Structure, Bonding, and Electronic Properties of Four Rare Earth Complexes with a Phenoxyacetic Acid Ligand: X‑ray Diffraction and DFT Studies

In this article, a new family of rare earth (RE) complexes with formula of [RE2(EPOA)6(H2O)3]·H2O, where RE = La, Nd, Er, Y and the HEPOA = 4-ethyl phenoxyacetic acid was synthesized. Their structures were characterized by single-crystal X-ray diffraction, FT-IR, and elemental analysis. The four complexes are isostructural and consist of two-dimensional networks. The decrease in Ln–O bond lengths reflects the lanthanide contraction. The structures of HEPOA ligand, the resulting dimer formed by hydrogen bond and their hydrogen binding energy were studied by density functional theory (DFT). In addition, atoms in molecules (AIMs) analysis revealed the presence of partial closed shell interactions between REs and oxygen atoms of HEPOA ligand in the four complexes. The values of bond degree (BD) have been calculated to evaluate the strength of interactions, suggesting that HEPOA ligand interacts more strongly with La and Nd than Er and Y. Investigations of the complexation of REs with phenoxyacetic acid-related ligand provide more useful information on the development of efficient extractants for RE separation.