Extraction and Complexation Studies of N-methyl-N-phenyl-2-(1H-benzimidazol-2-yl)pyridine-6-carboxamide with Trivalent Lanthanide

The extractability and complexation properties of trivalent lanthanides with N-methyl-N-phenyl-2-(1H-benzimidazol-2-yl)pyridine-6-carboxamide (MePhBIZA) were investigated. The MePhBIZA, containing two aza-aromatic donors and an oxygen donor in the molecule, was designed with regard to 2-(2-pyridyl)benzimidazole (Biz) and newly synthesized as an extractant for trivalent lanthanides, Ln3+, and actinides, An3+. The MePhBIZA exhibited satisfactory extractability of Eu3+ even under acidic conditions. A speciation diagram, based on the formation constants determined by spectroscopic titration experiments, indicated that the MePhBIZA formed complexes with Eu3+ in acidic solution. These results showed that the addition of the amide group promotes ligand coordination with Eu3+ over the competing protonation reaction in relatively acidic solution in comparison with Biz.