Syntheses, Crystal Structures And Photoluminescent Properties Of Coordination Polymers Based On Imidazole Derivatives

Metal-Organic Coordination Polymers as a novel functional supramolecular materials receive much concern due to the special tailorability and varied topology structure. In this work, using 8 sorts of imidazoly derivatives as the ligands (partly selecting different aromatic carboxylic acids as the second ligand) to react with Cd2+ and Zn²⁺ to synthesize 16 sorts of imidazolyl coordination polymers with novel topological structure by hydro-thermal method. The crystal structures of Metal-Organic Coordination Polymers was characterized by elemental analysis, thermogravimetric analysis and X-ray crystallography. Fluorescence spectra of the coordination polymers were measured, theoretically calculated and analyzed. And the synthetic conditions and the regulations were discussed, the types of topology structure for diferent crystal structures were analyzed and the effects of pH and the auxiliary ligands were investigated.Under different pH values, L1/L2 ligands react with Cd/Zn ions synthetizing 4 sorts of coordination polymers ({[Cd(L1)₂]·H₂O}_n(1), [Cd(L1)₂]_n(2), {[Cd(L1)₄ Cl₂]·6H₂O}_n(3), [Zn(L2)]_n(4))。coordination polymers 1 and 4 are of two dimensional reticular structure, coordination polymers 2 and 3 are of supermolecule two dimensional reticular structure and supermolecule three dimensional framework structure through the hydrogen bonds among the molecules. And the influences of pH value on the crystal structures were investigated.L3 ligand containing N and O and another rigid ligand containing carboxyl (as the second ligand) react with Cd ion synthetizing five sorts of novel coordination polymers ({[Cd₂(L3)₂(fuma)]·2H₂O}_n(5), [Cd₂(L3)₂(p-BDC)]_n(6), [Cd₂(L3)₂ (m-BDC)]_n(7), {[Cd₂(L3)(1,3,5-BTC)(H₂O)₂]·5H₂O}_n(8), [Cd(L3)(BTEC)_0.25]_n(9)). The mode of connection for coordination polymers 5 and 6 is similar, L3 and Cd ion cluster form one dimensional chain structure and furthermore form two dimensional reticular structure with the help of second ligand. coordination polymer 7 is a three dimensional 4-connetcted organic framework. coordination polymer 8 is a 2D(3,5)-mixed connected organic framework. Also, coordination polymer 9 presents a two dimensional reticular structure. The mode of coordination of L3 ligand was studied in detail and the effects of the second ligand on the system structure was discussed. From the description of the structrue, the auxiliary carboxyl ligand plays important role in the structure of coordination polymers.Ln (n=4, 5, 6, 7, 8) ligands containing N and another rigid ligand containing carboxyl (as the second ligand) react with Cd ion synthetizing 7 sorts of novel coordination polymers ({[Cd(L4)(m-BDC)(H₂O)]·H₂O}_n(10), {[Cd(L4)(m-BDC) (H₂O)]·H₂O}_n(11), [Cd₃(L4)(1,2,3-BTC)₂]_n(12), {[Cd(L5)(m-BDC)(H₂O)]·H₂O}_n (13), {[Cd(L6)(m-BDC)]·2H₂O}_n(14), {[Cd₂(L7)(BPTC)(H₂O)]·2H₂O}_n(15),{[Cd₂ (L8)(BPTC)]·4H₂O}_n(16)). Through the analyses of the structure of coordination polymers10¹4, it can be found that whether atom N on the picoline coordinates with the transition metal ions has a great effects on the structure. Coordination polymers 10, 11 and 13 all present one dimensional two-chain structure through the connection of hydrogen bonds, coordination polymer 14 is of three supermolecule structure through the connection of hydrogen bonds and coordination polymers 12, 15 and 16 present two dimensional laminar structure. The net of coordination polymers 16 defines a new type of (4,8)-connected topological framework previously unobserved and different from the known flu and scu networks.Frontier Molecular Orbital and density of states (DOS) of coordination polymers 1⁹ were analyzed and the results show photoluminescence can be mainly attributed to the ligands L1^L3 and metal ions have little contribution on it. The theoretical result explained the experiment results of fluorescence spectra well.