| Traditional inorganic bulk magnetic materials will not meet the needs raised by the rapid development of informatization and high-density information storage. Novel molecule-based magnets are good alternative, which hold magnetic feature in physics and supramolecular character in structure. Self-assembly method is the main synthetic strategy of molecule-based magnetic materials. The self-assembly reaction mainly depends on inner driving forces, which is difficult to control. However, as kind of exterior driving forces, magnetic field has been proved that it can be used as driving force in self-assembly reactions. Some products can be orientated and assembled to form ordered structure induced by external magnetic field. Also, the magnetic field can change the final products in some chemical reactions. Based on the above facts, it is believed that the supramolecular self-assembly involved paramagnetic metal ions reaction toward molecule-based magnet can be influenced by external magnetic field. It is also presumed that applied magnetic field can control the final products or enhance the magnetism of magnetic products. In addition, molecule-based magnet with diversity structural feature can be modified and redesigned in molecular structure, which will be helpful to obtain multifunctional molecular materials.Metal complexes have been achieving great interest due to their excellent physical properties. On the other hand, metal complexes have been also emphasized as reactant to prepare nanomaterials. What is more, the reactant can be redesigned and optimized, which may bring better nanostructure and properties of the product. The main parts of the dissertation are summarized below:1. Three novel carboxylate complexes have been successfully synthesized by mild hydrothermal reactions (CCDC 634401, 619820, 648810), and the structures have been also investigated. Metal ions play a vital role in self-assembly reaction. Based on the structural analysis, it is concluded that metal ions can determine the final molecular structure. Luminescence determinations of the complexes indicate that they hold strong blue-emitting ability centering at 409 and 426 nm. Variable temperaturemagnetic susceptibility studies show weak antiferromagnetism in complexes (TN< 4K). From the study of structure, magnetic and optical properties of the complex[CoL2]n (HL = 4-(imidazol-1-yl)-benzoic acid), it is found thatπ-conjugated ligandnot only holds good fluorescent emit ability but also can act as magnetic couplingpathway. Therefore, it may be a new and effective approach to use conjugated ligandsas building block for constructing novel multifunctional materials. For cobaltmononuclear complex, Co(HLc)2(H2O)2 (H2Lc = 9-ethylcarbazole-3,6-dicarboxylicacid), it is also found that the intermolecular H-bonds interactions between theadjacent molecules extents the mononuclear compound into two dimensionalsupramolecular framework in structure. Moreover, the H-bonding interactions showan important effect on the solid state fluorescent and magnetic property (J = -1.94cm-1). So we can draw so a conclusion that weak intermolecular interactions not onlycontribute to assemble and stabilize the compound, but also have a key modulationeffect on the properties. Thus, hydrogen bond provides us a new strategy to design ormodify novel functional materials with better performance.2. It is the first time to observe the magnetic field effect on self-assembly reaction toward molecule-based magnet. It is clearly showed that the antiferromagnetic metal complex [Co1.5?(N3)(OH)(L)]n (HL = isonicotinic acid) can be synthesized at a higher yield under a 0.20 T applied magnetic field. The result indicates that applied magnetic field can induced supramolecular self-assembly reaction toward [Co1.5?(N3)(OH)(L)]n with antiferromagnetism. Furthermore, variable temperature magnetic susceptibility study also shows that the XmT value has been reduced by 0.31 cm3 K mol-1, indicating an improved antiferrimagnetic coupling interaction induced by the magnetic field.3. It is the first time to observe a slight change in structure of the product synthesized under magnetic field. The change has been determined by XAFS technology. The experiment shows that the local Co-O bond length of magnetic metal complex [CoL2]n, synthesized under a 0.12 T external magnetic field, shortens at a level of about 0.03 A. And the local Co-O bond length shortens at a level of about 0.06 (?) while a 0.20 T magnetic field is applied. From the viewpoint of structure, the shortenness of Co-O bond will decrease the hydrogen bond length which can transfer the magnetic coupling interaction. As a result, the magnetic interaction may be enhanced. So, the results suggest that magnetic field can be used as a tool to control the structure and magnetism of molecule-based magnet.4. The carboxylate group has been introduced into the cyclopentadiene group of ferrocene by molecular design. The change leads to the thermal stability is reduced by about 230℃in air. The reduced thermal stability will make it possible that an external magnetic field created by permanent magnet can be applied to the pyrolysis reaction of ferrocenecarboxylic acid. Then a 0.20 T weak external magnetic field is applied to the solvothermal reaction involved ferrocenecarboxylic acid, oleic acid and acetone, it is found that the nanoparticles formed ordered nanochain. Furthermore, magnetic measurement shows that the Ms and Mr/Ms values of products will be continuously increased with the improvement of applied magnetic field. For instance, the Ms and Mr/Ms values enhance 13.76 emu/g and 0.038 after applied a 0.20 T magnetic field, respectively. The results indicate that magnetic field can be used to control and change the pattern and magnetic properties of the final products of self-assembly reaction.
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