Wu Haipeng, Li Min, Zhang Sheng, Ke Hongshan, Zhang Yiquan, Zhuang Guilin, Wang Wenyuan, Wei Qing, Xie Gang, Chen Sanping
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University , Xi'an 710127, China.
College of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences , Baoji 721013, China.
Inorg Chem. 2017 Sep 18;56(18):11387-11397. doi: 10.1021/acs.inorgchem.7b01840. Epub 2017 Sep 6.
Great interest is being shown in investigating magnetic interactions that efficiently influence lanthanide single-molecule magnet behavior. A series of heterometallic complexes [MLn(Hhms)(CHCOO)(CHOH)(HO)]·(NO) (M = Ni, Ln = Dy (1), Gd (2), and Y (3); M = Co, Ln = Dy (4), Gd (5), and Y (6)) have been prepared with a compartmental Schiff-base ligand, 1-(2-hydroxy-3-methoxybenzylidene)-semicarbazide (Hhms), featuring a zigzag-shaped M-Ln-Ln-M metallic core arrangement. In complexes 1-6, a unique monophenoxo/diacetate asymmetric bridging connects M ion with Ln ion, and four acetates bridge two Ln ions where acetates play essential roles as coligand in generating the tetranuclear units. Magnetic studies reveal the presence of predominant ferromagnetic coupling in Dy and Gd derivatives, and slow relaxation of magnetization is observed for {NiDy} and {CoDy} with an energy barrier of 16.0 K for {NiDy} and 6.7 K for {CoDy} under zero static field. Compared with the analogue {CoDy}, the {NiDy} shows longer relaxation time and an absence of the quantum tunnelling of the magnetization (QTM) at low temperatures. Ab initio calculations suggest that the zero-field QTM of {NiDy} is effectively interrupted thanks to the ferromagnetic exchange coupling generated between Ni and Dy ions. The presence of ferromagnetic exchange between Ni and Dy ions is more conducive to zero-field single-molecule magnet behaviors than in isomorphic {CoDy} where the exchange is antiferromagnetic.
人们对研究能有效影响镧系单分子磁体行为的磁相互作用表现出极大兴趣。已制备出一系列异金属配合物[MLn(Hhms)(CHCOO)(CHOH)(HO)]·(NO)（M = Ni，Ln = Dy（1）、Gd（2）和Y（3）；M = Co，Ln = Dy（4）、Gd（5）和Y（6）），其具有一个间隔 Schiff 碱配体 1-(2-羟基-3-甲氧基苄叉基)-氨基脲（Hhms），具有锯齿形 M-Ln-Ln-M 金属核排列。在配合物 1-6 中，一种独特的单酚氧基/二乙酸不对称桥连将 M 离子与 Ln 离子相连，四个乙酸根桥连两个 Ln 离子，其中乙酸根作为共配体在生成四核单元中起重要作用。磁性研究表明 Dy 和 Gd 衍生物中存在主要的铁磁耦合，在零静态场下，{NiDy}和{CoDy}观察到磁化强度的缓慢弛豫，{NiDy}的能垒为 16.0 K，{CoDy}的能垒为 6.7 K。与类似物{CoDy}相比，{NiDy}显示出更长的弛豫时间且在低温下不存在磁化强度的量子隧穿（QTM）。从头算计算表明，由于 Ni 和 Dy 离子之间产生的铁磁交换耦合，{NiDy}的零场 QTM 被有效中断。Ni 和 Dy 离子之间铁磁交换的存在比同构的{CoDy}（其中交换是反铁磁的）更有利于零场单分子磁体行为。
