Ma Xiufang, Chen Bingbing, Zhang Yi-Quan, Yang Jinhui, Shi Quan, Ma Yulong, Liu Xiangyu
State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering, National Demonstration Center for Experimental Chemistry Education, College of Chemistry and Chemical Engineering, Ningxia University, Yinchuan 750021, China.
Jiangsu Key Laboratory for NSLSCS, School of Physical Science and Technology, Nanjing Normal University, Nanjing 210023, China.
Dalton Trans. 2019 Sep 7;48(33):12622-12631. doi: 10.1039/c9dt02758k. Epub 2019 Aug 5.
The utilization of two isomorphic ligands with different substituents leads to two centrosymmetric Dy dimers, namely, [Dy(bfbpen)(HO)]·2I (1) and [Dy(bcbpen)(HO)]·2I·0.5HO (2) (Hbfbpen = N,N'-bis-(2-hydroxy-5-fluoro-benzyl)-N,N'-bis-(pyridin-2-ylmethyl)ethylenediamine and Hbcbpen = N,N'-bis-(2-hydroxy-5-chloro-benzyl)-N,N'-bis-(pyridin-2-ylmethyl)ethylenediamine). Although Dy ions in both compounds uniformly exhibit a square-antiprism geometry, the critical difference found in the terminal substituents of the two ligands fine-tunes the local crystal field around Dy centers and the dinuclear molecular structures of 1 and 2. Magnetic investigations unveil that both 1 and 2 display dynamic magnetic relaxation of single-molecule magnet (SMM) behaviour with different energy barriers of 20.9 K for 1 and 72.7 K for 2 under a zero direct-current (dc) field, as well as 26.9 K for 1 under a 1200 Oe dc field. Compared to 1, the stronger uniaxial anisotropy and magnetic exchange in 2 render it a better SMM as evidenced by the higher energy barrier. Ab initio calculations are also performed on both Dy compounds to rationalize the observed discrepancy in their magnetic behaviours. The contribution illustrates that the SMM behaviour could be effectively enhanced by means of deliberate local structural manipulation.
利用具有不同取代基的两个同构配体可得到两个中心对称的Dy二聚体，即[Dy(bfbpen)(HO)]·2I (1)和[Dy(bcbpen)(HO)]·2I·0.5HO (2)（Hbfbpen = N,N'-双-(2-羟基-5-氟苄基)-N,N'-双-(吡啶-2-基甲基)乙二胺，Hbcbpen = N,N'-双-(2-羟基-5-氯苄基)-N,N'-双-(吡啶-2-基甲基)乙二胺）。尽管两种化合物中的Dy离子均呈现均一的四方反棱柱几何构型，但在两个配体的末端取代基中发现的关键差异微调了Dy中心周围的局部晶体场以及1和2的双核分子结构。磁性研究表明，在零直流（dc）场下，1和2均表现出单分子磁体（SMM）行为的动态磁弛豫，1的能垒为20.9 K，2的能垒为72.7 K，在1200 Oe直流场下1的能垒为26.9 K。与1相比，2中更强的单轴各向异性和磁交换使其成为更好的SMM，更高的能垒证明了这一点。还对两种Dy化合物进行了从头算，以合理解释观察到的它们磁性行为的差异。该贡献表明，通过有意的局部结构操纵可以有效地增强SMM行为。
