X-ray Crystallographic Characterization of New Soluble Endohedral Fullerenes Utilizing the Popular C_(82) Bucky Cage. Isolation and Structural Characterization of Sm@C_(3v)(7)-C_(82), Sm@Cs(6)-C_(82), and Sm@ C_2(5)-C_(82)

摘要

Three isomers of Sm@C_(82) that are soluble in organic solvents were obtained from the carbon soot produced by vaporization of hollow carbon rods doped with Sm_2O_3/ graphite powder in an electric arc. These isomers were numbered as Sm@C_(82)(Ⅰ), Sm@C_(82)(Ⅱ), and Sm@C_(82)(Ⅲ) in order of their elution times from HPLC chromatography on a Buckyprep column with toluene as the eluent. The identities of isomers, Sm@C_(82)(Ⅰ) as Sm@C_s(6)-C_(8ν), Sm(2)C_(82)(Ⅱ) as Sm@ C_(3v)(7)-C_(82), and Sm@C_(82)(Ⅲ) as Sm@C_2(5)-C_(82), were determined by single-crystal X-ray diffraction on cocrystals formed with Ni(octaethylporphyrin). For endohedral fullerenes like La@C_(8ν), which have three electrons transferred to the cage to produce the M~(3+)@(C_(82))~(3-) electronic distribution, generally only two soluble isomers (e.g., La@C_(2ν),(9)-C_(82) (major) and La@ C_s(6)-C_(82) (minor)) are observed. In contrast, with samarium, which generates the M~(2+)(3)(C_(82))~(2-) electronic distribution, five soluble isomers of Sm(5)C_(82) have been detected, three in this study, the other two in two related prior studies. The structures of the four Sm@C_(82) isomers that are currently established are Sm@C_2(5)-C_(82), Sm@C_5(6)-C_(82), Sm@C_(3ν)(7)-C_(82), and Sm@C_(2ν)(9)- C_(82). All of these isomers obey the isolated pentagon rule (IPR) and are sequentially interconvertible through Stone-Wales transformations.