(I,0) Mixed-valence state of a diiron complex with pertinence to the [FeFe]-hydrogenase active site: an IR, EPR, and computational study.

Biphenyl-2,2'-dithiolate (bpdt) bridged Fe(2)(bpdt)(CO)(6) (1) undergoes two sequential electrochemically quasi-reversible reductions. The one-electron reduction product 1(-) is unusually stable against irreversible structural changes and could be characterized by IR and EPR spectroscopy supported by computational methods. Reduction to the (I,0) state does not trigger bridging coordination of CO but partial deligation of the dithiolate in 1(-) that ultimately forms a diamagnetic dimerization product.