Noninnocent dithiolene ligands: a new oxomolybdenum complex possessing a donor-acceptor dithiolene ligand

A combination of X-ray crystallography, electronic absorption spectroscopy, resonance Raman spectroscopy, and bonding calculations are applied to understand the considerable thiolate-thione character possessed by the monoanionic dithiolene ligand resulting from an admixture of an intraligand charge transfer excited state into the ground state wave function. A highly versatile donor-acceptor character exhibited by the unusual dithiolene which remarkably affected the Mo(IV/V) redox couple provide insight into a potentially noninnocent role of the pterin fragment in pyranopterin Mo enzymes.