Correlating magnetic anisotropy with the subtle coordination geometry variation of a series of cobalt()-sulfonamide complexes

Systematic substitution on the N -(pyridine-2-ylmethyl)-sulfonamide ligand leads to the subtle variation of the CoN 4 coordination geometry in a series of cobalt( ii ) complexes sharing the common formula of Co[R 1 (C 6 N 2 H 5 )R 2 ] 2 , where R 1 = H, R 2 = 4- tert -butylphenylsulfonyl ( t Buphs) 1 , R 2 = 5-(dimethylamino)naphthalen-1-ylsulfonyl (DNps) 2 , R 2 = mesitylsulfonyl (Ms) 3 , R 2 = tosyl (Tos) 4 , and R 2 = naphthalen-1-ylsulfonyl (Nps) 5 ; R 1 = Me, R 2 = t Buphs 6 . Magnetic studies show that the axial zero-field splitting parameter ( D ) is subtlely correlated with the coordination geometric variation subjected to the peripheral substituted groups. Specifically, the distortion from the ideal tetrahedral geometry ( T d symmetry) to the seesaw geometry ( D 2d symmetry) increases uniaxial magnetic anisotropy. The degree of distortion measured by the continuous symmetry measure (CSM) shows that a narrow interval of CSM (6-7), which corresponds to 14-15 degree deviation from the standard tetrahedron, is ideal for maximising the D value in this coordination geometry, while the direction of the D tensor is less sensitive to such a structural variation. The distortion degree from the ideal tetrahedral geometry has been correlated with the zero-field splitting parameter in a series of mononuclear cobalt( ii )-sulfonamide complexes with a CoN 4 coordination environment.