A novel nickel metal-organic framework with fluorite-like structure: gas adsorption properties and catalytic activity in Knoevenagel condensation

A new non-interpenetrating 3D metal-organic framework {[Ni-4(mu(6)-MTB)(2)(mu(2)-H2O)(4)(H2O)(4)]center dot 10DMF center dot 11-H2O}(n) (DMF = N, N'-dimethylformamide) built from nickel(II) ions as connectors and methanetetrabenzoate ligands (MTB4-) as linkers has been synthesized and characterized. The single crystal X-ray diffraction showed that complex exhibits CaF2-like fluorite structure topology and four types of 3D channels with sizes about 12.6 x 9.4 angstrom(2), 9.4 x 8.0 angstrom(2), 12.6 x 11.7 angstrom(2) and 14.9 x 14.9 angstrom(2), which are filled with guest molecules. Conditions of the activation of the compound have been studied and optimized by powder X-ray diffraction during in situ heating, thermogravimetric analysis and infrared spectroscopy. Nitrogen and carbon dioxide adsorption showed that the activated sample exhibits a BET specific surface area of 700 m(2) g(-1) and a carbon dioxide uptake of 12.36 wt% at 0 degrees C, which are the highest values reported for the compounds of the MTB4-series. The complex was tested in Knoevenagel condensation of aldehydes and active methylene compounds. Straightforward dependence of the substrate conversion on the size of used aldehyde was established. A possible mechanism of Knoevenagel condensation over a MTB4-containing a metal-organic framework was proposed.