Fluorinated fullerenes: Synthesis and characterization

The existence of the fully fluorinated fullerene, C₆₀F₆₀, is still subject to controversy. Mass spectrometric evidence shows that it exists, albeit in trace amounts five orders of magnitude in concentration below the most abundant C₆₀F_40-42. Generally, mixtures of C₆₀F_n are obtained where n ranges from 30 to 52, depending on fluorinating conditions. The species with n = 36 is particularly stable. Attempts to increase n by use of the strongly fluorinating halogen fluorides, ClF₃ or BrF₅, have led to products C₆₀F_XX_yO_z (X = Br or Cl), where the origin of the oxygen is probably hydrolysis during analysis. Fluorinated C₆₀ crystallizes as a mixture of hexagonal close packed (40%) and face-centered cubic (60%) phases. X-ray analysis yields an average C-F bond length of 1.49A. Fluorination of C₇₀ leads to mixtures with maximum average stoichiometries of C₇₀F₅₂.