23Na and 13C NMR investigation of Na2C60 and Na6C60 fullerides

Abstract

We report on 23Na and 13C NMR measurements on Na2C60 and Na6C60 compounds. The 23Na NMR spectrum of A2C60 shows one line at 73 ppm and the one of A6C60 presents two lines at 73 and 147 ppm. The intensity ratio of the latter lines is about 2:1. According topreviously reported x-ray data we attribute the line at 147 ppm to the Na tetramers in the octahedral sites and the line at 73 ppm to the Na cations in the tetrahedral ones which are singly occupied. The room-temperature 13C NMR spectra of Na2C60 and Na6C60 samples present a narrow isotropic line at 172 and 176 ppm, respectively. The Na6C60 resonance is shifted 20 ppm more down field than the resonances of A6C60 compounds with heavier alkalis, indicating a partial charge transfer to the threefold degenerate t1u level which is totally filled in the latter compounds.