After the identification of the cyano adduct-anions of C60 using electrospray mass spectrometry (EMS),2 we tried the same reactions with C70 to compare the results. Using negative-ion EMS of C70/CN- mixtures with different concentrations we were able to produce clear spectra for the mono- and di-anionic species C70(CN)n- for n=1,2,3 and C70(CN)n2- for n=2,4,6. At high resolution the isotopic ratios were in accordance with those calculated for these formulae.
In contrast to C60, the number of ions produced by EMS of the C70/CN- solutions was much greater. This enabled us to use a relatively high resolution to reveal the isotopic ratios, even for the doubly charged anions. In contrast with the buckminsterfullerene results, the fullerene-70 solutions were able to produce considerable amounts of ions even after more than two and a half hours following mixing. This indicates that the rate of formation of the neutral species in these solutions is much less than that in the C60 case. The formation of the dianionic species C70(CN)n2- appears to be much faster than for the analogous C60(CN)n2- and these are dominant at high concentrations of CN-.
Semi empirical calculations using MOPAC with the AM1 approximation are being undertaken and will be presented. These should give some indication of any structural differences between the neutral and anionic species.
1. R. Taylor and D. R. M. Walton, Nature, 363, 1993, 685-693.
2. G. Khairallah and J. B. Peel, J.Chem.Soc., In Press.