稀土单分子磁体的设计、合成及其磁性研究
文献类型：学位论文
| 作者 | 张鹏 |
| 学位类别 | 博士 |
| 答辩日期 | 2015-04 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 中国科学院长春应用化学研究所 |
| 导师 | 唐金魁 |
| 关键词 | 单分子磁体 低配位 磁各向异性 磁相互作用 磁动态学 |
| 中文摘要 | 本学位论文围绕如何提升稀土化合物的单分子磁体性质这一核心问题进行了深入、系统的研究。主要内容分为四个部分，涵盖了单核、双核及四核稀土单分子磁体的磁性调控。对于单核稀土单分子磁体，主要探索了低配位稀土化合物的磁性，发现了第一个赤道配位的Er单分子磁体。在Dy2化合物中通过配体的调整及构筑单元组装等方法有效增强了稀土离子的轴向性及磁相互作用，成功地提高了化合物的单分子磁体性质。对于更加复杂的Dy4化合物，我们通过配位阴离子的调节，实现了化合物中反铁磁到铁磁相互作用的转变并极大提高了有效能垒。这些研究成果为设计、合成新的稀土单分子磁体提供重要的依据。具体内容分为以下四个方面： 1. 从晶体结构、静态及动态磁学性质、理论计算等方面对一系列低配位稀土化合物（1-7）的单分子磁体性质进行了深入的研究。其中，三配位化合物（1, 2）具有明显的赤道类型晶体场，而在其他化合物（3-7）中，负电荷同样集中在稀土离子的赤道位置，这为探索赤道类型晶体场对稀土单分子磁体行为的影响创造了有利条件。研究结果表明，三配位ErIII配合物1是第一个赤道类型的稀土单分子磁体，并且随赤道类型晶体场的减弱，Er化合物的单分子磁体性质减弱，而DyIII化合物的单分子磁体性质则显著增强，这与静电排斥模型的预测完全一致，从头计算进一步支持了以上实验结果。然而，对于一系列DyIII化合物静电势的计算也启示我们在设计稀土单分子磁体时并不能简单地考虑晶体场类型即静电排斥模型，同时也应该注意到分子本身的对称性。 2. 围绕配位构型对Dy2单分子磁体弛豫行为的影响，我们设计了类似于皮考林酰腙配体的西弗碱配体H3L1和尾端弯曲的8-羟基喹啉酰腙配体H2L2。将两个新配体与稀土盐反应，分别得到了一个醇氧桥连的带有呼啦圈构型的Dy2化合物8及一个配体交叉且呼啦圈构型遭到明显破坏的Dy2化合物9，并对他们进行了磁学表征。化合物8中，强磁相互作用及强单离子各向异性两者结合，有效抑制了低温区的量子隧穿，表现出较强的单分子磁体行为。与此相反，由于轴向配位环境的破坏，在化合物9中没有观察到单分子磁体行为。 3. 利用多齿salen型西弗碱配体H2L3合成了一系列3d-4f配合物（10-13），通过实验条件的控制，实现了[DyM]（M = ZnII，CuII）单元的连接。在[DyZn]2分子中，两个[DyZn]构筑单元的连接明显改变了DyIII离子周围的配位构型，进而有效增强了DyIII离子的单轴各向异性，并且CO32-离子的连接促使Dy离子之间呈现了明显的铁磁相互作用。结果，与[DyZn]化合物相比，[DyZn]2化合物的单分子磁体行为显著提升。这是一个通过构筑单元的组装实现单分子磁体行为提升的范例，对新型分子磁性材料的设计具有重要的指导意义。 4. 通过salen型西弗碱配体合成了三个平面Dy4（14-16）及一个Dy2Ba2（17）配合物，四个分子都呈现了中心对称的双缺角立方烷结构。尽管14-16结构极为相似，然而配位阴离子的变化却造成了分子内磁相互作用由反铁磁到铁磁的转变，严重影响了配合物的弛豫行为。相比其他两个化合物，有SCN-配位的Dy4分子展示了更加清晰的双弛豫过程，有效能垒也得到了极大提高。由于该系列化合物结构类似，我们不能简单地将双弛豫过程归因于分子中存在的两个不同金属中心，其实，磁相互作用的调整也可能对弛豫动态学产生重要影响。 |
| 英文摘要 | The thesis focuses on how to enhance the magnetic properties of lanthanide single molecule magnets (SMMs), and can be divided into four main parts, containing the modulations of SMM properties in mono-, bi-, and tetranuclear lanthanide complexes, where some significant breakthroughs were obtained. Herein, the magnetic properties of low-coordinate lanthanide complexes were explored firstly, leading to the discovery of the first equatorially-coordinated Er-based SMM. Furthermore, the axial anisotropies and intramolecular magnetic interactions in Dy2 complexes were improved effectively through the elaborate choice of bridging ligand or the linking of building units, resulting in their enhanced SMM behaviors. Remarkably, in more complicated Dy4 complexes, the intramolecular magnetic interactions change from antiferromagnetic to ferromagnetic as a result of the changes of coordinate anions, which further leads to the observation of two-step relaxation and the obvious improvement of effective barriers. The above results serve as the important avenues to improve SMM properties. More details are as follows： 1. We have investigated the magnetic anisotropy and relaxation dynamics of low-coordinate lanthanide complexes (1-7) through a combined experimental, ab initio and electrostatic potential study. Herein, the almost