Cyanation of Fullerene(CF3)n Does Not Always Increase Electron Affinity: Experimental and Theoretical Study
Indeed, regioselective synthesis of a new SPP derivative with three unique addends, C60(CF3)4(CN)H, made possible due to the use of a new isomer of C60(CF3)4 as a substrate, resulted in the experimental and theoretical identification of a family of superhalogen fullerene radicals, species with the gas-phase electron affinity higher than that of the most electronegative halogens, F and Cl.2 The addition of one CN group to C60(CF3)4 increases the measured gas-phase electron affinity by more than 1 eV to 4.28(1) eV; such a large increase is likely due to a significant stabilization of the skew pentagonal pyramid pattern (SPP), and electron-withdrawing effect of CN group. In contrast, the measured electron affinity of another SPP open shell molecular species, C60(CF3)4H, is considerably lower, 3.96(1) eV.
Regioselective cyanation of several C70(CF3)n compounds has also been carried out using recently described technique.3 In the case of C1-C70(CF3)10, the addition of two CN groups results in an expected increase in the measured gas-phase electron affinity by 0.22 eV. Surprisingly, the addition of two electron-withdrawing CN groups to Cs-C70(CF3)8 results in a decrease in the measured gas-phase electron affinity! This decrease is observed for two different CN addition patterns. The underlying reasons and implications for the design of electrophilic fullerene derivatives are rationalized using DFT calculations.
1 Popov, A. A.; Kareev, I. E.; Shustova, N. B.; Stukalin, E. B.; Lebedkin, S. F.; Seppelt, K.; Strauss, S. H.; Boltalina, O. V.; Dunsch, L. J. Am. Chem. Soc. 2007, 129, 11551.
2 Clikeman, T. T.; Deng, S. H. M.; Avdoshenko, S.; Wang, X.-B.; Popov , A. A.; Strauss, S. H.; Boltalina, O. V. Chem. Eur. J. 2013, 19, 15404.
3 Clikeman, T. T.; Kuvychko, I. V.; Shustova, N. B.; Chen, Y.-S.; Popov, A. A.; Boltalina, O. V.; Strauss, S. H. Chem. Eur. J. 2013, 19, 5070.