Single Open Sites on FeII Ions Stabilized by Coupled Metal Ions in CN-Deficient Prussian Blue Analogues for High Catalytic Activity in the Hydrolysis of Organophosphates.

CN-deficient Prussian blue analogues (PBAs), [MN(H2O)x]y[FeII(CN)5(NH3)] (MN = CuII, CoII, or GaIII), were synthesized and examined as a new class of heterogeneous catalysts for hydrolytic decomposition of organophosphates often used as pesticides. The active species of the CN-deficient PBAs were mainly C-bound FeII ions with only single open sites generated by liberation of the NH3 ligand during the catalytic reactions. [CuII(H2O)8/3]3/2[FeII(CN)5(NH3)] showed higher catalytic activity than [CoII(H2O)8/3]3/2[FeII(CN)5(NH3)] and [GaIII(H2O)][FeII(CN)5(NH3)], although N-bound CuII species has been reported as less active than CoII and GaIII species in conventional PBAs. IR measurements of a series of the CN-deficient PBAs after the catalytic reactions clarified that a part of the NH3 ligands remained on [CoII(H2O)8/3]3/2[FeII(CN)5(NH3)] and that hydrogen phosphate formed as a product strongly adsorbed on the FeII ions of [GaIII(H2O)][FeII(CN)5(NH3)]. Hydrogen phosphate also adsorbed, but weakly, on the FeII ions of [CuII(H2O)8/3]3/2[FeII(CN)5(NH3)]. These results suggest that heterogeneous catalysis of the FeII ions with single open sites were tuned by the MN ions through metal-metal interaction.