Structures And Luminescence Properties Of Complexes Based On Azobenzenetetracarboxylic Acid

Metal-organic coordination polymers（MOCPs,containing Metal-organic frameworks,MOFs）are a fascinating class materials composed of metal ions/clusters and organic linkers,which promise great potential in numerous fields.In recent years,due to there unique crystallinity,adjustable porosities and diversity of luminescence mechanism,MOFs have become a potential chemical sensor,which can be used to detect small organic molecules,metal ions,anions and other environmental pollutants.MOFs-based sensors have the advantages of portability,low cost,high selectivity,high sensitivity and simple operation compared with traditional detection devices.For the acquisition of an excellent luminescent sensor based on MOFs,we select 3,3’,5,5’-azoxybenzenetetracarboxylic acid（H₄L）as a main ligand due to its large conjugated structure and multi-coordination sites.In this work,we synthesized three novel H₄L-based coordination polymers by solvothermal method,{[Co₃（phen）₂（HL）₂]·（H₂O）₂}_n（1）,[Pb₄（HL）₂H₂O]·（H₂O）（2）and[Co₃（HL）₂（phen）（H₂O）₁₀]_n（3）.The structures of compound 1,2 and 3 were characterized and analyzed,and the fluorescence properties of compound 1 and 2 were further studied.Compound 1 exhibits a 2D layered structure,which further extendsπ???πpack stack interaction to a 3D supramolecular framework;In compound 2,adjacent Pb²⁺are connected by L^4-ligand to generate a 3D architecture;Compound 3 exhibiats a zero-dimensional structure and forms a three-dimensional supramolecular structure via hydrogen bonding.Infrared spectrum and powder X-ray diffraction analysis showed that the three compounds were successfully synthesized with high purity.Remarkably,compound 1 and 2 have high thermal stability and excellent chemical stability in water with wide pH range of 2-11.Luminescence studies show compound 1 can recognize Fe³⁺and Al³⁺with high selectivity from mixed metal ions in aqueous solutions through the luminescence quenching and enhancement phenomenon,respectively.Furthermore,1 can also detect PA with good selectivity and sensitivity among large common nitro-aromatic compounds（NACs）.The luminescent properties of compound 2 have been exploited as an efficient dual detection fluorosensors for hexavalent chromate anions(CrO₄^2-)and PA.