Atoms inside fullerene cages

To facilitate discussion of these somewhat more complicated fullerenes with one or more atoms inside the cage, a special symbolism and nomenclature was introduced [66]. Thereby the symbol is used to indicate the atoms in the interior of the fullerene. All atoms listed to the left of the symbol are located inside the cage and all atoms to the right are a part of the cage structure, which includes heterofullerenes, e.g. C59B. A Cgg-caged metal species is then written as M Cgg, expanded as metal at Cgg . The corresponding lUPAC nomenclature is different from the conventional M C representation. lUPAC recommend that M C be called [rt]fuUerene-incar-lanthanum and should be written iMC [4]. 

Another arena in which topologically restrained molecules are of importance involves endothelial compounds for example, a small molecule or ion inside a fisular cage, such as a fullerene. The first of these to be discovered occurred when Diedrich et al. [5] doped C60 with potassium to encapsulate 3 potassium atoms inside the cage. The systemic name for this compound would now be formed by augmenting the name for fullerene that had been developed earlier in Formulas (42) or (43) of Chapter 3 with a semicolon, followed by a zero numbered locant branch e.g., °(K,K,K) — assuming that the three potassium atoms are independent of one another i.e.,... 

Emichment of these endohedral species can be obtained by heating the intact solid fullerene under 3000 atm of a noble gas at 650°C. Under these conditions, helium, neon, argon, krypton, and even xenon can be forced into the cavity within Cso- This process is believed to occur via a window mechanism in which a C—C bond of the fullerene breaks to provide a window through which the noble gas atom enters the fullerene. Subsequent reformation of the C—C bond can trap the noble gas atom inside the cage. Recent work on creating orifices in through chemical modification produced an interesting model system in which entry and exit of both He and H2 can be monitored, as shown in Fig. 

Fullerene Endohedral Complexes. The possibility of trapping atoms or molecules inside carbon frameworks is a very peculiar property of fullerenes. Today there is indeed strong evidence that metal atoms can actually be trapped inside fullerene cages. A nomenclature for this peculiar kind of compounds has been even suggested (M Cn) for a metal atom M located inside a C fullerene. 

Fig. 4.6 Schlegel diagram for C60H60 Th symmetry (48-exo, 12-endo). Black circles designate the atoms situated inside the fullerene cage...

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