A nickel containing polyoxometalate water oxidation catalyst

A new pentanickel silicotungstate complex, K10H2[Ni-5(OH)(6)(OH2)(3)(Si2W18O66)]center dot 34H(2)O (KH-1), has been synthesized and characterized by X-ray crystallography and several other methods. Dynamic light scattering, kinetics and other experiments confirm that 1 in the presence of [Ru(bpy)(3)](2+) (the photosensitizer for light-driven water oxidations) and [Ru(bpy)(3)](3+) (the oxidant in the dark water oxidations) exists in an equilibrium between solution (soluble) and a [Ru(bpy)(3)](n+)-1 complex (minimally soluble) form. This new pentanickel polyoxometalate catalyzes efficient water oxidation in both the dark and on irradiation with 455 nm LED light with 1.0 mM [Ru(bpy)(3)](2+) photosensitizer and 5.0 mM Na2S2O8, sacrificial electron acceptor. Four lines of evidence indicate that 1 in this solution (sic) Ru(bpy)(3)](n+)-1 complex equilibrium remains molecular and does not decompose to nickel hydroxide particles.