Heterogeneous catalysis over a barium carboxylate framework compound: Synthesis, X-ray crystal structure and aldol condensation reaction

A new three-dimensional alkaline-earth metal–organic framework (MOF) compound, [Ba(pdc)]n (1) (H2pdc = pyridine-2,5-dicarboxylate), has been hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction analysis. X-ray single-crystal analysis reveals that each metal ion in compound 1 is coordinated by seven O atoms from seven different carboxylate groups. While each pyridine-2,5-dicarboxylato (pdc2−) ligand coordinates to seven alkaline earth metal centers through two carboxylate groups adopting μ4-η2:η2-bridging and μ3-η2:η1-bridging coordination modes to afford a 3D network. Thermogravimetric analysis reveals that compound 1 is thermally stable up to around 560 °C. Compound 1 efficiently catalyzes aldol condensation reactions of various aromatic aldehydes with acetone and cyclohexanone under environment friendly heterogeneous condition, giving remarkable yields (up to 96%) with high selectivity (100%) within a short reaction time (6 h). The catalyst was recycled for five successive runs without significant loss of activity. There was no evidence of leaching of metal ions or no loss of structural integrity of the catalyst during the catalytic reaction.

A new three-dimensional alkaline-earth metal–organic framework (MOF) compound, [Ba(pdc)]n (1), has been synthesized through a hydrothermal route and is thermally stable up to ∼560 °C. The framework compound demonstrates excellent catalytic activities in aldol condensation reactions towards various aromatic aldehydes and displays remarkable yields with high selectivity within a short reaction time under heterogeneous condition. Notably, the catalyst can be recycled and reused several times without any loss of activity.Figure optionsDownload as PowerPoint slideHighlights
► A new 3D barium carboxylate framework compound has been synthesized via a hydrothermal route.
► The structure of the 3D Ba(II) compound has been determined by X-ray crystallography.
► The 3D barium carboxylate framework compound shows good catalytic activity in aldol condensation reactions.
► The catalyst can be recycled and reused several times without significant loss of activity.