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 Gd<sub>2</sub>C<sub>90</sub> to Gd<sub>2</sub>C<sub>124</sub> has been detected by mass spectrometry of the <i>o</i>-dichlorobenzene extract of the carbon soot produced by direct current arcing of graphite rods filled with a mixture of Gd<sub>2</sub>O<sub>3</sub> and graphite powder. Chromatographic separation has led to the isolation of pure samples of two isomers of Gd<sub>2</sub>C<sub>94</sub> and the complete series from Gd<sub>2</sub>C<sub>96</sub> to Gd<sub>2</sub>C<sub>106</sub>. Endohedral fullerenes of the type M<sub>2</sub>C<sub>2<i>n</i></sub> can exist as the conventional endohedral, M<sub>2</sub>@C<sub>2<i>n</i></sub>, or as the carbide-containing endohedral, M<sub>2</sub>C<sub>2</sub>@C<sub>2<i>n</i>−2</sub>. Crystallographic characterization of the more rapidly eluting isomer of Gd<sub>2</sub>C<sub>94</sub> reveals that it possesses the carbide structure, Gd<sub>2</sub>C<sub>2</sub>@<i>D</i><sub>3</sub>(85)-C<sub>92</sub>. Computational studies suggest that the more slowly eluting isomer of Gd<sub>2</sub>C<sub>94</sub> may be a conventional endohedral, Gd<sub>2</sub>@<i>C</i><sub>2</sub>(121)-C<sub>94</sub>.