Field-induced single-ion magnet behaviors in 1-dimensionally assembled tetrahedral cobalt(II) complexes with halide donors

Three tetrahedral cobalt(II) complexes [CoX₂(H₂thp)₂] were prepared and characterized (H₂thp = 2-(1,4,5,6-tetrahydropyrimidin-2-yl)phenol, X = Cl, Br, and I). X-ray crystallographic analysis indicates that the H₂thp ligand coordinates to a Co ion in monodentate fashion in zwitterionic form. In the crystal, all the complexes formed characteristic one-dimensional chain structures via N–H···X hydrogen-bonding interactions. The static magnetic measurements showed that the g-factors and axial zero-field splitting parameters for Br⁻ and I⁻ derivatives are quite similar despite the deference in the halide ligand. A significant frequency dependence was observed for all the complexes in dynamic magnetic measurements in the presence of an external field. The relaxation dynamics below 3 K for the Br⁻ and I⁻ derivatives were found to be dominated by Raman relaxation process, while that of the Cl⁻ derivative was dominated by Orbach process. The relatively long intermolecular Co···Co distances > 8 Å resulted in no influence in the static magnetic properties and the QTM phenomena.