Oxygenated species in the products of fluorination of [60]- and [70]-fullerene by fluorine gas

Abstract

Fluorination of pure [60]fullerene and [70]fullerene by fluorine gas shows batch variation, and is accompanied by colour changes as fluorine slowly penetrates the fullerene lattice. Attempted partial fluorination produces a mixture of highly and unfluorinated material due to this slow penetration. [60] Fullerene undergoes fluorination more slowly than [70]fullerene, due to better packing of the crystal lattice in the former, and this explains why [60]fullerene contaminated with [70]fullerene is fluorinated faster than pure [60]fullerene. The NMR spectrum of fluorinated [70]fullerene shows a number of singlets between δ–151.2 and –153.65, indicating the formation of a mixture of derivatives each possessing high symmetry. The IR of fluorinated [70]fullerene shows a broad band at 1112 cm^–1. The mass spectra of fluorinated [60]- and [70]-fullerenes reveals species containing up to eleven and sixteen oxygen atoms, respectively (DCl probe, deposition from dichloromethane), or up to eighteen oxygen atoms in each case (deposition from methanol). The maximum site occupancies of species detected (assuming that oxygen is present as the epoxide) are 68 and 70, respectively. Methylene- and (after reaction with methanol) trifluoromethyl-containing species are also evident in the mass spectrum of fluorinated [60]fullerene; corresponding species are not found in fluorinated [70]fullerene. The high level of epoxide formation with the fluorofullerenes indicates that the tendency for fullerenes generally to form epoxides derives from the strong electron withdrawal by the cages.