The single ion magnetic properties of Co(II) are affected by the details of the coordination geometry of the ion. Here we show that a geometry close to trigonal prismatic which arises when the ligand 6,6′-((1Z)-((piperazine-1,4-diylbis(propane-3,1-diyl))bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol) coordinates to Co(II) does indeed lead to enhanced single-ion behaviour as has previously been predicted. Synthesis of the compound, structural information, and static as well as dynamic magnetic data are presented along with an analysis using quantum chemical ab initio calculations. Though the complex shows a slight deviation from an ideal trigonal prismatic coordination, the zero-field splitting as well as the g-tensor are strongly axial with D = −41 cm⁻¹ and E < 0.01 cm⁻¹. For the lowest Kramers doublet (S = 1/2) g_∥ = 7.86 and g_⊥ < 0.05 were found. In contrast, the second Kramers doublet possesses a rhombic g-tensor with g_∥ = 2.75 and g_⊥ = 4.35. Due to large spin–orbit coupling resulting in very different g tensors, it is not possible to simulate the temperature dependence of the magnetic susceptibility with a spin Hamiltonian of the form H = D(S_z ² − S(S + 1)/3) + E(S_x ² − S_y ²) + μ_BgS·B using an effective spin S = 3/2. Calculations on model complexes show the influence of the coordinating atoms and the deviation from the ideal trigonal prismatic coordination. As the distortion is reduced towards idealised D_3h, the zero field splitting increases and the g-tensor of the second Kramers doublet also becomes axial.

Tuning of relaxation of magnetisation through 3d metal ion variations in 3d₂Dy₂ butterflies.

The anisotropy of a single Dy ^III can be steered through subtle changes in the coordination geometry of the Co ^II ions in CoII2DyIII2 butterfly compounds resulting from changing the coordinated solvent molecule on the Co ^II ion.