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

Abstract

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.