Perfluorofullerenes: Characterization and structural aspects

Characterization of highly fluorinated fullerenes (perfluorofullerenes) has revealed a wide range of x values. High reaction temperatures are limited by volatilization of the compounds. A good compromise is obtained for a reaction at 300 degrees C for several hours leading to a white C60F54 compound with a narrow range of x values (+/-2). X-ray powder diffraction reveals a f.c.c. lattice. Sublimation of C60Fx compounds is carried out under static vacuum and separate fractions are condensed successively. As sublimation temperature is increased, fractions move from the liquid state to solids. F-19 NMR spectroscopy reveals a single narrow peak for liquid fractions, with a chemical shift of -72 ppm/ CF3COOH thus suggesting a highly symmetrical species. The presence of oxygen is also detected when the starting material is exposed to air. The first fraction of air exposed compounds gives rise to a NMR signal at -55ppm. A relatively large quantity of liquid phase is obtained by direct condensation during C-60 fluorination. The NMR spectra is similar to that of the first sublimation fraction, exhibiting a peak at -72 ppm.