Complexation of Cm(III) and Eu(III) by glycolic acid: TRLFS studies

Complexation processes of Cm(III) and Eu(III) by glycolic acid are studied by time-resolved laser fluorescence spectroscopy (TRLFS). The experiments with curium are performed in 0.1 M and 3.0 M NaClO4. The glycolic acid concentration is varied between 0.01 mol/L and 0.5 mol/L at pH 3. Cm(III) and Eu(III) fluorescence emission spectra are obtained at a fixed glycolic acid concentration of 0.5 mol/L, the pH is varied between 3 and 11. In addition to the Cm3+ aquo ion, two Cm(III)-glycolic acid species are observed by peak deconvolution: Cm(gly)2+ and Cm(gly)2+. Above pH 5 a chelate Cm-glycolate complex is formed. This curium-glycolate complex is characterised by its emission spectrum (peak maximum at 611.2 nm) and its fluorescence emission lifetime (172 ± 8 µs). The corresponding chelate europium-glycolate complex with 300 ± 10 µs lifetime is obtained above pH 6.83. In the pH range 6 to 8 the decay behaviour of the excited state is different in the Cm(III)- and Eu(III)-glycolate system. While a bi-exponential decay behaviour was observed for the Cm-system, indicating slow exchange kinetics in comparison to the fluorescence decay of the exited state, the corresponding Eu-system shows mono-exponential decay behaviour. More over the reversibility of Eu-chelating is much faster than in the case of the Cm(III) complex. The results show that the strength and kinetics of the chelating is different for Cm(III) and Eu(III).