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 π interaction as supported by DFT calculations. Unexpectedly, its chemical or electrochemical reduction occurs irreversibly to yield EPR-detectable {(μ,η²:η²-abpy)[PtCl₂]₂}^•- and, as the main product of chloride dissociation, the structurally identified and DFT-calculated dinuclear [(μ,η²:η¹-abpy)PtCl]₂²⁺ 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^-I)(abpy)Pt₂Cl₂]^•+ at 1220 nm (ε = 3370 M^-1 cm^-1) which is attributed to a ligand-to-ligand intervalence charge-transfer transition.