Medium effects on the redox properties of tris(2,2′-bipyridyl)ruthenium complexes

Abstract The electrochemisty of the 2,2′-bipyridyl ruthenium complexes [Ru(Bipy) 3 ] n ± has been examined in a series of solvents with varying dielectric constant. The potential separation between the +1/0 and 0/−1 redox steps increases with decreasing solvent polarity and decreasing ionic strength of the supporting electrolyte. Electrochemically generated [Ru(Bipy) 3 ] n (where n = 0 or −1) is kinetically labile in these low oxidation states and capable of reacting with the very high dielectric solvent N -methylacetamide via an E r C i mechanism; k f for the following chemical reaction is 0.31±0.15 s −1 . Relationship is drawn between the dependence of the [Ru(Bipy) 3 ] potentials on solvent dielectric and the effect of local dielectric on protein redox potentials, and comment is made also on the solvent dependence of the potential of the ferricenium/ferrocene couple.