Inorg. Chem. 1987, I 0 -0.4 0.8 V vs. Ag/AgCl Figure 12. Cyclic voltammogram (200 mV/s) for a GClpoly-CobNMez)TPP film (r = 1.4 X mol/cm2) in a CH$N + 0.1 M Et4NCI04 solution (solid curve) and for the same solution after addition of 2 volumes of HzO (dashed curve).potentials for O2 reduction and larger slope. The slope for poly-Co(o-NH2)TPP in 1 M N a O H is in fact very close to the four-electron value; we have confirmed by the rotating ring-disk techniqueI4 that this situation produces virtually no H202 product. 26, 1017-1025 1017Assuming (as we have14) that the two waves for poly-Co(o-NH2)TPP reflect monomeric and dimeric species in the film, then the lower activity of the other cobalt porphyrins may be connected to their lower dimerization constants, as found for Co(p-0H)TPP and Cob-pyr)TPP solutions from absorbance spectroscopy (Table 11) * showed that Co(1) porphyrins placed in solutions and adsorbed or bound to G C electrodes34 react rapidly with water. Figure 12 shows a test for water reduction using an electropolymerized poly-Cob-NMe2)TPP film (GC electrode). Co(II/I) voltammetry of the film in dry 0.1 M Et4NCI04/CH3CN (solid curve) occurs at Eo' = -0.92 V, whereas upon addition of two volumes of water (dashed curve), an irreversible, split (ca. -0.68 and -1.01 V) wave, with greatly enhanced cathodic current and no reverse anodic wave, is observed. While it is reasonable to suppose that these waves represent H2 evolution, they are not very stable (as S p i r~~~ also experienced) and gradually decayed. N o further studies were done. This instability is not characteristic of the polymeric porphyrin films in dry solvent, which in the potential window 0 to -1.5 V are very stable to repeated potential cycling. Acknowledgment.A series of 19 mononuclear oxomolybdenum(V) compounds of the general formula LMoOXY (L = hydrotris(3,5-dimethyl-lpyrazoly1)borate; (X,Y) = C1-, NCS-, NC, OR-, SR-, and the dianions of ethylene glycol, mercaptoethanol, dimercaptoethane, catechol, o-mercaptophenol, o-aminophenol, o-aminobenzenethiol, and toluenedithiol) have been prepared and characterized by electron paramagnetic resonance spectroscopy (EPR), cyclic voltammetry, UV-visible spectroscopy, and mass spectrometry. The LMoO(SR)~ complexes possess the cis sulfur ligands proposed for the molybdenum cofactor. The structure of LMoO(SPh), was determined by X-ray crystallography: space group P2,/c, Z = 4, u = 13.079 (6) A, 6 = 14.438 (7) A, c = 15.836 (9) A, p = 104.73 (4)O. The molecule adopts the expectedfuc six-coordinate stereochemistry with cis thiolate groups. The average Mo-S distance is 2.382 (2) A, and the average Mo-0 distance is 1.676 (4) A. The Mo-N distances range from 2.164 (5) to 2.357 (5) A. The isotropic ( g ) and (A)(95*97Mo) values show an inverse correlation and cluster according to the nature of the donor atoms.Sulfur donor atoms lead to large ( g ) and small ( A ) values. The anisotropies of the g values for LMoO(OR), and LMoO(SR)~ complexes show marked differences between monodentate and chelated ligands. All ...

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The crystal and molecular structure of tris[2-aminobenzenethiolato(2-)-lV,S]molybdenum(VI), Mo(NHC6H4S)3, has been determined from a single-crystal X-ray study. The compound crystallizes in the orthorhombic space group J°212¡21 with four molecules per unit cell of dimensions a = 10.644 (1), b = 11.459 (2), c =15.113 (2) Á. The observed and calculated densities are 1.66 (2) and 1.674 g cm"3, respectively. Full-matrix least-squares refinement using 2084 unique reflections having 3.5°<2 < 55°and 7 > 3 (7) converged at R¡ = 0.027 and R2 -0.031. Each molybdenum atom in the discrete monomers is in a distorted trigonal-prismatic coordination environment. The average Mo-S and Mo-N distances are 2.418 (6) and 1.997 (8) Á, respectively. The two triangular faces, formed by the three sulfur atoms and by the three nitrogen atoms, having the average S-S and N-N sides of 3.251 (30) and 2.793 (10) Á, respectively, are nearly parallel but are relatively twisted by the average angle of 12.3 (10)°. Distortion from a trigonal prism in this compound is slightly greater than that observed in V(S2C2Ph2)3. The molecule conforms to approximately C3 point symmetry. Each 2-aminobenzenethiolate ligand is folded about its S-N vector. The protons of the NH groups are only 2.5 Á from the molybdenum atom and lie in the planes of the ligands.

