Intramolecular Electron-Transfer Reactions in Bridged Polynuclear RuII-CoII Complexes Containing a (μ-Carboxylato)bis(μ-hydroxo)bis (and a RuII(NH3)5 Structural Unit

Article abstract of DOI:10.1021/ja00331a022

Intramolecular electron transfer in Ru^II-L-Co^III_n trinuclear and pentanuclear complexes containing nicotinate, isonicotinate, pyrimidine-4-carboxylate, pyridine-2,6-dicarboxylate, and pyrazine-2,6-dicarboxylate anions as bridging ligands and N-coordinated Ru^II(NH3)5 units as internal reductants and (μ-carboxylato)bis(μ-hydroxo)bis<(amine)cobalt(III)> moieties as oxidants has been studied.The nonbridging amines coordinated to cobalt(III) are three NH3, diethylenetriamine, or 1,4,7-triazacyclononane, respectively.A linear correlation (slope 0.46) of ΔG^* vs. ΔG₀ has been established for the intramolecular electron-transfer reactions with (NH3)6Co2(μ-OH)2 units as oxidants and Ru^II(NH3)5L as internal reductants.Variation of nonbridging amine ligands at the Co(III) centers affects the rate of intramolecular rate constants markedly.Reactivity differences are accounted for by differing driving force due to varying redox potentials of Co(III)/Co(II) couples.The rates of electron transfer were found to be rather intensitive to changes of the bridging ligand, which is taken as an indication that the reactions approach the adiabatic regime, although strongly negative entropies of activation (-10 to -18 cal K^-1 mol^-1) are observed for the series of complexes.