Studies of the pathways open to copper water oxidation catalysts containing proximal hydroxy groups during basic electrocatalysis.

Water oxidation can lead to a sustainable source of energy, but for water oxidation catalysts to be economical they must use earth abundant metals. We report here 2:1 6,6′-dihydroxybipyridine (6,6′-dhbp)/copper complexes that are capable of electrocatalytic water oxidation in aqueous base (pH = 10–14). Two crystal structures of the complex that contains 6,6′-dhbp and copper(II) in a ratio of 2:1 (complex 1) are presented at different protonation states. The thermodynamic acid dissociation constants were measured for complex 1, and these show that the complex is fully deprotonated above pH = 8.3 (i.e., under water oxidation conditions). CW-EPR, ENDOR, and HYSCORE spectroscopy confirmed that the 6,6′-dhbp ligand is bound to the copper ion over a wide pH range which shows how pH influences precatalyst structure. Additional copper(II) complexes were synthesized from the ligands 4,4′-dhbp (complex 2) and 6,6′-dimethoxybipyridine (complexes 3 and 4). A zinc complex of 6,6′-dhbp was also synthesized (complex 5)....