TRLIFS study of Eu(III) spectroscopic properties to obtain structural and thermodynamic informations on lanthanide-malonamide complexes in the Eu(III)/NaNO3/TetraEthylMalonAmide system

Improvement of the nuclear fuel reprocessing involves separating the minor actinides (Am(III) and Cm(111)) from the fission products. In the French strategy, the first step consists in the separation of the trivalent actinides and lanthanides from high-level liquid waste, for which malonamides RR'NCO(CHR")CONRR' are promising ligands. These molecules have been optimized for reprocessing but still require basic chemical studies to describe the complexation mechanisms at a molecular scale. This paper discusses a thermodynamic and structural study of a Ln(III)-malonamide complex formed with the hydrosoluble tetraethylmalonamide ligand (TEMA = (C2H5)(2)NCOCH2CON(C2H5)(2)) dissolved in a nitrate medium. Despite the simplified chemical system obtained with TEMA, its weak chemical affinity and its physical properties pushed the analytical techniques to their limits. The sensitivity of Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLIFS) combined with the major luminescent spectroscopic properties of Eu(III) (hypersensitive band and fluorescence lifetime) were successfully used to determine the equilibrium constant and hydration number in the Eu(III), TEMA, and NO3- system. Fluorescence lifetimes, connected with the first coordination sphere of the solvated metal, clearly show the inner-sphere location of nitrate in the Eu(NO3)(2+) complex, the outer-sphere location of TEMA in the Eu(TEMA)(3+) complex, and the outer-sphere location of both ligands in the Eu(NO3)(TEMA)(2+) complex.