Herein we report the facile, green syntheses of three new polyoxomolybdate-based inorganic-organic hybrid materials using room temperature ionic liquid (RTIL), 1-butyl-3-methyl-imidazolium tetrafluoroborate (bmim)[BF4], as a green and reactive solvent. The organic imidazolium component of the RTIL was incorporated into all three structures, the μ5-oxo octamolybdate cluster compound (bmim)3NH 4[Mo8O26] (1) and two Keggin-type cluster compounds, one being a charge transfer salt (bmim)4[PMo VMo11O40] (2) and the other having the unreduced anion (bmim)3[PMo12O40] (3). Phase pure and highly crystalline samples were obtained. In 1 the Mo8O 26 moiety is a tetranionic cluster in its β phase. Compound 1 contains three bmim cations and an NH4+ molecule to complement the -4 charge on the octamolybdate anion. The α-phase Keggin-type anion in 2, [PMoVMo11O40] 4-, contains one Mo atom in the +5 oxidation state, indicating that 2 is a charge transfer complex. The α-phase Keggin-type anion in 3, [PMo12O40]3-, has 12 fully-oxidized Mo atoms. Compound 3 has a band gap ∼3.5 eV. The catalytic nature of compound 3 in the oxidation of styrene to benzaldehyde was investigated. The maximum styrene conversion was 83%, while the maximum selectivity to benzaldehyde was 96.5%. The catalyst was successfully used for five cycles without significant loss in activity or selectivity. The structure of the catalyst remains unchanged after repeated use. Our work points to the feasibility of generating a wide variety of new and useful POM-based compounds through a 'green' synthesis route.
ASJC Scopus subject areas
- Materials Chemistry