7Li and 23Na MAS solid state NMR studies of Na4C60 and Li4C60

We present 7Li and 23Na MAS-NMR measurements of Li4C60 and Na4C60 and discuss structural parameters for these materials. From 7Li NMR on Li4C60, we find good agreement with the recently proposed structure with single polymer bonds in one direction and double 'pair bonds' in the other. We observe NMR lines at 1.4 ppm accounting for half the intensity corresponding to two Li-ion in tetrahedral positions and two less symmetric lines at 3.0 and 6.6 ppm which correspond to the occupancy of one Li-ion in each of the sites which are close to the octahedral positions in the former C60 fcc lattice. For the Na4C60 sample, 23Na NMR gives a single line with a center of gravity at −21.3 ppm. As expected, this line shows a stronger quadrupole coupling than the 7Li signal but still the coupling could be considered as quite small which agrees with the occupancy of relatively symmetric tetrahedral sites in the Na4C60 structure.