Journal of the American Chemical Society
6264
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October I O , I979
Synthesis, Crystal Structure, and Properties of the Hexa(p-benzenethiolato)tetra( benzenethiolatocobaltate(11)) Dianion, the Prototype Cobalt(11)-Thiolate Molecular Cluster Ian G . Dance Contributionf r o m the School of Chemistry, Unicersity of New South Wales, Kensington, New South Wales 2033, Australia, and the Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706. Received March 13, 1979
Abstract: The complexes [(p-SPh)6(CoSPh)412-, [(~-sPh)6(Cosph)2(C0Cl)*]~-, and [Co(SPh)4I2- have been synthesized with Me4N+ and other cations, and the crystal structure of (Me4N)2[(p-SPh)6(CoSPh)4] has been determined. C r p t a l data fol1ow:a = 13.031 ( 2 ) A , b = 2 3 . 5 9 0 ( 4 ) A , c = 1 2 . 8 0 6 ( 2 ) A , a = 9 2 . 2 8 ( 1 ) 0 , f l = 115.04(1)o,y = 7 9 . 1 2 ( 1 ) ' . P l , Z = 2, 5121 observed reflections ( M o K a ) , R = 0.034. The [(p-SPh)6(CoSPh)4I2- molecular cluster contains a tetrahedron of cobalt(l1) atoms (Co-co 3.87 i 0.02 A) within an approximate octahedron of benzenethiolate ligands which bridge the edges of the Co4 tetrahedron. One terminal benzenethiolate ligand completes the pseudotetrahedral (p-SPh)j(SPh) coordination of each cobalt atom. Principal features of the structure and bonding follow: (a) the bridging thiolate groups maintain the cluster structure, but without angular rigidity such that the T d symmetry possible for the Co4S1o core is only approximate; (b) there is no evidence of direct Co-Co bonding, but indirect electronic coupling between cobalt atoms influences the magnetic susceptibility and the S+Co charge-transfer absorption; (c) charge-transfer spectral regions indicative of bridging benzenethiolate are described; (d) Co-Sterminal= 2.258 f 0.004 A, Co-Sbr;dging= 2.322 f 0.01 1 A. Spectrophotometric data are presented on the equilibrium sequence of species: [Co(SPh)z], (molecular structure) + [(p~-SPh)6(CoSPh)4]~- [ ( p SPh)2(Co(SPh)2)212[Co(SPh)412-. The benzenethiolate bridges of the {(p-SPh),jCodI cluster core are relatively stable (thermodynamically) to bridge-opening reactions, including hydrolysis.
reactions, drying and purification of normal laboratory reactants were found to be unnecessary, and they were used as received. The thiolate The monothiolate (mercaptide) group RS- is a fundamental anions were generated by in situ deprotonation of the thiols. The monodentate ligand type, but its coordination chemistry is charge of the deprotonating agent should be zero rather than negative, in order to decrease the coordinating ability of the deprotonating agent poorly developed in comparison with that of other elementary relative to that of the thiolate ligand in aprotic or partially aprotic ligand types. The object of our research program is exploration solvent systems. Thus tertiary amine bases are more satisfactory than of the syntheses, geometrical structures, electronic properties, hydroxide or alkoxide ions, and have been used. Inhibition of metaland reactivities of metal complexes containing only (or at least amine coordination is effected sterically, and is adequate in triethylpredominantly) the monothiolate ligand. Elucidation of Limine and higher trialkylamines. A useful isolatable source of the properties intrinsic to thiolate coordination requires the utilibcn7enethiolate ion as ligand is the crystalline acid-base complex zition of the simple monodentate RS- group and avoidance formed by dicyclohexylamine and benzenethiol. Benzenethiol ( 1 0 mL) of chelating ligands incorporating thiolate functions. in acetonitrile (40 mL) was added to dicyclohexylamine (18 mL) in Binary complexes of many metals with monothiolate ligands acetonitrile (300 mL) flushed with dinitrogen. The resulting white, crystalline precipitate was filtered, washed with acetonitrile, and have been encountered in conventional protic media as very vacuum dried. This complex is very soluble in chloroform, dichloroinsoluble compounds,l-4 generally reputed to be intractable, methane. and alcohols. and presumed (but rarely demonstrated5) to be structurally Thc metal-thiolate complex formation equilibria depend strongly nonmolecular with thiolate bridges. Thus Bradley and Marshh on solvent properties and solution temperature: metal-thiolate assoin a limited survey of the mercaptides of cobalt, nickel, copper, ciation is favored by aprotic solvents and reduced temperatures. and 7inc did not obtain recrystallizable compounds (except for Success in crystallization of salts of anionic metal-thiolate complexes Ni(SAm-n)?'). Williams et a1.,8 endeavoring to form low with inert cations (not the trialkylammonium conjugate acid of the molecular weight cobalt ( I I ) complexes of thioglycollate and deprotonating reagent) often depends on a balance between two opcysteine in aqueous media, encountered polymerization. posing factors. One is the desirability of aprotic solvents to promote the complex formation equilibria, and the other is the utility of alcohols There are several reasons for anticipating the occurrence in adjusting solubility for good crystal growth. of a broad range of metal-thiolate complexes with a variety In view of the partial dissociation of benzenethiolate-cobalt( I I ) of structures. Guided by consideration of the significant coniplcxes. particularly in protic solvents, recrystallization of isolated thermodynamic influences of solvation in synthetic procedures products does not always achieve purification or permit crystal growth. with anionic ligands, we have successfully crystallized anionic control of the preparative mixtures was frequently the precomplexes, [M,(SR)?.] z - , for the metals C O ( I I ) ,C~ U ( I ) , ' ~ - ' ~ Carcful fcrrcd method for grohth of well-formed. uncontaminated crystals. Ag(1),1',13 Zn(1l),l3 Sn(lV),I4 and O M O ( V ) . ~ ~Reported .'