Syntheses And Properties Of Azo Metal Organic Coordination Polymers

Azo metal organic coordination polymers are popular because of their excellent fluorescence properties,but their applications are influenced by the rupture of azo bonds at low temperature.In this paper,five kinds of azo ligands were successfully designed and prepared under many experiments.Six novel complexes 1⁶ were synthesized by using two kinds of azo ligands and metal ions(Zn²⁺、Co²⁺、Ni²⁺、Mg²⁺)in the condition of solvothermal（hydrothermal）technique.Six complex had been structurally characterized by infrared spectrum,elemental analysis,X-ray single-crystal diffraction and power X-ray diffraction.Thermal stability,fluorescent property and electrochemical property were detected on complexes 1⁶.In order to prepare azo complexes with better stability,the influence factors of azo metal organic coordination polymers properties had been explored,including the coordination modes of different ligands under different conditions,the optimum synthesis conditions,π-πstacking interaction and hydrogen bond,etc.In order to expand the application prospect of azo complexes,the potential optoelectronic properties of the complexes should be explored by the interaction between metal and azo ligands.4-[8-hydroxy-5-quinoline]azo-benzenesulfonate（H₂L1）was selected as ligand.Under suitable reaction conditions two complexes were successfully synthesized with Zn ion,[Zn₃L1₂（OH）₂（H₂O）₆]_n（1）and[ZnL1（H₂O）]_n（2）.Complex 1 was one dimensional（1D）chain structure and complex 2 was three dimensional（3D）structure.Complex 1 can be connected to form a 3D supramolecular network structure throughπ-πstacking interaction and hydrogen bond.The coordination mode of ligand was also studied to the structure of complex.It can be seen from the structural analysis that the steric configurations of the complexes were mainly determined by the coordination state of the sulfonic groups.The thermal stabilities of complexes 1-2were significantly enhanced than that of the ligand H₂L1.The fluorescence properties of complexes 1-2 were due to the charge transfer in the ligand.It can be seen from the fluorescence data of complexes 1-2 that the emission spectrum of complexes 1-2 were blue shifted to H₂L1 ligand.The electrochemical properties of complexes 1-2 were also determined.The photoelectric conversion efficiencies of complexes 1-2 were improved.Under alkaline conditions the ligand H₂L1 was occurred by nitrozation reaction in situ to produce 5-amino-8-hydroxyquinoline（HM）and 5-nitro-8-hydroxyquinoline（HN）,respectively.Furthermore,the complex 3,[ZnM₂],was synthesized with5-nitro-8-hydroxyquinoline（HM）and Zn²⁺ion.The complex 4,[（CoN₂）H₂O],was synthesized with 5-amino-8-hydroxyquinoline（HN）and Co²⁺ion.Complex 3 and complex 4 were zero dimensional（0D）structure and two dimensional（2D）layered structure,respectively.The two complexes were both connected into a 3D supramolecular network byπ-πstacking interaction and hydrogen bond interaction.Complexes 3-4 exhibited purple fluorescence properties because of the ligand-to-metal charge transfer.Two new complexes 5-6 were synthesized by azobenzene-4-4’-dicarboxylic acid（H₂L2）withNi²⁺andMg²⁺ions,{[Ni（L2）_0.5（en）]·DMF}_n（5）and{[Mg（L2）（phen）（H₂O）]·DMA}_n（6）.The complexes 5-6 were 1D zig-zag chain structures.The two complexes can be connected into 3D supramolecular network byπ-πstacking interaction and hydrogen bond interaction.The effects of1-10-phenanthroline（phen）and ethylenediamine（en）as auxiliary ligands were studied on the formation of complexes.Compared with the ligand H₂L2,the thermal stabilities of complexes 5-6 were better.It can be seen from the fluorescence data of complexes 5-6 that the emission spectrum of complexes 5-6 were red shifted to H₂L2ligand.Complexes 5-6 exhibited blue fluorescence properties.