Theoretical study of the magnetic anisotropy and magnetic tunnelling in mononuclear Ni(II) complexes with potential molecular magnet behavior
Theoretical study of the magnetic anisotropy and magnetic tunnelling in mononuclear Ni(II) complexes with potential molecular magnet behavior
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DOI：
10.1039/c3sc52984c
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发表时间：
2014-01-01
期刊：
影响因子：
8.4
通讯作者：
Garcia-Fernandez, Pablo
中科院分区：
文献类型：
--
作者：
Gruden-Pavlovic, Maja;Peric, Marko;Garcia-Fernandez, Pablo
从基本和应用的角度来看，呈现其磁化缓慢衰减的磁性分子(分子磁体)是非常有趣的。虽然许多方法都集中在寻找具有强磁各向异性的系统，从而产生较大的自旋反转势垒，但对磁隧道行为的了解较少，磁隧道行为也是分子磁行为的基本组成部分。在这项工作中，我们提出了一个模型来描述Ni(II)三角双锥配合物中的自旋翻转势垒和磁隧穿，该模型可以很容易地推广到其他过渡金属系统。在这个模型的基础上，我们给出了发现分子磁性的最佳络合物的判据。我们用多参考构型相互作用(MRCI)和配位场密度泛函理论(LF-DFT)第一性原理计算对几类单核镍(II)配合物进行了验证。结果表明，配合物[NiCl3(Hdabco)(2)](+)(dabco为1，4-二氮杂双环[2.2.2]-辛烷)与含有相同金属的其他体系相比，表现出很大的磁各向异性能量524 cm(-1)和较小的隧道分裂0.2 cm(-1)。我们预计，当使用小磁场来破坏隧道效应时，将观察到分子磁行为。之所以达到这些值，是因为选择了有利于通过自旋-轨道耦合和不熄灭的轨道动量完全摧毁Jahn-Teller扭曲的配体。
Magnetic molecules that present a slow decay of their magnetization (molecular magnets) are very interesting both from a fundamental and applied points of view. While many approaches focus strongly on finding systems with strong magnetic anisotropy giving rise to large spin-reversal barriers, less is known on the behavior of magnetic tunnelling, which is also a fundamental component of molecular magnet behavior. In this work, we propose a model to describe both the spin-reversal barrier and magnetic tunnelling in Ni(II) trigonal bipyramidal complexes, which could be easily extended to other transitionmetal systems. Based on this model, we show the criteria that lead to the optimal complexes to find molecular magnet behavior. We test our proposal with multi-reference configuration-interaction (MRCI) and ligand-field-density-functional-theory (LF-DFT) first-principles calculations applied over several families of mononuclear Ni(II) complexes. As a salient result, we find that the complex [NiCl3(Hdabco)(2)](+) (dabco is 1,4-diazabicyclo[2.2.2]-octane) displays both a very large magnetic anisotropy energy, 524 cm(-1), and a small tunnelling splitting, 0.2 cm(-1), when compared to other systems containing the same metal. We expect molecular magnet behaviour to be observed when small magnetic fields are employed to disrupt tunnelling. These values are reached due to the choice of ligands that favor a complete destruction of the Jahn-Teller distortions through spin-orbit coupling and an unquenched orbital momentum.