~ All operations &ere performed in an atmosphere of dinitrogen. here are details9 of the formation and properties of the struc(hle4NizCo4(SPh)lo.Benzenethiol (3.3 g. 30 mmol) and triethylturally molecular complex [Coq(SPh)lo]'- and the related :imine (3.0 g, 30 minol) were dissolved in acetonitrile (70 mL). iZ complexes [ C O J ( S P ~ ) ~ C I ~and ] ' - [Co(SPh)4I2-. The specsolution of C o ( N O ~ ) ~ . 6 H (2.9 z 0 g, I O mmol) in absolute ethanol (80 mL) at ca. 40 "C was added during several minutes, followed by adtroscopic and structural properties of [ C O ( S P ~ ) , ] ~have - been dition of a mlution of MeJNCl (4.0 g. 36 mmol) in boiling methanol descri bed. I (30 mL). The resulting dark broMn solution was maintained undisat 0 OC for 48 h, while the dark brown-black crystals developed. turbcd Experimental Section Thc crystals were filtered. Mashed with 2-propano1, and vacuum dried, The reagent grade thiols, amines, and solvents used in the solution nip (scaled tube) 204 "C dec. Anal. Calcd for CojSloN~Ch8H74:Co. I.i,97;S.21.73;N, 1.9O:C.55.35: H, 5.05, Found:Co, 15.94:S.22.20: spcctral measurements were distilled from appropriate drq ing agents and stored over molecular sieves. For the purposes of the synthetic N. 1.82:C.55.60;H. 5.17. (MeJN)ZCo4(SPh)toisreadil). solublein
Introduction
0002-78631791 IS01-6264$01 .00/0
0 1979 American Chemical Society
1kitic.e
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Molecular Cobalt(l1)-Thiolate Clusters
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acetone, acetonitrile, and DMF, producing intensely orange-brown solutions. It is slightly soluble in methanol and insoluble in higher alcohols and chloroform. In solution it is not hydrolyzed by water at room temperature, but it is subject to rapid oxidation by dioxygen producing a totally insoluble, dark maroon powder. It dissolves in neat or dilute pyridine to give an uncharacterized green solution, and forms [Co(SPh)4]*- on treatment with PhSH plus R3N. ( ( C ~ H ~ I ) ~ N H ~ ) ~ CBenzenethiol O ~ ( S P ~ ) (3.3 ~ ~ . g, 30 mmol) and dicyclohexylamine (5.4 g, 30 mmol) were dissolved together in ethanol (100 mL). Addition of a solution of Co(hO3)2.6H20 (3.7 g, 12.7 mmol) in ethanol (40 mL) generated an intensely brown solution and precipitated colorless crystals (presumably (CbH I I ) ~ K H ~ + N O ~ - ) . Slow addition of water caused these crystals to redissolve and initiated separation of the product as black crystals, which after filtration were washed with uater and vacuum dried, yield 4.6 g (85%). Anal. Calcd I'or C O ~ S I O Y > CC~, ~59.63; H ~ ~H :, 5.84: N, 1.66; S, 18.95. Found: C, 58.75: H. 5.81: N. 1.74;s. 15.0.19 (Me4N12Co(SPh)4.Benzenethiol (3.5 g, 32 mmol), tri-n-butylamine (4.5 g, 24 mmol), and tetramethylammonium chloride (2.2 g, 20 mmol) were dissolved together in methanol (70 mL). Co(N03)2-6H>O (1.0 g. 3.4 mmol) in methanol (10 mL) was added, followed bi l propanol (50 mL). and the emerald green solution stored at 0 "C while Figure 1. The [(p-SPh)6(CoSPh)4l2- cluster, showing atom labeling crystallization occurred. The separated product was washed with ?-propanol and vacuum dried. Anal. Calcd for C O S ~ N ? C ~C.~ H ~ ~ : Crystallography. (Me4N)zCo4(SPh)lo.The diffraction crystal was 59.69: H, 6.89; S, 19.92. Found: C , 58.48: H , 6.77: S, 20.01. The selected from the preparative reaction product and sealed in a cnierald green crystals are soluble in polar aprotic solvents, without Lindeman capillary. It was bounded by the forms {OlOl, { l o l l , and appreciable ligand dissociation. They are slightly soluble in the lower (001I, with the perpendicular distances between pinacoid faces equal alcohols. giving brown solutions indicative of benzenethiolate dissoto 0.24, 0.28, and 0.44 mm, respectively. The X-ray diffraction data ciation to yield [ C O ~ ( S P ~ ) , ~ ] ~ - . were obtained with a Syntex PI four-circle diffractometer equipped (Et4N)zCo(SPh)4.Benzenethiol (8.8 g, 80 mmol) and triethylamine with a graphite monochromator, using M o Kcu radiation. The unit cell (8.4 g, 83 mmol) were dissolved in acetonitrile (70 mL). Coparameters were determined and refined by least squares from 1 5 (N03)2*6HzO(4.0 g, 14 mmol) in ethanol (50 mL) was added, folaccurately centered diffraction maxima: a = 13.031 (2) A, b = 23.590 lowed by tetraethylammonium bromide (10 g, 48 mmol) in ethanol ( 4 ) A , c = 12.806(2)~.cu=92.28(1)0,p=l15.04(1)o,y=79.12 (50 mL). After addition of I-propanol (30 mL) the green solution was slowly pumped with stirring at room temperature to initiate crystal( 1 )". lization of the emerald green crystals. The separated product was Axial oscillation photographs did not reveal any lattke symmetry, washed with 2-propanol and vacuum dried. Anal. Calcd far and the assumed occurrence of space group PI containing CoS4N2C40H60: C , 