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Two-Dimensional Frameworks Formed by Pentagonal Bipyramidal Cobalt(II) Ion and Hexacyanometallates: Antiferromagnetic Ordering, Metamagnetism and Slow Magnetic Relaxation

Abstract

We herein report the syntheses, structures, and magnetic properties of two isostructural two-dimensional (2D) coordination polymers based on the pentagonal bipyramidal CoII unit [Co(TODA)]2+ and two hexacyanometallates, namely [MIII(CN)6]2[CoII(TODA)]3·9H2O (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 [MIII(CN)6]3- groups through three cyano groups in the facial positions. Magnetic investigation reveals the ferromagnetic coupling between the CrIII and CoII centres through cyanides in 1. Due to the antiferromagnetic interaction between the layers, compound 1 exhibits antiferromagnetic ordering below 11.4 K, and shows a metamagnetic phase transition under external dc field. Due to the disorder of the TODA ligands, compound 1 shows a spin glass behavior, which leads to the 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 the cyano-bridged Cr-Co molecular magnets. For compound 2 containing the diamagnetic [CoIII(CN)6]3- unit, field-induced slow magnetic relaxation was also verified, which makes compound 2 a rare example of a SIM assembled in a 2D network. 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 the hepta-coordinated CoII centers. These results show the efficiency of the strategy of combining the cyanometallates and pentagonal bipyramidal precursors for novel molecular magnetic materials.

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Publication details

The article was received on 24 May 2017, accepted on 13 Jun 2017 and first published on 13 Jun 2017


Article type: Paper
DOI: 10.1039/C7DT01893B
Citation: Dalton Trans., 2017, Accepted Manuscript
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    Two-Dimensional Frameworks Formed by Pentagonal Bipyramidal Cobalt(II) Ion and Hexacyanometallates: Antiferromagnetic Ordering, Metamagnetism and Slow Magnetic Relaxation

    D. Shao, Y. Zhou, Q. Pi, F. Shen, S. Yang, S. Zhang and X. Wang, Dalton Trans., 2017, Accepted Manuscript , DOI: 10.1039/C7DT01893B

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