Probing the Axial Distortion Effect on the Magnetic Anisotropy of Octahedral Co(II) Complexes

Three mononuclear octahedral Co(II) complexes are reported, [Co(py) (SCN) ] ( ), [Co(py) (Cl) ]·H O ( ), and [Co(py) (Br) ] ( ), that exhibit different distortions with compression ( ) or elongation ( and ) of the axial positions. Easy plane magnetic anisotropy was confirmed by magnetic, HF-EPR, and computational studies for all complexes. Further analyses indicate that both the sign and magnitude of zero-field splitting parameters experience a significant change ( ≥ ±150 cm ) by tuning of the axial and equatorial ligand field strength. Slow magnetic relaxation is observed for all compounds which is dominated by the Raman process involving both acoustic and optical phonons.