63.54; H, 8.00; S, 16.96. Found: C. 63.13: H, 7.94; (Me4N)*Co4(SPh)lo per asymmetric unit was confirmed by the ~ , = I .40 successful structure refinement: dcalcd = I .40 g c ~ n - d&d S, 17.18. g~ m - ~ . (Me4hl2Co4(SPh)&l2. A mixture of benzenethiol (3.5 g, 32 mmol) Intensity data (293 K ) were collected by the 8/28 scan technique, and triethylamine (3.1 g, 31 mmol) in acetone (60 mL) and tetrawith variable scan rates (2-24"/min). Two standard reflections methylammonium chloride (3.2 g, 29 mmol) in methanol (60 mL) monitored every 50 measurements showed no significant change in was prepared at room temperature. To this solution was added a sodiffraction intensity. A total of 6709 intensity observations were relution of C O ( ~ O ~ ) ~ (6.0 . ~ Hg, ~21O mmol) in methanol (60 mL), corded. Rith 28 < 40". Crystal absorption ( f i = 12.95 cm-') was asproducing an intensely green solution. Crystallization of the product (which can be initiated by slight heating) was allowed to continue for sessed empirically from the intensity variation during stepped complete rotation of the crystal about the diffraction vector. The transmission 4 h. The black, microcrystalline product was filtered, washed with 1 -propanol, and vacuum dried. Anal. Calcd for C O ~ S ~ C I Z N ~ C ~factor ~ H ~for ~ :F varied by less than 496, and absorption corrections were C, 50.64; H, 4.86; N , 2.1 I ; S, 19.31. Found: C, 49.21: H, 4.83; N, 2.1 5 ; not made. After exclusion of 1197 unobserved reflections ( I < 2 4 1 ) ) the data set consisted of 5121 symmetry-independent observed reS, I 5.0.19This formulation of this compound is not evident from the flections. available analytical data,I9 but was confirmed by the fact that it is isostructural (see supplementary Table I ) with the zinc analogue, The Patterson function21 revealed the tetrahedron of four cobalt which has been fully characterized by crystal structure determinaatoms. Successive Fourier syntheses, including one in space group P I tion.13 (Me4N)2C04(SPh)&12 was previously9 formulated incorrectly to improve the positions of the heavier atoms, permitted location of 311 nonhydrogen atoms. The least-squares refinement followed the a s (Me4N)2Co4(SPh)6Cl4. normal sequence of introduction of atom parameters. Hydrogen atoms Reaction mixtures similar to the above, but with small variation in the amount of Me4NCI or of aprotic solvent, have yielded products (Bise = 8.0 A2) were introduced a t calculated positions (H3C-NC3 with polycrystalline diffraction patterns different from that of conformation staggered), and the structure was checked with a dif(Me4N)zCo4(SPh)&l2. In the absence of full structure determination ference synthesis. The final least-squares refinement cycle was full these compounds are not formulated unambiguously; further invesmatrix for all parameters other than those of hydrogen, which were tigations are in progress. not refined. In the calculation of estimated errors in interatomic dis( M Q N ) ~ C O ~ ( S P ~is) soluble ~ C I ~ in acetonitrile and (to a lesser tances and angles the complete variance-covariance matrix for all extent) in acetone. Attempted recrystallization from acetonitrile/ parameters was employed. In the final difference synthesis all electron propanol did not improve crystal quality. In solution it is rapidly oxdensity was less than 0.4 e A-3. The scattering factors (neutral atom) idized by dioxygen to the maroon-black, insoluble product mentioned were those of Hanson et al.22afor nonhydrogen atoms and of Stewart above. et for hydrogen. Anomalous dispersion correction^^^ were inPhysical Measurements. Magnetic susceptibilities were measured cluded for cobalt and sulfur: R = 0.034, R, = 0.043, ((ZwlAFI2)/ on a Faraday balance with Nl(1) cryostat. Electronic spectra were (117 - n ) ) ' / ' = 1.20, m = 5121 data, n = 757 parameters. Atom larecorded with Cary 14 and Cary 17 spectrophotometers. Solutions beling for the [Co4(SPh),0l2- cluster is shown in Figure 1. The phenyl were prepared, and the cells filled, with rigorous deoxygenation using ring atoms on S ( n ) are C(nm), m = 1-6 (C(nl) bonded to S ( n ) ) ;the syringe/rubber septa transfer techniques. Reflectance spectra were hydrogen atom on C(nm) is H(nm). The Me4Nf atoms are N@), p obtained from powder samples smear-pressed into coarse filter paper = I, 2; C(qNp), 4 = 1-4; H@qr), r = 1-3. and mounted over the port of the integrating sphere; dilution of the Final atom coordinates and their estimated standard deviations are absorbing powder was easily achieved by further smearing. Polyset out in Table I for the nonhydrogen atoms. Complete listings of crystalline diffraction data (Co Ka radiation) for identification position parameters for the hydrogen atoms, and a summary of the purposes are provided in supplementary Table 1.20 atom thermal motion appear with the supplementary material.20
Journal of the American ChemicalSociety
6266 Table I. honhydrogen Atom Coordinates for
101:21
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October 10, 1979
(Me4N)*[(p-SPh)h(CoSPh)d] I0
9401.4 (6)O 6224.3 (6) 7730.6 (6) 6948.1 (6) 7196 ( I ) 9477 ( I ) 6378 ( I ) 8645 ( I ) 7949 ( I ) 5544 ( I ) 6419 ( I ) 5145 ( I ) 11101 ( I ) 7780 ( I ) 5930 (4) 5677 (5) 4726 (6) 4048 (5) 4300 (5) 5238 (5) 10581 (4) 10359 (5) I1249 (6) 12354 (6) 12558 (5) 11680 (5) 6859 (5) 6098 (5) 6466 (6) 7554 (6) 8303 (6) 7952 (5) 9734 (4) 9903 (5) I0771 (5) 11435 (5) 11271 (6) 10421 (6) 8481 (4) 9316 (5) 9755 (5) 9386 (61
