Unusual polymerization in the Li4C60 fulleride

Li4C60, one of the best representatives of lithium intercalated fullerides, features an unusual type of twodimensional polymerization. Extensive investigations, including laboratory x-ray and synchrotron radiation diffraction, 13C NMR, magic angle spinning, and Raman spectroscopy, show a monoclinic I2/m structure, characterized by chains of _2+2_-cycloaddicted fullerenes, sideways connected by single C–C bonds. This leads to the formation of polymeric layers, whose insulating nature, deduced from the NMR and Raman spectra, denotes the complete localization of the electrons involved in the covalent bonds.