Synthesis and Chemical and Structural Investigation of Molybdenum(IV) Thioxanthate Complexes: An Unusual Example of. µ³ Coordination for a Dithio Acid Ligand

The synthesis of the compounds MoO(S2CSR)2, R=i-C3H7 and;-C4H9, is reported. The electronic, IR, and proton NMR spectra are discussed and compared to those obtained for the parent dinners [Mo2O3(S2CSR)2]. The molecular structure of MoO(S2CS-i-C3H7)2 was revealed in a single-crystal x-ray diffraction study. The compound crystallizes in the triclinic crystal system, space group P, with α=6.14 (1) Å, b = 10.24 (1) Å, c=12.924 (8) Å, α=109.71 (1)°, α=93.25 (1)°, and γ = 99.80 (1)°, giving a density of 1.76 g cm-3 on the basis of two molecules per unit cell, in agreement with the measured density of 1.74 (2) g cm-3. The structure was solved using 1450 independent, statistically significant reflections collected on a full-circle automated diffractometer. The structure was solved by the usual Patterson and Fourier series methods to give a final value of the discrepency factor R1 of 0.059. The molecule is a pseudo-square-pyramidal monomer with two distinct ligand coordination types: one thioxanthate group exhibits the usual bidentate geometry, with Mo-S distances of 2.438 (4) and 2.454 (5) Å and a chelate ring angle S-Mo-S of 72.2 (1)°, while the second thioxanthate group displays unusual nonclassic coordination, with the Mo significantly displaced from the S2CS plane such that the Mo-central carbon bond distance is 2.25 (1) Å and the Mo-S distances are 2.375 (5) and 2.365 (4) Å, with a chelate ring angle S-Mo-S of 77.9 (2) Å. The oxo group completes the coordination about the Mo atom [Mo-O distance 1.66 (1) Å] which is displaced 0.86 Å from the plane generated by the four sulfur donors toward this approximately apical oxygen. Voltammetric studies of the monomers indicate an irreversible oxidation and a quasweversible reduction as the major electrode processes. Comparison of the voltammetric behavior of the monomers with that of the dimer complexes [Mo2O3(S2CSR)4] establishes the importance of dimer disproportionation into monomeric species in determining the overall electrochemical characteristics of these complexes. Oxidation-reduction mechanisms are proposed on the bases of these electrochemical studies, spectroscopic measurements, and isolation of electrode reaction products.