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7410.7 ( 3 ) 8202.9 (3) 7253.8 (3) 6538.1 (3) 6452 ( 1 ) 7334 ( I ) 8084 ( I ) 6683 ( I ) 8161 ( I ) 7374 ( I ) 5722 ( I ) 9031 ( I ) 7394 ( I ) 7010 ( I ) 6295 (2) 5746 (2) 5604 (3) 5993 (3) 6526 (3) 6684 (2) 6725 (2) 6251 (2) 5781 (2) 5793 (3) 6270 (3) 6736 (3) 8717 (2) 9242 (2) 9743 ( 2 ) 9723 (3) 9201 (3) 8702 ( 2 ) 6050 (2) 5708 (2) 5215 (3) 5059 (3) 5402 (3) 5896 (3) 8820 (2) 8914 (2) 9419 (3)
4 ~
atom
- 1520.9 (6) -25 14.0 (6) 291.5 (6) -2672.6 (6) -765 ( I ) 306 ( I ) -652 ( I ) -2696 ( I ) -2647 ( I ) -3334 ( I ) -3541 ( I ) -3537 ( I ) -1604 ( I ) 2001 ( I ) -722 (4) -1005 (5) -916 (5) -532 (5) -254 (5) -340 (5) 1025 (4) 1433 (5) 1953 (5) 2067 (5) 1684 (6) 1173 (5) 39 (4) -300 (5) 214 (6) 1050 (6) 1402 (6) 868 (5) -2183 (4) -1268 (5) -903 (5) -1488 (6) -2397 (7) -2743 (6) -2279 (4) -2612 (5) -2324 ( 6 ) -1716 ( 6 )
1 0 4 ~
8563 (7) 8107 (6) 5036 (4) 5645 (5) 5 189 (6) 41 18 (6) 3505 (5) 3961 (5) 65 I3 (5) 7497 (6) 7531 (8) 6573 (9) 5584 (7) 5560 (5) 3665 (5) 2839 (6) 1677 (6) 1321 (6) 2 I22 (6) 3288 ( 5 ) I I779 (4) I 1352 (5) I1903 (5) 12891 (6) I3327 ( 6 ) 12782 ( 5 ) 8716 (4) 9530 (5) 10222 (5) 10134 ( 6 ) 9351 (5) 8651 (5) 6313 (5) 7436 ( 1 3) 6204 (9) 5494 ( I 3) 6296 ( 1 5) I2559 (4) I2787 (7) 13272 (7) I 1343 (6) 12853 (8)
I0
4 ~
9724 (3) 9222 (3) 7482 (2) 7199 ( 2 ) 7260 (3) 7596 (3) 7874 (3) 7821 (2) 571 I (2) 5744 (3) 5746 (3) 5710 (3) 5654 (4) 5658 (3) 9080 (2) 9355 (3) 9423 (3) 9209 (3) 8929 ( 3 ) 8861 (3) 7940 (2) 8286 (2) 8731 (2) 8821 (3) 8474 ( 3 ) 8042 (3) 7337 (2) 7635 (2) 7888 (3) 7832 (3) 7523 (3) 7282 (2) 8951 ( 2 ) 9083 (6) 8548 (5) 9427 (5) 8633 (7) 6305 (2) 6580 (4) 5718 (3) 6268 (3) 6640 (3)
I0
4 ~
-1398 (8) - 1677 (6) -4853 (4) -5444 (5) -6631 (5) -7245 (5) -6663 (5) -5470 (5) -4889 (5) -4974 (7) -6058 (8) -7016 (7) -6962 (6) -5896 (5) -3888 (5) -4913 (6) -5185 (6) -4429 (6) -3428 ( 6 ) -3149(5) -776 (4) -92 (5) 509 (5) 448 (6) -206 (6) -817 (5) 3192 (4) 3 I72 (4) 4143 (5) 5182 ( 5 ) 5217 (5) 4249 (5) 3483 (4) 3985 ( I 6) 2540 (9) 3129 (14) 4316 (12) -4572 (4) -3476 (7) -4367 (8) -5169 (6) -5314 (7)
‘’ Estimated standard deviations in parentheses refer to the least significant digit quoted (Me4N)zCo(SPh)4.Oscillation and Weissenberg photography indicates space group P41212, with a = 10.34 8, c = 32.75 ..&, Z = 4, dcdlcd= I .22 g d&d = 1.26 g ~ m - Therefore ~ . the cobalt atoms must be separated by at least 8 8,and the molecular [Co(SPh)4I2units possess C2 point symmetry.
Results Synthesis. Mixtures in nonaqueous solvents of cobalt(I1) salts and benzenethiol, in the presence of hindered tertiary amine as deprotonating agent, readily yield a sequence of soluble cobalt(I1)-benzenethiolate complexes. It is significant that throughout the full range of PhS-/Co2+ molar ratios (0--) there is no evidence of any compound with very low solubility in the acetonitrile and/or alcohol solvent systems employed. Evidently all cobalt(I1)-benzenethiolate complexes have molecular structures, a t least in solution. This general solubility of cobalt(I1)-benzenethiolate complexes contrasts with the absence of any detectable solubility for their common oxidation product. The two complexes that can be formed in solution with high equilibrium concentration in solution are emerald-green [Co(SPh)4I2- and intense-brown [Co4(SPh)10l2-. In acetonitrile solution a t room temperature [Co(SPh)412- is the principal species when the PhS-/Co2+ ratio is greater than ca. 4, while [Co4(SPh),0l2- predominates when this ratio is less
than ca. 3 . Dark green solutions are formed when PhS-/Co2+ < ca. 2 and C1-/Co2+ 2 ca. 2 . A single experiment in which CoC12 is added to benzenethiol plus equimolar triethylamine, i n acetonitrile forms, in sequence, [Co(SPh)4I2-, then [Co4(SPh) lo]*-, then the dark green solution. One component of the dark green solution is [Co4(SPh)&l2l2-; other components, a t least one of which can be isolated, are not fully characterized. All three anionic complexes can be crystallized as Me4N+ salts from these preparative solutions. Other ammonium cations can be used. Crystallization of the dicyclohexylammonium salt of [Co4(SPh)1ol2- can be achieved by addition of water to a preparative mixture containing (C6H1,)2NH as base, thereby demonstrating the hydrolytic stability of [Co4(SPh)10l2-. Molecular Structure. Determination of the crystal structure of ( M ~ ~ N ) ~ C O ~ ( has S P revealed ~ ) I O the molecular structure of the [Co4(SPh) cluster, shown from different viewpoints in Figures 1 and 2 . The cluster is shielded over most of its periphery by the ten phenyl groups, and is bound in the crystal lattice only by weak interactions. The cluster contains four cobalt atoms located at the vertices of an approximate tetrahedron, with six benzenethiolate ligands (S(1 ) to S(6)) bridging along the edges of the tetrahedron and four benzenethiolate ligands terminally bonded one
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Molecular Cobalt(II)- Thiolate Clusters
