Two separate samples of Na3C60 were prepared by direct reaction of C60 with sodium metal vapor, and subjected to different annealing times of 10 days and 16 days. Solid-state13C and 23Na nuclear magnetic resonance, along with elemental analysis, powder X-ray diffraction and Raman spectroscopy, were used to characterize both samples. The Raman spectra of both materials had a single peak at 1447/cm which corresponded to the Ag peak of C603-, consistent with the stoichiometry of NaxC60 with x = 3. The powder X-ray diffraction patterns were also virtually identical for both samples. However, solid-state 23Na and 13C nuclear magnetic resonance spectra of the two samples were significantly different, suggesting a relationship between annealing times and the final structure of the alkali fulleride. Variable-temperature 23Na magic-angle spinning nuclear magnetic resonance experiments revealed the existence of two or three distinct sodium species and reversible temperature-dependent diffusion of sodium ions between octahedral and tetrahedral interstitial sites. 13C magic-angle spinning nuclear magnetic resonance experiments were used to identify resonances corresponding to free C60 and fulleride species, implying that the samples were segregated-phase materials composed of C60 and non-stoichiometric Na3C60. Variable-temperature 13C magic-angle spinning nuclear magnetic resonance experiments revealed temperature-dependent motion of the fullerides.

Solid-State 23Na and 13C NMR Characterization of Na3C60. Schurko, R.W., Willans, M.J., Skadtchenko, B., Antonelli, D.M.: Journal of Solid State Chemistry, 2004, 177[7], 2255-64