Sulfur K-edge XAS of WV=O vs. MoV=O bis(dithiolene) complexes:: Contributions of relativistic effects to electronic structure and reactivity of tungsten enzymes

Molybdenum- or tungsten-containing enzymes catalyze oxygen atom transfer reactions involved in carbon, sulfur, or nitrogen metabolism. It has been observed that reduction potentials and oxygen atom transfer rates are different for W relative to Mo enzymes and the isostructural Mo/W complexes. Sulfur K-edge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations on [(MoO)-O-V(bdt)(2)](-) and [(WO)-O-V(bdt)(2)](-), where bdt = benzene-1,2-dithiolate(2-), have been used to determine that the energies of the half-filled redox-active orbital, and thus the reduction potentials and M=O bond strengths, are different for these complexes due to relativistic effects in the W sites. (C) 2007 Elsevier Inc. All rights reserved.