【作者】 张居舟；

【导师】 陈乾旺；

【作者基本信息】 中国科学技术大学 ， 无机化学， 2008， 博士

【摘要】 信息化和高密度信息储存器件的发展对磁性介质提出了更高的要求，而传统的无机磁性材料难以满足它们的需要。新型的具有磁学物理特征的，在结构上以超分子化学为主要特点的分子磁体正好能满足这些发展的要求。目前分子磁体大都是通过自组装反应合成得到的，自组装反应大多取决于内驱动力，人为很难控制。而磁场作为一种外动力，已经证明能够被用来作为自组装的动力，用来控制排列和自组装的反应，得到有序材料，甚至能对产物进行选择性的合成。所以，我们认为在分子磁体的自组装过程中引入外加磁场则有可能对这些有顺磁性离子参与的超分子自组装反应产生一定的影响，甚至控制这些自组装反应方向，增强分子磁体的磁交换作用和改善磁性能等。此外，分子磁体具有结构多样性的特点，易于用化学方法在分子水平上对其进行修饰和剪裁而提高或改变其磁性能，这种分子水平上的剪裁和修饰也可以得到多功能性的分子磁性材料。金属配合物作为反应物来制备纳米材料也逐渐受到重视，但它们的热解反应温度较高，本论文致力于通过配合物的分子设计，改变其结构，从而使其热稳定性发生改变，以期降低反应温度，从而使外加永久磁场能够被引入到金属配合物分解制备磁性纳米粒子的反应中，以便观察磁场对产物的结构和性能的调控作用。论文详细内容归纳如下：1．在简单温和的水热条件下，利用自组装反应成功地合成了三种新的羧酸配合物（CCDC 634401，619820，648810），并解析了它们的晶体结构。从自组装反应结果看，金属阳离子能决定配合物的分子结构，即金属阳离子在自组装反应中起结构导向作用。光致发光测试表明它们都具有好的蓝光发射性能（发射波长分别为409和426 nm），磁性测量也显示它们具有弱的反铁磁性（T_N均小于4 K）。对于二咪唑苯甲酸合钴的配合物(CoL₂]_N（HL=对咪唑基苯甲酸），通过对其结构、磁和荧光性质的研究后发现，π-共轭配体既具有强的蓝荧光发光性质，又有利于磁的超交换作用。这为我们今后设计和合成多功能性的配合物提供了一条新的思路。对于钴的单核咔唑二羧酸配合物Co（HLc）₂（H₂O）₂（H2Lc=3，6-二羧基-9-乙基咔唑），我们也研究了它的结构、磁和发光等性质，我们发现氢键在配合物中不仅对其结构有重要的影响-氢键将单核配合物扩展成二维的超分子化合物；而且对配合物的性质具有重要的影响和控制作用-氢键传递了磁相互作用(J=-1．94 cm^-1)。这些现象表明，在超分子化合物中，分子间的弱相互作用不仅能影响分子的结构，而且还能调制其性质，这为我们今后设计和合成新材料提供了一种重要的设计思路。2．成功地观测到磁场对分子基磁性材料的自组装反应的影响。实验结果清楚地显示反铁磁性的金属配合物[Co^Ⅱ1．5（N₃）（OH）（L）]_n（HL=异烟酸）在外加磁场下能更容易被合成。这表明外加磁场能诱导这个超分子自组装反应向生成反铁磁性的配合物[Co^Ⅱ1．5（N₃）（OH）（L）]_n的方向进行。磁测量表明磁场下合成的配合物的磁化率降低了0．31 emu K mol^-1，这表明外加磁场还能增强分子磁体的磁相互作用。3．我们采用XAFS技术观测到反应中的弱外加磁场能使产物的分子结构发生细微的变化。从测试结果看，一个0．12 T外加磁场能使分子基磁体-钴的咔唑二酸配合物的近邻Co-O配位键收缩约0．03 （?），而0．20 T外加磁场能使分子基这个近邻Co-O配位键收缩约0．06 （?）。我们从晶体结构分析认为，Co-O键的收缩将使传递磁交换作用的氢键缩短，最终可能使分子磁体的磁相互作用增强。因此，可以认为磁场可以作为一种调控手段来改变分子的结构，从而改善分子磁体的磁性能。4．通过分子设计，我们在二茂铁芳环上引入羧基基团，发现其在空气中的分解温度较二茂铁降低了约230℃。使得将磁场（永久磁体）引入到二茂铁羧酸热解制备Fe₃O₄的反应体系中成为可能，我们将0．20 T的外加磁场引入到溶剂热反应体系中，发现Fe₃O₄粒子形成了较为有序的链状结构；磁性能测试进一步表明，随着外加磁场强度的增加，产物的饱和磁化强度Ms和剩磁比Mr/Ms值都逐渐增加。如，当0．20 T的外加磁场引入后，其Ms和Mr/Ms值分别增加了13．76emu／g和0．038。这些结果说明外加磁场能有效调控自组装反应产物的形貌和磁性能。更多还原

【Abstract】 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 （T_N< 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 [Co_1.5^?（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 [Co_1.5^?（N₃）（OH）（L）]_n with antiferromagnetism. Furthermore, variable temperature magnetic susceptibility study also shows that the X_mT 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.更多还原