Isolation of Three Isomers of Sm@C₈₄ and X-ray Crystallographic Characterization of Sm@<i>D</i>_3<i>d</i>(19)-C₈₄ and Sm@<i>C</i>₂(13)-C₈₄

Abstract

Three isomers with the composition Sm@C₈₄ were isolated from carbon soot obtained by electric arc vaporization of carbon rods doped with Sm₂O₃. These isomers were labeled Sm@C₈₄(I), Sm@C₈₄(II), and Sm@C₈₄(III) in order of their elution times during chromatography on a Buckyprep column with toluene as the eluent. Analysis of the structures by single-crystal X-ray diffraction on cocrystals formed with Ni^II(octaethylporphyrin) reveals the identities of two of the isomers: Sm@C₈₄(I) is Sm@<i>C</i>₂(13)-C₈₄, and Sm@C₈₄(III) is Sm@ <i>D</i>_3<i>d</i>(19)-C₈₄. Sm@C₈₄(II) can be identified as Sm@<i>C</i>₂(11)-C₈₄ on the basis of the similarity of its UV/vis/NIR spectrum with that of Yb@<i>C</i>₂(11)-C₈₄, whose carbon cage has been characterized by ¹³C NMR spectroscopy. Comparison of the three Sm@C₈₄ isomers identified in this project with two prior reports of the preparation and isolation of isomers of Sm@C₈₄ indicate that five different Sm@C₈₄ isomers have been found and that the source of samarium used for the generation of fullerene soot is important in determining which of these isomers form