Role of diluent in the unusual extraction of Am³⁺ and Eu³⁺ ions with benzene-centered tripodal diglycol-amides: local structure studies using luminescence spectroscopy and XAS

Two benzene-centered tripodal diglycolamide ligands (L_I and L_II) were used for the extraction of Am³⁺ and Eu³⁺ from nitric acid solutions into a diluent medium of n-dodecane modified with various amounts of isodecanol. The ligands showed preferential extraction of Eu³⁺ over Am³⁺ in most cases. While the extraction of the Am³⁺ ion was not much affected (with a slight increase) over the entire range of diluent compositions in the case of L_I, a gradual decline in the extraction of the Eu³⁺ ion suggested a reversal in the separation trend with Am³⁺ being preferentially extracted with a solution of L_I in pure isodecanol. On the other hand, a sharp decline was seen for the extraction of both Am³⁺ and Eu³⁺ in the entire range of diluents containing various fractions of isodecanol when L_II was used. The unusual extraction was attributed to the difference in the complexation behaviour of L_I and L_II, which was explained on the basis of photoluminescence (PL) spectroscopy as well as XAS studies. The PL studies suggested absence of any inner-sphere water molecules from the lifetime data, while the splitting of emission peaks and asymmetry ratio values gave an idea about the complex geometry. On the other hand, the XAS studies gave information about the bonding in the coordination complexes. (authors)