Crystalline functionalized endohedral C$_{60}$ metallofullerides
Résumé
Endohedral metallofullerenes have been extensively studied since the first experimental observation of La@C$_{60}$ in a laser-vaporized supersonic beam in 1985. However, most of these studies have focused on metallofullerenes larger than C60 such as (metal)@C$_{82}$, and there are no reported purified C$_{60}$-based monomeric metallofullerenes, except for [Li@C$_{60}$]+(SbCl$_6$)−salt. Pure (metal)@C$_{60}$ compounds have not been obtained because of their extremely high chemical reactivity. One route to their stabilization is through chemical functionalization. Here we report the isolation, structural determination and electromagnetic properties of functionalized crystalline C$_{60}$-based metallofullerenes Gd@C$_{60}$(CF$_3$)$_5$ and La@C60(CF$_3$)$_5$. Synchrotron X-ray single-crystal diffraction reveals that La and Gd atoms are indeed encapsulated in the Ih-C60 fullerene. The HOMO-LUMO gaps of Gd@C$_{60}$ and La@C$_{60}$ are significantly widened by an order of magnitude with addition of CF$_3$ groups. Magnetic measurements show the presence of a weak antiferromagnetic coupling in Gd@C$_{60}$(CF$_3$)$_3$ crystals at low temperatures
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