Creation and stabilisation of tuneable open metal sites in thiocyanato-bridged heterometallic coordination polymers to be used as heterogeneous catalysts

Abstract

A series of thiocyanato-bridged heterometallic coordination polymers with a 3D reticular network have been synthesised by the reaction of [Pt^IV(SCN)₆]²⁻ with M^II ions to form {M^II[Pt^IV(SCN)₆]}_n and {[M^II(CH₃OH)₂][Pt^IV(SCN)₆]}_n (M^II = Mn^II, Fe^II, Co^II, Ni^II or Cu^II) in water and methanol, respectively. Single-crystal X-ray analyses revealed the absence of open metal sites in {M^II[Pt^IV(SCN)₆]}_ns and the formation of potential open metal sites at the M^II ions of {[M^II(CH₃OH)₂][Pt^IV(SCN)₆]}_ns by the coordination of methanol. One of the two coordinating methanol molecules in {[Co^II(CH₃OH)₂][Pt^IV(SCN)₆]}_n was replaced with pyridine to stabilise the open metal sites, because the methanol molecules are too labile to maintain open metal sites in water. The heterogeneous catalysis of coordination polymers with and without open metal sites was examined for organophosphate hydrolysis and photocatalytic water oxidation to clarify the requisites for heterogeneous catalysts.