Non-covalently bonded 2D-3D metal-organic frameworks from the reactions of Cd(II) and Zn(II) with 3,5-dimethylpyrazole and carboxylate ligands

摘要

Seven new complexes, namely Cd(Hdmpz)_2(L1)_2 (1) (Hdmpz = 3,5-dimethylpyrazole, L1 = N-phenylmaleamate), Cd(Hdmpz) _4(L2)_2 (2) (L2 = 1,3-benzodioxole-5-carboxylate), Zn _2(μ-dmpz)_2(Hdmpz)_2(L3)_2 (3) (L3 = 2-chloronicotinate), Zn(Hdmpz)_2(L4)_2 (4) (L4 = 3,5-dinitrobenzoate), Zn(Hdmpz)_2(HL5)_2 (5) (HL5 = 5-chlorosalicylate), Cd(Hdmpz)_2(HL6) (6) (HL6 = 5-sulfosalicylate) and Cd2(Hdmpz)_4(L7)_2 (7) (L7 = maleate), have been synthesized from the self-assembly of the Zn/Cd ions, 3,5-dimethylpyrazole and carboxylate ligands at room temperature. All the complexes were structurally characterized by different techniques, including elemental analysis, IR spectra, TG and single crystal X-ray diffraction analysis. The X-ray studies suggest that these complexes display mononuclear to dinuclear structures with a tetrahedral geometry around each zinc center, and an octahedral geometry around each cadmium center. The pyrazole ligands in all the compounds except compound 3 are coordinated only in the monodentate fashion by its neutral N group. In 2, 3, 4, 5 and 6, the carboxylate groups behave as monodentate ligands. The COO~- group in 1 and the SO_3 ~- group in 6 both coordinate to the metal in a chelating bidentate fashion. The carboxylates in 7 functioned as a tetradentate bridging ligand. The uncoordinated oxygen atom of the carboxylate group in all of the compounds forms intramolecular hydrogen bonds with the N-H group of the coordinated 3,5-dimethylpyrazole ligand. On the basis of the X-ray crystallographic study, the rich intra- and intermolecular non-covalent interactions, such as classical hydrogen bonds, CH-Cl, CH _3-Cl, Cl?Cl, Cl?O, C-H?O, CH_3? O, C-H?π, CH_2?π, CH_3-π, O-π and π-π interactions, are analyzed. The various non-bonding interactions in these compounds are responsible for different structures, such as sheet, 3D network and 3D layer structures. The thermal stabilities of 1-7 were examined and the results show that the complexes seem to be good candidates for novel hybrid inorganic-organic materials with good thermal stability.