Enhancing electrocatalytic water oxidation: ligand complementarity in ternary Cu(<scp>ii</scp>) complexes

The electrocatalytic water oxidation activity of two mononuclear ternary copper(II) complexes, 1, [Cu(bipy)(HL1)](ClO₄)₂, [bipy = 2,2'-bipyridine, HL1 = <i>N</i>¹-(2-aminoethyl)ethane-1,2-diamine] and 2, [Cu(phen)(HL1)](ClO₄)₂, [phen = 1,10-phenanthroline], has been investigated. Complexes 1 and 2 exhibit turnover frequencies (TOF) of 483 s^-1 and 445 s^-1 at overpotentials of approximately 453 mV and 493 mV, respectively, in neutral phosphate buffer. These ternary complexes demonstrate superior catalytic performance compared to their binary counterparts. In these ternary complexes, both ligands act complementarily to enhance stability and redox activity, which are crucial for catalytic performance of the metal complexes. Electrochemical investigations further reveal that the structural flexibility of the aliphatic amine ligand moiety influences the overall catalytic efficiency of the ternary metal complexes.