Stable icosahedral hollow cage clusters: stannaspherene (Sn-12(2-)) and plumbaspherene (Pb-12(2-))

摘要

One of the major objectives of cluster science is to discover stable atomic clusters, which may be used as building blocks for cluster-assembled nanomaterials. The discovery and bulk synthesis of the fullerenes have sprouted new research disciplines in chemistry and nanoscience and precipitated intense interest to search for other similar stable clusters. However, despite major research efforts, no other analogous gas-phase clusters have been found and yielded to bulk syntheses. In this article, we review our recent discoveries in cluster beam experiments of stannaspherene (Sn-12(2-)) and plumbaspherene (Pb-12(2-)), which are highly stable and symmetric cage clusters. The names for these two clusters derive from their icosahedral (I-h) symmetry and delocalized spherical pi-bonding that are characteristics of buckminsterfullerene C-60. Stannaspherene and plumbaspherene have diameters comparable to that of C-60 and can be considered as inorganic analogues of the buckyball. The large internal space in Sn-12(2-) has been shown to be able to trap any transition metal atom to form new endohedral cage clusters, M@Sn-12(2-), analogous to endohedral fullerenes. The doped atom in M@Sn-12(2-) keeps its quasi-atomic nature with large magnetic moments. These endohedral cages form a rich class of new building blocks for cluster-assembled materials with tunable magnetic, electronic, and chemical properties. During our attempt to synthesize endohedral stannaspherenes, we crystallized a new Pd-2@Sn-18(4-) cluster, which can be viewed as the fusion of two Pd@Sn-12(2-) clusters. This result suggests that stannaspherene, plumbaspherene, and a large number of their endohedrally doped species can be synthesized in the bulk.