Stannaspherene (Sn 12 2- ) and Plumbaspherene (Pb 12 2- )

1. Stannaspherene (Sn122-) and Plumbaspherene (Pb122-) Lai-Sheng Wang, Washington State University, 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-Sn122- cluster, which was produced in the form of KSn12- (K+[Sn122-]). The Ih-Sn122- cage is shown to be bonded by four delocalized radial p 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. 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 [1]. 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 [2]. 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 [3]. [1] 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). [2] L. F. Cui, X. Huang, L. M. Wang, J. Li, and L. S. Wang, J. Phys. Chem. A 110, 10169(2006). [3] L. F. Cui, X. Huang, L. M. Wang, J. Li, and L. S. Wang, Angew. Chem. Int. Ed. 119, 756(2007).

2. Pd2@Sn184-): Fusion of Two Endohedral Stannaspherenes (Pd@Sn122-) Lai-Sheng Wang, Washington State University, DMR 0503383 One of the major objectives of cluster science is to discover stable atomic clusters, which may be used as building blocks for cluster-assembled materials.The discovery and bulk synthesis of the fullerenes have sprouted new research disciplines in chemistry, materials science, and nanoscience and precipitated intense interests to search for other similar stable clusters. Recently, we have discovered a stable icosahedral 12-atom Sn cluster (stannaspherene: Sn122–), which has also been shown to be able to trap all transition metals to form gaseous endohedral clusters (M@Sn12–). During exploratory solution syntheses of endohedralstannaspherenes, a new closo-deltahedral cluster, Pd2@Sn184–, has been isolated as a (2,2,2-crypt)K+ salt through the reaction of K4Sn9 and Pd[P(C6H5)3]4 in ethylenediamine solutions and characterized via X-ray crystallography. The new Pd2@Sn184– cluster has pseudo-D3d symmetry and is composed of 18 Sn atoms encapsulating two Pd atoms. It can be viewed as the fusion of two endohedral stannaspherenes (Pd@Sn122–) along their C3 axis by removing a Sn3 triangle on each Sn12 unit at the cluster-cluster interface. Electronic structure calculations show that Pd2@Sn184– consists of a Sn184– cage with two zero valent Pd atoms and possesses a highly stable electronic configuration. The new cluster can be viewed as an analogue of C70, whereas stannaspherene can be viewed as an analogue of the buckyball C60. Z. M. Sun, H. Xiao, J. Li, and L. S. Wang, J. Am. Chem. Soc. 128, 9560 (2007).

3. Broader Impacts and Educational Outreach Lai-Sheng Wang, Washington State University, DMR 0503383 A graduate level course (Phys. 581: Nanoclusters, Nanomaterials, and Nanotechnology) has been developed, which is based primarily on research results from this grant. Since 2003, this course has been offered during the summer on-site at Pacific Northwest National Laboratory and integrated as a course for the Joint Institute of Nanotechnology between PNNL and University of Washington, allowing students from all institutions in the pacific northwest to participates. During the two week course, students also gain hands-on research experiences by working on small research projects in the PI’s lab, as well as in others labs at the Environmental Molecular Sciences Laboratory of PNNL.