Solid-state Na-23 and C-13 NMR characterization of Na3C60

摘要

Two separate samples of Na3C60 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 C-13 and Na-23 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 NaxC60 with x = 3. The powder XRD patterns are also virtually identical for both samples. However, solid-state Na-23 and C-13 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 Na-23 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. C-13 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 Na3C60. Variable-temperature C-13 MAS NMR experiments reveal temperature-dependent motion of the fullerides. (C) 2004 Elsevier Inc. All rights reserved.