Amine templated open-framework vanadium(iii) phosphites with catalytic properties

摘要

Four novel amine templated open-framework vanadium(iii) phosphites with the formula (C_5N_2H_(14))_(0.5)[V(H _2O)(HPO_3)_2], 1 (C_5N _2H_(14) = 2-methylpiperazinium), and (L)_(4-x)(H _3O)_x[V_9(H_2O)_6(HPO _3)_(14-y)(HPO_4)_y(H_2PO _3)_(3-z)(H_2PO_4)z] ·nH_2O (2, L = cyclopentylammonium, x = 0, y = 3.5, z = 3, n = 0; 3, L = cyclohexylammonium, x = 1, y = 0, z = 0.6, n = 2.33; 4, L = cycloheptylammonium, x = 1, y = 0, z = 0, n = 2.33) were synthesized employing solvothermal reactions and characterized by single-crystal X-ray diffraction, ICP-AES and elemental analyses, thermogravimetric and thermodiffractometric analyses, and IR and UV/vis spectroscopy. Single-crystal data indicate that 1 crystallizes in the triclinic system, space group P1, whereas 2, 3 and 4 crystallize in the hexagonal space group P6_3/m. Compound 1 has a two-dimensional motif with anionic sheets of [V(H_2O)(HPO _3)_2]~- formula, whose charge is compensated by the 2-methylpiperazinium cations embedded between the layers. In contrast, 2, 3 and 4 present a pillar-layer network giving rise to a three-dimensional framework containing intersecting 16-ring channels with the primary amine templates and the crystallization water molecules enclosed in them. 1, 2, 3 and 4 behave as heterogeneous catalysts for the selective oxidation of alkyl aryl sulfides, with tert-butylhydroperoxide (TBHP) as the oxidizing agent, being active, selective and recyclable for several successive cycles of reaction.