Solid-state 23Na and 13C NMR characterization of Na 3C 60

Abstract

Two separate samples of Na 3C 60 were prepared by direct reaction of C 60 with sodium metal vapor, and subjected to different annealing times of 10 days and 16 days. Solid-state 13C and 23Na NMR, along with elemental analysis, powder X-ray diffraction (XRD) and Raman spectroscopy, were used to characterize both samples. The Raman spectra of both materials have a single peak at 1447 cm −1 which correspond to the A g peak of C 60 3−, consistent with the stoichiometry of Na x C 60 with x=3. The powder XRD patterns are also virtually identical for both samples. However, solid-state 23Na and 13C NMR spectra of the two samples are significantly different, suggesting a relationship between annealing times and the final structure of the alkali fulleride. Variable-temperature 23Na magic-angle spinning (MAS) NMR experiments reveal the existence of two or three distinct sodium species and reversible temperature-dependent diffusion of sodium ions between octahedral and tetrahedral interstitial sites. 13C MAS NMR experiments are used to identify resonances corresponding to free C 60 and fulleride species, implying that the samples are segregated-phase materials composed of C 60 and non-stoichiometric Na 3C 60. Variable-temperature 13C MAS NMR experiments reveal temperature-dependent motion of the fullerides.