Complexation properties and structural character of lanthanides complexes of O,N-hetero donor ligand BIZA

ABSTRACT

Complexation properties of N-methyl-N-tolyl-2-(1H-benzimidazol-2-yl)pyridine-6-carboxamide (MeTolBIZA) with trivalent lanthanides were investigated by spectroscopic titration study and discussed based on structural character determined by X-ray crystallography. As a result, it is revealed that one or two MeTolBIZA molecules coordinate with lanthanide ions as tridentate ligand via two nitrogen atoms in 2-(1H-benzimidazol-2-yl)pyridine moiety and one oxygen atom in amide group. The stability constant of 1:2 metal–ligand complex decreases with increase of atomic number of lanthanide, and the 1:2 complex cannot be formed with heavier lanthanides. This result can be attributed to steric hindrance between ligand molecules.

Abbreviations: MeTolBIZA: N-methyl-N-tolyl-2-(1H-benzimidazol-2-yl)pyridine-6-carboxamide; An³⁺: trivalent actinides; Ln³⁺: trivalent lanthanides; TPTZ: 2,4,6-tris(2-pyridyl)-1,3,5-triazine; BTP: 2,6-bis(1,2,4-triazin-3-yl)pyridine; PTA: N-alkyl-N-phenyl-1,10-phenanthroline-2-carboxamide; BIZA: N-alkyl-N-aryl-2-(1H-benzimidazol-2-yl)pyridine-6-carboxamide; MePhBIZA: N-methyl-N-phenyl-2-(1H-benzimidazol-2-yl)pyridine-6-carboxamide; D2EHPA: di-2-ethylhexyl phosphoric acid; EXAFS: extended X-ray absorption fine structure

KEYWORDS:

• Lanthanide
• complexation
• stability constant
• crystal structure

Acknowledgments

This study is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).