Fullerene cluster structure

Brant JA, Labille J, Bottero JY et al. (2006) Characterizing the impact of preparation method on fullerene cluster structure and chemistry. Langmuir. 22 3878-3885. 

Figure 6 The structures of endohedral fullerene clusters with linear tri- and tetraatomic guest molecules inside C70 ( >5/, ).

Figure 7 The structure of endohedral fullerene clusters with benzene and borazole molecules encapsulated into Cs4 ( >6a).

A group of nanomaterials, as the only criterion of membership becomes particle size, is very diversified. Particular members of the group differ from each other by molecular geometry (i.e., nanotubes, fullerenes, crystal structures, clusters, etc.) and physicochemical characteristics (i.e., organic, inorganic, semiconductors, isolators, metals, nonmetals, etc.). Thus, it may and should be assumed that they also differ by the mechanism of action and - in consequence - defining one common applicability domain and QSAR model for all of them is impossible. 

Keywords polymerized fullerenes, clusters and crystal structures, cubic symmetry, quantum-chemical calculations. 

For carbon, it is of course also tempting to study clusters of clusters, namely aggregation of C60 fullerenes [67-69]. This is not really a molecular cluster application since the inner structure of the fullerene, leading to dependence of the particle interaction on relative particle orientation, is largely or completely ignored. The Pacheco-Ramalho empirical potential is used frequently, and fairly large clusters up to n=80 are studied. There appears to be agreement that small fullerene clusters are icosahedral in this model. In contrast to LJ clusters, however, the transition to decahedral clusters appears to occur as early as at n=17 the three-body term of the potential is found to be responsible for this [67]. 

Clusters with hollow cage structures and more than 60 atoms are known as higher fullerenes. Their structures and modes of growth are a subject of study [667, 668, 669]. Experimentally, six different sizes (Ceo, C70, C76, C78, C82 and C84) are well characterised as possessing hollow closed cages,... 

In spite of the repeated recognition of fullerene-like polymorphs [23-25] it has so far been impossible to isolate them in amounts comparable to those obtained for Ceo and C70. There are only a few studies devoted to the fullerene-like structures, based on elements distinct from carbon or silicon [26-28]. The majority of investigations related to non-carbon clusters has been performed on silicon systems, perhaps because of silicon s applications in the microelectronic industry. 

Here, a first review is provided which summarizes the more recent development framework modified fullerenes like cluster opened structures and heterofullerenes. The key steps for such framework modifications are always defined activations of the fullerene cluster due to specific covalent addition reactions. Therefore, the principles of covalent fullerene chemistry [3-8] will be considered first ... 

Figure 8.2(a) demonstrates the fullerene molecule structure optimized by energy, and Figure 8.2(b) demonstrates the optimized structure of the cluster Qo[OI/]io. 

Most main group elements build solids that are either infinite arrangements or species of low dimensionality-chains or rings-packed in molecular solids. Exceptions to this behavior are carbon and phosphorus which lead to allotropic forms made up of cluster species. The best known of them is the elementary white phosphorus P4 which has a cluster structure itself and retains its shape in solution and in the gas phase. In the case of carbon a new allotropic form consisting of molecular clusters C, the fullerenes, has been discovered recently. These species are giant carbon cages with spherically shaped structures which lead to molecular solids and that are also stable in solution. 

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. 

Let us now see in brief the most cited computational studies for this very interesting class of cluster species. Behrman et al. (1994) have shown that ZnO dusters can form stable, fullerene-like structures while Hamad et al. (2005) provided evidences that ZnS clusters can form onion-like or alternatively double bubble structures. Matxain et al. (2000) studied systematically the structures of small ZnO clusters with up to nine atoms and demonstrated that three-dimensional structures may be envisioned as being built from Zu202 and ZnsOs rings. Also, the same group (Matxain et al. 2001,2003) have found that clusters built from ZnS, ZnSe, and CdO clusters can form stable one-dimensional ring structures (O Fig- 20-10). 

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