Theoretical Insights into the Selective Extractionof Americium(III) over Europium(III) with Dithioamide-Based Ligands

Separation of trivalent actinides An(III) from lanthanides Ln(III) is a worldwide challenge owing to their very similar chemical behaviors. It is highly desirable to understand the nature of selectivity for the An(III)/Ln(III) separation with various ligands through theoretical calculations because of their radiotoxicity and experimental difficulties. In this work, we have investigated three dithioamide-based ligands and their extraction behaviors with Am(III) and Eu(III) ions using the scalar-relativistic density functional theory. The results show that the dithioamide-based ligands have stronger electron donating ability than do the corresponding diamide-based ones. All analyses including geometry, Mulliken population, QTAIM (quantum theory of atoms in molecules), and NBO (natural bond orbital) suggest that the Am–S/N bonds possess more covalency compared to the Eu–S/N bonds, and the M–S bonds have more covalent character than the M–N bonds. Thermodynamic results reveal that N2,N9-diethyl-N2,N9-di-p-tol...