ], 4. Method A. To a 50 mL Schlenk flask charged with PdCl 2 (0.040 g, 0.22 mmol) was added MeCN (15 mL) via a syringe, and the mixture was heated at ∼70 °C until most solids dissolved.To this mixture was added a solution of [(tptbz)PdCl 2 ] (0.124 g, 0.225 mmol) in CH 2 Cl 2 (15 mL) via a cannula, which induced the immediate formation of a yellow precipitate.Stirring was continued at ambient temperature for 12 h.All volatile materials were removed in vacuo, and the remaining solids were collected as the product (0.165 g, 100%). 1  Method B. In a 50 mL Schlenk flask charged with PdCl 2 (0.112 g, 0.632 mmol), MeCN (10 mL) was added under an active N 2 flow.The mixture was heated to ∼70 °C until most of the solids dissolved, and the solvent was then removed under reduced pressure.Dichloromethane (20 mL) and solid tptbz (0.120 g, 0.320 mmol) were added, and the mixture was stirred at ambient temperature overnight.The solvent was again removed under vacuum, and the yellow solid residue was collected as the product.
[(mnt)Pd(tptbz)], 5. Method A. In a 25 mL Schlenk tube, Na 2 [mnt] (0.042 g, 0.23 mmol) was combined with dry CH 2 Cl 2 (10 mL) under an atmosphere of N 2 .To this mixture, solid [Cl 2 Pd-(tptbz)] (0.104 g, 0.188 mmol) was added along with an additional portion of dry CH 2 Cl 2 (5 mL).The mixture was then stirred at ambient temperature overnight, at which point it was then filtered.The filtrate was reduced to a volume of ∼0.5 mL before being combined with dry MeOH (∼15 mL).The resulting solid precipitate was collected and recrystallized as green plates from dry CH 2 Cl 2 (2 mL) by slow introduction of dry MeOH (50 mL).Yield: 0.0329 g, 0.0530 mmol, 28.1%. 1  Method B. In a 50 mL Schlenk flask, 2 (0.1080 g, 0.1957 mmol) was dissolved in 10 mL of dry CH 2 Cl 2 under an atmosphere of N 2 .To this mixture, solid [(mnt)SnMe 2 ] (0.0577 g, 0.200 mmol) was added under an outward flow of N 2 .While the mixture was stirred at room temperature overnight, it turned dark green.All volatiles were removed in vacuo, and the solid residue was purified on silica chromatography column packed with 1:1 hexanes/CH 2 Cl 2 and eluted with 1:2 hexanes/CH 2 Cl 2 .The product was collected as the leading deep blue band.After the removal of the solvents, the solid residue was crystallized by a layered diffusion of MeOH into a CH 2 Cl 2 solution.Yield: 0.0782 g, 0.126 mmol, 64.3%.
[(mnt)Pt(tptbz)], 6.In a 25 mL Schlenk flask, PtCl 2 (0.1046 g, 0.393 mmol) was combined with MeCN (10 mL) under a N 2 atmosphere and heated until a clear yellow solution was attained.This solution was then cooled to room temperature, whereupon solid tptbz (0.1493 g, 0.398 mmol) was added, and stirring was continued at ambient temperature overnight.The solvent was then removed in vacuo, and the solid residue was redissolved in CH 2 Cl 2 (10 mL).Solid [(mnt)SnMe 2 ] (0.1212 g, 0.419 mmol) was added, and stirring was maintained for an additional 12 h.The reaction mixture was then gravity filtered through paper, and the solid material thus separated was washed with further CH 2 Cl 2 (40 mL).The filtrate was taken to dryness under reduced pressure, and the resulting solid residue was purified on a silica gel column that was packed as a slurry in, and eluted with,  Syntheses and Structures.The tptbz ligand (1; Scheme 2) is attained in good yield from the corresponding 1,2,4,5-tetrachlorobenzene by straightforward reaction with i PrS − Na + in N,Ndimethylformamide 8 or hexamethylphosphoramide. 13 Although this approach is general in leading to arene tetrathioethers, other alkyl thiolates are less conveniently obtained (e.g., MeS − ) or less conducive to the formation of the crystalline material (e.g., n BuS − ).Slow evaporation of an acetonitrile solution of 1 reliably deposited columnar crystals in monoclinic P2 1 /c (no.14) with the central arene ring coincident with a crystallographic inversion center (Figure 2).The S−C arene bond lengths in 1 are ∼0.06Å shorter than the S− C iPr bond lengths, likely reflecting the effect of S p-π arene-π interaction.An earlier structural characterization reported for 1 was conducted at a somewhat higher temperature (200 vs 150 K) than that used here. 14urprisingly little well-defined coordination chemistry has been described with 1,2,4,5-arene tetrathioethers in general, and with tptbz in particular and its simpler homologue 1,2-bis(isopropylthio)benzene, no metal complexes of which we are aware have been reported.As expected for a chelating dithioether, the tptbz ligand shows affinity primarily for soft or borderline soft late transition metals.Thus, when introduced to 1 equiv of tptbz, both PdCl 2 and PtCl 2 are readily coordinated at one end, while NiCl 2 resists binding under the same conditions.Dithioether ligation for Ni 2+ is known, but the majority of well-defined complexes that are known have this donor atom set incorporated within tetradendate 15−17 or macrocyclic hexadentate ligands 18,19 whose kinetic and thermodynamic advantages overcome the otherwise tepid Ni−S thioether interaction.The use of 2 equiv of PdCl 2 in the reaction with 1 equiv of tptbz led to the formation of the dimetallic [Cl 2 Pd(tptbz)PdCl 2 ] (4), as marked by its immediate precipitation due to lowered solubility in consequence of its centrosymmetry.
