A Valence Bond Description of Dizwitterionic Dithiolene Character in an Oxomolybdenum-Bis(dithione) Complex

Metallodithiolene non-innocence is explored in an oxomolybdenumbis(dithione) complex, [Mo4+O(iPr2Pipdt)2Cl][PF6] (where Pipdt is N,N'-piperazine-2,3-dithione), which has a piperazine ring as an integral part of the dithiolene ligand. The title complex displays spectroscopic features that are unusual for a formally reduced MoIVdithiolene complex, namely a low-energy metal-to-ligand charge-transfer band with appreciable intensity and CC and CS stretching frequencies that are markedly different from those of oxomolybdenum complexes coordinated to dianionic dithiolene ligands. The electronic structure of the ligand has been described in valence bond terms as a resonance hybrid of dithione and dizwitterionic dithiolene structures.