Construction And Properties Of Metal-organic Frameworks Based On Aromatic Polycarboxylic Acid Ligands

Metal organic framework materials（MOFs）are characterised by high porosity,high specific surface area and tunable pore structure,making them highly sought after by researchers as star materials in the fields of catalysis and fluorescence recognition.Aromatic polycarboxylic acid ligands are the most commonly used class of ligands for the construction of MOFs because of their strong coordination ability and abundant coordination modes.In particular,the conjugated structures of aromatic carboxylic acids often have specific fluorescence or can effectively sensitise rare earth ions,giving MOFs excellent fluorescence emission,and are widely used in the construction and study of fluorescent MOFs.In this paper,we designed and synthesized an N heterocyclic rigid tricarboxylic acid ligand H₃bqca and an S heterocyclic rigid dicarboxylic acid ligand H₂btda,and successfully constructed and resolved four new MOFs by solvothermal method.in addition,we explored their properties in catalysis and fluorescence recognition based on the characteristics of these materials.The studies in this paper are as follows:1.New N heterocyclic rigid tricarboxylic acid ligands H₃bqca were designed and synthesised,and a new three-dimensional metal-organic framework material by solvothermal methods:[Mn₃（bqca）₂（DMF）₄]_n（1）.By thermogravimetric analysis 1 was found to have a thermal stability temperature of up to 450℃.In addition,the catalytic reaction conditions of 1 in the catalytic reaction of CO₂ with epoxide were mild（80℃,1 Mpa,5 h）and catalyst 1 had high selectivity,catalytic activity and excellent cyclic regeneration,and the catalytic mechanism of 1 after activation was investigated.2.New S-heterocyclic rigid dicarboxylic acid ligands H₂btda were designed and two transition-alkali metal MOFs were synthesised by the solvothermal method:{（Me₂NH₂）·[Zn M（btda）₂]·DMF}_n[M=Na（2）,K（3）].Fluorescence recognition experiments have shown that 2 and 3 can efficiently detect Fe³⁺,Mn O₄^-and nitrobenzene（NB）in the form of fluorescence bursts,and that the burst detection process is highly sensitive,resistant to interference and has good recycling performance.2 and 3 burst detection mechanism for Fe³⁺,Mn O₄^-and NB can be attributed to the existence of energy competition between the subject framework and the guest analyte for absorption.In the catalytic reactions of CO₂ with epoxides,2 and 3 exhibited high selectivity,catalytic activity and excellent recycling regeneration under mild reaction conditions of 25℃,1 MPa,24 h and 60℃,1 MPa,5 h,respectively,and the catalytic mechanisms of 2 and 3 after activation were investigated.3.Eu-MOF:[Eu₂（btda）₂·（HCOO）₂]_n（4）was synthesized by a solvothermal method using H₂btda as the ligand.Fluorescence recognition experiments showed that 4 can efficiently detect Fe³⁺,Mn²⁺and NB in the form of fluorescence bursts with high sensitivity,excellent interference immunity and good recycling performance of the detection process.4 burst mechanism for Fe³⁺,Mn²⁺and NB can be attributed to the existence of energy-competitive absorption between the subject framework and the guest analytes.In the catalytic reaction for the conversion of CO₂ to cyclic carbonate,the 4-catalyzed cycloaddition reaction conditions were mild（0.8 MPa,120℃,12 h）and the catalytic mechanism of 4 was investigated with good generality,high catalytic activity and excellent cyclic regeneration.