Trifluoromethyl Derivatives of Insoluble Small-HOMO-LUMO-Gap Hollow Higher Fullerenes. NMR and DFT Structure Elucidation of C 2 -(C 74 -D 3h )(CF 3 ) 12 , C s -(C 76 -T d (2))(CF 3 ) 12 , C 2 -(C 78 -D 3h (5))(CF 3 ) 12 , C s -(C 80 -C 2v (5))(CF 3 ) 12 , and C 2 -(C 82 -C 2 (5))(CF 3 ) 12 Natalia B. Shustova, ²,‡ Igor V. Kuvychko, ² Robert D. Bolskar, § Konrad Seppelt, ‡ Steven H. Strauss,* ,² Alexey A. Popov,* ,| and Olga V. Boltalina* ,²,‡ Contribution from the Department of Chemistry, Colorado State UniVersity, Fort Collins, Colorado 80523, Institut fu ¨r Anorganische und Analytische Chemie der Freie UniVersita ¨t Berlin, Berlin D14195, Germany, TDA Research Inc., 12345 West 52nd AVenue, Wheat Ridge, Colorado 80033, and Chemistry Department, Moscow State UniVersity, Moscow 119992, Russia Received July 19, 2006; E-mail: steven.strauss@colostate.edu; popov@phys.chem.msu.ru; ovbolt@lamar.colostate.edu Abstract: Reaction of a mixture of insoluble higher fullerenes with CF3I at 500 °C produced a single abundant isomer of C74(CF3)12,C76(CF3)12, and C80(CF3)12, two abundant isomers of C78(CF3)12 and C82(CF3)12, and an indeterminant number of isomers of C84(CF3)12. Using a combination of 19 F NMR spectroscopy, DFT calculations, and the structures and spectra of previously reported fullerene(CF3) n compounds, the most- probable structures of six of the seven isolated compounds were determined to be specific isomers of C2-(C74-D3h)(CF3)12, C s-(C76-T d(2))(CF3)12), C2-(C78-D3h(5))(CF3)12), C s-(C80-C2v(5))(CF3)12), C2-(C82-C2(5))- (CF3)12), and C2-(C82-C2(3))(CF3)12) containing ribbons and/or loops of edge-sharing para-C6(CF3)2 hexagons. The seventh isolated compound is a C1 isomer of C78(CF3)12 containing two such ribbons. This set of compounds represents only the second reported isolable compound with the hollow C74-D3h cage and the first experimental evidence for the existence of the hollow fullerenes C76-T d(2), C78-D3h(5), C80-C2v(5), and C82-C2(5) in arc-discharge soots. Introduction The hollow carbon polyhedra known as fullerenes 1-3 range in size from C 20 to cages with over 400 carbon atoms. 4,5 Only a tiny fraction of the geometrically possible isolated-pentagon- rule (IPR) hollow fullerene cages have been isolated and characterized. 6-12 The first two decades of hollow (i.e., non- endohedral) fullerene research were focused almost exclusively on soluble hollow fullerenes, especially with respect to exohedral derivatization 2,13,14 (see Supporting Information (SI) for ad- ditional references). However, it is generally believed that a considerable number of insoluble hollow higher fullerenes (HHFs) are also present in the soots, waiting to be discovered. Their insolubility has been attributed to their covalently linked polymeric nature, which is believed to be due to their small (or zero) HOMO-LUMO gaps. 15,16 In 1993, Yeretzian and co-workers reported (i) that the yield of insoluble C 74 in soots was similar to the yields of soluble HHFs C 2n with 2n > 74 and (ii) that C 74 was sufficiently stable to be sublimed. 17 In 1998, Diener and Alford demonstrated that insoluble HHFs included C 2n isomers with all values of 2n from 74 to 104. 16 They reported that insoluble small-gap and open- shell HHFs could be solubilized (and subsequently chromato- graphed) by electrochemical reduction to their respective closed- shell anions. 16 A sample of C 74 -enriched insoluble HHFs was subsequently fluorinated to yield D 3 -C 74 F 38 , the first derivative ² Colorado State University. ‡ Freie Universita ¨t Berlin. § TDA Research Inc. | Moscow State University. (1) Fowler, P. W.; Manolopoulous, D. E. An Atlas of Fullerenes; Clarendon: Oxford, 1995. 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