Cl₃V(μ-S(CH₃)₂)₃ VCl₃^2-: A first-row, face-shared bioctahedral complex with multiple metal-metal bonding

Density functional theory calculations have been used to investigate the structure and bonding of the d³d³ bioctahedral complexes X₃V(μ-S(CH₃)₂)₃ VX₃^2- (X = F^-, Cl^-, OH^-, SH^-, NH₂^-). According to geometry optimizations using the broken-symmetry approach and the VWN+B-LYP combination of density functionals, the halide-terminated complexes have a V-V bond order of approximately 2, while complexes featuring OH^-, SH^-, or NH₂^- as terminal ligands exhibit full triple bonding between the vanadium atoms. The tendency toward triple bonding in the latter complexes is consistent with an increased covalency of the vanadium-ligand bonds, and the influence of bond covalency is apparent also in the tendency for V-V bond elongation in the complexes with OH^- and NH₂^- terminal ligands. Detailed examination of the composition of molecular orbitals in all of the thioether-bridged V^II complexes substantiates the conclusion that the strong antiferromagnetic coupling which we have determined for these complexes (-J > 250 cm^-1) is due to direct bonding between metal atoms rather than superexchange through the bridging ligands. As such, these V^II complexes comprise the first apparent examples of multiple metal-metal bonding in first-transition-row, face-shared dinuclear complexes and are therefore of considerable structural and synthetic interest.