Bifunctional design of stable metal-organic framework bearing triazole–carboxylate mixed ligand: Highly efficient heterogeneous catalyst for knoevenagel condensation reaction under mild conditions

A highly water stable zinc metal–organic framework (ZnMOF), {[Zn(HL)₂]}_n, was synthesized using a triazole–carboxylate-based mixed ligand (L = 5-(4H-1,2,4-triazol-4-yl)isophthalic acid). A 2D MOF was formed by hydrothermal synthesis, and extended to a 3D supramolecular network through strong hydrogen bonding. This MOF was fully characterized by Fourier-transformation infrared spectroscopy, thermogravimetric analysis, single-crystal X-ray diffraction (XRD), powder XRD and elemental analysis. Owing to the d¹⁰ configuration of this ZnMOF, its luminescent properties were suitable for the sensing of the CN⁻ ions over other anions, as inferred from the florescence result. However, regarding the catalytic mechanism, this ZnMOF showed a strong ability to react with CN⁻, which might be due to the hydrogen bonding between the COOH groups without coordination. This interaction behavior with CN⁻ ions makes the ZnMOF a promising heterogeneous catalyst for Knoevenagel condensations using malononitrile and aldehyde derivatives as reactants under mild conditions. All reactions were conducted in water as a green solvent.