A new pentanickel silicotungstate complex, K10H2[Ni5(OH)6(OH2)3(Si2W18O66)]·34H2O (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 ![[right left harpoons]](http://www.rsc.org/images/entities/char_21cc.gif)
Ru(bpy)3]n+-1 complex equilibrium remains molecular and does not decompose to nickel hydroxide particles.
Dalton Transactions
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