Fullerenes with more than 84 carbon atoms

Enriched samples of fullerenes with more than 84 C-atoms were obtained as early as 1991.1 In the meantime Achiba and co-workers have been able to purify an impressive number of these large carbon cages. Based on 13C NMR data obtained for higher fullerenes such as C86, Css, C90, Cy2, and C94, they found many chiral isomers, with C2- and D2-symmetry being prevalent.58,73... 

With these newly developed 0(N) TBMD algorithms, simulations with more than 1000 atoms can be performed on sequential computers such as the IBM RISC-6000 workstation or vector computers such as the Cray. Qiu et al. have applied the 0 N) method to study the structure and energetics of giant fullerenes. Shown in Fig. 26 is the optimized geometry of a 1620-atom fullerene obtained using an IBM RISC-6000 workstation. Mauri and Galli have applied the 0 N) TBMD to study the structure and dynamic of C q striking a diamond surface [131] 1140 carbon atoms have been used in their simulation. 

Some of the special features appearing in the species distribution observed in the experiments on laser evaporation of graphite mentioned above (see for instance Figs. 4.18 and 4.22) can be understood by the mechanism of formation of fullerene already discussed. In the mass spectrum region corresponding to clusters with more than 30 atoms, only ions with an even number of carbon atoms are observed. This feature can be interpreted as a result of the relatively high kinetic stability of cluster structures as the fullerenes are. However the distribution of such species is rather peculiar. Some of them, especially buckmin-sterfullerene, appear to be considerably more stable than the others. The fullerene-70 follows C o in such distributions. 

Fullerenes with only one metal atom inside - mono-metallofullerenes. All rare earth metals can form mono-metallofullerenes. Although the carbon cages that can incorporate one metal atom range from Ceo to bigger than Cioo, as detected by mass spectrometry, the most extractable and stable species are exclusively M Cs2 normally, more than one cage isomer can be isolated. To date, only those mono-metallofullerenes with cages of C72 [32], C74 [33,34], and Cs2 [35] have been determined structurally. 

The isolation and characterization of D2 Synmictrical Cyg in 1991 [1] led to important conclusions It was shown that pure fuUerenes with more than 70 carbon atoms could be isolated in macroscopic quantities from soot produced by the Kratschmer-Huffrnan method [2] and that the vaporization of achiral graphite was able to generate chiral carbon cages. Mass spectrometric evidence for the presence of higher fullerenes - that is, carbon molecules (n > 70) - in crude fullerene soot extract had been obtained shortly before, and optimization of the fullerene purification protocol soon afforded milligram samples of material enriched in higher fullerenes [3]. 

Many elements can give rise to more than one elementary substance. These may be substances containing assemblages of the same mono- or poly-atomic unit but arranged differently in the solid state (as with tin), or they may be assemblages of different polyatomic units (as with carbon, which forms diamond, graphite and the fullerenes, and with sulfur and oxygen). These different forms of the element are referred to as allotropes. Their common nomenclature is essentially trivial, but attempts have been made to develop systematic nomenclatures, especially for crystalline materials. These attempts are not wholly satisfactory. 

Fullerene Cgo is easily fluorinated by elemental fluorine at temperatures less than 100°C [29,30] probably because of its nearly spherical surface and exposed it bonding. Direct fluorination of organic compounds by fluorine gas demonstrated that fluorine was preferentially bonded to a carbon atom with a high electron density [31,32], This may be a main reason why fullerene C60 is more easily fluorinated than graphite. On the contrary, the fluorination behavior of carbon nanotube is similar to that of graphite as already shown. 

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