La₂@C₇₂:  Metal-Mediated Stabilization of a Carbon Cage

Abstract

In this study, we report production, isolation, and characterization for the relatively small endohedral metallofullerene, La 2 @C 72 . As described, La 2 @C 72 is readily isolated from conventional electric-arc-generated carbon/metal soot. This new species was purified by HPLC chromatography and characterized by laser desorption mass spectrometry and UV−vis spectroscopy. The mass spectrum also demonstrates the presence of the monometal species, La@C 72, but the absence of empty-cage C 72 . Since empty-cage C 72 has not been successfully isolated to date, the results of the present study are in agreement with the argument for metal-mediated stabilization of the C 72 carbon cage by lanthanum ions. The chromatographic retention data suggest that the electronic structure of La 2 @C 72 is consistent with a (La 3+ ) 2 @C 72 6- species and the prediction of a relatively small dipole moment.