(Invited) Trapping Metallic Oxide Cluster inside Fullerene Cage

Abstract

The sub-nanometer sized void inside fullerene cage permits the accommodation of a single atom, atomic cluster or even small molecule, resulting in the formations of endohedral fullerenes. Particularly, clusterfullerenes can be formed by encapsulating multiple metallic ions in most cases along with non-metal ions (i.e., N3-, C2 2-, S2-, O2-) inside the fullerene cage. Such an association makes clusterfullerene more functional than empty fullerenes and conventional mono-metallofullerenes. Up to date, a variety of clusterfullerenes have been reported, including metal nitrides, carbides, oxides, sulfides, cyanides and so on. Among them, oxide clusterfullerenes (OCFs) can contain variable oxide clusters (i.e., M4O2, M4O3, M3O and M2O; M=Sc or other metal), yielding one of the most versatile families. Thus, OCFs may provide a more convenient platform for developing new functional molecules and for studying the previously less-explored topics such as formation mechanism of clusterfullerenes.In this Account, we review recent progress in the field of OCFs, including their synthesis, isolation, structural and electrochemical studies as well as the preliminary exploration in their potential functions and applications. Thanks for the concrete crystallographic results of an OCF series, we can track the transition of endohedral cluster and fullerene cage. It is suggested that the configuration and internal dynamics of oxide cluster are highly dependent on not only the cage size but also cage structure. On the other hand, based on the experimental observations, two competitive transformation pathways are established for the majority of OCFs, verifying the bottom-up or top-down formation mechanism. It is also found that the redox behaviors of OCFs are more or less comparable to their isoelectronic species with common cage structure and similar cluster geometry, but varied greatly with the cluster variety (i.e., Sc2O vs Sc4O2-3). The mechanism behind such phenomena has been discussed. In addition, the potential of Dy-based OCFs as single molecular magnets (SMMs) is presented theoretically. Nevertheless, experimental advance remains to be achieved. Figure 1