Study On Metal-organic Frameworks Constructed By Tetracarboxylate Ligands And Pyridyl Ligands And Their Properties

Metal-organic frameworks(MOFs)are a class of crystalline porous materials with periodic network structure formed by the self-assembly of inorganic metal ions or clusters and organic ligands through coordination bonds.Due to porosity,large BET surface area and rich functions sites,MOFs has been widely used in the fields of gas adsorption and separation,sensing,catalysis and electrochemistry.Compared with other porous materials,MOFs has the advantage of"customizable",which enables MOFs possess specific functional requirements by introducing some target structures.Among them,nitrogen-containing heterocyclic ligands have been extensively designed and applied in the synthesis of MOFs due to their abundant active sites.In addition,the open metal sites in the structure of MOFs can also be directionally designed and synthesized.In this paper,by studying the relationship between structure and performance,pyrazine carboxylic acid and functionalized ligands with pyridine linkers were selected to synthesize seven MOFs by solvothermal method,and their fluorescence detection,gas adsorption separation and catalysis were carried out.The main research results of this paper are as follows:1.First,we utilize H₄TCPP(2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine)with Aggregation-Induced Emission(AIE)effect and the pyridyl linker ligand 4,4'-bipyridine to constructs a novel paddle-wheel structure ZnMOF(compound 1).Compound 1 has two-fold interpenetrating three-dimensional structure,and the interpenetrating structure endows compound 1 with excellent water stability and acid-base stability.Compound 1 possesses permanent porosity with BET surface area of 630m² g^-1.Remarkably,Compound 1 displays excellent fluorescent property in virtue of the AIE effect of the H₄TCPP ligand,which can be highly quenched by small amounts of 2,4,6-trinitrophenol(TNP)and Fe³⁺ions.The excellent stability,high sensitivity and recyclability of compound 1 make it a potential outstanding chemical sensor for detecting TNP and Fe³⁺ions.On this basis,we introduced 1,4-bis(4-pyridyl)benzene as pyridyl linkers and H₄TCPP to construct MOFs.Two highly porous MOF isomers Zn₂(TCPP)(DPB)have been successfully synthesized using different solvents and acid species to adjust the topologies of these two MOFs(compounds 2 and 3).Both of them are constructed by paddlewheel[Zn₂(COO)₄],TCPP and DPB ligands.In compound 2,the[Zn₂(COO)₄]paddlewheel units are fit together by TCPP ligands to form two-dimensional layers,which are further connected each other by DPB ligands as pillars to construct the two-fold catenated 3D framework.While in compound 2,the cross-linkage of[Zn₂(COO)₄]paddlewheel units and TCPP ligands results in the three-dimensional framework of Zn-TCPP,in which DPB ligands coordinate to two axials vertical dinuclear[Zn₂(COO)₄].The structural difference between compounds 2 and 3 is mainly caused by the distortion of the TCPP ligand.Both activated MOFs have high BET surface areas and permanent porosity,and excellent adsorption and separation performance for CO₂ and other light hydrocarbons(C₁,C₂,and C₃).Then we introduced 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine(DPT)and H₄TCPP mixed to form a porous Zn-MOF(compound 4).Compound 4 and compound 3 have the same structural.Activated compound 4 possesses highly BET surface areas and permanent porosity and exhibits good adsorption performance for CO₂.What's more,compound4 shown good adsorption and separation performance for other light alkanes(C₁,C₂,and C₃).All in all,these four MOFs materials reported in the work in this chapter have the capability of fluorescent sensing and selective separation of CO₂ and light alkanes,and have great potential in the field of environmental protection.2.Following the work of the previous chapter,we used H₄TCPP and photoactive Lewis base structure ligand 2,5-bis(4-pyridyl)thiazolo[5,4-d]thiazole(DPTZTZ)to construct a novel MOFs materials compound 5.Compound 5 possess two-fold interpenetrating three-dimensional layer-pillars structure.Due to the introduction of an optically active Lewis base structural unit thiazolo[5,4-d]thiazole,compounds 5 can not only effectively catalyze CO₂ epoxidation under mild conditions,but also exhibit excellent photocatalytic benzylic linked performance.In order to explore whether the pyrazine building block and thiazolo[5,4-d]thiazole play a co-catalytic effect,we used another tetracarboxylate ligands H₄BTEB(1,2,4,5-tetrakis(4-carboxyphenyl)benzene)and DPTZTZ to construct compound 6,which has the same structure with compound5.we used compound 6 and compound 3 synthesized in the previous chapter to explore the catalytic center.Experiments show that in the CO₂ epoxidation reaction,MOFs with TZTZ structural units have the best catalytic effect,while in the photocatalytic benzylamine coupling reaction,the pyrazine structural unit and the TZTZ structural unit play a role in the catalytic process.Furthermore,EPR and electrochemical tests revealed the mechanism of photocatalytic benzylamine coupling.This work provides an idea for the future synthesis of MOFs with excellent catalytic activity.3.A 3D hybrid microporous highly connected Yttrium-organic framework(compound 7)based on H₄TCPP was favorably built via solvothermal reaction.H₄TCPP can be regarded as a 4-connected rectangular geometry node and 12-connected Y₉ cluster can be simplified as a hexagonal prism second building unit(SBU).The Y₉SBUs further interconnect with TCPP ligand resulted in a 3D framework with shp topology.Compound 7 not only exhibits outstanding chemical stability in organic phase and but also possesses permanent porosity with BET surface area of 1125 m² g^-1.Compound 7 exhibits excellent fluorescence properties and could be used to detect a small amount of furacillin in aqueous solutions.Moreover,fluorescence quenching effect was not affected by other kinds of antibiotics.In addition,compound 7 shows a medium adsorption capacity for CO₂ as well as excellent catalytic property for CO₂conversion into cyclic carbonates.The fluorescent MOF has potential application prospects in the field of toxic chemical detection and CO₂ cycloaddition.