THz-EPR-Based Direct Spectroscopic Determination of the Anisotropy Barrier of a Heteroleptic Bis-Chelate Cobalt(II) Complex with Bis(sulfonamido)benzene Ligand and its Dynamic Magnetic Properties

A new mononuclear, four-coordinate heteroleptic cobalt(II) complex 1 was synthesised utilising N,N′-1,2-Phenylenebis-(4-methylbenzenesulfonamide) and 6,6′-Dimethyl-2,2′-bipyridine as ligands and structurally characterised. Magnetic susceptibility and magnetisation measurements, along with ab initio calculations, revealed a large easy-axis type magnetic anisotropy of the cobalt(II) centre. Frequency-dependent ac susceptibility measurements revealed out-of-phase signals, indicating a slow relaxation of magnetisation, even in the absence of an additional static magnetic field. The corresponding relaxation behaviour can be attributed to a combination of Orbach and phonon-assisted processes within the observable temperature range. Using FD-FT THz-EPR spectroscopy, the magnetic anisotropy barrier was determined to be unexpectedly large with a value of 146.4 $$ . The deviation from the expected barrier, based on correlations with the elongation parameter $$ , is attributed to the charge distribution in the coordination environment.