Unusual polymerization in the fulleride Li4C60

Li4C60, one of the best representatives of lithium intercalated fullerides, features an unusual type of two-dimensional 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.