Magnetic Anisotropy in a Cubane-like Ni4 Complex: An Ab Initio Perspective.
Magnetic Anisotropy in a Cubane-like Ni4 Complex: An Ab Initio Perspective.
复制标题
DOI：
10.1021/acs.inorgchem.1c00047
复制
发表时间：
2021-04
影响因子：
4.6
通讯作者：
R. Maurice
中科院分区：
文献类型：
--
作者：
R. Maurice
在没有外部磁场的情况下，磁各向异性与能级的简并提升有关。在过渡金属络合物的标准情况下，这种性质通常由各向异性自旋哈密顿量建模，并且人们谈到自旋态的“零场分裂”（zero-field splitting，缩写为ZH）。虽然单核配合物的情况下，已被广泛描述的从头计算的量子力学计算的手段，与这些方法研究的多核配合物的文献是相当稀缺的。在这项工作中，先进的多组态波函数理论方法被应用于计算的实际四镍（II）配合物的基态S = 4状态的磁行为，显示低于0.5 K。首先，各向同性耦合计算的情况下的自旋-轨道耦合算子，在全复杂的，也在集群只有两个活性镍（II）中心，确认弱铁磁耦合在这个系统中的发生。第二，单网站的磁各向异性计算集群轴承只有一个活性镍（II）网站，表明单网站的各向异性轴没有定向在一个最佳的方式产生一个大的单轴分子各向异性。此外，在计算中只涉及几个局部轨道激发态的可能性进行了评估，实际上开辟了一个一致的和可管理的治疗的地面S = 4状态的电子束的方式。第三，多组态计算进行了完整的复杂，确认弱单轴各向异性发生这种状态，也有趣的是，揭示了最低的轨道激发S = 3状态的显着贡献。总的来说，通过与实验的比较，所报道的结果质疑了仅使用一种结构（特别是来自晶体学实验的结构）来计算磁各向异性参数的常见习惯。
Magnetic anisotropy, in the absence of an external magnetic field, relates to the degeneracy lift of energy levels. In the standard case of transition metal complexes, this property is usually modeled by an anisotropic spin Hamiltonian and one speaks of "zero-field splitting" (ZFS) of spin states. While the case of mononuclear complexes has been extensively described by means of ab initio quantum mechanical calculations, the literature on polynuclear complexes studied with these methodologies is rather scarce. In this work, advanced multiconfigurational wave function theory methods are applied to compute the ZFS of the ground S = 4 state of an actual tetranickel(II) complex, displaying a magnet behavior below 0.5 K. First, the isotropic couplings are computed in the absence of the spin-orbit coupling operator, in the full complex and also in clusters with only two active nickel(II) centers, confirming the occurrence of weak ferromagnetic couplings in this system. Second, the single-site magnetic anisotropies are computed on a cluster bearing only one active nickel(II) site, showing that the single-site anisotropy axes are not oriented in an optimal fashion for generating a large uniaxial molecular anisotropy. Furthermore, the possibility for involving only a few local orbital excited states in the calculation is assessed, actually opening the way for a consistent and manageable treatment of the ZFS of the ground S = 4 state. Third, multiconfigurational calculations are performed on the full complex, confirming the weak uniaxial anisotropy occurring for this state and also, interestingly, revealing a significant contribution of the lowest-lying orbitally excited S = 3 states. Overall, by comparison with the experiment, the reported results question the common habit of using only one structure, in particular derived from a crystallography experiment, to compute magnetic anisotropy parameters.