Syntheses of four porous 3-D Cd(ii) metal–organic frameworks from a new multidentate ligand 5-(imidazol-1-yl)-N′-(pyridin-4-ylmethylene) nicotinohydrazide and their characterization and adsorption properties

Herein, a new multidentate ligand, 5-(imidazol-1-yl)-N′-(pyridin-4-ylmethylene) nicotinohydrazide (L), with an acylhydrazone group was synthesized and characterized. Subsequently, four porous Cd(ii)-MOFs, i.e. [Cd(L)(NO(3))](n) (1), [Cd(L)Cl](n) (2), [Cd(L)Br](n) (3), and [Cd(L)I](n) (4), were assembled using the ligand L by a solvothermal method and characterized by single-crystal X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. Structural analysis shows that the coordination environments around Cd(ii) in all the four compounds are different due to the different coordinated anions. Among them, the coordination geometries and the arrangement of five-coordinated groups of the compound 1 containing the coordinated NO(3)(−) anions are significantly different from those of the other three compounds containing halides. However, all the four MOFs have similar one-dimensional rhombic channels. In these channels, both the nitrate ions and the halide ions are attached to the inner walls of the pores. The CO(2) adsorption properties of 1–4 were studied at 273 K, and the results showed that these compounds exhibit different adsorption capacities for CO(2) due to the presence of different ions in their pores.