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Table 11. Sclccted Interatomic Distances and Anglesu in (Me4N)2[(pL-SPh)6(CoSPh)4] Sterminal-CO-Sbridging S(9)-CO( I)-S(2) 116.00 (5) S(9)-cO( I)-s(4) 104.53 (6) S(9)-co( I)-S(5) 113.34 (6) 118.01 (6) S(8)-Co(2)-S(3) S(S)-Co(2)-S(5) 102.38 (6) S(8)-Co(2)-S(6) 1 14.02 (6) S( IO)-C0(3)-S( I ) 101.59 (6) S(1 o)-co(3)-s(2) 116.06 (6) S( 1 O)-co(3)-s(3) 114.62 (6) 107.64 (6) S(7)-C0(4)-S( I ) S(7)-C0(4)-S(4) 1 1 1.94 (6) S(7)-C0(4)-S(6) 115.61 (6) mean Stermlnal-Co-Sbridging 1 1 1.3 f 5.8”
Co-stermni Co( I)-S(9) 2.254 (2) Co(Z)-S(S) 2.263 (2) Co(3I-S IO) 2.256 (2) Co(4)-S(7) 2.259 (2) mean CO-S,,~,,,,~,I2.258 f 0.004’ Co-Sbridging Co( I)-S(Z) 2.312 ( I ) Co( I)-S(4) 2.316 ( I ) Co( I )-S(5) 2.330 ( I ) CO(2)-S(3) 2.331 (2) Co(Z)-S(S) 2.309 (2) 2.328 ( I ) Co( 2) -S(6) CO(3)-S( I ) 2.320 ( 1 ) CO(3)-S( 2) 2.312 (2) Co(3)-S(3) 2.342 ( I ) Co(4)-S( I ) 2.336 (2) Co(4)-S(4) 2.31 I (2) Co(4)-S(6) 2.326 ( I ) mean Co-Sbrldglng 2.322 f 0.01 I mean S-C,, 1.776 i 0.01 I
Sbridging-CO-Sbridging S(2). Co(I)-S(4) 1 13.30 (6) S(4)-Co( I)-s(5) 95.54 (5) 1 12.07 (5) S ( S ) - c o ( 1 )-S(2) 1 15.29 (5) S(3)-Co(2)-S(5) S(S)-Co(Z)-S(6) 106.41 (5) S ( ~ ) - C O ( ~ ) -3) S( 100.64 (5) S( I)-Co(3)-S(2) 106.10 (6) S(2)-Co(3)-S(3) 108.28 (6) S( 3)-Co( 3)-S( I ) 109.53 (5) S( l)-C0(4)-S(4) 109.53 (5) S(4)-Co(4)-S(6) 110.24 (5) S(6)-Co(4)-S( I ) 101.20 (5) mean Sbridglng-Co-Sbridging 107.3 f 5.8’
’
mean C-C (ring) 1.377 & 0.0146 mean N-C (cation) 1.43 f 0.06’
mean CO-Sbridgjng-CO 1 12.8 i 1 . 1 Nonbonding Distances co-co
Sbridging-Sbridging
Co( I)-Co(2) 3.881 ( I ) C O ( I)-CO(3) 3.862 ( I ) Co( I ) - c o ( 4 ) 3.858 ( I ) CO(2)-CO(3) 3.845 ( I ) Co(2)-C0(4) 3.880 ( I ) c0(3)-c0(4) 3.894 ( I ) mean Co-Co 3.870 f 0.0186
mean
Sbridging-Sbridging
3.702 (2) 3.807 (2) 3.196 (2) 3.602 (2) 3.712 (2) 3.866 (2) 3.850 (2) 3.919 (2) 3.584 (2) 3.440 (2) 3.805 (2) 3.713 (2) 3.74 i 0. 146
’
(I Distances in ingstroms, angles in degrees. Estimated standard deviations in parentheses refer to the least significant digit quoted. Estimated jtandard deviationbf the sam&.
on each cobalt atom. The cluster is thus formulated as [(pS P h ) , j ( c ~ S P h ) d ] ~ -The . Co(p-SPh)3(SPh) coordination is approximately tetrahedral a t each cobalt atom. The complete cluster possesses no crystallographic symmetry, nor any approximate symmetry. Details of the dimensions of the cluster may, however, be considered with reference to an obvious idealization of the structure. Disregarding the phenyl rings, the C04S10 core can be idealized as possessing Td point-group symmetry: the four cobalt atoms are arrayed as a tetrahedron, the six bridging sulfur atoms as an octahedron, and the four terminal sulfur atoms as an outer tetrahedron. The cluster can be idealized further, without increase in symmetry, by requiring all interatomic angles a t the cobalt and bridging sulfur atoms to be 109.5’. Selected dimensions of the CodSlo core, relating to these idealizations, are presented in Table 11. The following points can be made about the geometry of this core: (a) The C04 polyhedron is effectively the idealized tetrahedron. (b) The (Sbr)6 polyhedron is strongly and irregularly distorted from the idealized octahedron. (c) This distortion is not due to variations in Co-S distances, nor to significant variations in
the co-sbr-co angles, but arises in variations in the St-CO-sbr and Sbr-CO-Sbr angles. (d) The angular distortions are most pronounced in the atom sequence S(8), C0(2), S ( 5 ) , Co( I ) , S(4), S(9). The question then arises as to whether these distortions result from interion packing forces in the lattice. There are no unusually short interion contacts (see supplementary materia120), and no close approximately parallel phenyl rings, to which specific cluster distortions could be attributed. Therefore it is concluded that the [ ( ~ - S P ~ ) ~ ( C O S P ~ ) ~ ] ~ cluster i s angularly floppy. A similar conclusion was reached in connection with the more compact [ (pSPh)&u4] 2- cluster and the hypothetical [ ( p S P h ) 1 & ~ 8 ] ~cluster.I0 The cluster displays several regular geometrical characteristics. The cobalt atoms are displaced slightly outward along the pseudo-threefold axes. This displacement is manifest in the mean values of angles, s&o-sb, (1 1 1.3’) > S b r - C O - S b r (107.3’), and of distances, co-CO (3.87 A) > S b r - S b r (3.74 A); it can also be expressed in terms of the ratio of the mean Co-Co distance to the mean co-sbr distance, which ratio is found to be 1.666 in contrast to the idealized value of 1.633 when all cluster angles are tetrahedral. In view of this elon-
6268
Journal of the American Chemical Society
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Table 111. Magnetic Susceptibility Data for ( M ~ ~ N ) ~ [ ( ~ - S P ~ ) ~ ( C C I S P ~ ) ~ ]
106[Xm (obsd)
T. K
1 OhXe
1 06xm(cor)
106x,,,(calcd)b
X4.8 94.5 104.2 113.9 129.8 145.2 160.4 176.0 192.1 20x.2 224. I 240.3 256.6 273.2 295.0 295.0
15.53 14.84 14.29 13.79 13.10 12.56 12.1 1 11.66 11.28 10.93 10.62 10.33 10.08 9.83 9.32 9.38
23 770 22 750 21 940 21 200 20 180 19 380 18 720 18 060 17 500 16 980 16 520 16 100 I 5 720 15 360 I 4 600 I4 700
22 500 22 100 21 680 21 250 20 540 19 870 19 230 18 600 17 980 17 390 16 840 16 310 15 800 15 310 14 710 14 710
- Xni (ca1cd)l 1270 650 260 -50 -360 -490 -510 -540 -480 -410 -320 -210 -80 50 -1 I O -10
(' The diamagnetic correction applied was that calculated for (Me4N),[(pSPh)6(CoSPh)d], -850 X IOw6 cgs units. niodcl de\cribed in the text, with parameters TIS = 0, J = -16.9 cm-I, g = 2.00. p~ per cobalt atom.
