Chemical, electrochemical, and photochemical catalytic oxidation of water to dioxygen with mononuclear ruthenium complexes

Four new Ru^II-Cl and Ru^II-H₂O complexes containing the meridional 2,2′:6′,2 ′′-terpyridine (trpy) ligand and the chelating 2-(5-phenyl-1H-pyrazol-3-yl)pyridine (H3p) ligand of general formula in- and out-[Ru^II(trpy)(H3p)(X)]ⁿ⁺ (X = Cl, n = 1; X = H₂O, n = 2) have been prepared, isolated and thoroughly characterized both in solution and in the solid state. In solution, all the complexes are characterized spectroscopically by UV/Vis and NMR, and their redox properties investigated by means of cyclic voltammetry, square wave voltammetry, and coulometry. In the solid state, monocrystal X-ray diffraction analysis was carried out for the in and out Ru-Cl complexes. The capacity of the Ru-aqua complexes to act as water oxidation catalysts (WOCs) was also investigated chemically, electrochemically, and photochemically. The performance of these complexes has also been compared to two previously described complexes of general formula in- and out-(Ru^II(trpy)(Hbpp)(H₂O)]²⁺ (Hbpp is 2,2′-(1H-pyrazole-3,5-diyl)dipyridine)), the capacity of which as WOCs had not been previously described.