Advancements in endohedral metallofullerenes: novel metal-cage interactions driving new phenomena and emerging applications.

Since the discovery of La@C, a wide array of endohedral metallofullerenes (EMFs) have been synthesized and documented. Various metals, including lanthanides, transition metals, alkali metals, alkaline earth metals and actinides, have been successfully incorporated into the inert fullerene cavities. The interaction between these encapsulated metal species and the fullerene cage isomers plays a crucial role in determining distinct molecular structures and imparting versatile chemical behaviors to these compounds. In particular, recent advancements in EMFs with medium-sized carbon cages, which are among the most versatile categories of EMFs, have marked a significant breakthrough in fundamental coordination chemistry and opened up a wide range of potential applications. The formation of various abnormal metal clusters, possessing unique chemical bonding character and geometric conformations, has been shown to be influenced by novel electron transfer mechanisms between the metal atoms and the carbon cage. Moreover, these specialized metal-cage interactions have also facilitated the stabilization of giant fullerene families and promoted the exploration of these structures in greater detail, particularly with respect to the unanticipated metallofullertubes. Therefore, this review aims to highlight the new phenomena arising from these novel metal-cage interactions in the fundamental study of pristine EMFs. On this basis, we also discussed innovative applications of EMF-based supramolecular complexes that stem from their unique host-guest association.