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 M2C2n can exist as the conventional endohedral, M2@C2n, or as the carbide-containing endohedral, M2C2@C2n−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.