NMR and high-resolution x-ray diffraction evidence for an alkali-metal fulleride with large interstitial clusters:: Li12C60

NMR and high-resolution x-ray diffraction of several lithium-doped fullerides LixC60 show that the stoichiometry x = 12 represents a stable Li doping for a high symmetry C-60-like phase, which might extend to much larger x. Li12C60 is fee at high temperature, and it distorts to tetragonal upon cooling. We have evidence from C-13 NMR that the C-60 units are static in the tetragonal phase at least up to T = 373 K. Rietvelt refinement of the fee phase favors a hybrid cluster intercalated structure with shortening of selected Li-C distances. [S0163-1829(99)00414-2].