Compounds 2 and 3 are isostructural (Table 1 and Figure 2) and reveal quite similar bond lengths and degrees of planarity (Table 2).The M−S thioether bond lengths in these complexes are, within experimental resolution, shorter than the M−Cl bond lengths by 0.035 and 0.059 Å for Pd and Pt, respectively.This difference appears to reflect a modest contribution from the chelate effect, as the (Pt− Cl) ave − (Pt−S) ave difference in cis-[PtCl 2 (SMe 2 ) 2 ] is 0.047 Å. 20 A modest difference with no clearly discernible explanation is the S− C isopropyl distance at the metalated end (∼1.86Å) vs the open end (∼1.79Å).Compared to the S−C isopropyl distance in the free tptbz ligand (∼1.83 Å), this difference appears to have equal contribution from S−C isopropyl elongation at the metalated end and S−C isopropyl contraction at the open end.The structure of 4 occurs on an inversion center in triclinic P-1, its unique half being effectively indistinguishable from 2 in all metrical details (Table 2).The intramolecular Pd••• Pd separation of 8.651(1) Å is slightly shorter than the 8.857 Å observed for [Cl 2 Pd(tpbz)PdCl 2 ]. 2 When introduced to [Cu(MeCN) 4 ][PF 6 ] in CH 2 Cl 2 , tptbz forms a 1D cationic coordination polymer (9; Scheme 2 and Figure 2) similar to that formed by hexakis(methylthio)benzene and Cu(I) and Ag(I). 21The intraligand tptbz bond lengths in 9 differ little from those of the free ligand.With the 1,2,4,5-tetramethylmercaptobenzene (tmmb) ligand, Cu(I) halide precursors yield halide-linked 1D or 2D polymers, 22 as well as discrete halide-bridged dimetallic species, 23 instead of homoleptic thioether polymers.
−3,24−29 Thus, [(mnt)Pd-(tptbz)] ( 5) is produced in modest yield (28%) from the heterogeneous reaction between 2 and Na 2 mnt in CH 2 Cl 2 but, as has been our consistent observation, in appreciably better yield (64%) via chloride-for-mnt 2− exchange with [(mnt)SnMe 2 ].The better margins produced by such tin reagents are likely due to the effect of greater homogeneity in the reaction solution.Similar reactions of 3 with [(mnt)SnMe 2 ] and [(pdt)Sn n Bu 2 ] (7) afforded [(mnt)Pt-(tptbz)] ( 6) and [(pdt)Pt(tptbz)] (8).Compounds 5 and 6, as well as their precursors 2 and 3, are indefinitely stable to moisture and air, both in the solid state and in solution.In contrast, while 8 is amenable to purification by column chromatography and to crystallization in the open air, its solutions slowly deteriorate to a dark orange oily material over a period of days if not maintained in the dark under a protecting N 2 atmosphere.Considering the quite extensive body of heteroleptic dithiolene compounds of the group 10 metals, which includes many dithiolene-dithione compounds, 30−33 it  f All values are averages for three independent molecules in the asymmetric unit of the cell.g Because of static disorder afflicting one of the S i Pr groups, this table entry is a single, unaveraged bond length.h θ = angle between S 2 Cu chelate planes.i θ = angle between S 2 , dithiolene M and S 2,dithioether M planes.
