Stabilizing an easy axis of magnetization in an octahedral Co(II) complex is an extremely challenging task, which is evident from reports that more than 90% possess easy-plane anisotropy. Here, we report a six-coordinate complex, [Co(L₁)₄(Cl)₂] (1, L₁ = thiourea [H₂N-CS-NH₂]), that exhibits a D value of −63(10) cm⁻¹. The presence of an easy axis of magnetization associated with 1 is experimentally proven by detailed magnetic studies and polarized neutron diffraction studies, and the experimental observations are well corroborated by theoretical calculations. From the combined experimental and theoretical investigations (on 1 and many model systems), we unveil the parameters that control stabilization of negative D in a thermodynamically favorable and air-stable Co(II) ion in the common distorted octahedral geometry. This study paves the way for overcoming the current impediments to alleviate the easy axis of magnetization using rational ligand choice.

稳定八面体Co（II）络合物中的易磁化轴是一项极富挑战性的任务，这从90％以上的报告具有易平面各向异性的报道中可以明显看出。在这里，我们报告一个六坐标的配合物[Co（L ₁）₄（Cl）₂ ]（1，L ₁  =硫脲[H ₂ N-CS-NH ₂ ]），其D值为-63（ 10）厘米^-1。通过详细的磁研究和极化中子衍射研究，实验证明了与1相关的易磁化轴的存在，而理论计算也很好地证实了实验观察结果。通过组合的实验和理论研究（在1个模型系统上），我们揭示了在常见的扭曲八面体几何形状中控制热力学有利且空气稳定的Co（II）离子中负D稳定的参数。这项研究为克服目前使用合理的配体选择来减轻易磁化轴的障碍铺平了道路。