Issue 48, 2018

Effects of coordination sphere on unusually large zero field splitting and slow magnetic relaxation in trigonally symmetric molecules

Abstract

Geometric control in mononuclear complexes has come to the forefront in the field of molecular magnets due to its profound effects on relaxation pathways and blocking temperature in single molecule magnets (SMMs). Herein we report the synthesis and magnetic characterization of six trigonally symmetric, divalent Fe, Co, and Ni molecules, with the rigid geometry enforced via the use of the tris-anionic, tetradentate ligand MST (N,N′,N′′-[2,2′,2′′-nitrilotris-(ethane-2,1-diyl)]tris(2,4,6-trimethylbenzenesulfonamide)). A systematic study on the effect of converting between trigonal monopyramidal complexes, (Me4N)[M(MST)], and trigonal bipyramidal complexes, (Me4N)[M(MST)(OH2)] was conducted experimentally and computationally. It was found that (Me4N)[Ni(MST)] exhibits a very large, near record zero-field splitting parameter (D) value of −434 cm−1, owing to an extremely low lying first excited state. The trigonal monopyramidal cobalt and iron complexes exhibit slow magnetic relaxation under applied fields, resulting in barriers of 45 K and 63.9 K respectively. Coordination of a single water molecule in the open axial site of the trigonal monopyramidal complexes exerts drastic dampening effects on the D value as well as slow relaxation. Computations reveal that coordination of water rotates the Dzz axis away from the C3 axis of symmetry resulting in a smaller D value. The aquo species (Me4N)[Co(MST)(OH2)] also exhibits magnetic relaxation under an applied field, but the barrier is reduced to 9.9 K. Water coordination totally quenches the magnetic behavior in the iron complex, and reduces the D value for nickel to −185 cm−1. These results showcase the drastic effect that a small change in the coordination environment can have on magnetic behavior, as well as that trigonal monopyramidal geometry can lead to near record D values.

Graphical abstract: Effects of coordination sphere on unusually large zero field splitting and slow magnetic relaxation in trigonally symmetric molecules

Supplementary files

Article information

Article type
Edge Article
Submitted
26 Jun 2018
Accepted
15 Sep 2018
First published
20 Sep 2018
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2018,9, 9018-9026

Effects of coordination sphere on unusually large zero field splitting and slow magnetic relaxation in trigonally symmetric molecules

K. A. Schulte, K. R. Vignesh and K. R. Dunbar, Chem. Sci., 2018, 9, 9018 DOI: 10.1039/C8SC02820F

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