Enhancing the magnetic properties of Dy(iii) single-molecule magnets in octahedral coordination symmetry by tuning the equatorial ligands

Conventionally, octahedral (O_h) coordination symmetry of lanthanide centers is not ideal for constructing high-performance single-molecule magnets (SMMs). However, introducing a strong ligand field in the axial direction to increase crystal field splitting can potentially overcome this limitation. Herein, we successfully obtained two dysprosium(III) single-molecule magnets, [Dy(OC^tBu₃)X₂(py)₃] (X = Cl (1), I (2), py = pyridine), in O_h coordination symmetry. The two complexes differ only in the coordinating anions on the equatorial plane, yet their magnetic performances are distinctly different. When chloride is replaced by a weaker donor iodide, the energy barrier is dramatically improved from 29 cm^-1 (1) to 860 cm^-1 (2), highlighting the importance of weakening the transverse ligand field and maximizing the axial ligand field for high-performance SMMs.