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

Conventionally, octahedral (Oh) 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(OCtBu(3))X-2(py)(3)] (X = Cl (1), I (2), py = pyridine), in Oh 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.