Specific cation effect on quenching reactions of excited tris(α,α′-diimine) ruthenium(II) and chromium(III) complexes by cyanide complexes in aqueous solutions

Abstract

Specific salt effects were studied on the quenching reaction of excited [Ru(NN) 3] 2+ (NN=2,2′-bipyridine(bpy), 1,10-phenanthrorine(phen)) and [Cr(bpy) 3] 3+ by [Cr(CN) 6] 3−, [Fe(CN) 6] 3− and [Ni(CN) 4] 2− in aqueous solutions as a function of alkali metal ions which were added for adjustment of ionic strength. The quenching rate constants in [Ru(NN) 3] 2+–[Cr(CN) 6] 3− and [Cr(bpy) 3] 3+–[Cr(CN) 6] 3− systems are changed by the cations as Li +>Na +>K +≈Rb +≈Cs +. On the other hand, the rate constants in [Ru(NN) 3] 2+–[Fe(CN) 6] 3− and [Ru(NN) 3] 2+–[Ni(CN) 4] 2− systems, which are diffusion-controlled reactions, are not varied by the alkali metal cations. The obtained order (Li +>Na +>K +≈Rb +≈Cs +) of the quenching rate constant is quite different from salt effects, Li +<Na +<K +<Rb +<Cs +, which have been obtained in the electron transfer reactions between complex anions.