Photo-Induced Water Oxidation Based on a Mononuclear Cobalt(II) Complex

Photo-induced water oxidation based on first row transition metal complexes has drawn much attention recently as a part of the efforts to design systems for solar fuel production. Here, the classic tetradentate ligand TPA (tris(2-pyridylmethyl)amine) is used together with cobalt(II) in CH3CN to form a mononuclear cobalt complex [Co(TPA)Cl]Cl. Single crystal X-ray diffraction shows that [Co(TPA) Cl] Cl is composed of discrete cationic units with a penta-coordinate cobalt center, along with chloride counter ions. In borate buffer, the Co complex acts as a water oxidation catalyst, as shown by the presence of a catalytic wave in electrochemistry. Under visible light irradiation, in the presence of photosensitizer and electron acceptor, the Co complex catalyzes O-2 evolution with a turnover frequency (TOF) of 1.0 mol(O-2)center dot mol(Co)(-1)center dot s(-1) and a turnover number (TON) of 55 mol(O-2)center dot mol(Co)(-1) in pH 8 borate buffer.