Using novel open-framework copper borovanadate as an effective catalyst in the conversion of cyclohexanol to cyclohexanone

A new open-framework copper borovanadate containing two oxidation states of V⁴⁺ and V⁵⁺ cations {[Cu₅(1,2-dap)₁₀][V^V₂V^IV₁₀B₁₈O₅₄(OH)₆(H₂O)]}·2H₃BO₃·9H₂O (1,2-dap: 1, 2-propylene diamine) (1) using 1,2-dap as template agent has been successfully prepared. It is composed of five coordination cations [Cu(1,2-dap)₂]²⁺and one borovanadate anion [V^V₂V^IV₁₀B₁₈O₅₄(OH)₆(H₂O)]^10- constructed by one {B₁₈O₃₀(OH)₆} and two {V₆O₁₈} subunits, as well as two isolated H₃BO₃ molecules and nine H₂O molecules. The compound exhibits for the first time penta-coordinated copper cations, uncoordinated H₃BO₃ molecules and 1, 2-dap ligands in the series of open-framework borovanadates. Its UV diffuse-reflectance spectrum, Mott-Schottky curve, fluorescent emission, chromaticity and second-order lifetime were investigated in detail. The stable pH range (5.8–2.3) of the borovanadate anion in DMF solution was explored by means of fluorescence and UV spectra. In particular, it showed effective catalytic activity in the conversion of cyclohexanol to cyclohexanone (conversion: 86.8 %, selectivity: 97.4 %). The possible catalytic mechanism for the catalytic reaction had been also established. The studies revealed that the borovanadate could be used as a potential stable catalyst for the selective oxidation of cyclohexanol.