State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry , Chinese Academy of Sciences , Changchun 130022 , P. R. China.
University of Chinese Academy of Sciences , Beijing 100049 , P. R. China.
Inorg Chem. 2018 Oct 1;57(19):12213-12221. doi: 10.1021/acs.inorgchem.8b01878. Epub 2018 Sep 18.
Single-ion anisotropy is one of the crucial properties for mononuclear and even polynuclear single-molecule magnets (SMMs), which can be enhanced by the judicious choice of the coordination geometry around the metal centers. Meanwhile, magnetic interactions also play a significant role in high-performance polynuclear SMMs, especially the dinuclear SMMs. For exploring the influence of those two factors on the magnetic properties, we report a novel series of lanthanide complexes, [Dy(L)(HL)(THF)] (1), [Dy(PyCO)(CFSO)(HO)]·CHCN (2), and [Dy(PyCO)(PhCOO)(MeOH)]·MeOH (3), with hula-hoop-like geometries around the Dy ions. All three complexes display slow relaxation of magnetization under a zero applied direct-current field with anisotropy barriers of 169 and 51 K for 1 and 3, respectively, while the slow relaxation of magnetization of complex 2 may mainly result from Raman relaxation. Besides, complex 1 demonstrates butterfly-type hysteresis below 4 K, and complex 2 shows no opening of the hysteresis loop with an inflection of around 0.25 T. Although complexes 2 and 3 have similar structures, the different coordinate anions induce distinct magnetic interaction states, antiferromagnetic and ferromagnetic for 2 and 3, respectively. Ab initio calculations reveal that the better SMM behavior of complex 1 should be ascribed to stronger single-ion anisotropy compared with complexes 2 and 3. The small value of the dipolar interaction results in an overall antiferromagnetic interaction for complex 2, while the large value of the dipolar interaction causes an overall ferromagnetic interaction for complex 3, where the dipolar interactions are ferromagnetic for both complexes.
单离子各向异性是单核甚至多核单分子磁体（SMM）的关键性质之一，可以通过合理选择金属中心周围的配位几何形状来增强。同时，磁相互作用在高性能多核 SMM 中也起着重要作用，特别是双核 SMM。为了探索这两个因素对磁性质的影响，我们报道了一系列新型镧系元素配合物，[Dy(L)(HL)(THF)]（1）、[Dy(PyCO)(CFSO)(HO)]·CHCN（2）和[Dy(PyCO)(PhCOO)(MeOH)]·MeOH（3），它们在 Dy 离子周围具有呼啦圈状的几何形状。所有三个配合物在零直流场下的磁化强度都表现出缓慢的弛豫，其中 1 和 3 的各向异性势垒分别为 169 和 51 K，而 2 的磁化强度缓慢弛豫可能主要归因于 Raman 弛豫。此外，配合物 1 在低于 4 K 时表现出蝴蝶型磁滞回线，而配合物 2 在约 0.25 T 处的拐点处没有磁滞回线的打开。尽管配合物 2 和 3 具有相似的结构，但不同的配位阴离子诱导出不同的磁相互作用状态，分别为 2 的反铁磁和 3 的铁磁。从头算计算表明，与配合物 2 和 3 相比，配合物 1 具有更好的 SMM 行为，这归因于更强的单离子各向异性。由于偶极相互作用较小，配合物 2 导致整体反铁磁相互作用，而由于偶极相互作用较大，配合物 3 导致整体铁磁相互作用，其中两个配合物的偶极相互作用都是铁磁的。
