Syntheses, Structures And Properties Of Coordination Polymers With 1,5-dihydroxy -naphthalene-2,6-dicarboxylic Acid

Coordination Polymers (CPs, also known as Metal-organic frameworks or MOFs) are an emerging class of porous materials constructed from metal ions and organic lingand. Due to the great advantages of varied synthesis methods and their structural and functional tunability, the area of MOFs has become one of the fastest growing fields in chemistry, on the other hand, MOFs also have great potential applications in the fields of gas adsorption/separation, catalysis, fluorescence and magnetism.In this thesis, a rigid organic ligand 1,5-dihydroxynaphthalene-2,6-dicarboxylic (H4DHNDC) acid was used to construct new coordination polymers with transition metal ions and lanthanide metal ions. What’s more, we investigated the stability, fluorescence and magnetic properties of some compounds.1. Construction of new coordination polymers with transition metal ions:We used the rigid organic ligand 1,5-dihydroxynaphthalene-2,6-dicarboxylic acid to construct six new coordination polymers with transition metal ions through solvothermal reactions and room-temperature reactions. Compound [Zn(H2DHNDC)(H2O)4] (1)and Compound [Co(H2DHNDC)(H2O)4] (3)are isomorphous. In the structures, metal ions are bridged by the ligand to form 1-D chains, which are further associated via O-H.....O hydrogen bonds to form a 3-D supramolecular architecture with the pcu topology. Compound [Cd2(H2DHNDC)2(DMF)(H2O)2]-2DMF (2) is a 3D framework in which Cd(II) chains with μ-O, O’- and μ-O, O:O’-carboxylate bridges are interlinked by the naphthalene backbones. The compound exhibits a new topology, with point symbol (4.102)(4.122)(42.103.12).Compound [Mn(H2DHNDC)(DMF)2] (4) exhibits a rhombohedral 1-D chain with double μ-O, O’-carboxylate bridges, and the chains are connected by the H2DHNDC2-ligand to form a 3-D dmd network. Compound [Cu2(DHNDC)(DMF)3] (5), a 2-D coordination polymer, was obtained by room-temperature synthesis. Notably, the ligand in 5 adopts an unusual coordination mode different from those in the other compounds we obtained. In 5, the ligands are fully deprotonated and all of the hydroxyl and carboxylate oxygens are involved in coordination, while in other compounds the hydroxyl group is protonated and uncoordinated. In 5, the copper ions are chelated by the ligand via a hydroxyl oxygen and a carboxyl oxygen or via a carboxylate group. The coordinated the copper ions Cu2+ together with the o-position hydroxyl group. Compound [Mg2(H2DHNDC)2(DMF)1.5(H2O)]·XDMF (6) displays a 2D sql network based on a binuclear magnesium unit and H2DHNDC2-linkers between units. Compounds 1 and 2 both show ligand-based blue fluorescence. Magnetic studies were carried out with compounds 4 �'� 5. In 4, the adjacent Mn(Ⅱ) ions along the chain are antiferromagnetically coupled through double μ.-O, O’-carboxylate bridges, with J=-1.1cm-1. In 5, there are ferromagnetic exchange between Cu(Ⅱ) ions within the chain (J=-10.2cm-1.), consistent with the equatorial-equatorial syn-anti bridging mode of the carboxylate bridges.2. Construction of new coordination polymers with Ianthanide metal ions: Seven new coordination polymers, compounds 7-13, were synthesized by solvothermal methods in DMF-ethanol. These compunds are isostructural and of general formula [Ln2(H2DHNDC)3(DMF)4] (Ln=La、Ce、Pr、Nd、Eu、Gd�'�Tb, The uncoordinated solvent molecules are not included in the formula) The compounds are isomorphous except for compound 7, for which the unit cell is doubled。All of these seven compounds display the ordinary 3D pcu networks with 3D interconnected pore systems, in which binuclear units with quartiple carboxylate bridges are interlinked by the H2DHNDC2-linkers. In this series, the Ln-O bond distance decreases with the atomic number, consistent with the Lanthanide contraction, but the variations in cell volume and pore volume is non-monotonic. Both parameters show sudden decrease and sudden increase from La to Ce and from Pr to Nd, respectively. These could be related to the variation of the relative coordination orientation of the organic linkers between the binuclear units. Unfortunately, all of theses compounds are unstable in air, and the frameworks collapse upon solvent loss or exchange at ambient temperature. This prevents us from further studies with the porosity. Fluorescence measurements were performed with 11 and 13. They only show ligand-centered luminescence, and the characteristic Eu(Ⅲ) and Tb(Ⅲ) peaks were not observed, indicating that the H2DHNDC2-ligand in the collapsed framworks is not a good light antenna for energy transfer to the lanthanide centers.