Trigonal antiprismatic Co^II complexes: why don't they work like single-molecule magnets in a zero-field?

Authors

Aritz Landart-Gereka, Pedro J Jabalera-Ortiz, Laura Cuevas-Contreras, J Krzystek, Mykhaylo Ozerov, Maria Mar Quesada-Moreno, Maria A Palacios, Enrique Colacio

Published in

Dalton transactions (Cambridge, England : 2003). Oct 21, 2026. Epub Oct 21, 2026.

Abstract

This paper describes the synthesis, crystal structures, detailed dc and ac magnetic properties, far-infrared magnetic spectroscopy (FIRMS), and theoretical calculations of two further examples of the scarce trigonal antiprismatic Co^II complexes (octahedral complexes distorted along the C₃ axis). One has been prepared from the scorpionate ligand hydridotris(1,2,4-triazolyl)borate (Ttz^-) and the other from the tridentate bridging ligand 1-methylimidazole-2-carboxamide oxime (HL). The first complex has the formula [Co^II(Ttz)₂]·5.5H₂O (1), whereas the second, [Co₃(L)₆](NO₃)₂·6H₂O (2), is a mixed-valence Co^III-Co^II-Co^III trinuclear complex. In 1, the pseudo-C₃ axis of the trigonal antiprismatic high spin Co^IIN₆ coordination sphere lies along the B⋯Co⋯B direction, whereas in 2 the C₃ axis of the Co^IIO₆ unit lies along the Co^IIICo^IICo^III direction. Although both complexes exhibit very strong easy-axis magnetic anisotropy, they do not show slow magnetic relaxation under zero field but rather behave like field-induced single-ion magnets (SIMs). Experimental and theoretical magneto-structural correlations carried out on all the trigonal antiprismatic Co^II complexes reported to date, as well as on related model complexes, confirm, on the one hand, that the axiality g_xy/g_z increases when the s/h ratio decreases, that is to say when the compounds are more elongated along the C₃ or pseudo C₃ axis, and on the other hand, that all of them exhibit easy-axis magnetic anisotropy but with significant intrinsic transversal anisotropy (g_xy/g_z > 0.1), which prevents SIM behaviour in a zero-field. Furthermore, the results of the theoretical studies suggest that the use of neutral ligands based on scorpionate-tris(pyrazole)methane with bulky substituents could cause sufficient elongation along the C₃ axis, due to steric hindrance, to reduce the quantum tunneling of magnetization (QTM) and increase the relaxation time to such an extent that SIM behavior would be observed at zero field.

PMID:
42904730
Bibliographic data and abstract were imported from PubMed on 23 Oct 2026.

Read full publication at:
Please sign in to see all details.

Stats

1-terrible, 9-excellent. How would you rate this publication? Sign in in to submit your rating.

Post a comment

You need to be signed in to post comments. You can sign in here.

Comments

There are no comments yet.