Organic–inorganic hybrids based on four-electron reduced Keggin β-isomer phosphododecamolybdates and diazines

Abstract

Six salts of diazonium cations (C₄H₅N₂⁺) with the four-electron reduced β-Keggin phosphododecamolybdate, (1,2-C₄H₅N₂)₃[H₄PMo₁₂O₄₀]·9H₂O (1), (1,3-C₄H₅N₂)₂[H₅PMo₁₂O₄₀]·(1,3-C₄H₄N₂)·10H₂O (2), (1,4-C₄H₅N₂)₃[H₄PMo₁₂O₄₀]·5H₂O (3), (1,2-C₄H₅N₂)₃[H₄PMo₁₂O₄₀]·2H₂O (4), (1,3-C₄H₅N₂)₃[H₄PMo₁₂O₄₀]·2H₂O (5), and (1,4-C₄H₅N₂)₂[H₅PMo₁₂O₄₀]·½(1,4-C₄H₄N₂)·5H₂O (6), have been synthesised in aqueous solution. Compounds 1–3 were obtained photochemically using methanol as electron donor, and compounds 4–6 were prepared using thiophosphate as reducing agent. These compounds contain the four-electron reduced β-Keggin polyanion with a variable degree of protonation. The crystal packing in compound 1 consists of chains formed by pairs of polyanions hydrogen bonded along the [010] direction. The diazonium cations are connected, via NX1–HX1⋯Ow hydrogen bonds, to a ten-membered ring of hydrogen bonded water molecules. The crystal packing in compound 6 is formed by antiparallel chains of polyanions connected through the hydrogen bond OH_poly⋯O_poly along the [010] direction. These polyanion chains are embedded in a 3D-channel structure formed by a helicoidal arrangement of the diazine species hydrogen bonded via the water molecules. The dimensions of these tunnels are approximately 14 × 13.5 Å. Ab initio RHF calculations have been performed on idealised α- and β-Keggin isomers in order to get information about stability and protonation sites and interactions between the organic rings and the surface of the Keggin anions.