Other covalent and mixed clusters

Clusters of several elements or compounds have also been produced and studied in some detail. Two cases that have attracted considerable attention are clusters of Si and the so called metallo-carbohedrenes or met-cars . These two classes of clusters exhibit certain similarities to the fullerenes and have been considered as possible building blocks of novel materials, so we discuss them briefly here. 

Lastly, we discuss briefly the case of met-car clusters which were discovered by Castleman and coworkers [230]. There are two interesting aspects to these clusters. 

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