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

Abstract 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.