Endohedral fullerenes characterization

While there are no studies of the toxicity of endohedral fullerenes in general, or gadofullerenes in particular, there are several preliminary studies regarding empty fullerenes and their derivatives. In initial steps toward characterizing the safety of water-soluble fullerene derivatives, a cytotoxicity study of various fullerene materials, including underivatized C60, C60[C(COOH)2]3, and two C.0(OH)r species, was conducted (Sayes et al., 2004). The results clearly showed that water-soluble derivatives were significantly less toxic than underivatized C60, and the trend was one of... 

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]. 

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. 

Zuo, T.M., Olmstead, M.M., Beavers, C.M. etal. (2008) Preparation and structural characterization of the 7h and the Dsh isomers of the endohedral fullerenes TmsNOCgo icosahedral Cgo cage encapsulation of a trimetallic nitride magnetic cluster with three uncoupled Tm + ions. Inorganic Chemistry, 47, 5234-5244. 

Olmstead, M.M. de Bettencourt-Dias, A. Stevenson. S. Dorn, H.C. Balch. A.L. Crystallographic characterization of the structure of the endohedral fullerene Er C82 Isomer I with Cs cage symmetry and multiple sites for... 

La Cg2 was reported in macroscopic quantities (Chai et al. 1991). It was in the same study, where the symbol was introduced to denote that the former atom or molecule is encaged inside the fullerene molecule. These species containing atoms or molecules inside the fullerene cages are called endohedral fullerenes (EFs). The most studied compounds are the so-called endohedral metallofullerenes (EMFs) due to their high abundancy (Akasaka and Nagase 2002). In 1991, the first structural characterization by X-ray diffraction of an EMF was reported (Chai et al. 1991). 

This review covers all organometallic complexes of Sc, Y and the lanthanides reported in the year 2000 and their reactions. Endohedral fullerene complexes of the lanthanides have, as usual, been excluded. Highlights this year include striking reports of lanthanides in non-classical oxidation states (Sections 3.2 and 5), a remarkable reversible dinitrogen activation described in Section 3.9.2 and evidence for the existence of the divalent hydrides LnH2(THF)2 (Ln = Sm, Yb) (Section 3.10). In addition Evans has assessed the utility of electrospray mass spectrometry for the characterization of organolathanides. The results are promising and the spectra and dissociation patterns show sensitivity to the metal and its oxidation state. ... 

Crystal structures of a few fullerenes containing endohedral atoms have been recently solved (apart from the noble gas trapping Kr C60,22a the metal atoms containing Sc3 N C78,22b Sc3 N C80 and Sc2 ErN C80>22c Y C82,22d Sc C82,22e Er2 C82,22f Sc3 Cs2,228 Sc2 C84,22h Sc2 C2 C84,221), but unfortunately their electrochemical behaviour is not known. Electrochemical information is also limited for those endohedral complexes which lack definitive structural characterization.23... 

The carbon arc is a versatile method to generate a wide variety of nanostruct-ured carbon materials such as fullerenes (7,11), endohedral metallofullerenes (12-14), nanotubes (6,8-10,15), nanocapsules filled with metals (or carbides) (16-18), and so forth. Arc discharge is characterized by the high electric current... 

This review describes the preparation, characterization, and properties of all nonpolymeric complexes that contain a metal removed from the fullerene also are included. The article does not cover the essentially ionic fullerides MmC (4) or the endohedral metallofullerenes MmC (8), which have been reviewed previously. The extended fullerenes, or so-called carbon nanotubes, which have hollow centers and can be filled with metal salts, also are not discussed. The majority of complexes involve 7r-bonds and, apart from alkyl lithium fullerides, the potentially useful synthetic area of o- complexes has not been explored. Table I shows the occurrence of metal-bound adducts across the periodic table. 

The purification of endohedral metallofullerenes via HPLC had been difficulf, mainly because fhe content of metallofullerenes in raw soot is normally very limited and, furthermore, the solubility in normal HPLC solvents is generally lower than that of various empty higher fullerenes. It took almost two years for mefallofullerenes to be completely isolated by the HPLC method (Kikuchi et al., 1993 Shinohara et al., 1993a) after the first extraction of La Cg2 by the Rice group (Chai et al., 1991). Following these first isolations of metallofullerenes, isolation with different HPLC columns was also reported (Savina et al., 1994 Yamamoto et al., 1994a). The success of the purification/isolation was a real breakthrough for further characterization of the endohedral metallofullerenes. 

In this chapter on chemically modified fullerenes, I will discuss only a few representative molecules which incorporate fullerenes, and focus attention on the best-characterized compounds. A comprehensive review of chemical reactions with fullerenes has just been published by Taylor and Walton.[Ta93] It is not appropriate here to attempt a synthesis of the emerging field of the chemical properties of the fullerenes. Covered elsewhere in this book are ioni-cally bonded fullerides, such as the superconductor KsCeo (Chapter IV) and endohedral complexes, in which various atoms are captured inside the hollow carbon shell (Chapter VI). 

The accessibility of the fullerenes [1] in macroscopic quantities [2] opened up the unprecedented opportunity to develop a rich three-dimensional chemistry of spherical and polyfunctional all carbon molecules. [3-8] A large multitude of fullerene derivatives like exohedral covalent addition products, salts, cluster opened and defined degradation products, heterofullerenes and endohedral derivatives can be imagined and numerous examples, especially of covalent adducts have been synthesized and characterized. [3-8] Within a few years the fullerenes became essential building blocks in organic chemistry. Most of the chemistry of fullerenes has so far been carried out with Ceo (1) with little work on C70 and few experiments with C76 and Cg4. This is simply due to the fact that Ceo... 

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