Covalency and magnetic anisotropy in lanthanide single molecule magnets: the DyDOTA archetype
Covalency and magnetic anisotropy in lanthanide single molecule magnets: the DyDOTA archetype
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DOI：
10.1039/c9sc01743g
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发表时间：
2019-08-14
期刊：
影响因子：
8.4
通讯作者：
Totti, Federico
中科院分区：
文献类型：
--
作者：
Briganti, Matteo;Garcia, Guglielmo Fernandez;Totti, Federico
当镧系离子与聚氨基-聚羧酸螯合剂络合时，形成一类在几个研究和技术领域，特别是在磁共振和分子磁性领域中极其重要的化合物。事实上，钆衍生物是磁共振成像中最常用的造影剂之一，而镝衍生物属于T-2加权MRI的新一代造影剂。在分子磁学中，含有镧系离子的单分子磁体（SMM）由于记录的磁化反转能垒的报道而在化学和物理界变得很受欢迎。镧系元素配合物的成功在于它们的大的各向异性，这是由于未猝灭的轨道角动量的贡献。然而，到目前为止，只有很少的努力来理解f-轨道如何受到周围配体的影响。结果已合理化，使用纯静电扰动模型。原型化合物[Na{Dy（DOTA）（H2O）}]中心点4 H（2）O（Na{DyDOTA}中心点4 H（2）O）发现了一个意想不到的易磁化轴，该轴垂直于分子的伪四轴。有趣的是，主磁化轴的取向依赖于配位顶端水分子（AWM）的简单旋转-与MRI对比度高度相关-用从头计算方法预测了Dy-O-AWM键周围的电子结构。然而，这种行为在随后的论文中受到了质疑，证明了他们对纯静电假设的结论。在本文中，我们想阐明的微妙影响的性质引起的水分子的DyDOTA原型复合物的磁性。因此，我们批判性地回顾了文献中已经发表的结构模型，沿着新的结构模型，显示了易轴方向如何危险地依赖于所选择的模型。不同的计算行为的易磁化轴的方向已被合理化作为一个功能之间的能隙的地面和第一激发的双重。磁结构的相关性，连同通过多极扩展的Dy（III）离子周围的配体产生的静电势的映射也被用来证明和量化的AWM轨道的共价贡献。
Lanthanide ions when complexed by polyamino-polycarboxylate chelators form a class of compounds of paramount importance in several research and technological areas, particularly in the fields of magnetic resonance and molecular magnetism. Indeed, the gadolinium derivative is one of the most employed contrast agents for magnetic resonance imaging while the dysprosium one belongs to a new generation of contrast agents for T-2-weighted MRI. In molecular magnetism, Single Molecule Magnets (SMMs) containing lanthanide ions have become readily popular in the chemistry and physics communities since record energy barriers to the reversal of magnetization were reported. The success of lanthanide complexes lies in their large anisotropy due to the contribution of the unquenched orbital angular momentum. However, only a few efforts have been made so far to understand how the f-orbitals can be influenced by the surrounding ligands. The outcomes have been rationalized using mere electrostatic perturbation models. In the archetype compound [Na{Dy(DOTA) (H2O)}]center dot 4H(2)O (Na{DyDOTA}center dot 4H(2)O) an unexpected easy axis of magnetization perpendicular to the pseudo-tetragonal axis of the molecule was found. Interestingly, a dependency of the orientation of the principal magnetization axis on the simple rotation of the coordinating apical water molecule (AWM) - highly relevant for MRI contrast - around the Dy-O-AWM bond was predicted by ab initio calculations, too. However, such a behaviour has been contested in a subsequent paper justifying their conclusions on pure electrostatic assumptions. In this paper, we want to shed some light on the nature of the subtle effects induced by the water molecule on the magnetic properties of the DyDOTA archetype complex. Therefore, we have critically reviewed the structural models already published in the literature along with new ones, showing how the easy axis orientation can dangerously depend on the chosen model. The different computed behaviors of the orientation of the easy axis of magnetization have been rationalized as a function of the energy gap between the ground and the first excited doublet. Magneto-structural correlations together with a mapping of the electrostatic potential generated by the ligands around the Dy(iii) ion through a multipolar expansion have also been used to evidence and quantify the covalent contribution of the AWM orbitals.