Coupling Dy3 Triangles Enhances Their Slow Magnetic Relaxation
Coupling Dy3 Triangles Enhances Their Slow Magnetic Relaxation
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DOI：
10.1002/anie.201002691
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Powell, Annie K.
中科院分区：
文献类型：
--
作者：
Hewitt, Ian J.;Tang, Jinkui;Powell, Annie K.
单分子磁体 (SMM) 行为的发现，其中磁化强度的弛豫和量子隧道是基于分子的，由于存在阻塞各向异性，[1] 被认为是基于分子的磁性领域的重要突破。这导致合成化学家积极致力于生产适合物理学家详细研究的系统。进一步的目标是生产和表征新分子，目的是识别与最初研究的例子相比增强甚至发现新特性的相关特征。最近，结合[2]或仅由 4f 金属离子制成的分子[3]的例子表明，镧系元素离子可以产生令人着迷的磁性行为，不仅通过它们贡献高自旋的潜力，而且还由于 f 电子壳的性质而向分子引入各向异性。很大程度上来说，此类系统的磁性行为很难用简单的自旋模型来解释，因此需要开发新的范式。这种范式转变的一个例子是我们在化合物[Dy3 (μ3-OH) 2L3Cl2 (OH2) 4][Dy3 (μ3-OH) 2L3Cl-(OH2) 5] Cl5· 19 H2O(1a) 和[Dy3 (μ3-OH) 2L3Cl-(OH2) 5] Cl3· 4H2O· 中描述的三核镝配合物提供的。 2 MeOH· 0.7 MeCN (1b)(L= o-vanillato；方案 1)。[3d] 这些 Dy3 三角形具有本质上抗磁性的基态，我们能够使用单晶研究将其识别为伊辛非共线模型的分子原型。[4]这些分子表现出由激发自旋态引起的 SMM 行为，从而赋予系统前所未有的磁性。作为我们对此类三核系统持续研究的一部分，[3i]我们发现了一种连接两个此类单元的方法，使 Dy6 分子具有更奇特的磁性。在合成类似的 Ln3 三角形以对该系统进行系统研究（将在别处描述）的过程中，并再次使用香草醛作为配体，发现对于铥 (III) 化合物，六核络合物，[Tm6 (μ3-OH)形成4L4L’2(H2O)10]Cl6·18H2O(2)。这种形成是由于每个三角形上的三个邻香草酸配体之一的醛还原为醇而形成的。所得醇盐在两个三角形 Tm3 基序之间形成双桥。考虑到 Dy3 三角形有趣的磁性行为，我们通过故意在反应中添加 2-羟甲基-6-甲氧基苯酚 H2L' 来合成 Dy6 类似物，从而以良好的产率形成 [Dy6 (μ3-OH) 4L4L'2-(H2O) 9Cl] Cl5·15 H2O (3)。这种金属离子催化的配体转化现在在文献中相对频繁地报道，与这项工作最相关的例子是涉及丙酮和邻香兰素的镝 (III) 激活的 [3h] 转化。化合物2和3是同晶的，在三斜空间群P1中结晶，Z=1（支持信息），但在3的一个末端位置上水和氯的无序性为1:1。这里我们仅进一步讨论3的结构特征，因为这是显示出最有趣的磁性行为的化合物。 3 中看到的 Dy6 结构可以被认为是由 1 中两个 Dy3 三角形的配体还原形式的醇盐进行形式连接而产生的，同时伴随着两个末端氯配体的形式损失（图 1）。 3 中的三角形 Dy3 单元比 1,[3d] 中的三角形 Dy3 单元更不等边，Dy…Dy 距离为 3.5127 (3)、3.5371 (3) 和 3.5797 (3)。三角形间 Dy3… Dy3’ 距离为 3.7262 …
The discovery of single-molecule magnet (SMM) behavior, where relaxation and quantum tunneling of the magnetization is molecule-based due to the presence of a blocking anisotropy,[1] is recognized as an important breakthrough in the field of molecular-based magnetism. This has led to intense activity on the part of synthetic chemists to produce systems suitable for detailed study by physicists. A further aim is to produce and characterize new molecules with the goal of identifying features of relevance to enhancing or even discovering new properties compared with those of the originally studied examples. Recently, examples of molecules either incorporating [2] or made exclusively from 4f metal ions [3] have shown that lanthanide ions can produce fascinating magnetic behavior, not only through their potential to contribute high spins, but also to introduce anisotropy to a molecule as a result of the nature of the f-electron shell. Largely speaking, the magnetic behavior of such systems is difficult to explain in terms of simple spin models and therefore requires the development of new paradigms. An example of such a paradigm shift is provided by the trinuclear dysprosium complexes we described in the compounds[Dy3 (μ3-OH) 2L3Cl2 (OH2) 4][Dy3 (μ3-OH) 2L3Cl-(OH2) 5] Cl5· 19 H2O(1a) and[Dy3 (μ3-OH) 2L3Cl-(OH2) 5] Cl3· 4H2O· 2 MeOH· 0.7 MeCN (1b)(L= o-vanillato; Scheme 1).[3d] These Dy3 triangles have an essentially diamagnetic ground state, which we were able to identify using single-crystal studies as the molecular archetype of the Ising non-collinear model.[4] These molecules display SMM behavior arising from an excited spin state, thereby giving a system with unprecedented magnetic properties. As part of our continuing studies on this type of trinuclear system,[3i] we have discovered a means of linking two such units to give a Dy6 molecule with even more exotic magnetic properties.In the course of synthesizing analogous Ln3 triangles for a systematic study of the system, which will be described elsewhere, and again using vanillin as ligand, it was found that for the thulium (III) compound, the hexanuclear complex,[Tm6 (μ3-OH) 4L4L’2 (H2O) 10] Cl6· 18 H2O (2) formed. This formation results from the reduction of the aldehyde to an alcohol for one of the three o-vanillinato ligands on each triangle. The resulting alkoxides lead to a double bridge between two of the triangular Tm3 motifs. With the interesting magnetic behavior of the Dy3 triangle in mind, we directed the synthesis to the Dy6 analogue by deliberately adding 2-hydroxymethyl-6-methoxyphenol, H2L’, to the reaction, leading to the formation of [Dy6 (μ3-OH) 4L4L’2-(H2O) 9Cl] Cl5· 15 H2O (3) in good yields. Such metal-ioncatalyzed ligand transformations are now relatively frequently reported in the literature, and the most relevant example to this work is the dysprosium (III)-activated [3h] transformation involving acetone and o-vanillin. Compounds 2 and 3 are isomorphous, crystallizing in the triclinic space group P1 with Z= 1 (Supporting Information) but with 1: 1 disorder of water and chloride on one terminal site in 3. Herein we only discuss the structural features with reference to 3 further, as this is the compound displaying the most interesting magnetic behavior. The Dy6 structure seen in 3 can be considered as resulting from the formal linkage by the alkoxides of the reduced form of the ligand of two of the Dy3 triangles in 1 with the concomitant formal loss of the two terminal chloride ligands (Figure 1). The triangular Dy3 unit in 3 is less equilateral than found for 1,[3d] with Dy··· Dy distances of 3.5127 (3), 3.5371 (3), and 3.5797 (3). The inter-triangle Dy3··· Dy3’distance is 3.7262 …