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The complex Mo2OS(g-S2)(S2CNR2)2 (R2 = Me2, Et2, n-Bu2, (CH2)5) was synthesized by the reaction of K2MoS4 and NaS2CNR2 in water in the presence of Na2S204 and by the reaction of m-Mo02(S2CNR2)2 or Mo202(m-0)(S2CNR2)4 with hydrogen sulfide in chloroform. It could not be prepared by oxo-sulfido exchange with mixtures of 202(µ-S2)(S2CNEt2)2 and Mo2S2(g-S2)(S2CNEt2)2 nor by the reaction of elemental sulfur with Mo202(g-S2)(S2CNEt2)2. The structure of Mo2OS(g-S)2(S2CNEt2)2 was determined by X-ray crystallography. The compound crystallizes in space group P2i/a with a = 17.540 (3) A, b = 6.859 (1) A, c = 17.854 (2) Á, ß = 104.67 (1)°, dabsi =1.916 (10) g cm"3, dcM = 1.920 g cm"3, and Z = 4. The stereochemistry of the dimer involves syn fusion of the basal edges of two tetragonal pyramids. The equatorial positions of each pyramid are occupied by the two bridging sulfido groups (Sb) and by two sulfur atoms from a S2CNEt2 ligand (St). The apical position of one pyramid is occupied by a terminal oxo group and that of the other pyramid by a terminal sulfido group. An approximate twofold disorder of the molecule in the crystal precludes accurate determination of the terminal Mo=0 and Mo=S distances and obscures any differences between the two halves of the dimer. In view of the disorder, the least-squares refinement was terminated after convergence of the model with isotropic atoms with = 0.086 for the 1789 data with F02 > 3 ( 02) and 26 < 40°. The ••• distance is 2.826 (3) A, the average Mo-Sb distance is 2.317 A and the average Mo-S¡ distance is 2.466 A. The dihedral angle between the two Mo(Sb)2 planes of the dimer is 149.4°. Mo2OS(^-S2)(S2CNEt2)2 reacted with triphenylphosphine or cyanide to give 202(µ-S2)(S2CNEt2)2 and either triphenylphosphine sulfide or thiocyanate. This reaction with cyanide is reminiscent of the removal of sulfur from the molybdo enzymes xanthine oxidase and aldehyde oxidase. The possible interrelationships of these reactions is discussed and speculation concerning the function of the cyanide-labile sulfur atom in the enzymes is presented.3 (/) gave final discrepancy indices = 0.040 and R2 = 0.043. Refinement of 2 based on the 1398 unique data having 3.5°< 20 < 50°and I > 3 ( ) converged at = 0.047 and R2 = 0.046. Compounds 1 and 2 have similar geometries. Both are monomeric with distorted octahedral geometry around each molybdenum atom. The Mo022+ grouping in 2 has the expected cis configuration with an O-Mo-O angle of 106.3 (3)°. The MoOCl2+ unit of 1 also has a cis configuration, contrary to earlier proposals, with a Cl-Mo-O angle of 103.0 (2)°. In 1 Mo-Cl = 2.342 (2) A and Mo-0 = 1.716 (4) A. The average Mo-0 distance in 2 is 1.703 (12) A. The Mo-N bonds trans to the oxo groups (2.408 (6) A in 1 and 2.374 (9) and 2.382 (9) A in 2) are ~0.2 A longer than the Mo-N bond of 1 which is trans to the chlorine atom (2.210 (6) A). The mean Mo-S distances are 2.409 (7) A for 1 and 2.411 (1) A for 2, respectively. The 8-mercaptoquinolinate ligands are folded along their S-N vectors in both compounds.

trans configuration of the two thiocyanate ligands, but the broadness of the IR absorbance, as well as the small (but real) displacement of the Raman absorbance maximum from the position of the IR absorbance, leads to the not unexpected conclusion that ideal Dlh symmetry does not obtain, presumably due (in part) to the nonlinearity of the NCS ligand.The structural inferences summarized above would seem to be important with respect to devising synthetic strategies involving Ru complexes that are intended for use as model compounds in a variety of physicochemical studies. In particular, the use of such complexes in the study of electron-transport processes in model systems having biological significance is being actively pursued in these laboratories. A clearer understanding of the stereochemistry of these materials would appear to be crucial in the pursuit of such studies.