pcif
2.0 1 2.07 2.14
2.20 2.29 2.37 2.45 2.52 2.59 2.66 2.72 2.78 2.84 2.90 2.93 2.94
Calculated for the
[
molecular cluster, in which two of the terminal benzenethiolate ligands of [ ( ~ - S P ~ ) ~ ( C O S Pare ~ ) replaced ~ ] ~ - by chloride ligands. Magnetic Properties. Magnetic susceptibility data for (M~~N)z[(~-SP~)~(COSP~)~] are presented in Table 111. The electron spins a t different cobalt atoms are clearly subject to weak antiparallel coupling. These data are examined hereZ6 in terms of a coupling model which involves three simplifying assumptions. The first is that the susceptibility due to each pseudotetrahedral cobalt site in the absence of coupling is only that of an orbitally nondegenerate 4A2ground state. The second arises in the use of the isotropic Heisenberg exchange Hamiltonian2'
which assumes that interatomic exchange coupling of spins is much less than intraatomic exchange coupling.28Thirdly, on the basis of the structural data it is postulated that the six coupling constants J between the four cobalt atoms should be very similar, whatever be the orbital overlap responsible for Figure 2. The [ ( ~ - S P ~ ) ~ ( C O S Pcluster, ~ ) ~ ] showing ~thermal ellipsoids the spin coupling, and the present model assumes that they are of 50% probability. identical. The manifold of cluster spin states is then Si = (i - l ) , i = 1-7, with multiplicities wi = 4 , 9 , 11, 10,6,3, 1, respectively, i = 1-7. The model contains two additional parameters: g gation of the Co-Co distances no thermodynamically signifi(applied equally to all cluster spin states) and a single correccant direct Co-Co bonding can be proposed. It is clear that the tion, TIS, for all unaccounted temperature-independent susexistence of the cluster is a consequence of the thiolate ceptibility (such as inadequacies in calculated closed-shell bridging. susceptibilities and second-order Zeeman contributions). The Double bridging by benzenethiolate extends the Co-S bond parameters J , g, and T I S were optimized by least-squares length by 0.064 A. The bonding stereochemistry around the minimization of Z(Xcor(obsd) - X(calcd))*. Results for opsulfur atoms, bridging and nonbridging, is effectively tetratimizations with different combinations of parameters variable hedral: for the bridging sulfur atoms the angles between the are given in Table IV. When permitted to vary, g, which coC,,-S vector and the normal to the Co-S-Co plane have a varies strongly with TIS, drops to an unreasonable value of ca. mean value of 36.3', close to the tetrahedral value of 35.3'. 1.9. Since TIS is unlikely to be negative by more than 400 X The question of preferred disposition of the nonbonding eleccgsu, and is expected to be positive, it is concluded from tron pair on the sulfur atom of each bridging thiolate ligand, in Table IV that the best representation of the data a disposition d i s t i n g u i ~ h a b l and e ~ ~possibly ~ ~ ~ ~ i g n i f i c a n t l ~ . ~the ~ . ~results ~ in hand is TIS = 0, J = -1 7 cm-I, g = 2.00. The discrepancy in other systems, does not arise in [(p-SPh)6(CoSPh)4]*-, since between observed and calculated susceptibility, although each Sbr-C, bond is axial to one and equatorial to another of generally less than experimental error, shows a systematic the Co& chairs which constitute the Co& core. trend (Table 111) which possibly reflects the neglect of the more The crystallographic data on (Me4N)2Co(SPh)4 indicate that it contains the structurally molecular [ C O ( S P ~ ) ~ion, ] ~ - complex susceptibility of.the uncoupled cobalt centers.29 which possesses crystallographic symmetry higher (C2) than The coupling parameter J is slightly larger than that ( - J that of the same complex ion in (Ph4P)2Co(SPh)4.18 = 13-16 cm-I) obtained by Brookes and Martin30 for the p4-oxo-tetracQbalt(II) complex O C O ~ ( C ~ H ~(where N~)~ Crystalline ( M ~ ~ N ) ~ C O ~ ( S Pisostructural ~ ) & I ~ , with its zinc analogue,13 contains the [ (~-SP~)~(COSP~)~(COC~)~]~C7HsN2- is the conjugate base of 7-azaindole), which is,
6269
12005-
10000-
1
,
/
,
32
1
/
30
1
28
,
1
26
/
I
/
24
1
,
2.2
I
1
I
2.0
18
u
pm-l
,
1
1
16
I
,
11
I 12
,
I
10
,
I
,
08
Figure 3. Absorption spectra, t. (Mco)-’ crn-I. in acetonitrile solution: A. (Me4N)z[(~~-sPh),(CosPh)4], 6.01 SPh)6(CoSPh)2(COCl)2],4.13 X M Co; C, ( M ~ ~ N ) ~ [ C ~ ( S 3.36 P ~ )XJ ] , M c o .
