Hydrothermal Synthesis, Crystal Structure, and Catalytic Potential of a One-Dimensional Molybdenum Oxide/Bipyridinedicarboxylate Hybrid

Abstract

The reaction of MoO3, 2,2'-bipyridine-5,5-dicarboxylic acid (H(2)bpdc), water, and dimethylformamide in the mole ratio 1:1:1730:130 at 150 degrees C for 3 days in a rotating Teflon-lined digestion bomb leads to the isolation of the molybdenum oxide/bipyridinedicarboxylate hybrid material (DMA)[MoO3(Hbpdc)]center dot nH(2)O (1) (DMA = dimethylammonium). Compound 1 was characterized by scanning electron microscopy, FT-IR and C-13{H-1} CP MAS NMR spectroscopies, and elemental and thermogravimetric analyses. The solid state structure of 1 was solved and refined through Rietveld analysis of high resolution synchrotron X-ray powder diffraction data in conjunction with information derived from the above techniques. The material, crystallizing in the noncentrosymmetric monoclinic space group Pc, is composed of an anionic one-dimensional organic-inorganic hybrid polymer, (1)(infinity)[MoO3(Hbpdc)](-), formed by corner-sharing distorted {MoO4N2} octahedra, which cocrystallizes with charge-balancing DMA(+) cations and one water molecule per metal center. In the crystal structure of 1, the close packing of individual anionic polymers, DMA(+) cations, and water molecules is mediated by a series of supramolecular contacts, namely strong (O-H center dot center dot center dot O, N+-H center dot center dot center dot O-) and weak (C-H center dot center dot center dot O) hydrogen bonding interactions, and pi-pi contacts involving adjacent coordinated Hbpdc(-) ligands. The catalytic potential of 1 was investigated in the epoxidation reactions of the bioderived olefins methyl oleate (Ole) and DL-limonene (Lim) using tert-butylhydroperoxide (TBHP) as the oxygen donor and 1,2-dichloroethane (DCE) or (trifluoromethyl)benzene (BTF) as cosolvent, at 55 or 75 degrees C. Under these conditions, 1 acts as a source of active soluble species, leading to epoxide yields of up to 98% for methyl 9,10-epoxystearate (BTF, 75 degrees C, 100% conversion of Ole) and 89% for 1,2-epoxy-p-menth-8-ene (DCE, 55 degrees C, 95% conversion of Lim). Catalytic systems employing the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as solvent could be effectively recycled.