Syntheses,Structures And Properties Of Metal-Organic Frameworks With Pyrazole Carboxylic Acid Ligands

Metal-organic frameworks（MOFs） is a kind of inorganic-organic hybrid materials self-assembed by metal ions and organic ligands, it has provoked great interest not only because of its rich and colorful skeleton structure, but also owing to its great application in luminescence materials, magnetic materials, gas adsorption and separation, chemical sensing, drug release, chemical catalysis and so on.At present, the rational design and synthesis of organic ligands with multifunctional properties to construct a novel metal-organic framework have become one of the main research directions. As we known, the N atom and the O atom are used as the electron donating group, when they construct MOFs with organic ligands and metal ions. Carboxylic acid ligands are the most used organic ligands containing O atoms, they have a variety of coordination modes, which can be used for constructing MOFs with a lot of topological structures. N-containing organic ligands with N atoms for the electron donating group, heterocyclic ligands is the most used N-containing organic ligands, generally including pyridine, imidazole, pyrazole and so on. The pyrazole organic ligand is a class of five ring organic ligands with two neighboring nitrogen atoms, which is easy to be protonated, so it has a negative charge, and it is easy to coordinate with metal ions to form numberous coordination modes. Combining the advantages of pyrazole organic ligands and carboxylic acid organic ligands, we choose 1H-pyrazole-4-carboxylic acid as organic ligand, by controlling the reaction conditions, a series of new MOFs were synthesized and their structures and properties were studied. The main contents of this thesis are listed as follows:1. Using solvothermal synthesis method, we choose 1H-pyrazole-4-carboxylic acid and Cu（NO₃）₂·3H₂O as reaction materials, by adjusting the reaction conditions, Cu²⁺ take situ reaction, part or all of the Cu²⁺ ions translate to Cu⁺ ions. We synthesis six novel MOFs. [Cu2K（C₄H₂N₂O₂）₂]（1）, [Cu₃Li₂（C₄H₂N₂O₂）₃]·H₂O（2）, [Cu₃（C₄H₂N₂O₂）₂·2NH₃]（3）,（NH4）·[Cu（C₄H₂N₂O₂）]（4 and 5）and [Cu₃Li₂（C₄H₂N₂O₂）₄（C₃H₇NO）₄]（6）. In compounds 1-5, Cu⁺ coordinate with N atoms of organic ligands, it forms the indefinite extension of the one-dimensional chain structure, K+, Li⁺ and Cu²⁺ coordinate with O atoms, they were coordinated by organic ligands link to form novel 3D structures of compounds 1-3. In isostructural compound 4 and 5, hydrogen bonds are formed through carboxylate oxygen atoms and NH⁴⁺. In compound 6, we build a novel 3D structure using Cu²⁺ and Li⁺.we study fluorescence properties of organic ligand and compounds 1-5. The results show that compounds 1, 2, 4 and 5 have redshift phenomenon, because of weak intramolecular interactions between metal and metal, and the shorter the distance between the Cu---Cu in the molecule, the more obvious redshift phenomenon. In compound 3, the lengths of intramolecular Cu---Cu bonds are longer than compounds 1, 2, 4 and 5, almost no intramolecular interaction between metal and metal, so it shows the emission wavelength of organic ligand.2. Using the solvothermal synthesis method, we choose 1H-pyrazole-4-carboxylic acid and Co（NO₃）₂·6H₂O as reaction materials, by adjusting the pH of the reaction solution and we synthesis two novel MOFs, [Co₃（OH）（C₄H₂N₂O₂）（CHO₂）₃（H₂O）（C₃H₇NO）]（7）, [Co₃（C₄H₂N₂O₂）₄] ·（2H₃O）·2H₂O（8）. In compound 7, the coordination number of Co²⁺ is six, while in compound 8, the coordination number of Co²⁺ is four. Both of them form 3D skeleton structures with pore channel. The pH of the reaction solution was further verified to have a great influence on the synthesis of MOFs materials.