Synthesis?structure And Properties Of Organic-metal Complexes Based On 3,3',5,5'- Azobenzene Tetracarboxylic Acid Ligands

Metal-organic complexes have been extensively studied in the fields of fluorescence,magnetism,gas adsorption,separation and catalysis due to their structural diversity and wide application prospects.In the self-assembly process of such materials,the choice of organic ligands and metal ions is particularly important.It not only determines the structure of the organic complex,but also the key factor of its performance.In addition,the reaction temperature,the pH and the ratio of organic solvents also have a non-negligible effect.In this paper,3,3?,5,5?-azobenzenetetracarboxylic acid?H₄abtc?was selected as the organic bridging ligand,and five novel metal organic complexes 1-5 were successfully prepared by solvothermal method.The basic structures of the complexes were characterized by single crystal X-ray diffraction,powder X-ray diffraction,elemental analysis,infrared analysis,and thermal stability analysis.At the same time,the fluorescence properties of complex 1 was studied,and the magnetism of complex 6 that previously synthesized metal-containing dysprosium was also explored.The main contents are as follows:1.The molecular formulas of complexes 1-6 are[Eu?abtc?]_n?1?,{[Tb₂?abtc?_1.5?H₂O?₃?DMA?]·H₂O}_n?2?,{[Dy₂?abtc?_1.5?H₂O?]·H₂O}_n?3?,[Eu₂?H₃abtc?₃?DMF?]_n?4?,{[Co?H₂aobtc??H₂O?₂]·H₂O·C₄H₁₀N₂}_n?5?and[Dy?Habtc??H₂O?₃]·2H₂O?6?,respectively.Structural analysis shows that the deprotonated abtc^4-in the complex 1 connects the metal center Eu?III?ion to form a coordination polymer with 3D network structure.Although the ligands in the complexes 2 and 3 have different coordination modes,they are respectively connected to the central metal ions Dy?III?and Tb?III?to form a 3D structure with 1D open channels.The adjacent metal center Eu?III?in the complex4 is connected by a partially deprotonated H₃abtc^-to form a dimer[Eu₂?COO?₂]unit and then connected to form a 3D structure.The complex 5 is a mononuclear Co?II?molecule,which forms a three-dimensional supramolecular structure through intermolecular hydrogen bonding and?···?stacking interactions.Complex 6 is a three-dimensional structure that contains two1D channels with different pore diameters.Structural analysis shows that the metal center Dy³⁺ion has a square antiprism configuration.2.The synthesis and basic characterization indicate that complex 1 has high yield,high thermal stability and chemical stability.Fluorescence performance testing shows that 1 does not show the characteristic peak of rare earth Eu?III?in solid state or dispersed in various solvents,and there was only one ligand peak at 472 nm.Fluorescence recognition experiment showed that 1 has selective recognition and good sensitivity to CrO₄^2-ions.More importantly,the complex 1 shows a strong response and a special selectivity to 2,6-pyridinedicarboxylic acid?DPA?.When complex 1 is placed in an aqueous solution of 2,6-pyridinedicarboxylic acid,it will show the characteristic emission peaks of Eu?III?at 595 nm and 616 nm.3.The magnetic properties of[Dy?Habtc??H₂O?₃]·2H₂O?6?were studied.The magnetic study shows that there is no peak value of?"ac susceptibility in the zero field of 6,but it shows a slow magnetic relaxation behavior accompanied by quantum tunneling effect.After the external field is applied,the quantum tunneling effect is effectively suppressed,and the complex6 shows an obvious Orbach process of thermal activation.The effective energy barrier of complex 6 is 16.33k.