Raman spectra and structure of iodine and bromine intercalated fullerenes C60 and C70

Raman spectra of pure C60 and C70 microcrystals and their complexes with iodine and bromine prepared by several methods were recorded and analyzed in comparison with those of weak electron donor-acceptor complexes. Iodine intercalated C60 prepared by gas diffusion as well as by dissolution in CS2 gives the Raman characteristics of molecular iodine I2 with an I2 stretching frequency at 198 cm−1 while free solid iodine I2 oscillates at 212 cm−1. This frequency shift can be interpreted by a charge transfer between C60 and I2. This electron donor-acceptor interaction is higher than that in the I2/benzene complex where vI2 vibrates at 205 cm−1, but weaker than in aggregated solid iodine (I2)n which give vI2 at 180 cm−1. A lowering of the tangential stretching frequency of the C = C bonds confirms a loss of charge and double bond character. In the I2-C70 complex, vI2 is located at 197 cm−1. The interaction has thus the same nature. With C60Brx prepared in CS2, two series of crystals are obtained. In the first series, an electron-donor-acceptor complex between C60 and Br2 is observed and in the other series, the appearance of C-Br stretching vibrations attests that a bromide was obtained.