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

A novel asymmetric diglycolamideN,N-dimethyl-N′,N′-dioctyl diglycolamide (L^II) was synthesized. The Nd(iii) extraction behavior from HNO₃and loading capability of the solution of L^IIin 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 ligandN,N′-dimethyl-N,N′-dioctyl diglycolamide (L^I), 1 : 3 Nd(iii)/L^IIcomplexes formed. Under the same experimental conditions, the distribution ratio and limiting organic concentration of L^IItowards Nd(iii) were smaller than those of L^I, but the critical aqueous concentration of L^IIwas larger, which implies that L^IIexhibited poorer extraction and loading capabilities towards Nd(iii) than L^I, and L^IIhas 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^IIdisplayed certain differences compared with L^I. This inhomogeneity in L^IIaffected the interaction between L^IIand Nd(iii), as supported by QTAIM and bonding nature analysis, and it seemed to reflect in the extraction performance towards Nd(iii).