The Syntheses, Structures And Properties Of Coordination Complexes Based On Rigid Polycarboxylic Acid Ligands

The rigid polycarboxylic acid ligands have been widely used in design and preparation of metal–organic coordination complexes recently. In addition to the strong coordination ability and varieties of coordination modes of carboxyls, the more important reason is that the rigidity of the ligand, making the conformation of ligand structure not change easily in the self-assembly process, provides the potential to form large-pore coordination complex. Besides, the hydrogen bonding forces and π…π stacking can form easily in the structures of the polycarboxylic acid complex, which would be favorable for construction of high-dimensional structure. In this paper, we choose 6-(3,5-dicarboxyl phenyl) nicotinic acid(H3L1),2,2’-Bipyridine-5,5’-dicarboxylic acid(H2L2) and p-terphenyl-4,4″-dicarboxylic acid,2′,5′-dimethyl(H2L3) as organic ligands to coordinate with different transition metal ions, twelve novel complexes have been prepared successfully. All complexes(1)-(12) were characterized by single crystal X-ray diffraction, elementary analysis, Infrared Radiation spectra(IR), thermal gravity analysis and PXRD. At the same time, the UV spectrum, fluorescence and magnetic properties of the parts of metal-organic frameworks have also been investigated. The main contents are as follows:First, single crystal X-ray diffraction analysis shows Co3(L1)2(H2O)4(1), Cd3(L1)2(H2O)7(2), Cd3(L1)2(H2O)11(3), Cd3(L1)2(DMF)2(H2O)(4) and Co3(L3)3(bpy)2(11) with 3D network structure; [Ni(L2)(H2O)]CH3OH(8), [Co(L2)(H2O)]H2O(9), Cu(L3)1(H2 L3)0.5(bpy)(10) and Cu(L3)(bpy)(12) with 2D plane structure; [Zn(L2)(H2O)4](H2O)2(5), [Co(L2)(H2O)4](H2O)2(6) and [Ni(L2)(H2O)4](H2O)2(7) with 0D structure. In self-assembly processes of(2)-(4), it can be found that the degree of the muti-carboxylate ligand deprotonated and the proportion of metal ions and ligands have a significant impact on diversity of final structures. Meantime, the π…π stacking and hydrogen bonding forces exist in the structures of(5),(6),(7) and(9).Second, the temperature-dependent magnetic susceptibility data of(1) has been measured at an applied magnetic field of 1000 Oe in the temperature range of 2-300 K, the result shows the occurrence of an antiferromagnetic of(1).Third, the luminescence properties of(2)–(4) and free ligand H3L1 have been investigated in the solid state at room temperature, the results show that only fluorescence spectrum of(4) has a little red-shift.Fourth, the thermal behaviors of(1)–(12) were studied by TGA.