Theoretical insights on the extraction separation of Am(III)/ Eu(III) based on four different nitrogen-containing symmetrical coordination skeleton ligands

Understanding the interaction between actinide An(III)/lanthanide Ln(III) and the N donor extractant is of great significance for the efficient separation of An3+/Ln3+ in the advanced nuclear fuel cycle. Four N-donor extractants with different skeletons were introduced in this article. The electronic structures and properties of the four ligands and the coordination structures and bonding properties of the complexes formed by the four ligands with Am(III) and Eu(III) have been systematically studied by scalar relativistic density functional theory (DFT), and their complexation capacity and extraction selectivity for Am(III) and Eu(III) have been investigated by thermodynamic analysis. All analyses of the geometric structure, Wiberg bond index, QTAIM (quantum theory of atoms in molecules), and NBO (natural bond orbitals) of the complexes indicate that the Am-N bond has more covalent features than the Eu-N bond, meaning that the interaction between the ligand and Am(III) ion is stronger compared to Eu(III) ion. The results of thermodynamic analysis of the four N-donor extractants in the solvent extraction process show that they have good extraction selectivity and separation performance for Am (III) and Eu(III). This study will provide some theoretical support for designing extractants containing nitrogen donor with excellent separation performance based on different skeletons.