Sc2(μ2-O) Trapped in a Fullerene Cage: The Isolation and Structural Characterization of Sc2(μ2-O)@Cs(6)-C82 and the Relevance of the Thermal and Entropic Effects in Fullerene Isomer Selection

The new endohedral fullerene, Sc2(μ2-O)@Cs(6)-C82, has been isolated from the carbon soot obtained by electric arc generation of fullerenes utilizing graphite rods doped with 90% Sc2O3 and 10% Cu (w/w). Sc2(μ2-O)@Cs(6)-C82 has been characterized by single crystal X-ray diffraction, mass spectrometry, and UV/vis spectroscopy. Computational studies have shown that, among the nine isomers that follow the isolated pentagon rule (IPR) for C82, cage 6 with Cs symmetry is the most favorable to encapsulate the cluster at T > 1200 K. Sc2(μ2-O)@Cs(6)-C82 is the first example in which the relevance of the thermal and entropic contributions to the stability of the fullerene isomer has been clearly confirmed through the characterization of the X-ray crystal structure.