Electron Transfer Dynamics in Molten Salts of Mono- and Dinuclear Ruthenium Complexes

Abstract

We have synthesized highly viscous, room-temperature, molten salts by associating various Ru(NH3)5L cations (L = 4,4‘-bipyridine, pyrazine, pyridine, 3-chloropyridine, benzonitrile) with polyether-tailed sulfonate anions. Microelectrode voltammetry in the undiluted melts yields, on the basis of charge transport occurring by electron hopping, electron self-exchange rate constants (kEX) for the various Ru3+/2+ couples. The rate constant (and activation barrier) for the pyrazine bridged binuclear pentaamineruthenium melt (Creutz-Taube ion) is similar to those obtained for mononuclear pentaammine[ligand]ruthenium melts, meaning that charge transport in the former is dominated by the rate of intermolecular, not intramolecular, electron transfer. The data at 35 °C are (Creutz−Taube ion) kEX = 3.7 × 104 M-1 s-1, (pyridine) 1.1 × 104 M-1 s-1, (3-chloropyridine) 2 × 104 M-1 s-1, and (benzonitrile) 3 × 104 M-1 s-1. All kEX values are smaller than those for [Ru2+/3+(bpy)3] in semisolid melts having equivalent MePEG ...