First Unsymmetrical Bisfullerene, C121: Evidence for the Presence of Both Homofullerene and Methanofullerene Cages in One Molecule
AuthorDragoe, Nita; Shimotani, Hidekazu; Wang, Jian; Iwaya, Mitsuhiro; de Bettencourt-Dias, Ana; Balch, Alan L.; Kitazawa, Koichi
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The authors report the isolation and characterization of the bisfullerene C121, the 1st all-carbon mol. to contain a homofullerene (also called a fulleroid) cage. This unsym. isomer of C121, along with a sym. isomer of C121 and C122, were obtained by thermolysis of a mixt. of C60CBr2 and C60 and sepd. by HPLC. The predominant isomer of C121 has a spiro carbon atom bridge that connects to one of the cages through an open [5.6] ring junction (i.e., between a pentagon and a hexagon) and to the other through a closed [6.6] ring junction. Ab initio calcns. indicate that the unsym. structure is more stable than either of the sym. alternatives, with the bridging carbon atom attached to both C60 cages through closed [6.6] ring junctions or attached to each cage through open [5.6] ring junctions. Exptl. evidence for the unsym. structure comes from the 13C NMR and UV/visible spectra. Electrochem. redn. of this bisfullerene shows three pairs of distinct, reversible peaks that correspond to each of the 1st three redns. of the fullerene cages. This is consistent with the presence of a homofullerene unit and shows the similarity of the redox behavior to that of C60. The 1st redn. potential of C121 is slightly shifted toward more pos. values than that of fullerene.