State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, P. R. China.
Shandong Provincial Key Laboratory, of Chemical Energy Storage and Novel Cell Technology, School of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng, 252000, P. R. China.
Chemistry. 2018 Jul 11;24(39):9928-9939. doi: 10.1002/chem.201801523. Epub 2018 Jun 25.
The magnetic relaxation and magnetization blocking barriers of tailor-made homo- and heterodinuclear compounds [Dy (opch) (OAc) (H O) ]⋅MeOH (1) and [DyMn(opch) (OAc)(MeOH)(H O) ] (2), where H opch is (E)-N'-(2-hydroxy-3-methoxybenzylidene)pyrazine-2-carbohydrazide, were systematically investigated and the change in single-molecule magnet behavior originating from targeted replacement of one dysprosium site in the Dy compound with manganese was elucidated through a combination of experimental and theoretical studies. A detailed comparative study on these closely related model compounds revealed remarkable changes of the crystal-field splitting and anisotropy of the Dy site and the total exchange spectrum due to the replacement of Dy by Mn. The blocking barriers of these two compounds, which explain their different relaxation behaviors, were analyzed. The two Ising doublets arising from the magnetic interaction in the case of 1 are strongly uniaxial, with tunneling splittings smaller than 10 cm , and this leads to magnetic relaxation at temperatures exceeding the exchange energy (2.14 cm ), which involves transition via the excited states corresponding to local transitions on the excited doublet at the Dy site. The third and fourth exchange doublets in 2 (located at 2.16 and 3.25 cm , respectively) show much larger tunneling splittings (of 10 and 10 cm , respectively), and thus open an important path for magnetic relaxation.
经系统研究了定制同核和异核配合物[Dy(opch)(OAc)(H_2O)]·MeOH(1)和[DyMn(opch)(OAc)(MeOH)(H_2O)] (2)的磁弛豫和磁化阻断势垒，其中 H_opch 是(E)-N'-(2-羟基-3-甲氧基苄叉基)吡嗪-2-甲酰肼。通过实验和理论研究相结合，阐明了通过靶向取代 Dy 化合物中一个 Dy 位点为锰而导致单分子磁体行为发生变化。对这些密切相关的模型化合物进行了详细的比较研究，揭示了由于 Dy 被 Mn 取代，Dy 位的晶体场分裂和各向异性以及总交换谱发生了显著变化。对这两种化合物的阻断势垒进行了分析，这些势垒解释了它们不同的弛豫行为。在 1 中，由磁相互作用产生的两个 Ising 双峰是强单轴的，隧道分裂小于 10 cm，这导致在超过交换能（2.14 cm）的温度下发生磁弛豫，这涉及通过对应于 Dy 位上激发态的局部跃迁的激发态的跃迁。2 中的第三个和第四个交换双峰（分别位于 2.16 和 3.25 cm）显示出更大的隧道分裂（分别为 10 和 10 cm），从而为磁弛豫开辟了重要途径。