is noteworthy that 5, 6, and 8 appear to be first heteroleptic dithiolene-dithioether complexes made by deliberate synthesis.A platinum bis(trifluoromethyl)dithiolene (tfd) dithioether complex, formed serendipitously by the addition of 2 equiv of 2,3-dimethyl-1,3butadiene to [Pt(tfd) 2 ], stands as the only prior example. 34ompounds 5, 6, and 8 retain the near ideal planarity of 2 and 3, as gauged by θ values of ∼3−7°(Table 2).The principal metrical change in the immediate metal ion environment is a substantial lengthening of the M−S thioether bond lengths by ∼0.05 Å compared to the precursor dichlorides (Table 2), which reflects the appreciably greater ligand field strength of the chelating dithiolene ligand.The Pt−S dithiolene bond length in 8 is shorter than that observed in a series of [(pdt)Pt(C�NR) 2 ] complexes by a modest, but significant, amount within experimental resolution, ∼0.01 Å. 35 The comparative binding weakness of tptbz that is implicated by this difference is borne out in the finding that 8 is not directly accessible from [(pdt) 2 Pt] by dithiolene displacement with tptbz, though such an approach is efficacious for the synthesis of a range of other heteroleptic dithiolene complexes of the group 10 metals. 33,35,36n the crystalline state, the packing arrangement for isostructural 5 and 6 is such that the square planar molecules form orderly, columnar stacks that arrange approximately along the a-axis of the monoclinic cell (Figure S23).Compound 8, however, occurs in triclinic P-1 with an atypical three full molecules in the asymmetric unit such that Z = 6.The disposition of these separate molecules relative to one another is not simply described, as they are not coplanar or mutually orthogonal or related by any pseudosymmetry operation.Rather, the planes defined by their PtS 4 coordination cores form angles of ∼56°, ∼64°, and ∼67°with one another that appear to be guided by intermolecular S thioether •••S thioether close contacts (Figure S24).Distances of 3.414 Å separating S(4) of molecule 1 from S(10) from molecule 2 and 3.508 Å between S(9) of molecule 2 and S(15) of molecule 3 are less than twice the crystallographic van der Waals radius for sulfur (1.8 Å) 37 and suggest that soft−soft dispersion-type forces may be operative in the crystal packing.Furthermore, C−H••• arene centroid hydrogen bonding contacts likely play an additional role in dictating the packing, as seen in the pair of H-bonds that relate molecule 3 of compound 8 to its inversion counterpart (Figure S25).
Electrochemistry and Electronic Structure.The tptbz ligand sustains a reversible oxidation at +0.73 V vs Fc + /Fc (Figure 3, top) because the four thioether sulfur atoms collectively impart appreciable π-electron density to the arene ring.The oxidation potential for this ring system, when it is implemented as a chelating ligand, is anticipated to shift to higher potential owing to the diversion of two sulfur lone pairs in σ donation to a metal cation.
For [(mnt)Pd(tptbz)] ( 5) and [(mnt)Pt(tptbz)] ( 6), the nearly ∼3.5 V potential window that is accessible in CH 2 Cl 2 reveals a single oxidation wave that is reversible in appearances for 6 at +0.94 V vs Fc + /Fc (Figure 3, middle) but only quasireversible for 5 at +1.00 V (Figure S47).Upon reversal of the scanning potential, 5 reveals a minor current maximum at +0.71 V, which, owing to the absence of a comparable feature on the initial anodic pass, is attributable to decomposition product forming on the timescale of the oxidative scanning.These oxidation processes for 5 and 6 are ene-1,2-dithiolate to radical monoanion oxidations (Scheme 1, (a) → (b)), as confirmed by the DFT calculation (Figure S49).The ∼0.06 V milder potential for the oxidation in 6 vs 5 likely is due to a greater degree of the modest metal d character that is mixed into this largely ligandbased HOMO.In the cathodic direction, 5 and 6 reveal irreversible reduction processes that are of a qualitatively similar irreversible appearance but positioned at quite different potentials.The cathodic current maximum for this wave occurs at −2.17 V for 6 vs −1.40 V for 5(Figure S48).The LUMOs for 5 and 6, which are the expected Md x 2 −y 2 S-p σ* interaction, reflect this difference in reduction potentials by their energies relative to the HOMO.The HOMO−LUMO gap calculated for 6 in the gas phase exceeds that for 5 by more than 0.5 eV.The higher energy for this σ* MO in 6 is fully in accordance with the greater ligand field strength for the third row metal vs its second row counterpart.For both 5 and 6, irreversibility upon reduction likely is due to dissociation of the tptbz ligand.
