Functionalization of Endohedral Metallofullerenes

Since the serendipitous discovery of C-60 and subsequent finding of other fullerenes, scientists have focused on the discovery of the physical and chemical properties of these nanomaterials and their incorporation in biomaterials and nanodevices [1,2]. The development of a particular family of fullerenes which incarcerates a metal, metals, or a metallic cluster in the interior of their carbon cages, the endohedral metallofullerenes, is quickly becoming one of the most interesting research areas within the field of carbon-based compounds because of the scope of electronic properties not accessible with empty-cage fullerenes [3-7]. Even though mass spectrometric evidence of their existence was already available in the first paper reporting the discovery of Buckminsterfullerene in 1985 [8, 9], there was controversy about the location of the metals, since fullerenes with exohedral metals were also observed. It was not until 1991 that Smalley and coworkers unequivocally showed that a lanthanum atom was encapsulated in a C-82 fullerene shell as La@C-82 [10], and since then, many analogous species have been isolated. However, the exploration of the physical, chemical and electronic properties of endohedral metallofullerenes has become a reality only in the last few years when technological advances have been made in the production of macroscopic quantities of these nanomaterials [11, 12]. In this section, an overall view of the effect of the encapsulated metal species on the exohedral reactivity of the carbon cages will be addressed and the differences between empty cage fullerenes and endohedral metallofullerenes will be emphasized. It is our intent to suggest that endohedral metallofullerenes are the fullerenes of the future.