Direct evidence for enhanced inner-sphere chloro complexation of Eu(III) and Cm(III) in anion exchange resin phase studied by time-resolved laser-induced fluorescence spectroscopy

In anion exchange resin systems with LiCl-aqueous and LiCl-(H2O+CH3OH) solutions, the extent of chloro complexation of M(III) (M=Eu, Cm) was estimated from inner-sphere hydration number (N-H2O), i.e., the number of water molecules in the first coordination sphere of M(III) and from peak area ratio (A(2)/A(1)) of D-5(0) --> F-7(2) transition (A(2)) to D-5(0) --> F-7(1) transition (A(1)) in emission spectrum of Eu(III), which reflects the ligand environment both in the inner- and outer-spheres of Eu(III). The N-H2O of M(III) both in the solution and resin phases decreased with an increase of LiCl and CH3OH concentrations, indicating the formation of an inner-sphere M(III)-chloro complex. From the comparison of N-H2O between the both phases, it was found that the extent of the inner-sphere chloro complexation of M(III) in the resin phase is higher than that in the solution phase. The A(2)/A(1) ratio in the both phases increased with an increase of interaction of Eu(III) with Cl-, which are well correlate with the results of N-H2O. The sorption equilibrium of M(III) was discussed by comparing the extent of the chloro complexation with the distribution coefficient.