Spectroscopically, the generation of [8] + by a controlled-potential one-electron oxidation is attended by the onset of broad, low-energy absorptions at ∼692 and ∼865 nm that likely conceal the presence of multiple unresolved excitations (Figure 4).Subsequent one-electron oxidation to [8] 2+ at a higher potential induces the disappearance of these features.A TD-DFT simulation of this absorption spectrum points to the contribution of multiple transitions to these low-energy features, most of them involving the [Ph 2 C 2 S − S • ] 1− -based SOMO as the acceptor (Figure S50).The lowest-energy absorption is described most simply as an intraligand excitation from the π-systems of the Ph substituents, with a minor admixture of metal 5d character, to the C 2 S 2 fragment of the ligand.
To assist the interpretation of the second oxidation process observed for 8, calculations were undertaken upon [(pdt)Pt(tptbz)] 2+ as a closed shell singlet, where the second oxidation is dithiolene based and produces the α-dithione form of the ligand, as a triplet with one spin on each ligand, and as a singlet diradical (broken symmetry) with an unpaired electron on each organic ligand but with opposite spin.Of these several scenarios, the closed shell singlet arising from successive oxidation of [Ph 2 C 2 S 2 ] 2− to the dithione is assessed as modestly lower in energy by ∼0.5 kcal/mol than the open shell singlet diradical, and the desired triplet state is the highest energy configuration by ∼7 kcal/mol.Regardless of the net spin state, a dicationic form of [(pdt)Pt(tptbz)] that could be formulated as [(Ph 2 C 2 S − S • )Pt 2+ (tptbz •,+ )] 2+ is fundamentally interesting from the perspective of materials engineering and the potential for insight into how physical properties might be tailored with better control.
One suggestion arising from the electrochemistry depicted in Figure 3 is that oxidations from each of the two different organosulfur ligands might be observable if either the aromatic dithioether ligand is made more electron rich or the phenyl dithiolene ligand is rendered more electron deficient such that its second oxidation to the dithione ((b) → (c), Scheme 1) is disfavored relative to radical cation formation in the tetrathioarene ring.The known 1,2,3,4,5,6-hexakis-(isopropylthio)benzene, C 6 (S i Pr) 6 , is a plausible candidate as more electron rich relative to tptbz and is prepared by a similar route.However, the oxidation potential found for C 6 (S i Pr) 6 is nearly identical to that found for tptbz (Figure S46).That C 6 (S i Pr) 6 is not more easily oxidized in proportion to its greater number of pendant sulfur atoms is possibly due to steric crowding of the S i Pr substituents around the ring periphery such that optimal S p-π arene-π overlap is impeded.The greater value of δ for C 6 (S i Pr) 6 vs tptbz (Table 2) aligns with this supposition.
Complexes featuring polychlorophenyl-substituted dithiolene ligands have not been reported, but they are likely accessible via the same benzoin/P 4 S 10 route that has been implemented to prepare [Ni(S 2 C 2 (C 6 H 4 -p-Cl) 2 ) 2 ] 38,39 and other complexes with arenesubstituted dithiolene ligands.We have computationally investigated the 3,5-dichlorophenyl analogue of 8 for its effect in drawing downward in energy the dithiolene-based C 2 S 2 −HOMO and making the tptbz-based ligand competitive as the site of a second oxidation.Figure 5 illustrates the frontier MOs in the structures of gas-phase optimizations of both [(pdt)Pt(tptbz)] + and [(Cl 2 -3,5-pdt)Pt-(tptbz)] + .In [(pdt)Pt(tptbz)] + , the MO housing the dithiolene radical is ∼1.72 eV higher in energy than the tptbz-based HOMO−1 (Figure 5, left), but in [(Cl 2 -3,5-pdt)Pt(tptbz)] + , while the qualitative ordering is the same, the energy difference is substantially narrowed to ∼0.13 eV (Figure 5, right).This outcome suggests that, in [(Cl 3 -2,4,6pdt)Pt(tptbz)] + , where the number and placement of chlorine substituents are such as to further lower the dithiolene-based MOs, successive one-electron oxidations would occur on the opposing dithiolene and dithioether ligands.

Figure 2 .
Figure 2. Thermal ellipsoid plots (50% ellipsoids) of selected compounds characterized by X-ray diffraction.For clarity, all H atoms are omitted, and disorder in the alkyl groups of 5 and 7 is not shown.

a
Uncertainties are propagated according to Taylor, J. R.An Introduction to Error Analysis; 2nd ed.; University Science Books: Sausalito, CA, 1997, pp 73−77.The square bracket represents the uncertainties propagated in the averaging of chemically identical values.b δ = mean displacement of S atoms from the C 6 arene plane.c σ = range of S atom displacements from the C 6 arene plane.d θ = fold angle between S 2 Sn and S 2 C 2 planes.e θ = angle between Cl 2 M and S 2 M planes.

Table 1 .
Unit Cell Refinement Data for Crystallographically Characterized Compounds a refl.coll.= total reflections collected.