l
i
06
X
M CO: B, (Me4N)z[(p-
Absorption Spectraa Table 1V. Magnetic Parameters for ( M ~ ~ N ) ~ [ ( C L - S P ~ ) ~ ( C OTable S P ~V. ) ~Electronic ] variable parameter values 2 I Xobsd - Xcaicd 1 / parameters‘] - J . cm-I 2 106T1S,cgsu ZXobsd J J . fi
J , TIS J . g, TIS
16.9 14.9 15.9 14.8
2.00 1.92 2.00 1.90
0 0 -816 +268
0.020 0.017 0.018 0.017
compd
0.65 sh 0.76 1.32 1.40 1.615 2.16 2.75
( M C ~ N ) ~ C O ~ ( S P ~ ) ~0.68 CI~
(138)
0.84 sh 1.357 1.467 1.620 2.1 sh 2.66 sh
(1 15) (467) (491) (487) (1300) (2700)
0.615 0.745 0.86 sh 1.350 1.467 1.615 2.1 sh 2.58
0.670 0.78 sh 1.362 1.442 1.60 sh
(244) (228) (840) (985) (640)
(’Sce text for description of model.
-
reflectance v, Wm-I
(160) (185) (645) (604) (695) (4000) (5800)
(M~dN)zCoa(SPh)io
however, quite different geometrically and electronically from [(p-SPh)6(CoSPh)dl2-. It must be remembered that the parameter J is the mean of 4S2 = 9 orbital interactions between each pair of cobalt atoms,31and therefore the dominant spin pairing interaction energy may be as large as 150 cm-’ in [(p-SPh)6(CoSPh)4I2-. Nevertheless, this energy is negligible as a chemical-bonding influence. Electronic Spectra. Comparison of crystal phase reflectance spectra for (MedN)z[ (p-SPh)6(CoSPh)4I1 (Me4N)2[ ( p SPh)6(CoSPh)z(CoC1)2],and (Me4N)2[Co(SPh),] with absorption spectra of the same compounds dissolved in dry acetonitrile (see Figure 3 and Table V) leads to the conclusion that all three complexes undergo no appreciable structure modification with phase change. There are four distinct absorption regions in these spectra: region I, 0.55-1.0 p m - l , the 4A1 4T1(F) transition ( v 2 ) of tetrahedrally coordinated Co(I1); region 11, 1.3-1.7 pm-], the 4A2 4T1(P) transition (Q) of tetrahedral Co(I1); region 111, 1.7-2.1 pm-I, a low-energy metal-ligand charge-transfer absorption region; region IV, 1.9-3.2 pm-l, a high-energy metal-ligand charge-transfer region. Higher frequency absorption contains contributions from the phenyl substituents. There have been two previous reports of the solution spectrum of [Co(SPh)4]*-. The data reportedlsb for (Ph4P)2Co(SPh)4 in acetonitrile are in general agreement in band frequencies but include intensities slightly less than those found
solution (CH3CN) M-l cm-I)
v, pm-l
(Me4h)zCo(SPh)4
-
0.67 shC 0.78 1.324 1.398 1.630 2.27 sh 2.85 sh
2.40
(4380)
0.650 0.80 1.360 1.440 1.56sh 1.85 2.40
See Figure 3. Minor unresolved absorption bands are shown only Molar extinction coefficient, per cobalt atom. Shoulder.
on the figure.
here. However, the data r e p ~ r t e d ”for ~ ( B u ~ N ) ~ C O ( SinP ~ ) ~ dichloromethane differ substantially in the frequencies of prominent peaks in region 11, and intensities throughout are low. Possibly solvolytic dissociation of the type described below was caused by impurities in the dichloromethane. The previous
Journal of the American Chemical Society
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can be applied to the charge-transfer absorption, with chromophores /Co-SPhter,,,al) and {CO-SPhbrldgl,g-CO). It can be seen that in the 1 i-2.1-pm-I region the absorption of [ ( p S P ~ ) ~ ( C O S P ~is) substantially ~]~greater than that of [ ( p S P ~ ) ~ ( C O S P ~ ) ~ ( C Oplus C ~[Co(SPh)4]*-, )~]~while in the 2.8-3.2-pm-l region it is substantially less. A simplistic model with noninteracting {Co-SPh,,-rm,nalJand {CO-SPhbrldglng-CO) chromophores is inadequate. Although the symmetrical idealized structures of [ ( ~ - S P ~ ) ~ ( C O S P ~[(p-SPh)6)~]~-, ( C O S P ~ ) ~ ( C O C I ) ~and ] ~ -[Co(SPh)4I2, might appear to favor them in development of the charge-transfer spectroscopy of Co(I1)-thiolate coordination, progress in this area will depend on the availability of further complexes, including [ ( p SR)6(COX)4I2-, with alkylthiolate ligands. Nevertheless, the charge-transfer spectra contain some features with diagnostic value: (a) Rising absorption in the I .X-2.0-prn-l region is clearly correlated with the presence of bridging benzenethiolate. (b) A broad maximum in the 2.6-2.8-pm-' region occurs in the compounds with bridging benzenethiolate. (c) Strongly rising absorption at energies higher than 2.8 pm-' occurs in the complex with only terminal 1 benzenethiolate: a reduced amount of Co-SPh,,,,,,,l bonding 19 18 17 18 15 14 13 V pm-' decreases the absorption in this higher energy region. Solution Equilibria. The equilibria existing in solutions Figure 4. Absorption spectra, 6, (McJ-' cm-I, in acetonitrile solution. PhS-/Co*+ ratios: 2, A: 3, 9;4. C: 5 , D. The dotted trace is the spectrum containing Co(l1) and benzenethiolate, involving [ ( ~ - s P h ) ~ or [Co(SPh)d]?