Two-dimensional frameworks formed by pentagonal bipyramidal cobalt() ions and hexacyanometallates: antiferromagnetic ordering, metamagnetism and slow magnetic relaxation

• Published in: Dalton transactions : an international journal of inorganic chemistry 2017, Vol.46 (28), p.988-996
• Main Authors: Shao, Dong, Zhou, Yan, Pi, Qian, Shen, Fu-Xing, Yang, Si-Run, Zhang, Shao-Liang, Wang, Xin-Yi
• Format: Article
• Language: English
• Subjects: Antiferromagnetism; Coercivity; Coordination polymers; Cyano groups; Diamagnetism; Ferromagnetism; Honeycomb structures; Hysteresis loops; Magnetic anisotropy; Magnetic induction; Magnetic materials; Magnetic properties; Magnetic relaxation; Magnetism; Magnets; Phase transitions; Spin glasses
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c7dt01893b

We herein report the syntheses, structures, and magnetic properties of two isostructural two-dimensional (2D) coordination polymers based on a pentagonal bipyramidal Co II unit [Co(TODA)] 2+ and two hexacyanometallates, namely [M III (CN) 6 ] 2 [Co II (TODA)] 3 ·9H 2 O (M = Cr ( 1 ), Co ( 2 ), TODA = 1,4,10-trioxa-7,13-diazacyclopentadecane). Structure analyses show that both complexes have 2D honeycomb structures where the [Co(TODA)] 2+ units are bridged by the [M III (CN) 6 ] 3− groups through three cyano groups in the facial positions. Magnetic investigation reveals ferromagnetic coupling between the Cr III and Co II centres through cyanides in 1 . Due to the antiferromagnetic interaction between the layers, compound 1 exhibits an antiferromagnetic ordering below 11.4 K, and shows a metamagnetic phase transition under an external dc field. Due to the disorder of the TODA ligands, compound 1 shows a spin glass behavior, which leads to slow magnetic relaxation in 1 . A butterfly-shaped hysteresis loop at 1.8 K can be observed with a coercive field of 720 Oe, which is quite large for cyano-bridged Cr-Co molecular magnets. For compound 2 containing the diamagnetic [Co III (CN) 6 ] 3− unit, field-induced slow magnetic relaxation was also verified, which makes compound 2 a rare example of an SIM assembled in a 2D network. An easy-plane magnetic anisotropy with a positive D value (29.9 cm −1 by PHI and 26.5 cm −1 by Anisofit2.0) was deduced for hepta-coordinated Co II centers. These results show the efficiency of the strategy of combining cyanometallates and pentagonal bipyramidal precursors for novel molecular magnetic materials. Two-dimensional frameworks constructed by pentagonal bipyramidal Co II and [M(CN) 6 ] 3− units have been synthesized and characterized structurally and magnetically.