Chapter 2: Endohedral Fullerenes

Endohedral fullerenes have unique electronic properties and structures that are stabilised by the charge transfer from the encaged species to the carbon cage. In this charpter, an extensive discussion of different endohedral fullerene families are presented, focusing on their structural features and electrochemical properties, along with their chemical reactivities. Classical EMFs are the earliest members in this family and have been extensively investigated. Recently, metallic nitride, metallic carbide and metallic oxide fullerenes have been reported and their special electronic structures have been found to be strongly dependent on the clusters encapsulated. Metallic nitride EMFs with I_h-C₈₀ cages can be prepared in exceptionally high yields and large families of lanthanum metals and group III metals have been encapsulated as trimetallic nitride clusters. Furthermore, the surprising ability of carbon cages to encapsulate larger clusters was demonstrated by the generation of Sc₄O₃@C₈₀ and Sc₄C₂@C₈₀. Chemical functionalisation of endohedral fullerenes enhances their solubility and allows manipulation in multiple applications. Several types of reactions, including photochemical reactions, Diels–Alder, 1,3-diplar cycloaddictions, Bingel–Hirsch, free radicals and other reactions are extensively discussed. Classical EMFs exhibit higher reactivities because of their much easier reduction and oxidation compared with empty fullerenes and the reactivity and regioselectivity of metallic nitride EMFs has been found to be especially affected by the nature of the endoderal clusters. On the other hand, exohedral funtionalisation significantly affects the position and motion of the entrapped moieties. Finally, nanostructures based on endohedral fullerenes and some potential applications are presented.