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

Abstract

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), Zn2(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 SO3- 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, CH3–Cl, Cl⋯Cl, Cl⋯O, C–H⋯O, CH3⋯O, C–H⋯π, CH2⋯π, CH3–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.