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 (k_q) 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.