Fluorinated fullerenes: synthesis and characterization

Fluorination of the fullerene, C60, has been previously reported. In one case the reaction was reported to proceed rapidly, initially, but final products obtained were not fully fluorinated, although molecules up to stoichiometry C60F52 were observed [H. Selig et al., J. Am. Chem. Soc., 113 (1991) 5475]. Another report claims that the fluorination proceeds extremely slowly, but that the fully fluorinated C60F60 was obtained [J.H. Holloway et al., J. Chem. {Soc., Chem. Comm.}, (1991) 966]. We discuss here possible explanations for the reported discrepancies. The fluorinated product of average stoichiometry C60F42 crystallizes in a face-centered cubic lattice with cell constant a0=17.1 A, implying 12.1 A separation between the fluorinated molecules. This is consistent with expansion of the C60 sphere to a fluorinated one. Although mostly C60Fx with even x are obtained, there is some evidence that very low concentrations with odd x are also produced. These latter compounds give rise to an ESR signal which is split into a doublet by adjacent fluorines. The fluorinated molecules are soluble in many organic solvents giving yellow solutions with aromatic solvents and colorless solutions with saturated solvents, such as cyclohexane, with a strong absorption at 212 nm. The solutions can be spin-cast giving very thin layers of the fullerenes and fluorinated fullerenes. The lubrication properties of such films have been measured indirectly and compared with Teflon. Fluorination experiments with C70 will be discussed.