Ding You-Song, Han Tian, Zhai Yuan-Qi, Reta Daniel, Chilton Nicholas F, Winpenny Richard E P, Zheng Yan-Zhen
Frontier Institute of Science and Technology (FIST), State Key Laboratory for Mechanical Behavior of Materials, MOE Key Laboratory for Nonequilibrium Synthesis and, Modulation of Condensed Matter, and School of Science, Xi'an Jiaotong University, 99 Yanxiang Road, Xi'an, Shaanxi, 710054, P.R. China.
Department of Chemistry, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
Chemistry. 2020 May 7;26(26):5893-5902. doi: 10.1002/chem.202000646. Epub 2020 Apr 21.
Although the development of single-molecule magnets (SMMs) is rapid, there are only two families of high energy barrier (U ) dysprosium(III) SMMs known so far: the cyclopentadienyl (Cp) family with a sandwich structure and the pentagonal-bipyramidal (PB) family with D symmetry. These high-barrier SMMs, which usually possess U >500 cm allow the separate study of the four magnetic relaxation paths, namely, direct, quantum tunnelling, Raman and Orbach processes, in detail. Whereas the first family is chemically more challenging to modify the Cp rings, it is shown herein that the latter family, with the common formulae [DyX X (L ) ] , such as X /X = OCMe , OSiMe , OPh, Cl or Br ; L =THF/pyridine/4-methylpyridine, can be readily fine-tuned with a range of axial and equatorial ligands by simple substitution reactions. This allows unambiguous confirmation that the U mainly depends on the identity of X and X , rather than on L . More importantly, the fitted parameters are barrier dependent. If X is an O donor and X is a halide, 500<U <600 cm , log τ (s)=-10.66, log C (s K )= -5.05, n =4.1 and T =9 K (in which τ is the pre-exponential factor for the Orbach relaxation process, C and n are parameters used to describe Raman relaxation, and T is the highest temperature at which magnetic hysteresis is observed). For cases in which both X and X are O donors, 900<U <1300 cm , log τ (s)=-11.63, log C (s K )= -6.03, n =4.1 and 18<T <25 K. Based on these results, it can be further concluded that U not only has a linear correlation to the axial Dy-X bond lengths, but also to T for these PB SMMs. This represents the first systematic study of a family of lanthanide SMMs and derives the first magneto-structural correlation in Dy SMMs.
尽管单分子磁体（SMMs）的发展迅速，但迄今为止已知的高能垒（U）镝（III）单分子磁体只有两个家族：具有夹心结构的环戊二烯基（Cp）家族和具有D对称性的五角双锥（PB）家族。这些高垒单分子磁体通常具有U>500 cm，能够详细地分别研究四种磁弛豫路径，即直接、量子隧穿、拉曼和奥尔巴赫过程。虽然第一个家族在化学上修饰Cp环更具挑战性，但本文表明，后一个家族，其通式为[DyX X (L ) ] ，例如X /X = OCMe 、OSiMe 、OPh、Cl或Br；L =THF/吡啶/4-甲基吡啶，可以通过简单的取代反应很容易地用一系列轴向和赤道配体进行微调。这使得能够明确确认U主要取决于X和X的身份，而不是L。更重要的是，拟合参数与势垒有关。如果X是氧供体且X是卤化物，则500<U<600 cm，log τ (s)= -10.66，log C (s K )= -5.05，n = 4.1且T = 9 K（其中τ是奥尔巴赫弛豫过程的指数前因子，C和n是用于描述拉曼弛豫的参数，T是观察到磁滞的最高温度）。对于X和X都是氧供体的情况，900<U<1300 cm，log τ (s)= -11.63，log C (s K )= -6.03，n = 4.1且18<T<25 K。基于这些结果，可以进一步得出结论，对于这些PB单分子磁体，U不仅与轴向Dy-X键长呈线性相关，而且与T也呈线性相关。这代表了对镧系单分子磁体家族的首次系统研究，并得出了镝单分子磁体中的第一个磁结构相关性。
