Magnetic Metal-Organic Frameworks Constructed By Pyridine-Carboxylic Acid Ligands

Metal-organic frameworks (MOFs) are becoming one of the hot topics due to their intriguing potential applications, such as photoelectric and magnetic materials. This thesis focused on magnetic MOFs, which have shown potential applications on high density information storage, quantum devices and so on. Sixteen MOFs with various unprecedented structures were synthesized based on three organic ligands containing heterocyclic carboxylic acid. The structures and detailed properties of all these MOFs were characterized and studied by abundant measurements, such as X-ray single crystal diffraction, infrared spectroscopy, elemental analyses, thermogravimetrical analyses, powder X-ray diffraction patterns and variable temperature magnetic susceptibility measurement. The main contributions are list as follows:1. One transition MOF with2D structure and four heterometallic MOFs with three different topologies based on3-aminopyrazine/hydroxypyrazine-2-carboxylic acid have been synthesized via hydro/solvothermal methods. Isostructural MOFs2and3are constructed with {OLn6} octahedron unit and further linked by CuⅡ ions to form3D structures. Magnetic studies reveal that2shows a large entropy change of35.76J kg-1K-1, while3exhibits slow relaxation of the magnetization at low temperature.2. Seven heterometallic MOFs based on4-carboxy-2-(pyridinium-4-yl)-1H-imidazole-5-carboxylic acid have been synthesized via solvothermal methods. Magnetic studies reveal that12shows frequency-dependent out-of-phase signals, indicating the presence of slow relaxation of the magnetization at low termperature.3. Four transition MOFs based on5-(4-pyridyl)-isophthalic acid have been successfully synthesized via solvothermal methods. Isostructural MOFs13and15are fromed based on trinuclear secondary build units (SBUs). MOF14is constructed from dinuclear nickle core.16contains CuⅡ paddle-wheel SBUs. Magnetic studies reveal that15is a molecule-based magnet with the critical temperature of18.5K, whose coercive field and residual magnetism at2K are778Oe and0.17Nβ, respectively.