Synthesis And Properties Of Metal-Organic Frameworks With Halogen-Substituted Aromatic Carboxylate Ligands

As a new type of porous materials, metal-organic frameworks (MOFs) have several potential applications in the areas of catalysis, sensors, and gas storage. In this paper, MOFs with halogen-substituted aromatic carboxylate ligands were synthesized. Furthermore, the research work about structure and properties of them were done.Three kinds of organic ligands of 2,3,5,6-tetrachloroterephthalonitrile, 1,3,5-trichloro- 2,4,6-tricyanobenzene and 1,3,5-tribromo-2,4,6-tricyanobenzene were synthesized. The structures were characterized by IR and elemental analysis. With 2,3,5,6- tetrachloroterephthalic acid as raw material, 2,3,5,6-tetrachloroterephthalonitrile was synthesized in three-step reaction, sulfonyl chlorination, ammonolysis and dehydration, correspondently. The total yield is up to 72.5%. Through chlorination, bromination, oxidation, sulfonyl chlorination ammonolysis and dehydration, 1,3,5-trichloro-2,4,6-tricyanobenzene was obtained from starting material mesitylene. The total yield reaches to 32.8%. Aldehyde was also gained from mesitylene as raw material through bromination, hydrolysis and oxidation. Through dehydration reaction of oxime from aldehyde, 1,3,5-tribromo-2,4,6- tricyanobenzene was prepared in total 21.7% yield.Using 2,3,5,6-tetrachloroterephthalonitrile as a precursor with Cd(NO3)2·4H2O, coordination polymer [Cd(C8Cl4O4)(C5H5N)3]n was synthesized by solvothermal method in yield 82%. The structure was characterized by elemental analysis, IR and single crystal X-ray diffraction determination. Property about luminescent and thermal stability were investigated. Cd(II) ion center adopts six coordination modes in the basal structure unit of coordination polymer. Cd(II) ion center coordinates to two oxygen atoms of carboxyl of 2,3,5,6-tetrachloroterephthalic acid in a bidentate fashion, to one oxygen atom of carboxyl of 2,3,5,6-tetrachloroterephthalic acid in a monodentate fashion and to three nitrogen atoms of the three trispyridyl ligands. The overall geometry around the Cd(II) ion center can be described as a distorted octahedral. Carboxyl acid coordinate to Cd(II) ion forming 1D zigzag chain by trans monodentate and bidentate coordination modes. The luminescent properties of free organic ligand and its metal complex were mensurated with wavelength in 282nm and 287nm, respectively. The result showed that an obvious increase occured in the luminescent intensity of complex. Thermal gravimetric analysis was performed on the coordination polymer. It suggested high thermal stability that there was no weight loss until the temperature up to 180 degree.In conclusion, we focused on research work in the complex with the aromatic carboxylate ligand. The results would be in favor of our further work.