Cation effect on energy transfer reactions from [Tb(2,6-pyridinedicarboxylate)3]3− to anionic chromium(III) and neodymium(III) complexes in aqueous solutions

Cation effects are studied on the excitation energy transfer reaction between anionic complexes, i.e., [Tb(dpa)3]3− (dpa=2,6-pyridinedicarboxylate) quenched by [Cr(ox)3]3− (ox=oxalate ion), [Cr(mal)3]3− (mal=malonate ion) and [Nd(dpa)3]3− in aqueous solutions in the presence of alkali metal ions added for adjustments of ionic strengths. In the quenching reaction of [Cr(ox)3]3−, magnitudes of quenching rate constants (kq) and energy transfer rate constant in encounter complex (k1) are changed by the cations in the order of Li+ < Na+ < K+ ≈ Rb+ ≈ Cs+, that is quite contrary of the cation effect on energy transfer reaction between [Ru(N–N)3]2+ and [Cr(ox)3]3−, reported in the previous paper. On the other hand, the rate constants in quenching reactions by [Cr(mal)3]3− and [Nd(dpa)3]3− remain almost constant. This result indicates that more separated donor-acceptor pair is not sensitive to coexisting cations.