Synthesis, Structures And Properties Of The MOFs Constructed From2-(4’-Carboxyphenyl)-1H-Imidazole-4,5-Dicarboxylic Acid

Metal-Organic Frameworks(MOFs), as a new type of important porous materials, exhibits attractive application prospect in the fields of gas absorption and separation, catalyzer, magnetic materials as well as optical materials for its high porosity, good chemical stability and some other advantages, bringing the new dawn for the porous materials science. Imidazole-4,5-dicarboxylic acid, which possesses strong coordination ability for its multiple coordination sites and various coordination modes, is favored by scientific workers when constructing MOFs. Purposefully changing the substituent group on the2-position of imidazole-4,5-dicarboxylic acid has been an effective way to obtain excellent ligands which can be used to construct MOFs with rapidly changing spatial and topological structures. Based on this principle, a novel rigid aromatic tricarboxylic acid,2-(4’-carboxyphenyl)-1H-imidazole-4,5-dicarbo-xylic acid, has been synthesized and used for constructing MOFs. The main works of this paper are listed as following:1. Sixteen MOFs with novel structures were synthesized under hydrothermal or solvothermal conditions by using2-(4’-carboxyphenyl)-1H-imidazole-4,5-dicarbo-xylic acid (H4L) as the chief ligand,1,10-phenanthroline(phen),4,4’-bipyridine(bipy),1,3-di(4-pyridyl)-propane(bpp) and1,4-bis(1-imidazolyl)butane(bimb) as the auxiliary ligands.2. These MOFs were characterized by elemental analysis, IR spectroscopy, and their structures were determined by single crystal X-ray diffraction. According to the structural analysis results, these sixteen MOFs could be devided into ten types: 1～4[M(H3L)2]·2H2O (M=Co, Ni, Zn, Cd),5～6[M(H2L)(H2O)](M=Mn, Cd),7～8[M3(HL)2(H2O)4]·4H2O (M=Mn, Ni),9[Cd3(HL)2(H2O)6],10[Cd2(L)(phen)2]-3H2O,11[Cd2(L)(bimb)]-H2O,12[Zn3(HL)2(bipy)(H2O)]-4H2O,13[Zn2(L)(bpp)]-H2O,14[Cd6(L)(HL)2(H2L)(phen)6]·H20,15～16M(HL)(H2O)2]-3H2O (M=Gd, Dy). In particular, complex10exhibited single helix structure which was similar to the double helix structure of DNA. The auxiliary ligands in the complex11and13were different, however, both of them exhibited analogous three-dimensional network and (4,5)-connected topological structure. Complex12possessed an interesting (3,8)-connected three-dimensional topological structure. Complex14was a hexanuclear three-dimensional network.3. The luminescent properties of the ligand and some complexes were also studied. The results indicated that the ligand exhibited green fluorescence of a certain intensity. The fluorescence intensities of zinc, cadmium complexes were enhanced with some red shift or blue shift compared with the ligand, which could be classified as two types according to the mechanism, namely metal ion perturbation ligand luminescence and charge transfer transition luminescence. While other complexes exhibited fluorescence quenching phenomenon.4. The interactions between the ligand, some complexes and DNA had also been carried out by employing an EB fluorescent probe method. The results showed that the ligand could insert into DNA intensively. And the insertion intensity of complex10, which contained rigid phen, was the strongest. While other tested complexes exhibited weaker intensity than the ligand.