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)Ru II (pz)Ru III (edta)] + and [(CN) 4 Ru II (bpz)Ru III (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) 4 Ru II (bpz)Ru II (NH 3 ) 5 ], and a trinuclear species, of formula {(CN) 4 Ru II (bpz)[Ru II (NH 3 ) 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.