The Study Of Metal-organic Frameworks And Properties Based On N-heterocylic Aromatic Carboxylic Acids

Metal-organic frameworks,as a class of crystalline materials with periodic structures,combine the characteristics of organic-inorganic materials.Compared with traditional inorganic porous materials,metal-organic frameworks have superior designability and unique application prospects in the fields of luminescence sensing,gas storage and separation,magnetism and catalysis.How to design functional metal organic materials has become a challenge in the field of crystalline materials.In this work,based on two N-heterocyclic aromatic carboxylic acid ligands:1,4-bis?imidazol-1-yl?terephthalic acid?H₂BTA?and4-?3,5-dicarboxyphenyl?picolinic acid?H₃DPPA?,and metal ions(Mn²⁺,Fe²⁺,Co²⁺,Ni²⁺,Cu²⁺,Zn²⁺,Pb²⁺,Pr³⁺,Nd³⁺and Eu³⁺),16 kinds of metal-organic frameworks were synthesized and characterized.The detail work is as follows:Four 3D pseudo-supramolecular isomers?1-4?were synthesized by using H₂BTA ligand and Zn²⁺,respectively.Their framework structures are the same,but the diverse solvents leads to differences in porosity,fluorescence,and adsorption properties in their structures.Besides,two 3D isomers 5 and 6 were synthesized by using H₂BTA ligand and Pb²⁺in different solvents.Two 3D antiferromagnetic complexes 7 and 8 were synthesized by Mn²⁺and Co²⁺ions.And complex 7 has a two-fold structure.Finally,complex 9 was synthesized by using H₂BTA ligand and Pr³⁺.Two 2D heteromorphic complexes 10 and 11 were prepared by using H₃DPPA and Fe³⁺and Co²⁺ions,wherein the six-coordinate structure contained five coordinated water molecules.Two heteromorphic complexes 12 and 13 were obtained by using H₃DPPA and Eu³⁺/Nd³⁺ions,each of them has four coordinating water molecules in asymmetric unit.In addition,two complexes 14 and 15 were synthesized by using Mn²⁺ions and H₃DPPA.And a unique 3D complex 16 was obtained by using Ni²⁺and H₃DPPA ligand.The dimension of complexes are generally low,which may be more related to the coordination of water molecules after H₃DPPA and metal ions.All metal-organic frameworks were characterized by X-ray single crystal diffraction,X-ray powder diffraction,TGA and elemental analysis.Their properties such as fluorescence,gas adsorption and separation,and magnetic properties were studied.Complexes 1-6 and 9show fluorescence quenching in the acetone solvent.And they all have good recognition ability to Fe³⁺and Cr₂O₇^2-.The K_svv of complex 2 to Fe³⁺can reach 1.04×10⁵ M^-1,and the K_svv of Cr₂O₇^2-can reach 4.23×10⁵ M^-1,which are obviously better than other complexes.The gas adsorption experiments of 1 and 2 show selective adsorption performance for carbon dioxide,and the adsorption amount of 1 to carbon dioxide can reach 62.1 cm³·g^-11 at 273K.