Cage Engineering of Dysprosium Carbide Metallofullerenes Toward Tunable Single-Molecule Magnet Performance

Lanthanide-doped metallofullerenes represent a unique class of single-molecule magnets (SMMs) characterized by their exceptional ability to protect spin systems. Unraveling the impact of interactions between the endohedral units and the carbon cage on the magnetic properties is important for developing high-performance SMMs. Herein, a series of dysprosium carbide cluster fullerenes (Dy-CCFs) with cages ranging from C₈₂ to C₉₆ were isolated, enabling systematic comparison of their magnetic properties. Magnetometry measurements revealed that cage isomerism and dysprosium carbide (Dy₂C₂) cluster geometry were closely related to the magnetic performance. Dy₂C₂@C_3v(8)-C₈₂ exhibited a broad hysteresis loop and a blocking temperature exceeding 4 K, making it the top-performing molecular magnet among the M₂C₂-based cluster fullerenes. Dy₂C₂@C₂(157)-C₉₆ showed a peanut-shaped hysteresis loop with two inflections, a feature rarely reported for cluster fullerenes. Magnetic relaxation dynamics analyses revealed that the decay path of Dy₂C₂@C_3v(8)-C₈₂ was best described by an Orbach mechanism, while two Orbach paths existed for Dy₂C₂@C₂(157)-C₉₆. Magneto-structural analyses revealed that the relative position of the pentagon on the fullerene cage, with respect to the magnetic axis connecting the Dy atom and the center of the C₂ unit, was crucial for magnetic performance. Our findings demonstrate that the magnetic properties of metallofullerene molecules can be finely tuned through cage engineering.