13C NMR investigation of fullerene-cubane C60•C8H8 cocrystals

The rotor-stator molecular cocrystal C-60 center dot C8H8 (fullerene-cubane) has been investigated by C-13 nuclear magnetic resonance (NMR). The room-temperature spectrum obtained using H-1-C-13 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 C-60 and C8H8. The temperature dependence of the spin-lattice relaxation time of the ordering transition around 145K. The activation energies of large-angle C-60 reorientations above and below the ordering transitions are 260K and 570K, respectively. The transition temperature and the activation energies are significantly lower than in other C-60 compounds. The C-13 spectrum remains narrow down to 115K indicating that similarly to pristine C-60, the molecular reorientational motion is still fast in the ordered phase on the NMR time scale. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim