Synthesis,Structure And Properties Of Metal-Organic Frameworks (MOFs) Constructed By Heterocyclic Carboxylic Acid Ligand Containing Nitrogen

Metal-Organic framework(MOFs)is a periodically infinitely extended network consisting of metal ions or metal clusters connected by organic ligands,also known as coordination polymers.Due to their high porosity and specific surface area,MOFs play an increasingly important role in the fields of gas,liquid phase storage and separation,sensing,proton conduction and drug release.In this dissertation,six metal-organic frameworks(MOFs)materials with high thermal stability and good fluorescence properties were constructed by using carboxylic acid ligands with nitrogen heterocycles and transition metal(Zn(II)and Cd(II))and lanthanide metal(Sm(III),Nd(III)and Pr(III)),respectively.Not only analyzed the structure of the compounds,we also studied their applications in gas adsorption and fluorescence detection.The thesis mainly includes four sections.The first section is the introduction chapter,which briefly recommends the development history,related concepts,synthesis methods and influencing factors of the metal-organic frameworks.The research status and application of MOFs constructed with nitrogen-containing heterocyclic carboxylic acid ligands are emphatically introduced,and the research basis and significance of the article are summarized.The second part introduces three transition metals MOFs 1-3 constructed with 6-(4-pyridyl)-terephthalic acid as ligand and transition metal Zn(?)and Cd(?)under hydrothermal conditions.The basic characteristics of MOFs were characterized by IR,elemental analysis,PXRD and TG Single crystal structures of MOFs were determined by X-ray single crystal diffraction.The coordination modes of 6-(4-pyridyl)-terephthalic acid ligand and the structural characteristics of MOFs were discussed.What's more,we also studied the topological structure,thermal stability,gas adsorption(3)and fluorescence properties(1 and 3)of MOFs.Finally,the selective detection of acetone solvent by 3 was investigated.The synthesis conditions indicated that the metal center,reaction temperature,the ratio of reactants and auxiliary ligands would affect the self-assembly process of the complexes,and then the structure and properties of the compounds could be optimized.Through the structural analysis of the three MOFs,we found that 1 is a two-dimensional layer and then connected by hydrogen bond to form a three-dimensional supramolecular structure,while 2 and 3 exhibit more complex three-dimensional structures.Compared with the TG curves of 1-3,the decomposition temperatures of the three compounds(the decomposition temperatures of 1-3 are 402 ?,420 ? and 422 ?,respectively)are different,and the lowest decomposition temperature is 402 ?,which indicates that they all have excellent thermal stability.The fluorescence properties show that 1 and 3 have good fluorescence properties,and 3 can detect small molecules in acetone solvent by fluorescence quenching effect.The main reason for the fluorescence recognition of acetone is the energy transfer between acetone solvent molecules and organic ligands in the compounds.The third part selects lanthanide metals(Sm,Nd,and Pr)as metal centers and hydrothermally reacts with 2-(4-carboxyphenyl)imidazole[4,5-f]-1,10-phenanthroline and 2,5-thiophene dicarboxylic acid construct three 3D lanthanide metal-organic frameworks(Ln-MOFs)with good thermal stability:[Sm(NCP)(TDC)]n(4),[Nd(NCP)(TDC)]n-2n(H2respectively.It was also characterized by IR,TQ PXRD and elemental analysis.Single crystal 0)0.5(5)and Pr(NCP)(TDC)]n-n(H20)0.5(6),diffraction of X-ray single crystal was used to determine the single crystal structure of MOFs.The structural characteristics and thermal stability of MOFs were investigated.Structural analysis shows that 4-6 are three isomorphic structures,and their structures are two adjacent Ln(?)ions formed by two TDC2-and two NCP-anion carboxylic bridges to form a dual nucleus Ln(?)two polymer[Ln2(COO)4],and adjacent two polymer[Ln2(COO)4]through two reverse anions interconnected to form a one-dimensional double chain.Finally,a three-dimensional frame structure with Pcu topological symbol{412-63} is formed by fully deprotonated TDC2-anions.The difference in the number of crystalline water molecules in a frame is the difference between them.By analyzing and comparing TG data,the lowest decomposition temperature of three MOFs(the decomposition temperatures of 4-6 are 420?,406? and 401?,respectively)is 401 ?,which shows that both of them have excellent thermal stability.The fourth part makes a brief summary of the research of this paper,and prospects the future research work.