Electron distribution in the nonclassical bis(dithiolene) electron transfer series [M(CO)(2)(S2C2Me2)(2)](0/1-/2-) (M = Mo, W): Assessment by structural, spectroscopic, and density functional theory results

The electron-transfer series [M(CO)(2)(S2C2Me2)(2)](0/1-/2-) (series 2) hav e been established, and the previously reported series [M(S2CwMe2)(3)](0/1- /2-) (series 3) confirmed, by voltammetry (M = Mo, W). Redox reactions are reversible with E-Mo > E-W, and all members of each series have been isolat ed. Members of a given series have very similar distorted trigonal prismati c structures; isoelectronic complexes are isostructural. The existence of t hese series with structurally characterized members facilitates examination of geometric and electronic properties over three consecutive oxidation st ates. Upon traversing the series in the reducing direction, M-S, S-C, and C -O bond distances increase, and M-C, chelate ring C-C, and vco values decre ase. Density functional calculations identify the electroactive orbital, wh ich is well separated in energy from other orbitals. Trends in bond lengths and vibrational frequencies in a given series are fully accountable in ter ms of increasing population of this orbital, whose composition is roughly c onstant across the series and is dominantly ligand (ca. 80%) in character. Consequently, redox reactions in the two series are essentially ligand-base d. The noninnocent nature of dithiolene ligands in oxidized complexes has b een long recognized. The results of DFT calculations provide a contemporary description of the delocalized ground states in the two series. The trends in parameters involving the carbonyl groups provide a particularly clear i ndication of the classical behavior of a Jc-acceptor ligand in isostructura l molecules subject to consecutive reductions over three oxidation states.