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

A novel asymmetric diglycolamide N,N-dimethyl-N′,N′-dioctyl diglycolamide (L(II)) was synthesized. The Nd(iii) extraction behavior from HNO(3) 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).