Crystal structure and oxygen reduction reaction (ORR) activity of copper(II) complexes of pyridylmethylamine ligands containing a carboxy group

Abstract

Abstract To discuss the relationship between the structure and the oxygen reduction reaction (ORR) activity of pyridylmethylamine copper complexes containing carboxy groups, CuII complexes of a N,N-bis(2-pyridylmethyl)phenylmethylamine tridentate ligand (L1) or its carboxy derivatives (2-{[bis(2-pyridylmethyl)amino]methyl}benzoic acid: L2, 3-{[bis(2-pyridylmethyl)amino]methyl}benzoic acid: L3, or 4-{[bis(2-pyridylmethyl)amino]methyl}benzoic acid: L4) were synthesized and characterized. The X-ray crystal structures of mononuclear CuII complexes ligated by L2–L4 were obtained as dichloride complexes, and a crystallographic analysis revealed that all of them have a square pyramidal geometry. The ESR spectroscopy showed that these complexes also had a square pyramidal geometry in a neutral aqueous solution. Cyclic voltammetry analysis in a neutral aqueous solution suggested that only the CuII complex of L2 shows intramolecular interaction between the carboxy group and copper ion in the aqueous solution. The introduction of a carboxy group dramatically increased the amount of the CuII complexes adsorbed on carbon black, which can slightly increase the ORR activity.