A comparative study on the coordination of diglycolamide isomers with Nd(iii): extraction, third phase formation, structure, and computational studies

Abstract

A novel asymmetric diglycolamide N,N-dimethyl-N′,N′-dioctyl diglycolamide (L^II) was synthesized. The Nd(III) extraction behavior from HNO₃ and loading capability of the solution of L^II in 40/60 (v/v)% n-octanol/kerosene were studied. Analyses by the slope method, ESI-MS, and FT-IR indicated that, similar to the previously studied isomer ligand N,N′-dimethyl-N,N′-dioctyl diglycolamide (L^I), 1 : 3 Nd(III)/L^II complexes formed. Under the same experimental conditions, the distribution ratio and limiting organic concentration of L^II towards Nd(III) were smaller than those of L^I, but the critical aqueous concentration of L^II was larger, which implies that L^II exhibited poorer extraction and loading capabilities towards Nd(III) than L^I, and L^II has a tendency to be less likely to form the third phase. The quasi-relativistic density functional theory (DFT) calculation was performed to provide some explanations for the differences in their extraction behaviors. The electrostatic potential of the ligands indicated that the electron-donating ability of the amide O atoms in L^II displayed certain differences compared with L^I. This inhomogeneity in L^II affected the interaction between L^II and Nd(III), as supported by QTAIM and bonding nature analysis, and it seemed to reflect in the extraction performance towards Nd(III).