Contrary to a recent suggestion that externally fluorinated C&Fe0 may posses I rather than 1s symmetry, we report theoretical ab initio evidence favoring an Ih equilibrium structure. However, as with C60H60, we find that the lowest minimum structure contains fluorine atoms inside the Cso cage.
The initial report
[ 1 ] describing the remarkable properties of the C6,, molecule contained a reference to C60F60, a compound presumed to have interesting super-lubricant properties. Following the availability of CeO in macroscopic quantities [ 2 1, fluorinated derivatives of C6,, have been studied both theoretically [ 3-7 ] and experimentally [ 8,9]. Ab initio calculations at the SCF level of theory employing basis sets of double-zeta plus polarization quality (dzP) indicated the existence of a stable, I,, symmetry CaoFb,, molecule [ 31. Experimentally [ 8,9], a number of fluorinated C6,, intermediates have been identified, and the single line observed in the 19F NMR spectrum was associated with an icosahedral C60F60 species [ 8 1. It was later pointed out by Fowler, Kroto, Taylor and Walton [ 71 (FKTW)
that the experimental evidence of a single NMR line is compatible with both I,, and I symmetry Ce0F6,, isomers. FKTW further suggested that the twisted I isomer, while preserving the 60-fold equivalence of the F and C nuclei, would allow for a relief of steric strain from the "pincushion" I,, isomer (fig. 1). However, recent semiempirical MNDO calculations by Bakowies and Thiel (BT ) [ 6 1, as well as the ab initio results reported below, do not support this interpretation.