Static Magnetism and Vibration-Modulated Magnetic Relaxation Mechanism of DySc2N@C80 Single-Molecule Magnets

Abstract The effects of carbon cage isomerism, Dy–N bond vibration, and endohedral cluster low-frequency vibration on the magnetic behavior of DySc2N@C80 single-molecule magnets (SMMs) were elucidated. C80 cages containing a maximum of three pairs of fused pentagonal rings were screened and optimized via the PM3 method, yielding 25 low-energy host frameworks. A total of 150 molecular models were constructed by encapsulating the DySc2N cluster along three orthogonal planes and subsequently optimized. Key magnetic parameters, including the effective energy barrier (Ueff), magnetization quantum tunneling time (τQTM), and blocking temperature (TB), were evaluated using CASSCF/RASSI calculations. The encapsulated DySc2N cluster exhibits a quasi-planar geometry, and shortened Dy–N bonds strengthen the axial ligand field, increasing both Ueff and TB. Investigations of five high-performance isomers revealed that low-frequency cluster vibrations (54.68–68.73 K) are comparable to the experimental energy barriers and critically influence magnetic performance. Low-frequency in-plane Dy3+ librations parallel to the fullerene cage dominate the spin-vibrational coupling. DySc2N@C80-Ih-31924 exhibited the highest Ueff and a simulated relaxation time consistent with experimental results, whereas both non-IPR DySc2N@C80-C1-30233 and DySc2N@C80-C1-30431 emerged as promising high-TB SMMs. These findings provide theoretical insights for designing high-performance dysprosium-based endohedral fullerene SMMs.