C-13 and Na-23 NMR studies of Na2C60 and Na6C60 fullerides

We report on C-13 and Na-23 NMR measurements on Na2C60 and Na6C60 compounds. The room-temperature C-13 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 Ag6C60 compounds with heavier alkalis, indicating a partial charge transfer to the threefold degenerate t(1u) level which is totally filled in the latter compounds. The Na-23 NMR spectrum of A(2)C(60) shows one line at 73 ppm and the one of A(6)C(60) presents two lines at 73 and 147 ppm. The intensity ratio of the latter lines is about 2:1. According to previously 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.