Construction and isomeric transformation of polyoxometalates directed by 1,ω-bis(pyridinium)alkane templates

Ten novel inorganic–organic hybrid polyoxometalates, namely, [1,3-bis(pyridinium) propane]2[α-Mo8O26] (1), [1,4-bis(pyridinium)butane]2[1D-Mo8O26] (2), [1,5-bis(pyridinium)pentane]2[θ-Mo8O26] (3), [1,6-bis(pyridinium)hexane]2[1D-Mo8O26] (4), [1,7-bis(pyridinium)heptane]2[β-Mo8O26] (5), [1,8-bis(pyridinium)octane]2[θ-Mo8O26] (6), [1,9-bis(pyridinium)nonane]2[(α + β)-Mo8O26] (7), [1,10-bis(pyridinium)decane]2[β-Mo8O26] (8), [1,11-bis(pyridinium)undecane]2[β-Mo8O26] (9), [1,12-bis(pyridinium)dodecane]2[γ-Mo8O26] (10), (Scheme 1) were synthesized by cation templated self-assembly with octamolybdate anions under hydrothermal reaction conditions. Crystal data analysis revealed that these compounds were all composed of discrete organic cations and polyacid anions [Mo8O26]4− interacting by electrostatic and hydrogen bond interactions. Interestingly in these compounds the anion fraction could take on α-, β-, θ-, γ-[Mo8O26]4− 0D isomers or rare 1D- polymeric frameworks with a simple length modification of the alkane components. Moreover, these polyacid compounds had definite catalytic activities on the oxidation reaction of acetaldehyde to acetic acid and the relationship of structure/catalytic activities were initially demonstrated.