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 fullerid es 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. L i12C60 is fee at high temperature, and it distorts to tetragonal upon cooli ng. We have evidence from C-13 NMR that the C-60 units are static in the te tragonal phase at least up to T = 373 K. Rietvelt refinement of the fee pha se favors a hybrid cluster intercalated structure with shortening of select ed Li-C distances. [S0163-1829(99)00414-2].