Study on the extraction of lanthanides by isomeric diglycolamide extractants: an experimental and theoretical study

Two isomeric diglycolamide (DGA) extractants, N,N'-dimethyl-N,N'-dioctyl diglycolamide (L^I) and N,N-dimethyl-N',N'-dioctyl diglycolamide (L^II), were used to perform a comparative study on the extraction performances towards several lanthanides by extraction experiments and theoretical calculations. The experimental results show that both L^I and L^II show a positive sequence on the extraction of lanthanides, and L^I exhibits the higher complex ability with these lanthanides than L^II, except for La and Ce. Slope analysis shows that 1:2 or 1:3 complexes are formed between the two ligands and the metal ions. The geometrical structures of the complexes were optimized in the gas phase by density functional theory (DFT) on the basis of complex compositions. The results of bond lengths, MBOs and topological analysis indicated that the electrostatic interaction between metal ions and two amide O atoms in the L^II ligand is not as homogeneous as in L^I, and this inhomogeneity is likely to be related to the poor extraction performance of L^II.