Endohedral metallofullerenes (EMFs), a new class of hybrid molecules formed by encapsulation of metallic species inside fullerene cages, exhibit unique properties that differ distinctly from those of empty fullerenes because of the presence of metals and their hybridization effects via electron transfer. This critical review provides a balanced but not an exhaustive summary regarding almost all aspects of EMFs, including the history, the classification, current progress in the synthesis, extraction, isolation, and characterization of EMFs, as well as their physiochemical properties and applications in fields such as electronics, photovoltaics, biomedicine, and materials science. Emphasis is assigned to experimentally obtained results, especially the X-ray crystallographic characterizations of EMFs and their derivatives, rather than theoretical calculations, although the latter has indeed enhanced our knowledge of metal–cage interactions. Finally, perspectives related to future developments and challenges in the research of EMFs are proposed. (381 references)

Recent breakthroughs achieved in the chemical functionalization of endohedral metallofullerenes (EMFs), especially single crystallographic X-ray characterizations of their derivatives, have presented fundamentally new insights into the structures and properties of these metal–carbon hybrid molecules, and have also brought immense potential applications. In particular, the interplay between the encapsulated metallic species and the fullerene cage has been well investigated. On one hand, the position and motion of the encapsulated metals can be effectively controlled by exohedral modification. On the other hand, the cage structures, the chemical behaviours of cage carbons and thus the chemical reactivity of the whole molecule are also apparently influenced by the electronic configuration and geometrical conformation of the internal metals via strong metal–cage interactions. In this article, we contribute a systematic review of the important chemical transformations of EMFs reported to date, including disilylation, 1,3-dipolar cycloaddition with ylides, cyclopropanation with carbenes and carbanions, cycloaddition with dienes and benzyne, radical reactions, and other miscellaneous reactions, in addition to noncovalent interactions such as supramolecular complexation. The roles that internal metals play in controlling the reactivity of cage carbons are particularly emphasized. Finally, some applicable materials based on EMFs and their derivatives are summarized and practical perspectives are proposed.

Structural and electronic properties of metal-doped silicon clusters $M{\mathrm{S}\mathrm{i}}_n$s ($M=\mathrm{W}$, Zr, Os, Pt, Co, etc.) in a large size range of $8\le n\le 20$ are investigated via ab initio calculations. Different from a recent experimental suggestion that the metal atom is endohedral in $M{\mathrm{S}\mathrm{i}}_n$, we reveal that the formation of endohedral structure strongly depends on the size of the ${\mathrm{S}\mathrm{i}}_n$ cluster. Two novel structures of the chemically stable endohedral species are manifested. The suitable $M@{\mathrm{S}\mathrm{i}}_n$ building blocks of self-assembly materials vary in the range of $10\le n\le 16$. The thermodynamical magic numbers are found to coincide with the chemical magic numbers for five clusters.