Isolation of Three Isomers of Sm@C84 and X-ray Crystallographic Characterization of Sm@D3d(19)-C84 and Sm@C2(13)-C84

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 NiII(octaethylporphyrin) reveals the identities of two of the isomers: Sm@C84(I) is Sm@C2(13)-C84, and Sm@C84(III) is Sm@ D3d(19)-C84. Sm@C84(II) can be identified as Sm@C2(11)-C84 on the basis of the similarity of its UV/vis/NIR spectrum with that of Yb@C2(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.