Molecular Motion of Endohedral Fullerenes in Single-Walled Carbon Nanotubes

摘要

Spherical carbon cages of fullerene molecules interact by van der Waals forces to form close-packed arrangements in the solid state, such as the face-centered cubic lattice formed by C60 at room temperature. Owing to the low directionality and low energy of the interfullerene interactions neutral fullerene molecules (such as C_(60)) are freely rotating in the crystal at room temperature. Contrasting to the empty fullerene cages, metal-containing endohedral fullerenes are known to have large electric dipole moments of 3-4 Debye. Therefore, it should be expected that intermolecular interactions in the solid M@Cn, (M=metal center) are dominated by strong dipolar interactions. For example, fullerene Ce@C_(82) has a large dipole moment owing to the transfer of three valence electrons from the Ce atom to C_(82) cage. This fullerene crystallizes in a hexagonal or a face-centered cubic close pack arrangement. However, despite the dipole moment the fullerene Ce@C_(82) has been shown to retain its rotational freedom in the crystalline state with an energetic barrier of only 1.3 kJ mol~(-1).