Enhanced catalytic activity of solubilised species obtained by counter-cation exchange of K{Co [Fe(CN)]} for water oxidation.

A cyano-bridged coordination polymer, K{Co [Fe(CN)]} {(K)Co-Fe}, reported as a highly active heterogeneous catalyst for water oxidation was solubilised by a conventional counter-cation exchange of K with MeN ions to provide the homogeneous catalyst of (MeN){Co [Fe(CN)]} {(MeN)Co-Fe}. (MeN)Co-Fe exhibited enhanced catalytic activity for photocatalytic water oxidation using [Ru(2,2'-bipyridine)] and SO as a photosensitiser and a sacrificial electron acceptor, respectively, in terms of the initial reaction rate (1.26 μmol min), which is about twice that of (K)Co-Fe (0.61 μmol min). Powder X-ray diffraction, pair distribution function and electrospray ionization mass spectrometry measurements of (MeN)Co-Fe manifested that small heptanuclear clusters of {Co[Fe(CN)]} formed by depolymerisation are catalytically active species in solution.