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 (k(1)) are changed by the cations in the order of Li+ < Na+ < K+ approximate to Rb+ approximate to 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. (C) 2004 Elsevier B.V. All rights reserved.