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

Conventionally, octahedral () 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(OCBu)X(py)] (X = Cl (1), I (2), py = pyridine), in 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) to 860 cm (2), highlighting the importance of weakening the transverse ligand field and maximizing the axial ligand field for high-performance SMMs.