Methoxy and Methoxide Adducts of Fullerene-60: Semiempirical Theoretical Studies

Abstract

Semi empirical molecular orbital calculations utilising the AM1 approximation with the MOPAC program have been used to suggest the likely stable isomeric structures of the smaller methoxylated adducts of C₆₀, namely the anions C₆₀(OMe)^-_n, n = 1,3,5,7, and the neutral species C₆₀(OMe)_n, n = 2,4,6. While the OMe species is expected to behave similarly to the F atom in respect of its electronegativity and electrophilicity, its greater size and asymmetric geometry influences the role of non-bonded interactions in determining the favoured configurations and relative chemical stabilities of the respective isomers of each structure. The 'string' model which describes the localised addition pattern observed in the case of the bromine adducts, C₆₀Br_2n, for n values up to 12, is also appropriate in describing the stable OMe and OMe^- adducts of C₆₀. The five-fold symmetric C₆₀(OMe)^-₅ anion is of particular interest as it is revealed as the most stable species, in agreement with its observation as the most abundant species occurring in electrospray mass spectra. This suggests that metal salts of the general type M⁺C₆₀L^-₅ may be isolable under appropriate experimental conditions.