The complex [Co^II(qpy)(OH₂)₂]²⁺ (qpy = 2,2′:6′,2′′:6′′,2′′′-quaterpyridine) is an efficient visible light-driven catalyst for both water oxidation and reduction. It catalyses photochemical oxygen evolution from water at pH 8.0 with [Ru^II(bpy)₃]²⁺/S₂O₈ ²⁻ (λ = 457 nm, max TON = 335, bpy = 2,2′-bipyridine). It also catalyses photochemical hydrogen generation from [Ir^III(dF(CF₃)ppy)₂(dtbbpy)]⁺/TEOA (dF(CF₃)ppy = anion of 2-(2,4-difluorophenyl)-5-trifluoromethylpyridine, dtbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine, TEOA = triethanolamine) in aqueous acetonitrile (λ > 420 nm, max TON = 1730).