RAMAN-SPECTRA AND STRUCTURE OF IODINE AND BROMINE INTERCALATED FULLERENES C-60 AND C-70

Raman spectra of pure C60 and C70 microcrystals and their complexes wi th iodine and bromine prepared by several methods were recorded and an alyzed in comparison with those of weak electron donor-acceptor comple xes. Iodine intercalated C60 prepared by gas diffusion as well as by d issolution 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 in teraction is higher than that in the I2/benzene complex where nu(I2) v ibrates at 205 cm-1, but weaker than in aggregated solid iodine (I2)n which give nu(I2) 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, nu(I2) is located at 197 cm-1. The i nteraction has thus the same nature. With C60Brx prepared in CS2, two series of crystals are obtained. In the first series, an electron-dono r-acceptor complex between C60 and Br2 is observed and in the other se ries, the appearance of C-Br stretching vibrations attests that a brom ide was obtained.