Porous magnesium carboxylate framework: synthesis, X-ray crystal structure, gas adsorption property and heterogeneous catalytic aldol condensation reaction

Abstract

A new three-dimensional alkaline-earth metal–organic framework (MOF) compound, [Mg(Pdc)(H₂O)]_n (1) (H₂Pdc = pyridine-2,5-dicarboxylic acid), has been synthesized and structurally characterized by single crystal X-ray diffraction analysis. Compound 1 features a 3D porous framework afforded by the Mg₂-diad centers through formation of interconnected chair like structural motifs. A nitrogen adsorption study confirms the microporosity of compound 1 with a BET surface area of 211 ± 12 m² g⁻¹. Upon dehydration, the BET surface area of 1 is enhanced to a value of 463 ± 36 m² g⁻¹ due to removal of coordinated water molecule. After rehydration, the compound reverts to its original form as evidenced by powder X-ray diffraction and IR spectroscopic analysis and N₂ sorption measurement. Compound 1 retains its pore structure with a variable BET surface area in several cycles of dehydration and rehydration processes indicating robustness of the framework in [Mg(Pdc)(H₂O)]_n (1). Compound 1 catalyzes the aldol condensation reactions of various aromatic aldehydes with acetone and cyclohexanone in heterogeneous conditions. Notably, the catalytic activity of the compound is enhanced upon dehydration. The catalyst can be recycled and reused several times without significant loss of activity.