The low-doped Li x C 60 compounds (x 6) were investigated using laboratory X-ray and synchrotron radiation diffraction, 13 C NMR and Raman spectroscopy. Li 4 C 60 shows an unusual 2D polymerisation in which the C 60 units are connected both by [2 þ 2] cycloaddition and by single carbon-carbon bonds, a unique feature among the known polymerised fullerene compounds. This picture is fully supported also by static NMR and Raman measurements. The charge transfer to C 60 in the polymeric phase was evaluated from the shift of the A g (2) mode. The depolymerisation process was investigated as well; despite the presence of two different bonds, the polymer-tomonomer transition induced by thermal treatments is a single-step phenomenon.