Preyssler Polyoxometalate Supported Transition Metal Bipyridine Coordination Complexes

We have synthesized two Preyssler-type polyoxometalate ({NaP₅W₃₀O₁₁₀}^14-)-based compounds [{Co^II(C₁₀H₈N₂)₃}₄{Co^III(C₁₀H₈N₂)}_0.74H₄NaP₅W₃₀O₁₁₀]·24H₂O (1) and [{Cu^II(C₁₀H₈N₂)₂}₄(C₁₀H₁₀N₂)₃NaP₅W₃₀O₁₁₀]·6H₂O (2) by solvothermal synthesis. The crystal structure of compound 1 consists of Preyssler polyoxometalate (POM) coordinated to {Co^III(2,2'-bpy)} (bpy = 2,2'-bipyridine, C₁₀H₈N₂) complex and two uncoordinated {Co^II(2,2'-bpy)₃} complexes. The molecular structure of compound 2 consists of four {Cu^II(2,2'-bpy)₂} complexes coordinated to terminal oxygens of Preyssler polyanion and three 2,2'-bipyridinium cations. Compounds 1 and 2 have been characterized unambiguously by single-crystal X-ray crystallography including PXRD, FT-IR, TGA, and DRS spectroscopy. In this work, compounds 1 and 2 are used as photocatalysts in the degradation of environmentally hazardous methylene blue (MB) dye via UV light irradiation. Compound 2 outperforms compound 1 in catalytic efficiency for the degradation of MB dye, achieving 78.1% efficiency compared to 72.3% for compound 1. The redox activities of compounds 1 and 2 have been investigated by electrochemical studies. Interestingly, compounds 1 and 2 exhibit solid-state fluorescence at room temperature.