The rotor-stator molecular cocrystal C60·C8H8= (fullerene-cubane) has been investigated by 13C nuclear magnetic resonance (NMR). The room-temperature spectrum obtained using 1H-13C cross-polarization technique shows two lines with chemical shifts identical with the shifts of the original molecular constituents demonstrating the lack of a strong electronic interaction between C60 and C8H8. The temperature dependence of the spin-lattice relaxation time of the fullerene component confirms the existence of a first-order orientational ordering transition around 145 K. The activation energies of large-angle C60 reorientations above and below the ordering transitions are 260K and 570 K, respectively. The transition temperature and the activation energies are significantly lower than in other C60 compounds. The 13C spectrum remains narrow down to 115K indicating that similarly to pristine C60, the molecular reorientational motion is still fast in the ordered phase on the NMR time scale.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics