Two-Coordinate Co(II) Imido Complexes as Outstanding Single-Molecule Magnets

The pursuit of single-molecule
magnets (SMMs) with better performance
urges new molecular design that can endow SMMs larger magnetic anisotropy.
Here we report that two-coordinate cobalt imido complexes featuring
highly covalent CoN cores exhibit slow relaxation of magnetization
under zero direct-current field with a high effective relaxation barrier
up to 413 cm–1, a new record for transition metal
based SMMs. Two theoretical models were carried out to investigate
the anisotropy of these complexes: single-ion model and Co–N
coupling model. The former indicates that the pseudo linear ligand
field helps to preserve the first-order orbital momentum, while the
latter suggests that the strong ferromagnetic interaction between
Co and N makes the [CoN]+ fragment a pseudo single paramagnetic
ion, and that the excellent performance of these cobalt imido SMMs
is attributed to the inherent large magnetic anisotropy of the [CoN]+ core with |MJ = ± 7/2⟩ ground Kramers doublet.