Coligand effects on the architectures and magnetic properties of octahedral cobalt(II) complexes with easy-axis magnetic anisotropy

Two mononuclear azido-cobalt(II) complexes, with formulas [Co(3,3-Hbpt)2(N3)2(H2O)2] (1) and [Co(abpt)2(N3)2]·H2O (2) (3,3-Hbpt = 1H-3,5-bis(3-pyridyl)-1,2,4-triazole, abpt = 4-amino-3,5-bis(2-pyridyl)-1,2,4-triazole), have been prepared by alternating the pyridyl-triazole coligands. In both complexes, Co(II) centers feature hexa-coordinated environments with distorted octahedrons in which the axial sites are identical, whereas the equatorial environments are finely modulated by the varying chemical natures of the different coligands. It is worth noting that the distinct intermetallic distances in two complexes (10.302 A for 1 and 6.576 A for 2) unambiguously cause the disparity of intermolecular interactions, implying the dissimilar magnetic behaviours. As a result, alternating current dynamic susceptibility measurements show that only 2 exhibits field-induced slow relaxation of the magnetization with an effective energy barrier of 11.29 K, though large easy-axis magnetic anisotropies for both complexes are unveiled by the combined analyses of the magnetic data and the ab initio calculations.