Structural Diversity and Sensing Properties of Metal-Organic Frameworks with Multicarboxylate and 1H-Imidazol-4-yl-Containing Ligands

Abstract

Two 1H-imidazol-4-yl-containing ligands 1,3-di(1H-imidazol-4-yl)benzene (L1) and 4,4′-di(1H-imidazol-4-yl)biphenyl (L2) were employed to react with corresponding metal salt together with varied carboxylate ligands under hydro- and solvothermal conditions, and six new metal-organic frameworks (MOFs) [Cd(L1)(oba)]·DMF (1), [Ni3(L1)2(BPT)2(H2O)4] (2), [Zn2(L1)2(HBPT)2]·H2O (3), [Ni(L1)(BPTC)0.5(H2O)2] (4), [Ni2(μ2-O)(L2)3(Hoba)2(H2O)2] (5), and [Ni2(L2)3(BPTC)(H2O)2]·6H2O (6) [H2oba = 4,4′-oxybis(benzoic acid), H3BPT = biphenyl-3,4′,5-tricarboxylic acid, H4BPTC = biphenyl-3,3′,5,5′-tetracarboxylic acid, DMF = N,N-dimethylformamide] were achieved and structurally characterized. MOFs 1, 3, 4, and 5 are different two-dimensional networks, which are further joined together by hydrogen bonds to generate three-dimensional (3D) supramolecular frameworks. 2 is a (4,4)-connected binodal 3D framework with a point symbol of {3·4·5·83}4{32·82·92}, while 6 is a diamond 3D framework. The results show that coordination geometry of the metal centers and coordination mode of the ligands play important roles in the formation of MOFs with diverse structures. Moreover, luminescent studies showed that 1 and 3 represent highly efficient quenching for detecting Fe3+ ions and acetone molecules. In addition, 6 exhibits selectively adsorption of CO2 over N2.