Syntheses Of Metal-organic Frameworks And Their Fluorescent Recognition For Nitro Antibiotics

Antibiotics are widely used to treat microbial and protozoan infections in domestic animals and are synthesized in large quantities due to their widespread demand worldwide.The widespread use of antibiotics poses a severe pollution threat.As the representative of nitro-antibiotics,nitrofurans and nitroimidazole are used in the treatment of bacterial infections and used as additives to promote animal growth driven by interests.However,their potential carcinogenicity and toxicity pose a threat to human beings and the ecological environment,and they have been banned in many parts of the world.In recent years,metal-organic frameworks（MOFs）have become excellent materials for the preparation of sensing probes.Luminescent metal-organic frameworks（LMOFs）have received much attention.As a branch of MOFs,it has the unparalleled advantages over other materials,such as good crystallinity,adjustable porosity,structural diversity,and most importantly,easily induced fluorescence emission.Moreover,the photoluminescence properties of LMOFs can be adjusted by changing organic ligands and metal ions or metal clusters in a mixture system.Among various sensing applications,it is important to use LMOFs as a chemical sensor to detect the environmental pollution caused by nitro antibiotics.In this paper,we designed and selected semi-rigid phenylacrylic acid ligands and4,4’-（pyrazine-2,6-diyl）dibenzoic acid to react with rare earth metal ions Eu（III）and transition metal ions Zn（II）,Mn（II）and Co（II）through solvothermal reaction to construct five coordination polymers.Their structures and properties were characterized,respectively.The experimental results show that the complexes based on Eu（III）and Zn（II）can be used for the recognition of nitro antibiotics.The main contents are as follows:1.Syntheses,structures,and properties of Eu（Ⅲ）complexes（1-2）based on phenylacrylic acid ligands.Two coordination polymers（1-2）were prepared by assembling semi-rigid m-phenylenediacrylic acid and m-phenyltriacrylic acid with lanthanide ions Eu（Ⅲ）,respectively.Through structural analysis,complexes 1-2 are all three-dimensional structures based on the Eu-O-C-O rods’infinite helix.1 is a three-dimensional periodic framework assembled from infinite helical Eu-O-C-O rods,which consisted of a series of alternating nine-coordinated Eu ^IIIcenters.Because there are two opposite helix chains in it,1 presents an asymmetric structure.2 is a chiral structure with no center of symmetry.Through the characterization of its fluorescence properties,complexes 1-2 have the characteristic emission peak of Eu³⁺in both solid-state and ethanol solution.In recognition of antibiotics,NFAs have an obvious fluorescence quenching effect on 1 and 2,indicating that the two complexes have fluorescence selective detection function for NFAs,with a pretty high detection recognition degree,which naked eyes can observe.These materials can be used as potential practical sensors for detecting antibiotics in an ethanol solution and have potential application value in environment protection.Also,the fluorescence quenching mechanism is discussed by density functional theory and electron/energy transfer mechanism.2.Syntheses,structures,and properties of complexes（3-5）based on DCPP ligand and Zn（Ⅱ）,Mn（Ⅱ）,Co（Ⅱ）Three isomorphic coordination polymers（3-5）were synthesized by the reaction of a trifunctional pyrazine dicarboxylic acid ligand,4,4’-（pyrazine-2,6-diyl）dibenzoic acid（DCPP）,with transition metals Zn（Ⅱ）,Mn（Ⅱ）and Co（Ⅱ）.The complexes are all based on binuclear metal units linked by monodentate carboxylate,which are connected by three-connected ligands to form a two-dimensional layered structure.These layers are stacked parallel to form a porous supramolecular framework by hydrogen bonding interaction.The uncoordinated DMF molecules in the channel participate in hydrogen bonding and stabilize the 3D supramolecular framework.Therefore,3 has good thermal stability and chemical stability.Experiments show that3 is an efficient selective detection material for nitro antibiotics,which can detect nitro antibiotics in a wide linear range and be used as a promising luminescent material.Besides,we also studied the fluorescence quenching mechanism.