perfect equatorial crystal field occurs in three coordinate complexes (1, 2),while in other complexes ligands with negative charges are still concentrated in the equatorial positions of lanthanide ions, which enables us to explore the effects of equatorially shaped crystal field on the magnetic performances of theses complexes. Therefore, the three coordinate Er complex behaves as the first equatorially coordinated mononuclear Er SMM. In contrast, SMM behaviors are weakened gradually with the changing coordination geometries from triangle to tetrahedron and trigonal bipyramid in Er-based complex due to the breaking of equatorially coordinating crystal field, and reversely the obvious SMM behavior occurs in five-coordinateDy complex. Significantly, the results of theoretical calculations rationalized the change of SMM behavior originating from the equatorially coordinating crystal field. Nevertheless, the comparison of electrostatic potential maps for three Dy-based complexes revealed that one should simultaneously take a look at both the shape of the crystal field and molecular symmetry to tune the magnetic properties of a SMM. 2. Two novel Dy2 compounds (8 and 9) have been assembled from different types of ligands (H3L1 and H2L2), where H3L1 resembles the previous picolinoylhydrazone ligand, while a bended end is present in H2L2. Compound 8 with H3L1 represents the rare alkoxide-O bridged Dy2 complex and displays the hula hoop-like coordination geometry around each DyIII ion, thus leading to the typical SMM behavior combined with the strong ferromagnetic interactions between DyIII ions. The distorted coordination geometry around DyIII ion and much weaker interactions were observed in compound 9 due to the introduction of bent H2L2, thus resulting in the disappearance of SMM behavior 3. The reactions between a salen ligand (H2L3) and different metal salts lead to the formation of four 3d-4f [MDy] and [MDy]2 (M = Zn/Cu) compounds (10-13), where the [MDy]2 can be considered as resulting from the assembly of two [MDy] building blocks. The [ZnDy]2 compound (11) demonstrates typical single molecule magnet (SMM) behavior, which should originate from the high axial anisotropy of Dy ions correlating to the change of coordination geometry and enhanced ferromagnetic interactions between Dy ions via the coupling of two [DyZn] units. The result suggests the positive effects of coupling blocking units to enhance their SMM behavior, presenting a promising strategy for constructing efficient heterometallic SMMs. 4. Three planar Dy4 (14-16) and one Dy2Ba2 (17) SMMs have been assembled using a multidentate salen-type ligand. Although |
| 语种 | 中文 |
| 公开日期 | 2016-05-03 |
| 源URL | [http://ir.ciac.jl.cn/handle/322003/64486]  |
| 专题 | 长春应用化学研究所_长春应用化学研究所知识产出_学位论文 |
| 推荐引用方式 GB/T 7714 | 张鹏. 稀土单分子磁体的设计、合成及其磁性研究[D]. 中国科学院长春应用化学研究所. 中国科学院研究生院. 2015. |
入库方式： OAI收割
来源：长春应用化学研究所
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