Tuning of the Reorganization Energies by Innocent Co-ligands in Novel Mixed-Valent Dinuclear Ruthenium Complexes

Abstract

Two novel mixed-valent ruthenium complexes, of formulae [(tpy)(bpy)RuII(pz)RuIII(edta)]+ and [(CN)4RuII(bpz)RuIII(edta)]3- (where tpy = 2,2′:6′,2″-terpyridine, bpy = 2,2′-bipyridine, pz = pyrazine, bpz = 2,2′-bipyrazine, edta = ethylenediaminetetraacetate), were prepared and spectroscopically characterized in aqueous solutions and as solid salts with suitable counterions. For comparison purposes, two new ruthenium complexes: a dinuclear species, of formula [(CN)4RuII(bpz)RuII (NH3)5], and a trinuclear species, of formula {(CN)4RuII(bpz)[RuII (NH3)5]2}2+, were also prepared and characterized in aqueous solutions. From spectral data of metal-to-metal charge transfer (MMCT) absorption bands, a Hush analysis was made, and the reorganization energies for the intramolecular electron transfers were calculated. A dramatic change in these values was disclosed when comparing both mixed- valent species, which can be explained on the basis of the influence exerted by the 'innocent' co-ligands (polypyridines or cyanides) bonded to the ruthenium centers. This tuning is an important factor in devising molecular devices for energy conversion. © 2002 Elsevier Science Ltd. All rights reserved.