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

The
reaction of MoO3, 2,2′-bipyridine-5,5-dicarboxylic
acid (H2bpdc), water, and dimethylformamide in the mole
ratio 1:1:1730:130 at 150 °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)]·nH2O (1) (DMA = dimethylammonium). Compound 1 was characterized by scanning electron microscopy, FT-IR
and 13C­{1H} 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[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···O,
N+–H···O–) and
weak (C–H···O) hydrogen bonding interactions,
and π–π 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
°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 °C, 100% conversion of Ole)
and 89% for 1,2-epoxy-p-menth-8-ene (DCE, 55 °C,
95% conversion of Lim). Catalytic systems employing the ionic liquid
1-butyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide as solvent
could be effectively recycled.