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The carbon soot obtained by electric arc vaporization of carbon rods doped with Sm(2)O(3) contains a series of monometallic endohedral fullerenes, Sm@C(2n), along with smaller quantities of the dimetallic endohedrals Sm(2)@C(2n) with n = 44, 45, 46, and the previously described Sm(2)@D(3d)(822)-C(104). The compounds Sm(2)@C(2n) with n = 44, 45, 46 were purified by high pressure liquid chromatography on several different columns. For endohedral fullerenes that contain two metal atoms, there are two structural possibilities: a normal dimetallofullerene, M(2)@C(2n), or a metal carbide, M(2)(μ-C(2))@C(2n-2). For structural analysis, the individual Sm(2)@C(2n) endohedral fullerenes were cocrystallized with Ni(octaethylporphyrin), and the products were examined by single-crystal X-ray diffraction. These data identified the three new endohedrals as normal dimetallofullerenes and not as carbides: Sm(2)@D(2)(35)-C(88), Sm(2)@C(1)(21)-C(90), and Sm(2)@D(3)(85)-C(92). All four of the known Sm(2)@C(2n) endohedral fullerenes have cages that obey the isolated pentagon rule (IPR). As the cage size expands in this series, so do the distances between the variously disordered samarium atoms. Since the UV/vis/NIR spectra of Sm(2)@D(2)(35)-C(88) and Sm(2)@C(1)(21)-C(90) are very similar to those of Gd(2)C(90) and Gd(2)C(92), we conclude that Gd(2)C(90) and Gd(2)C(92) are the carbides Gd(2)(μ-C(2))@D(2)(35)-C(88) and Gd(2)(μ-C(2))@C(1)(21)-C(90), respectively.

Four isomers with the composition SmC(90) were obtained from carbon soot produced by electric arc vaporization of carbon rods doped with Sm(2)O(3). These were labeled Sm@C(90)(I), Sm@C(90)(II), Sm@C(90)(III), and Sm@C(90)(IV) 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(octaethylporphyrin) reveals the identities of the individual isomers as follows: I, Sm@C(2)(40)-C(90); II, Sm@C(2)(42)-C(90); III, Sm@C(2v)(46)-C(90) and IV, Sm@C(2)(45)-C(90). This is the most extensive series of isomers of any endohedral fullerene to have their individual structures determined by single-crystal X-ray diffraction. The cage structures of these four isomers can be related pairwise to one another in a formal sense through sequential Stone-Wales transformations.

The carbon soot obtained by electric arc vaporization of carbon rods doped with Sm(2)O(3) contains a series of monometallic endohedral fullerenes, Sm@C(2n), along with smaller quantities of the dimetallic endohedrals Sm(2)@C(2n) with n = 44, 45, 46, and the previously described Sm(2)@D(3d)(822)-C(104). The compounds Sm(2)@C(2n) with n = 44, 45, 46 were purified by high pressure liquid chromatography on several different columns. For endohedral fullerenes that contain two metal atoms, there are two structural possibilities: a normal dimetallofullerene, M(2)@C(2n), or a metal carbide, M(2)(μ-C(2))@C(2n-2). For structural analysis, the individual Sm(2)@C(2n) endohedral fullerenes were cocrystallized with Ni(octaethylporphyrin), and the products were examined by single-crystal X-ray diffraction. These data identified the three new endohedrals as normal dimetallofullerenes and not as carbides: Sm(2)@D(2)(35)-C(88), Sm(2)@C(1)(21)-C(90), and Sm(2)@D(3)(85)-C(92). All four of the known Sm(2)@C(2n) endohedral fullerenes have cages that obey the isolated pentagon rule (IPR). As the cage size expands in this series, so do the distances between the variously disordered samarium atoms. Since the UV/vis/NIR spectra of Sm(2)@D(2)(35)-C(88) and Sm(2)@C(1)(21)-C(90) are very similar to those of Gd(2)C(90) and Gd(2)C(92), we conclude that Gd(2)C(90) and Gd(2)C(92) are the carbides Gd(2)(μ-C(2))@D(2)(35)-C(88) and Gd(2)(μ-C(2))@C(1)(21)-C(90), respectively.