Isolation endohedral fullerenes

Wang T, Chen N, Xiang J et al (2009) Russian-doll-type metal carbide endofullerene synthesis, isolation, and characterization of Sc4C2 Cgo. J Am Chem Soc 131 16646-16647 Chen N, Chaur MN, Moore C et al (2010) Synthesis of a new endohedral fullerene family, Sc2S C2n (n = 40-50) by the introduction of SO2. Chem Commun 46 4818 820... 

Up to 1999, only metal atoms [1-5], metal clusters [6,7], metal nitrides [55-57], and noble gas atoms [58-60] were observed to be encaged inside C60, C70, or various sizes of higher fullerenes. The experimental evidence for carbon atoms or metal-carbon compounds (carbides) being encapsulated inside fullerenes had not yet been observed. In 2000, Shinohara et al. succeeded in the first production, isolation, and spectroscopic characterization of a scandium carbide endohedral fullerene (Sc2C2) C84. Following this, the first experimental evidence based on synchrotron X-ray diffraction was presented and revealed that the Sc carbide is encapsulated in the form of a lozenge-shaped Sc2C2 cluster inside the D2d-C84 fullerene [8]. 

To date, all the confirmed isolable endohedral fullerenes contain metals either scandium, yttrium, or one of the f-block elements may be encapsulated, and compounds containing up to three metals have been reported. The proportions of the endohedral fiillerenes observed depends upon the manner by which they are extracted from the soot. For lanthanum, predominantly La Cg2 and l. i2 C%o are isolated by solvent extraction techniques, whereas direct sublimation from the soot yields La C6o, La C7o, La C74, and La C82- An explanation for this behavior is that most of the endohedral fullerenes are present as insoluble salts, e.g. [La C6o]" [Ceo], and only La Cg2 and La2 C8o are sufficiently redox stable to be extracted as the neutral molecules. 

The endohedral fullerenes U C28 and U C6o have been reported to be sufficiently stable to allow chemical isolation. Endohedral complexes of the smaller fullerenes (C2 , 2n < 60) are conunonly observed in molecular beam experiments (Section 4.1), but this stabilization of C28 by uranium atom encapsulation is remarkable. A theoretical study of [7i-C28]" and Td-C2iiU (25) indicate that they are stable molecules, and that the laboratory preparation of their derivatives may be viable. ... 

Olmstead, M.H., de Bettencourt-Dias, A., Duchamp, J.C. etal. (2001) Isolation and structural characterization of the endohedral fullerene Sc2N C-i%. Angewandte Chemie International Edition, 40, 1223-1225. 

Yang, H., Lu, C., Liu, Z. et al (2008) Detection of a family of gadolinium-containing endohedral fullerenes and the isolation and crystallographic characterization of one member as a metal-carbide encapsulated inside a large fullerene cage. Journal of the American Chemical Society, 130, 17296-17300. 

Beavers, C.M., Zuo, T.M., Duchamp, J.C. etal. (2006) Tb3N C84 an improbable, egg-shaped endohedral fullerene that violates the isolated pentagon rule. Journal of the American Chemical Society, 128, 11352-11353. 

Olmstead, M.M., Lee, H.M., Duchamp, J.C. et cd. (2003) ScsNOC g folded pentalene coordination in an endohedral fullerene that does not obey the isolated pentagon rule. Angewandte Chemie International Edition, 42, 900-902. 

The possible formation of the endohedral fullerene CH2 C70 was recently communicated by Dunsch.91 The IC was isolated in >90% purity by HPLC and, remarkably, was stable for months even though CH2 is normally only short-lived. 

The triscandium endohedral fullerene Sc3 C82 has been isolated and studied by ESR.96 Synchrotron X-ray studies indicate that the three scandium atoms form a triangle and this trimer has a formal charge of three allowing formulation of the compound as (Sc3)3+C323-.113 The temperature-dependent metal cluster position inside the C82 cage has been studied.114... 

As seen before, the inside of the fullerene cages is empty, so it is self-suggesting to try to fill this cavity with atoms or molecules. Indeed the isolation of so-called endohedral fullerenes succeeded quite soon after the discovery of fullerenes themselves. In endohedral species, single or even several atoms are situated inside the carbon cage, so it is purely topological circumstances that prevent them from breaking out of these compounds. 

Another stabilizing feature is the abihty to stabilize nonisolated pentagon rule fullerenes when a metal or cluster is encapsulated. All empty ftillerenes to date obey the isolated pentagon rule, in that there are no [5, 5] junctions that cause strain that destabilizes the molecule, because all pentagons are connected to hexagons. Nonisolated pentagon rule endohedral fullerenes such as Sc2 C66 and ScjN C68 are known to exist. ... 

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