Insight into selective separation of Am(III)/Eu(III) with novel ligands using (1,10-phenanthroline-2,9-diyl)bis(indolin-1-ylmethanones) as a new skeleton: A scalar relativistic DFT study

Abstract

There are the similar physical and chemical properties between the trivalent actinides (An(III)) and the lanthanides (Ln(III)), which makes the separation process very difficult for nuclear waste reprocessing. Designing efficient ligands with the strong ability to separate An(III)/Ln(III) is one of the ways to solve the problem, and various ligands with 1,10-Phenanthroline as the skeleton have become a hotspot in recent years. Herein we designed a series of novel ligands using (1,10-phenanthroline-2,9-diyl)bis(indolin-1-ylmethanones)(IDL-DAPhen) as a new skeleton. Using scalar relativistic density functional theory (DFT), we systematically unraveled the properties of four IDL-DAPhens modified with electron-donating groups (–CH3, –OCH3) at different substitution sites, and explored the structures of the ligands L1, L2, L3 and L4, bonding properties and thermodynamic behaviors of their complexes coordinated with Am(III)/Eu(III). Molecular orbitals (MOs), IGMH, ETS-NOCV and other analyses showed that the selectivity of the four ligands to Am(III) was higher than that to Eu(III). The bond length, dihedral angle, WBI, QTAIM and thermodynamic results and other ones indicated that L3 and L4 with para-substituents have stronger coordination ability, while L1 and L3 with methyl-substituted exhibit better Am(III)/Eu(III) separation selectivity. The ΔΔG values of L1 for Am(III)/Eu(III) reached −7.71, −7.77 and −11.57 kcal/mol in water, 1-octanol and aniline, respectively. This study provides theoretical guidance for the design of novel ligands for efficient separation of Am (III)/Eu (III), and could expand a new pathway for the design of ligands with better potential selectivity for An (III)/Ln (III) separation.