Effect of the Introduction of Amide Oxygen into 1,10-Phenanthroline on the Extraction and Complexation of Trivalent Lanthanide in Acidic Condition

The extractability and complexation properties of lanthanides with N-alkyl-N-phenyl-1,10-phenanthroline-2-carboxamide were investigated. These ligands, which contain two aza-aromatic donors and an oxygen donor in a molecule, are newly developed extractants for actinides and lanthanides. N-Octyl-N-tolyl-1,10-phenanthroline-2-carboxamide exhibited high extractability of Eu3+ even under acidic conditions. In addition, strong complexation in acidic media was confirmed by spectroscopic titration experiments. Investigation of the complexation equilibrium revealed that the presence of an oxygen donor promotes ligand coordination with lanthanides over the competing protonation reaction in acidic solution.