Pentafluoroethyl derivatives of [60]fullerene C 60 (C 2 F 5 ) n (n = 6, 8, and 10) were synthe sized by the reaction of C 60 with C 2 F 5 I in glass ampoules at 380-440 °C. Isomers of composi tion C 60 (C 2 F 5 ) 6 (one isomer), C 60 (C 2 F 5 ) 8 (five isomers), and C 60 (C 2 F 5 ) 10 (two isomers) were isolated by chromatographic separation. Their molecular structures were established by X ray diffraction. The relative stabilities of isomers were compared by density functional theory calculations.Perfluoroalkyl derivatives of fullerenes are thermally and electrochemically stable compounds. Due to the pres ence of attached electron withdrawing groups, these com pounds hold promise for the use in photovoltaics. A cer tain advantage of these compounds over fluorofullerenes is associated with high chemical stability, in particular, with resistance against hydrolysis.Perfluoroalkyl derivatives of fullerenes were synthe sized for the first time in 1993. 1 The reactions of fullerene with reagents, which readily release fluoroalkyl radicals on heating or irradiation (fluoroalkyl iodides or fluoro acyl peroxides), produced compounds containing up to 16 fluoroalkyl groups. Mixtures of trifluoromethyl (3-14 CF 3 groups), pentafluoroethyl (9-16 C 2 F 5 groups), and perfluorohexyl (6-12 C 6 F 13 groups) deriva tives of fullerene C 60 were characterized by mass spec trometry. Subsequent studies have been focussed prima rily on the synthesis and investigations of trifluoromethyl derivatives. Trifluoromethyl radicals were generated by thermal dissociation of either silver trifluoroacetate 2 or trifluoromethyl iodide. 3,4 As a rule, individual isomers are isolated by the HPLC separation of mixtures produced in the synthesis. The derivatives C 60 (CF 3 ) n (n = 8-12 (see Refs 3-6) and 16-18 (see Ref. 7)) and C 70 (CF 3 ) m (m = 6-18) 8-13 were isolated and characterized by X ray diffraction.Data on individual pentafluoroethyl derivatives are more scarce. The reaction of C 2 F 5 I vapor with [60]fullerene at 440 °C afforded a mixture of products, from which one isomer of C 60 (C 2 F 5 ) 6 and one isomer of C 60 (C 2 F 5 ) 8 were isolated and structurally characterized. 14 Oxide C 60 (C 2 F 5 ) 4 O was isolated from a mixture prepared analogously, and its molecular structure was established. 15 In the present study, we performed the high tempera ture ampoule synthesis of the pentafluoroethyl derivatives C 60 (C 2 F 5 ) n (n = 6 (1), 8 (2), and 10 (3)) with the use of C 2 F 5 I. The separation of the resulting mixtures allowed us to isolate eight new isomers containing from six to ten attached pentafluoroethyl groups. These isomers were studied by X ray diffraction. The relative energy stabili ties of the pentafluoroethyl derivatives were investigated by quantum chemical methods, and these results were compared with the data for trifluoromethyl analogs.
ExperimentalSynthesis. The reaction of fullerene C 60 with C 2 F 5 I was carried out in evacuated glass ampoules. A mixture of fullerene C 60 (99.98%, TermUSA; 30-50 mg) and C 2 F 5 ...