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

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+