Hu Zhao-Bo, Feng Xin, Li Jing, Zhang Yi-Quan, Yin Lei, Wang Zhenxing, Ouyang Zhongwen, Kurmoo Mohamedally, Song You
State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
Dalton Trans. 2020 Feb 21;49(7):2159-2167. doi: 10.1039/c9dt04403e. Epub 2020 Jan 29.
The effect of screening the Co moment of monomeric [CoL(HO)] (L = 8-hydroxyquinaldine), having a trigonal bipyramid coordination, by diamagnetic Zn in CoZn solid solutions on its magnetic relaxation was explored using ac-susceptibility, high-field electron-spin-resonance measurements and CASPT2 calculations. The retention of the crystal structure for all the solid solutions was demonstrated using single crystal diffraction. The dc-magnetization and theoretical fittings of the susceptibility for Co and CoZn gave a large zero-field-splitting (ZFS) D of 50 ± 6 cm, and very weak dipole interaction between the nearest neighbors, while EPR and calculations confirmed the positive sign of the axial component (D). Consistent parameters were obtained from experiments and theory. Importantly, only field-induced relaxation was observed for the samples with less than 50% Co and a gradual change in the barrier energy to moment reversal and relaxation times was observed between 11% and 20% Co, while both were enhanced for higher dilutions. The results establish a clear barrier for extending the longevity of the magnetism for this type of single-ion species by lowering the intramolecular interactions. The results suggest that the magnetic interaction persists up to the second sphere, that is, for a dilution of 1 in 9 (11% Co). Importantly, this method is applicable to all single-ion magnet systems, that is, the optimum dilution concentration to restrain the dipole field can be given only by the single crystal structure.
利用交流磁化率、高场电子自旋共振测量和CASPT2计算，研究了在CoZn固溶体中，具有三角双锥配位的单体[CoL(HO)]（L = 8-羟基喹哪啶）的Co矩被抗磁性Zn屏蔽对其磁弛豫的影响。使用单晶衍射证明了所有固溶体的晶体结构得以保留。Co和CoZn的直流磁化率及其理论拟合给出了50±6 cm的大零场分裂（ZFS）D，以及最近邻之间非常弱的偶极相互作用，而电子顺磁共振和计算证实了轴向分量（D）的正号。从实验和理论中获得了一致的参数。重要的是，对于Co含量小于50%的样品，仅观察到场诱导弛豫，并且在Co含量为11%至20%之间观察到矩反转的势垒能量和弛豫时间逐渐变化，而对于更高的稀释度，两者均增强。结果为通过降低分子内相互作用来延长此类单离子物种的磁寿命建立了明确的障碍。结果表明，磁相互作用一直持续到第二配位层，即对于1:9的稀释度（11% Co）。重要的是，该方法适用于所有单离子磁体系统，也就是说，抑制偶极场的最佳稀释浓度仅由单晶结构给出。
