Molecular Carbon Clusters. The Fullerenes

The chemical species with spherically shaped structures are found only seldom in the chemistry of main group elements. Some examples of this type of compounds are the boranes and carboranes described above and some post-transitional deltahedral clusters to be described later in this Chapter. 

In this section, some aspects of the chemistry of a family of carbon cluster species describing large polycyclic structures with nearly spherical symmetries called fullerenes are discussed. 

The Discovery of the Fullerenes. In experiments carried out at Rice University in 1985 associated with the presence of carbon in stars and space [Kroto HW, Heath JR, O Brien SC, Curl RF, Smalley RE (1985) Nature 318 162], the Ceo molecule was discovered. This species is one of the many carbon clusters which can be generated when a plasma of carbon vapor produced in the surface of graphite by laser irradiation is cooled by an inert gas jet. The detection of this type of carbon aggregate which appears to constitute a third allotropic and the first molecular form of carbon by mass spectroscopy is illustrated in Fig. 4.18. 

Clusters produced by vaporization of graphite are indeed a big family. Thus, some mass spectrometric determinations have shown the presence of clusters with mass peaks up to 720. The experiments reveal, however, that the size distribution is not statistic and that only ions with even number of carbon atoms are detected. Moreover, as illustrated in Fig. 4.18, the intensity of the C o peak is always the highest its relative intensity depends however upon the experiment conditions. As shown in Fig. 4.19, in particular cases, conditions are found for 

Synthesis of Fullerenes. As mentioned above, the experiments leading to the first observation of the fullerenes involved the formation of carbon vapor plasma by 

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