Role of Halide Ions in the Nature of the Magnetic Anisotropy in Tetrahedral Co Complexes.

A series of mononuclear tetrahedral Co complexes with a general molecular formula [CoL X ] [L=thiourea and X=Cl (1), Br (2) and I (3)] were synthesized and their structures were characterized by single-crystal X-ray diffraction. Direct-current (dc) magnetic susceptibility [χ T(T) and M(H)] and its slow relaxation of magnetization were measured for all three complexes. The experimental dc magnetic data are excellently reproduced by fitting both χ T(T) and M(H) simultaneously with the parameters D=+10.