Detection of a Family of Gadolinium-Containing Endohedral Fullerenes and the Isolation and Crystallographic Characterization of One Member as a Metal−Carbide Encapsulated inside a Large Fullerene Cage

A series of di-gadolinium endohedrals that extends from Gd₂C₉₀ to Gd₂C₁₂₄ has been detected by mass spectrometry of the o-dichlorobenzene extract of the carbon soot produced by direct current arcing of graphite rods filled with a mixture of Gd₂O₃ and graphite powder. Chromatographic separation has led to the isolation of pure samples of two isomers of Gd₂C₉₄ and the complete series from Gd₂C₉₆ to Gd₂C₁₀₆. Endohedral fullerenes of the type M₂C_2n can exist as the conventional endohedral, M₂@C_2n, or as the carbide-containing endohedral, M₂C₂@C_2n−2. Crystallographic characterization of the more rapidly eluting isomer of Gd₂C₉₄ reveals that it possesses the carbide structure, Gd₂C₂@D₃(85)-C₉₂. Computational studies suggest that the more slowly eluting isomer of Gd₂C₉₄ may be a conventional endohedral, Gd₂@C₂(121)-C₉₄.