Syntheses And Properties Of Coordination Polymers Based On Carboxylic Acid Ligands

Coordination polymers（CPs）,which combine organic and inorganic components,are a new kind of multifuncational materials.They are constructed by self-assembly of metal ions or metal clusters with organic ligands containing nitrogen and oxygen atoms.The development of CPs is based on multiple disciplines such as coordination chemistry,organic chemistry,inorganic chemistry,material chemistry and topology.It can be widely used in the fields of gas separation and stotage,magnetism,catalysis,sensing and so on.In this thesis,different carboxylic acid ligands are selected to coordinate with transition/lanthanide metal ions to obtain several different crystalline materials.Through single X-ray diffraction,power X-ray diffraction,thermogravimetry,elemental analysis,infrared spectroscopy and fluorescence spectra,the crystal structure of the material is analyzed and the basic properties are characterized and the sensing performance is explored.The main research content is divided into the following three aspects:1. Based on solvothermal method,1,1’:4’,1”-terphenyl]-2’,4,4”,5’-tetracarboxylic acid（L1）andlanthanide metal ions are coordinated and assembled to construct six kinds of CPs with same crystal structure（EuL1,GdL1,TbL1,DyL1,HoL1,ErL1）.Their luminescent properties show differentiation.GdL1,DyL1,HoL1,ErL1 exhibit only ligand-based emission bands.EuL1 reveals only characteristic emission peaks of Eu³⁺ions;TbL1 exhibits strong characteristic emission peaks of Tb³⁺ions and a very weak emission band of ligand.It is worth noting that GdL1 has dual emission of fluorescence and phosphorescence at 77 K.In addition,these materials have high thermal stability.2. In this work,they construct a kind of fluorine-based Tb-CP by solvothermal method,TbL2·7DMF·5H₂O（TbL2,L2=4,4’-（9,9-dimethyl-9H-fluorene-2,7-diyl）dibenzoic acid）,showing strong blue emission.The crystal structure of TbL2 is constructed by the staggered 2D network which consisted of a series of parallel-aligned Tb-O-C chains.Meanwhile,TbL2 exhibits excellent sensitivity for picric acid（PA）.Its fluorescence intensity has a good linear relationship with the concentration of PA（0-30μM）,showing a high detection efficiency,with a quenching constant of4.5×10⁴ M^-1 which approaches the best reported CPs-based on PA sensor up to now.In addition,TbL2can be reused multiple times.Finally,the mechanism of luminescent quenching of PA can be attributed to the synergistic effect of resonance energy transfer（RET）and competitive absorption.These results indicate the TbL2 material has potential application in chemosensor.3. Based on the solvothermal method,N,N’-bis（3,5-dicarboxylphenyl）-thiophene-2,5-dicarboxamide（L3）is coordinated with Cd Cl₂ to form CdL3.This MOF shows excellent chemical stability,which can stably exist in water for long time（three months）and soak in the p H range of 2-11 in aqueous solutions（24 h）.CdL3 displays highly sensitivity detection of PA with K_sv of 3.2×10⁴M^-1 in the concentration range of 0-40μM.Interestingly,it can be recycled by washing with water and the operation is simple.Furthermore,the possible quenching mechanisms between CdL3 and PA can be attributed to competitive absorption,RET and electrostatic interactions.In summary,CdL3 is also a highly stable PA sensing material.