X‑ray Crystallographic Characterization of New Soluble Endohedral Fullerenes Utilizing the Popular C82 Bucky Cage. Isolation and Structural Characterization of Sm@C3v(7)‑C82, Sm@Cs(6)‑C82, and Sm@C2(5)‑C82

Three isomers of Sm@C82 that are soluble in organic solvents were obtained from the carbon soot produced by vaporization of hollow carbon rods doped with Sm2O3/graphite powder in an electric arc. These isomers were numbered as Sm@C82(I), Sm@C82(II), and Sm@C82(III) in order of their elution times from HPLC chromatography on a Buckyprep column with toluene as the eluent. The identities of isomers, Sm@C82(I) as Sm@Cs(6)-C82, Sm@C82(II) as Sm@C3v(7)-C82, and Sm@C82(III) as Sm@C2(5)-C82, were determined by single-crystal X-ray diffraction on cocrystals formed with Ni­(octaethylporphyrin). For endohedral fullerenes like La@C82, which have three electrons transferred to the cage to produce the M3+@(C82)3– electronic distribution, generally only two soluble isomers (e.g., La@C2v(9)-C82 (major) and La@Cs(6)-C82 (minor)) are observed. In contrast, with samarium, which generates the M2+@(C82)2– electronic distribution, five soluble isomers of Sm@C82 have been detected, three in this study, the other two in two related prior studies. The structures of the four Sm@C82 isomers that are currently established are Sm@C2(5)-C82, Sm@Cs(6)-C82, Sm@C3v(7)-C82, and Sm@C2v(9)-C82. All of these isomers obey the isolated pentagon rule (IPR) and are sequentially interconvertable through Stone–Wales transformations.