-. (CoSPh)4I2-, [Co(SPh)4I2-, and possibly other species, have been investigated by means of the electronic spectra of two series of solutions. Figure 4 shows spectra of oxygen-free solutions prepared as mixtures of Co(N03)2*6H20 in CH3CN derivation32of pseudotetrahedral ligand-field parameters for and PhSH plus Et3N in CH3CN, with PhS-/Co(Il) molar [ C O ( S P ~ ) ~remains ]~valid. ratios of 2, 3, 4, and 5 in solutions 4A, 4B, 4C, and 4D, reThe 4Ar 4 T ~ ( Fand ) 4A2 4 T ~ ( P band ) envelopes for [ (p-SPh)6(CoSPh)4] 2- and [ ( p - ~ ~ h > ~ ( ~ o ~ P2- h ) ~spectively. ( ~ o ~ ~Figure ) ~ ] 5 shows spectra of solutions prepared as mixtures of (Et4N)zCoBr4 in CH3CN and PhSH plus Et3N are not significantly different in frequency from those of in CH3CN, with PhS-/Co(II) molar ratios of 0, 2, 3.5, and [Co(SPh)4I2-. The major difference is increased splitting of I O in solutions 5A, 5B, 5C, and 5D, respectively. The spectra the 4A2 4Tl(P) envelope in the two cluster compounds, probably a consequence of the ligand inequivalence in the of solutions 4B, 4C, and 4D reveal isosbestic points at 1.39 and 1.55 pm-' and spectrum 4B is that of [(p-SPh)6(Coclusters. In the absence of detailed data on resolved transitions SPh)4]2-.35 Spectrum 5D is that of [Co(SPh)4]*-, and is in regions I and 11, further modeling of the electronic structure spectrum on Figure 4. of [(pc~-SPh)6(CoSPh)4]~and [ ( p - ~ ~ h ) ~ ( ~ o ~ ~ h ) ~ ( ~marked 0 ~ 1 )asZa1reference ~Consider first the behavior of solutions 4B, 4C, and 4D, in cannot be attempted. W e conclude simply that the ligand field which [PhS-] is increasing above that required for [ ( p parameters A, and B for the two ligand types PhS-terminal and S P ~ ) ~ ( C O S P ~ The ) ~ ] isosbestic ~-. point a t 1.55 pm-l is conPhS-br,dglng are not appreciably different. As previously sistent with the equilibrium co-occurrence of [ ( p noted,32 A,(PhS-) > At(Cl-). It is noteworthy that both S P ~ ) ~ ( C O S P ~and ) ~ [Co(SPh)412-, ]~but the spectra in the [(p-SPh)6(CoSPh)4]*- and [(~-SP~)~(COSP~>~(CO~I)~]~have a well-resolved absorption a t 1.62 pm-l, which is essen- vicinity of the 1.39-pm-' isosbestic point are not. Also, the high absorbance in the 1.8-1.9-pm-' region is not consistent with tially absent in [Co(SPh)412-. This absorption may therefore formation of a substantial proportion of [Co(SPh)4I2- in sobe characteristic of the bridging Co-SPh-Co function. The charge-transfer regions I11 and IV are of greater interest lution 4D, but is indicative of bridging benzenethiolate. Therefore it is probable that the species in equilibrium with for these compounds, owing to the limited published infor[ ( ~ - S P ~ ) ~ ( C O S Pin~these ) ~ ] solutions ~is not [ C O ( S P ~ ) ~ ] ~ on structure/spectra relationships for thiolate libut another complex with tetrahedral coordination and a low gands in terminal and in bridging positions, and also for related halide and pseudohalide ligands with terminal or bridge proportion of bridging thiolate. An obvious suggestion is [(p.-SPh)2(C0(SPh)2)2]~-,with edge-shared coordination bonding. The absorption in these regions is definitely due to tetrahedra. Acetonitrile solutions of Co(N03)2.6H20 with ligand-metal charge-transfer transitions, since all Zn(I1)larger excesses of PhS- than 4D contain only [Co(SPh)4]*-. benzenethiolate compounds, including (Me4N)2[(p-SPh)6Therefore it appears that the solution equilibria, in the absence (ZnSPh)4], which is isostructural with (Me&)2[(p-sPh)b(CoSPh)4], show no absorption less than 3.0 pm-I, with the of halide ligands, should be written lowest energy absorption maximum a t 3.2 pm-l. [ (p-SPh)6(CoSPh)4] 2- 4- 2PhSReferring to the solution spectra in Figure 3, two general e ~ [ ( ~ U - S P ~ ) ~ ( C O ( S(2) P~)~)~~~points can be made. First, it can be seen that there are few well-resolved charge-transfer transitions, particularly in the [(p-SPh)z(Co(SPh)2)2l2- 2PhS- + 2[Co(SPh)4I2two clusters, and it appears that these complexes contain a (3) sequence of poorly separated thiolate levels. I n terms of electronic structure, the angular distortions from possible high Spectrum A in Figure 4 also shows absorbance in the bridging symmetry in [ ( ~ - S P ~ ) ~ ( C O S Pwould ~ ) ~ ] be ~ - expected to benzenethiolate region (1.8-1.9 pm-I) greater than can be cause minor splitting of degenerate levels. The evidence of accounted for by [(p-sPh)6(cosPh)4]2-. The PhS-/Co(II) broad overlapping transitions suggests that spreading of energy ratio in this solution is only 2, and it is possible that all benlevels is characteristic of the { (p-SPh)6Co41 core. Secondly, the zenethiolate ligands are bridging, in a molecular aggregate of ] , ~high . solubility of the components question can be raised as to whether chromophore factoring type [ ( ~ - S P ~ ) ~ C OThe
-
-
-
+
1)utir.t~/
Molecular Cobalt (11)- Thiolate Clusters
627 I 1
1000 :
\
'
l
l
l
l
D
1
1
I
I
-
l
E-
Figure 5 . Absorption spectra, t , (Mc,,)-' cm-', in acetonitrile solution. PhS-/CoBrd*- ratios: O, A; 2, B; 3.5, C; 10, D.
of solutions with PhS-/Co(II) ratio
