Slow magnetic relaxation in dinuclear Co(III)-Co(II) complexes containing a five-coordinated Co(II) centre with easy-axis anisotropy

Mengyao Liu; Yimou Yang; Rong Jing; Shaojun Zheng; Aihua Yuan; Zhenxing Wang; Shu-Chang Luo; Xiangyu Liu; Hui-Hui Cui; Zhong-Wen Ouyang; Lei Chen

doi:10.1039/d2dt00857b

Slow magnetic relaxation in dinuclear Co(III)-Co(II) complexes containing a five-coordinated Co(II) centre with easy-axis anisotropy

Dalton Trans. 2022 May 31;51(21):8382-8389. doi: 10.1039/d2dt00857b.

Authors

Affiliations

¹ School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, P. R. China. chenlei@just.edu.cn.
² Wuhan National High Magnetic Field Center & School of Physics, Huazhong University of Science and Technology, Wuhan 430074, P. R. China. zxwang@hust.edu.cn.
³ School of Chemical Engineering, Guizhou University of Engineering Science, Bijie 551700, P. R. China. lsc840927@126.com.
⁴ 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, P. R. China. xiangyuliu432@126.com.
⁵ School of Chemistry and Chemical Engineering, Nantong University, Nantong 226019, P. R. China.

PMID: 35587605
DOI: 10.1039/d2dt00857b

Abstract

Two air-stable Co(III)-Co(II) mixed-valence complexes of molecular formulas [Co^IICo^III(L)(DMAP)₃(CH₃COO)]·H₂O·CH₃OH (1) and [Co^IICo^III(L)(4-Pyrrol)₃ (CH₃COO)]·0.5CH₂Cl₂ (2) (H₄L = 1,3-bis-(5-methyl pyrazole-3-carboxamide) propane; DMAP = 4-dimethylaminopyridine; and 4-Pyrrol = 4-pyrrolidinopyridine) were synthesized and characterized by single-crystal X-ray crystallography, high-field electron paramagnetic resonance (HFEPR) spectroscopy, and magnetic measurements. Both complexes possess one five-coordinated paramagnetic Co(II) ion and one six-coordinated Co(III) ion with octahedral geometry. Direct-current magnetic susceptibility and magnetization measurements show the easy-axis magnetic anisotropy that is also confirmed by low-temperature HFEPR measurements and theoretical calculations. Frequency- and temperature-dependent alternating-current magnetic susceptibility measurements reveal their field-assisted slow magnetic relaxation, which is a characteristic behavior of single-molecule magnets (SMMs), caused by the individual Co(II) ion. The effective energy barrier of complex 1 (49.2 cm^-1) is significantly higher than those of the other dinuclear Co(III)-Co(II) SMMs. This work hence presents the first instance of the dinuclear Co(III)-Co(II) single-molecule magnets with a five-coordinated environment around the Co(II) ion.