X‑ray Crystallographic Characterization of New Soluble Endohedral Fullerenes Utilizing the Popular C₈₂ Bucky Cage. Isolation and Structural Characterization of Sm@<i>C</i>_3<i>v</i>(7)‑C₈₂, Sm@<i>C</i>_<i>s</i>(6)‑C₈₂, and Sm@<i>C</i>₂(5)‑C₈₂

Abstract

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@<i>C</i>_<i>s</i>(6)-C₈₂, Sm@C₈₂(II) as Sm@<i>C</i>_3<i>v</i>(7)-C₈₂, and Sm@C₈₂(III) as Sm@<i>C</i>₂(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 (<i>e.g.</i>, La<i>@C</i>_2<i>v</i>(9)-C₈₂ (major) and La@<i>C</i>_<i>s</i>(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@<i>C</i>₂(5)-C₈₂, Sm@<i>C</i>_<i>s</i>(6)-C₈₂, Sm@<i>C</i>_3<i>v</i>(7)-C₈₂, and Sm@<i>C</i>_2<i>v</i>(9)-C₈₂. All of these isomers obey the isolated pentagon rule (IPR) and are sequentially interconvertable through Stone–Wales transformations