Magnetic Relaxation Studies on Trigonal Bipyramidal Cobalt(II) Complexes

Feng Shao; Benjamin Cahier; Yi-Ting Wang; Feng-Lei Yang; Eric Rivière; Régis Guillot; Nathalie Guihéry; Jia-Ping Tong; Talal Mallah

doi:10.1002/asia.201901511

Magnetic Relaxation Studies on Trigonal Bipyramidal Cobalt(II) Complexes

Chem Asian J. 2020 Feb 3;15(3):391-397. doi: 10.1002/asia.201901511. Epub 2020 Jan 16.

Authors

Feng Shao^{1

2

3}, Benjamin Cahier^{1

4}, Yi-Ting Wang^{1

2}, Feng-Lei Yang^{1

2

5}, Eric Rivière¹, Régis Guillot¹, Nathalie Guihéry⁶, Jia-Ping Tong^{2

7}, Talal Mallah¹

Affiliations

¹ Institut de Chimie Moléculaire et des Matériaux d'Orsay, CNRS, Université Paris-Sud, Université Paris-Saclay, 91405, Orsay Cedex, France.
² State Key Laboratory of Physical Chemistry of Solid Surfaces, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, P. R. China.
³ Present address: Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British, Columbia, V6T 1Z1, Canada.
⁴ Present address: Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470, Mülheim an der Ruhr, Germany.
⁵ School of Chemistry and Material Science, Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Jiangsu Normal University, Xuzhou, Jiangsu, 221116, P. R. China.
⁶ Laboratoire de Chimie et Physique Quantiques, Université Toulouse III, Paul Sabatier, 118 route de Narbonne, 31062, Toulouse, France.
⁷ Lab of Chemical Materials and Devices, Training Base of Army Logistics University of PLA, Xiangyang, 441000, P. R. China.

PMID: 31851414
DOI: 10.1002/asia.201901511

Abstract

We report the preparation and the full characterization of a novel mononuclear trigonal bipyramidal Co^II complex [Co(NS₃ ^iPr )Br](BPh₄ ) (1) with the tetradentate sulfur-containing ligand NS₃ ^iPr (N(CH₂ CH₂ SCH(CH₃ )₂ )₃ ). The comparison of its magnetic behaviour with those of two previously reported compounds [Co(NS₃ ^iPr )Cl](BPh₄ ) (2) and [Co(NS₃ ^tBu )Br](ClO₄ ) (3) (NS₃ ^tBu =N(CH₂ CH₂ SC(CH₃ )₃ )₃ ) with similar structures shows that 1 displays a single-molecule magnet behaviour with the longest magnetic relaxation time (0.051 s) at T=1.8 K, which is almost thirty times larger than that of 3 (0.0019 s) and more than three times larger than that of 2 (0.015 s), though its effective energy barrier (26 cm^-1 ) is smaller. Compound 1, which contains two crystallographically independent molecules, presents smaller rhombic parameters (E=1.45 and 0.59 cm^-1 ) than 2 (E=2.05 and 1.02 cm^-1 ) and 3 (E=2.00 and 0.80 cm^-1 ) obtained from theoretical calculations. Compounds 2 and 3 have almost the same axial (D) and rhombic (E) parameter values, but present a large difference of their effective energy barrier and magnetic relaxation which may be attributed to the larger volume of BPh₄ ^- than ClO₄ ^- leading to larger diamagnetic dilution (weaker magnetic dipolar interaction) for 2 than for 3. The combination of these factors leads to a much slower magnetic relaxation for 1 than for the two other compounds.

Keywords: magnetic anisotropy; magnetic relaxation; molecular magnetism; single molecule magnets.