Construction And Properties Of Rare Earth Metal-Organic Framework Based On Polycarboxylic Acid Ligands

Rare earth metal-organic frameworks（RE-MOFs）combine the advanced properties of metal organic framework materials with the unique properties of rare earth elements,allowing them to be potentially multifunctional materials.In recent years,RE-MOFs with diverse structures and rich properties have attracted extensive attention from researchers.In this thesis,different organic ligands and rare earth ions were selected to construct 18 new RE-MOFs under hydrothermal/solvothermal conditions,and their multifunctional properties such as fluorescence,magnetism and conductivity were studied in detail.The contents of this thesis are as follows:1 A series of isomorphic RE-MOFs were synthesized by solvothermal method using2′,5′-dimethoxy-[1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid（H₂TPDC-2OMe）ligands.Structural analysis shows that RE-MOFs 1-4 are three-dimensional framework structures with rare earth metal chains as nodes,in which a large number of coordinated H₂O molecules form a rich hydrogen bond network along the direction of metal chains.All of these RE-MOFs shows good solvent,acid-base and thermal stability.Eu-MOF 1 and Tb-MOF 3 exhibit the characteristic luminescence.Eu-MOF 1 can be used as a ratiometric fluorescent sensor to quickly and efficiently detect these two amino acids in aqueous solution through photoelectron transfer originated from weak interactions between the methoxy group in the ligand and L-arginine or L-lysine.Moreover,they all have good proton conduction properties,and the conductivity increases with the decrease of RE^III ionic radius,proving that the central ionic radius has an important influence on proton conduction.Furthermore,magnetic studies show that Gd-MOF 2 and Dy-MOF 4 also have magnetocaloric effect and field-induced slow magnetic relaxation properties,respectively.2 Two types of RE-MOFs with different structures were obtained using 2′,5′-dihydroxy-[1,1′:4′,1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid（H₄DTTP-2OH）as ligand under different solvothermal conditions.Dy-MOF 5 is a three-dimensional framework structure with rare earth metal chains as nodes,while Dy-MOF 6 is a three-dimensional framework structure with Dy₂ binuclear metal clusters as nodes.Although there are a large number of coordinated or free H₂O molecules in both structures,it is easier to form an ordered hydrogen bond network between the coordinated H₂O molecules in the metal chain base structure,resulting in Dy-MOF 5 showing more excellent proton conductivity.Moreover,the ferromagnetic interaction between Dy^III ions in the metal chain is stronger,so Dy-MOF 5 exhibits field-induced Single molecule magnet（SMM）behavior with U_eff=37.22 K.Finally,Dy-MOF 5 also shows obvious second-order nonlinear optical properties.3 Two types of RE-MOFs with different structures were obtained using 2′,5′-dihydroxy-[1,1′:4′,1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid（H₄DTTP-2OH）as ligand under different solvothermal conditions.RE-MOFs 7-11 are three-dimensional structures with binuclear RE₂metal clusters as nodes.Abundant and order hydrogen bond network is formed among free H₂O molecules,dimethylamine cations and phenolic hydroxyl groups in the structure.Therefore,they all have good proton conductivity,and their proton conductivity at room temperature reaches the conductivity of 10^-4 S cm^-1 for superconducting materials.Eu-MOF8 and Tb-MOF 10 also exhibit the characteristic emission of Eu^III and Tb^III ions,respectively.Eu-MOF 8 can detect tetracycline in aqueous solution through the phenomenon of fluorescence quenching.The hybrid MOF material Ce-MOF 7@Li obtained by introducing Li⁺ions into the Ce-MOF 7 by ion exchange,combined with the redox properties of hydroquinone/quinone in the ligand,can be used as a potential cathode material for lithium batteries.Dy-MOF 12 and Ho-MOF 13 are three-dimensional structures with metal chains as nodes,and the coordination configurations of the central Dy^III and Ho^III ions have near-perfect D_5h symmetry.Magnetic studies show that Dy-MOF 12 exhibits SMM properties at zero field,and a open hysteresis loop at 2.3 K is observed,which is extremely rare in MOF materials.Its magnetic properties can be regulated by Li⁺ion exchange and ligand oxidation.Ho-MOF 13also exhibits field-induced SMM properties.4 Four isostructural RE-MOFs were synthesized by solvothermal method using flexible N,N’,N"-tris（isophthalic acid）-1,3,5-benzamide（H₆TPBTM）ligands and rare earth nitrates.They are anionic macroporous framework structures with hexagonal channels,the overall porosity reaches 60%,and they all have good solvent stability and thermal stability.Eu-MOF14 and Tb-MOF 16 exhibit high-efficiency characteristic luminescence of Eu^III and Tb^III ions,respectively,and by adjusting the ratio of Eu^III and Tb^III ions,a mixed-metal RE-MOF close to white light emission can be obtained.The specific surface area of Tb-MOF 16 reaches1,123.61 m² g^-1;the maximum adsorption capacity for CO₂ reaches 48.20 cm³ g^-1 due to the amide groups present in the ligand.Taking advantage of its macropore and anionic framework properties,the photosensitizer[Ru（bpy）₃]²⁺can be loaded into the pores of Tb-MOF 16through adsorption to realize the photocatalytic conversion of methyl phenyl sulfide to methyl phenyl sulfoxide.In addition,Dy-MOF 17 also exhibits a field-induced slow magnetic relaxation phenomenon.