Structure, magnetic anisotropy and relaxation behavior of seven-coordinate Co() single-ion magnets perturbed by counter-anions

• Published in: Dalton transactions : an international journal of inorganic chemistry 2020-06, Vol.49 (22), p.762-7627
• Main Authors: Yi, Gangji, Zhang, Chunyang, Zhao, Wen, Cui, Huihui, Chen, Lei, Wang, Zhenxing, Chen, Xue-Tai, Yuan, Aihua, Liu, Yuan-Zhong, Ouyang, Zhong-Wen
• Format: Article
• Language: English
• Subjects: Anions; Coordination compounds; Crystal structure; Crystallography; Crystals; Direct current; Electron paramagnetic resonance; Magnetic anisotropy; Magnetic induction; Magnetic properties; Magnetic relaxation; Magnets; Single crystals
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d0dt01232g

A series of mononuclear seven-coordinate Co( ii ) complexes [Co II (BPA-TPA)](ClO 4 ) 2 ·H 2 O ( 2-ClO 4 ), [Co II (BPA-TPA)](PF 6 ) 2 ( 3-PF 6 ) and [Co II (BPA-TPA)](BPh 4 ) 2 ( 4-BPh 4 ) have been synthesized based on the ligand 2,6-bis(bis(2-pyridylmethyl)amino)methylpyridine (BPA-TPA), and their structures have been characterized by single-crystal X-ray diffraction. All these complexes feature an intermediate coordination polyhedron between a capped trigonal prism and a capped octahedron, which is perturbed by the variation of the counter anions. Easy-plane magnetic anisotropies for all complexes were revealed via the analyses of the direct-current magnetic data and high-field electron paramagnetic resonance (HFEPR) spectra. They show slow magnetic relaxation under applied direct current field, which is similar to the previously reported complex [Co II (BPA-TPA)](BF 4 ) 2 ( 1-BF 4 ) with a capped trigonal prism. This work provides a new example of modulating the properties of single-ion magnets (SIMs) by changing the counter anions. A series of mononuclear seven-coordinate complexes with the same coordination unit [Co(BPA-TPA)] 2+ (BPA-TPA = pentapyidyldiamine) display the different slow magnetic relaxation processes perturbed by the variation of the counter anions.