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Complex Reduction Chemistry of (abpy)PtCl2, abpy = 2,2‘-Azobispyridine:  Formation of Cyclic [(μ,η21-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

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posted on 20.09.2004, 00:00 by Akbey Dogan, Biprajit Sarkar, Axel Klein, Falk Lissner, Thomas Schleid, Jan Fiedler, Stanislav Záliš, Vimal K. Jain, Wolfgang Kaim
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,η22-abpy)[PtCl2]2}•- and, as the main product of chloride dissociation, the structurally identified and DFT-calculated dinuclear [(μ,η21-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.