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 II 1.5 [Fe II (CN) 6 ]} {(K) Co-Fe }, reported as a highly active heterogeneous catalyst for water oxidation was solubilised by a conventional counter-cation exchange of K + with Me 4 N + ions to provide the homogeneous catalyst of (Me 4 N){Co II 1.5 [Fe II (CN) 6 ]} {(Me 4 N) Co-Fe }. (Me 4 N) Co-Fe exhibited enhanced catalytic activity for photocatalytic water oxidation using [Ru(2,2′-bipyridine) 3 ] 2+ and S 2 O 8 2− as a photosensitiser and a sacrificial electron acceptor, respectively, in terms of the initial reaction rate (1.26 μmol min −1 ), which is about twice that of (K) Co-Fe (0.61 μmol min −1 ). Powder X-ray diffraction, pair distribution function and electrospray ionization mass spectrometry measurements of (Me 4 N) Co-Fe manifested that small heptanuclear clusters of {Co 4 [Fe(CN) 6 ] 3 } 4− formed by depolymerisation are catalytically active species in solution. A water-soluble anionic polynuclear-metal complex, {Co 4 [Fe(CN) 6 ] 3 } 4− , derived from a water insoluble K{Co 1.5 [Fe(CN) 6 ]} by counter cation exchange of K + with Me 4 N + ions showed enhanced activity for photocatalytic water oxidation.