Li Lei-Lei, Su Hong-Dan, Liu Shuang, Wang Wen-Zhen
College of Chemistry and Chemical Engineering, Xi'an Shiyou University, Xi'an, 710065, ShaanXi, China.
Dalton Trans. 2020 May 28;49(20):6703-6709. doi: 10.1039/d0dt00905a. Epub 2020 May 5.
Based on a phosphine oxide ligand, HMPA (hexamethylphosphoric triamide), two mononuclear Ho-pentagonal bipyramidal complexes were synthesized with the formulas [Ho(HMPA)(HO)]Cl·2HMPA·2HO (1) and [Ho(HMPA)(HO)]Br·2HMPA (2). Single-crystal X-ray diffraction results show that all Ho ions in both the two complexes are hepta-coordinated and are located in pentagonal bipyramidal {HoO7} coordination polyhedrons constructed by two axial HMPA ligands and five equatorial water molecules. However, due to the employment of different halide ions as counterions, the second coordination sphere surrounding each [Ho(HMPA)(HO)] moiety is different in the two complexes: in 1, three Cl ions, one water molecule and one HMPA ligand; in 2, three Br ions and two HMPA ligands. Ac magnetic susceptibilities under zero dc field show that both the two complexes are single-ion magnets with effective energy barriers of 290 K and 320 K for 1 and 2, respectively. Compared with 1, the enhancement in the energy barrier of 2 is believed to be induced mainly by the change in the second coordination sphere rather than the minor differences in the {HoO7} polyhedrons.
基于氧化膦配体六甲基磷酰三胺（HMPA），合成了两种单核钬五角双锥配合物，化学式分别为[Ho(HMPA)(H₂O)₅]Cl·2HMPA·2H₂O（1）和[Ho(HMPA)(H₂O)₅]Br·2HMPA（2）。单晶X射线衍射结果表明，两种配合物中的所有钬离子均为七配位，位于由两个轴向HMPA配体和五个赤道面水分子构成的五角双锥{HoO₇}配位多面体中。然而，由于使用了不同的卤离子作为抗衡离子，两种配合物中每个[Ho(HMPA)(H₂O)₅]部分周围的第二配位层不同：在1中，有三个Cl离子、一个水分子和一个HMPA配体；在2中，有三个Br离子和两个HMPA配体。零直流场下的交流磁化率表明，两种配合物均为单离子磁体，1和2的有效能垒分别为290 K和320 K。与1相比，2的能垒增强主要被认为是由第二配位层的变化引起的，而不是{HoO₇}多面体中的微小差异。
