The new endohedral fullerene, Sc-2(mu(2)-O)@C-s(6)-C-82, 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). Sc-2(mu(2)-O)@ C-s(6)-C-82 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 C-82, cage 6 with C-s symmetry is the most favorable to encapsulate the cluster at T > 1200 K. Sc-2(mu(2)-O) C-s(6)-C-82 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.