ИСТИНА

Fullerenes and their derivatives in neutral and anionic states show a variety of physical properties making these compounds as prospective organic semi-, superconductors and ferromagnets.1 Electrochemical studies of fullerene derivatives make possible to reveal the reduction potentials, electrochemical gaps and chemical transformation due to electronic transfer. Electrochemical behavior of trifluoromethulfullerenes C70(CF3)n, n=2–20 can be separated to reversible (for the majority, up to four electrochemically reversible single-electron reductions)) and irreversible. Irreversible reductions are due to chemical transformations: dimerization (C1-p7mp-C70(CF3)10)2 or the leaving of the CF3 group in the case of skew-pentagon-pyramid patterns of CF3 addends3,4. For example, major isomer of C70(CF3)12 and spp-C70(CF3)16 isomer display ECE mechanism during reduction yielding C70(CF3)11– and C70(CF3)15– anionscorrespondingly. Furthermore, oxidation of C70(CF3)15– is electrochemically reversible process at moderate voltammetric scan rates evidencing relatively high stability of the respective radicals C70(CF3)15•. Thus, the electron-transfer-induced detachment of CF3 group is a promising approach to synthesis of novel fullerene derivatives and fullerene-based stable radicals. Here we report novel isomer p9mp-C70(CF3)12, its structure, proved by19F and 19F–19F COSY NMR spectroscopy and interesting results of CVA studies, which is similar to C1-p7mp-C70(CF3)10. According to cyclic voltammetry studies, new C70(CF3)12 exhibits two reduction process at –1.05 (irreversible) and –1.68 and oxidation process at –0.43 V vs Fc0/+ at moderate scan rates. The electrochemical reversibility of the first reduction step can be achieved at the scan rate of more than 20 V s–1. The process has been assigned to recombination of anion-radical species yielding [C70(CF3)12]22–. ESR spectroscopy of chemically generated p7-C70(CF3)8–• and p7mp-C70(CF3)10–• and p9mp-C70(CF3)12–• reveals unresolved singlet signals for all studied anionic compounds with typical g-values of 2.002 and line widths of 1 G. Bond energy between fullerene cage in dianionic dimers of [C70(CF3)8]22–, [C70(CF3)10]22– and [C70(CF3)12]22– were estimated as –31, +54, +47 kJ mol–1 according to DFT calculation.