NMR investigation of the azafullerene (C59N)2 and the alkali fullerides NAXC60 with X = 2, 4 and 6 Original Research Article

We present 13C MAS NMR measurements on the (C59N)2 dimer. The room temperature NMR spectrum obtained by spinning the sample at 10 kHz shows a weak line at 90 ppm and a group of lines around 140 ppm. The simulation of the obtained spectra allows us to attribute the line at 90 ppm to the sp3 carbons forming the expected interball single bond and the other lines to the sp2 carbons of the dimer molecules. The distortion of the C59N molecules due to the introduction of the nitrogen atom into the C60 cage and the 13C14N dipolar coupling must be at the origin of the observed group of resonances. We also report on 13C NMR measurements on NaxC60 (x = 2, 4 and 6) compounds. The NMR spectrum of the Na2C60 sample presents a narrow isotropic line at 172 ppm. The Na6C60 resonance appears at 176 ppm and is 20 ppm more shifted down field than the resonances of A6C60 compounds with heavier alkalis, reflecting a strong polarization of the transferred electrons to the C60 molecules. The Na4C60 polymer phase shows several isotropic resonances with the corresponding side bands in the region from 100 to 250 ppm and a single line at 76 ppm. We attribute the former group of lines to the inequivalent sp2 carbons on the C60 molecules and the latter line to the sp3 carbons of the single interball bondings.