Syntheses And Properties Of Quinoline Azo Metal Organic Coordination Polymers

Quinoline azo metal organic framework compounds,as a series of important crystal materials,have attracted the attention of many researchers in related fields.However,their applications are greatly limited because azo bonds are easy to break at low temperature.In this paper,five kinds of azo ligands have been successfully designed and synthesized through a large number of experiments.Four new azo coordination polymers were synthesized by using three azo ligands and transition metal ions(Zn²⁺,Ni²⁺and Cd²⁺)by solvent/hydrothermal synthesis to improve the thermal stability of azo compounds.Four complexes were characterized by single crystal X-ray diffraction,powder X-ray diffraction,infrared spectroscopy and elemental analysis.At the same time,the thermal stability,fluorescence and electrochemical properties of the complexes were studied.By selecting appropriate transition metal ions to coordinate with quinoline azo ligands,the stability of quinoline azo compounds can be improved and their optical and electrochemical properties can be enriched.So that the quinoline azo compounds will have more widely used in many fields.Complex[Zn?L??H₂O?₂]_n?1?was prepared by 4-[?8-hydroxy-5-quinoline?azo]-benzoic acid?H2L1?with zinc ions under suitable conditions.Complex 1 is a 1D zig-zag chain structure.Because of the interaction of hydrogen bonds and?-?stacking,complex 1 can be connected to form a 3D supramolecular network structure.According to the results of thermogravimetric analysis of ligand H2L1 and complex 1,the thermal stability of complex 1 was significantly enhanced Complex 1 had good fluorescence properties because of the electronic transition in the ligand.In addition,the electrochemical detection of complex 1 was also carried out.The results showed that the modification of the TiO₂ electrode with complexes 1 and N719 not only extends the photoresponse of DSSC to the ultraviolet region,but also enhances the spectral absorption.That is to say,complex 1 has potential application prospects in the fields of photochemistry and electrochemistry.4-[?8-hydroxy-5-quinoline?azo]-benzenesulfonic acid?H₂L2?was selected as ligand to coordinate with transition metal Ni²⁺.Two complexes with different structures were prepared by adjusting reaction conditions:[Ni₂?L?₂?en?₄]?2?and{[NiL?en?]·DMF}n?3?.Complex 2 is a zero-dimensional structure.The asymmetric structural unit of complex 2 contains two[Ni?L??en?₂]molecules.Asymmetric unit molecules A and B can be linked to form two 1D chains by N-H…O hydrogen bonding,and the two chains are connected by all kinds of N-H…O hydrogen bonds to form a two-dimensional layer structure.Complex 3 wss a 1D zig-zag chain structure.The experimental resulted show that the thermal stability of the two complexes is obviously improved compared with the ligand H₂L2.The fluorescence properties showed that both of them had blue shift relative to the ligands,showing good blue light fluorescence properties.Azobenzene-4,4'-dicarboxylic acid?H₂L3?was selected as ligand,and the new ligand p-nitrobenzoic acid?HA?was produced by its reaction in-situ to synthesize a new complex with transition metal ion Cd²⁺:[Cd?p-nitrobenzoic acid?₂?en?H₂O]?4?.The single crystal X-ray diffraction analysis showed that complex 4 is a discrete structure.Because of the existence of hydrogen bonds,complex 4 can be linked into a three-dimensional supramolecular network structure.Thermogravimetric analysis of ligand H2L3 and complex 4 showed that the thermal stability of complex 4 is significantly improved.The fluorescence properties of complex 4 were tested.Because of the charge transfer of ligand to metal,the peak position of complex 4 had a large red shift.Complex 4 had good blue light fluorescence property.