Stannaspherene (Sn122-) and Plumbaspherene (Pb12

2-)Lai-Sheng Wang, Washington State University

Award # (DMR-0503383)During photoelectron spectroscopy (PES) experiments aimed at understanding the semiconductor to metal transition in tin clusters, the spectrum of Sn12

- was observed to be remarkably simple and totally different from the corresponding Ge12

- cluster, suggesting that Sn12- is

a unique and highly symmetric cluster. Structural optimization starting from an icosahedral (Ih) cluster led to a slightly distorted cage with C5v symmetry. However, adding an electron to Sn12

- resulted in a stable closed-shell Ih-Sn12

2- cluster, which was synthesized in the form of KSn12

- (K+[Sn122-]) with a similar PES spectrum as Sn12

-. The Ih-Sn12

2- cage is shown to be bonded by four delocalized radial bonds and nine delocalized on-sphere tangential bonds from the 5p orbitals of the Sn atoms, whereas the 5s2 electrons remain largely localized and nonbonding. The bonding pattern in Sn12

2- is similar to the well-known B12H12

2- cage, with the twelve 5s2 localized electron pairs replacing the twelve B-H bonds. Both the -bonding and the highly spherical symmetry of the 12-atom Sn cluster are analogous to the C60 fullerene and a name “stannaspherene” is coined for this highly special cluster. The corresponding 12-atom Pb cluster is also found to be an icosahedral cage cluster and a name “plumbaspherene” has been coined to describe its -bonding and high symmetry. Both stannaspherene and plumbaspherene have diameters exceeding 6 Å and can host most transition metal atoms in the periodic table, giving rise to a large class of endohedral chemical building blocks (M@Sn12 or M@Pb12) for potential new cluster-assembled nanomaterials.

L. F. Cui, X. Huang, L. M. Wang, D. Y. Zubarev, A. I. Boldyrev, J. Li, and L. S. Wang, J. Am. Chem. Soc. 128, 8390 (2006)

L. F. Cui, X. Huang, L. M. Wang, J. Li, and L. S. Wang, J. Phys. Chem. A 110, 8/31 (2006)