Singh Saurabh Kumar, Gupta Tulika, Rajaraman Gopalan
Department of Chemistry, Indian Institute of Technology-Bombay , Mumbai 400076, India.
Inorg Chem. 2014 Oct 20;53(20):10835-45. doi: 10.1021/ic500772f. Epub 2014 Sep 26.
Magnetic anisotropy is a key component in the design of single-molecule magnets (SMMs) possessing a large barrier height for magnetization reversal. Lanthanide-based SMMs are the most promising candidates in this arena as they offer a large magnetic anisotropy due to the presence of strong spin-orbit coupling. Among lanthanides, Er(III) complexes are gaining attention in the area of SMMs, because of their intriguing magnetic properties and attractive blocking temperatures. Here, we have undertaken detailed ab initio calculations on four structurally diverse Er(III) SMMs to shed light on how the magnetic anisotropy is influenced by the role of symmetry and structural distortions. The employed CASSCF+RASSI calculations have offered rationale for the observed differences in the estimated Ueff values for the studied complexes and also offered hints to the mechanism of magnetic relaxation. The differences in the mechanism of magnetic relaxations are further analyzed based on the Er-ligand interactions, which is obtained by analyzing the charges, densities, luminescent behavior and the frontier molecular orbitals. Our calculations, for the first time, have highlighted the importance of high symmetry environment and ligand donor strength in obtaining large Ueff values for the Er(III) complexes. We have examined these possibilities by modeling several structures with variable coordination numbers and point group symmetry. These results signify the need of a detailed understanding on the shape of the anisotropy and the point group symmetry in order to achieve large Ueff values in Er(III) single-ion magnets.
磁各向异性是设计具有高磁化反转势垒高度的单分子磁体（SMM）的关键要素。基于镧系元素的SMM是该领域最有前景的候选者，因为强自旋 - 轨道耦合的存在使其具有较大的磁各向异性。在镧系元素中，Er(III)配合物因其有趣的磁性质和吸引人的阻塞温度而在SMM领域受到关注。在此，我们对四种结构不同的Er(III) SMM进行了详细的从头算计算，以阐明磁各向异性如何受到对称性和结构畸变作用的影响。所采用的CASSCF + RASSI计算为所研究配合物估计的Ueff值中观察到的差异提供了理论依据，也为磁弛豫机制提供了线索。基于Er - 配体相互作用进一步分析了磁弛豫机制的差异，这是通过分析电荷、密度、发光行为和前沿分子轨道得到的。我们的计算首次强调了高对称环境和配体供体强度对于获得大的Er(III)配合物Ueff值的重要性。我们通过对具有可变配位数和点群对称性的几种结构进行建模来研究这些可能性。这些结果表明，为了在Er(III)单离子磁体中获得大的Ueff值，需要详细了解各向异性的形状和点群对称性。
