Study On Synthesis, Characterization And Catalytic Performance Of Metal-Organic Frameworks

Metal-Organic frameworks, as a new category of porous materials, have the properties of high specific surface area, highly designable channel, versatile structures and easily functionalized frameworks. All this leads to the widespread attention both in academia and industry. In this paper, the synthesis, characterization and the catalytic performance of the coordinated polymers constructed by the flexible or rigid carboxylic ligands were studied.Nine kinds of coordination polymers are constructed from the assembly reaction of the metal ion and the flexible dicarboxylic acid(iminodiacetic acid, succinic acid and adipic acid) in the presence of additional nitric heterocyclic ligands. [Mn(iminodiacetate)]n(1), [Cu(succinate)(imidazole)2]n(2), [Cd(succinate)(4,4'-bipy)]n(3), [Co(adipate)(4,4′-bipy)]n(4), {[Cd4(adipate)4(1,10'-phen)4]·12H2O}n(5), {[Y2(succinate)3·(H2O)2]·0.5H2O}n(6), [Nd2(succinate)3(H2O)2]n(7), {[Nd(succinat -e)1.5·(H2O)]·1.25H2O}n(8), [La2(succinate)3(H2O)2]n(10). The coordination polymer(1) shows good thermal stability for its high decomposition temperature at 450℃. The coordination polymer (5) has a double-strand helical chain structure, and Cd2+ adopted six and seven coordinated numbers.The crystal structure analysis showed that the flexible dicarboxylate ligands tend to connect the metal ions to form bi- or poly-nuclear structure unit, which could be a beneficial for high thermal stability. When the high coordinated rare-earth metal ions were employed, the flexible dicarboxylate ligands adopted five- or six-dentate coordinated fashion. The diverse extending direction of the flexible chain could give rise to form isomerous complex (coordination polymer (7) and coordination polymer (8)), and it also prevent the additional ligand from coordination to some extent.Five kinds of coordination polymers are synthsized from the assembly reaction of the metal ion and the rigid aromatic carboxylic acid (1,3,5-benzenetricarboxylic acid (H3BTC) and 1,3-benzenedicarboxylic acid (H2BDC)) in the presence of additional competition ligands. {[Nd2(BDC)3(1,10'-phen)(H2O)]·0.5H2O}n(9), [Co3(BTC)2 (H2O)12]·0.25H2O}n(11), [Ni2Zn(BTC)2(H2O)12]n(12), [Zn(BTC)(2,2'-bipy)H2O]n (13),{[Zn2(HBDC)2(BDC)]·(1,10'-phen)·1.5H2O}n (14). The coordination polymer (12) is a novel heterometallic complex.The crystal structure analysis indicated that two aromatic carboxylate ligands but have different coordination character for their different carboxyl numbers; The chelate bipy-like ligands could reduce coordination numbers of metal ions; All these five coordination polymers have various hydrogen bonds networks, by which 3D framework are constructed; The luminescence spectra indicated the aromatic carboxylate ligand could influence the luminescence intensity and the peak positions.In the aspect of catalytic perfomance of MOFs: four coordination polymers [(6), (8), (11) and (12)]are used as catalysts in the accetalization of benzaldehyde with trimethylorthoformate, all of them showed good catalytic activity and high selectivity. The conversion of benzaldehyde reached 81.3% when catalyzed by [Ni2Zn(BTC)2]n(12). The coordination polymer (2) [Cu(succinate)(imidazole)2]n could catalyze the oxidation of benzyl alcohol at room temperature. The catalytic activity was improved with the increasing temperature, while the selectivity of benzaldehyde decreased.