Complex reduction chemistry of (abPY)PtCl2, abpy=2,2′-azobispyridine:: Formation of cyclic [(μ,η2:η1-abpy)PtCl]22+ with a new coordination mode for abpy and a near-infrared ligand-to-ligand intervalence charge transfer absorption of the one-electron reduced state

The structurally characterized (abpy)PtCl2, abpy = 2,2'-azobispyridine, reveals a strong metal/ligand T interaction as supported by DFT calculations. Unexpectedly, its chemical or electrochemical reduction occurs irreversibly to yield EPR-detectable {(mu,eta(2):eta(2)-abpy)[PtCl2](2)}(.-) and, as the main product of chloride dissociation, the structurally identified and DFT-calculated dinuclear [(mu,eta(2):eta(1)-abpy)PtCl](2)(2+) with a novel coordination mode for abpy and isolated as tetrachlorozincate. Stepwise reversible one-electron reduction of that dimer, separated by 0.24 V, exhibits an intense near-infrared band for the monocationic intermediate [(abpy(-1))(abpy)Pt2Cl2](.+) at 1220 nm (epsilon = 3370 M-1 cm(-1)) which is attributed to a ligand-to-ligand intervalence charge-transfer transition.