PNNL

Abstract

One of the major objectives of cluster science is to discover stable atomic clusters, which may be used as building blocks for clusterassembled materials. The discovery and bulk synthesis of the fullerenes1,2 have sprouted new research disciplines in chemistry and nanoscience and precipitated intense interests 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. Recently, a 12-atom Sn cluster (Sn12 2-), named stannaspherene, was discovered serendipitously to be a highly stable icosahedral cage during gas-phase photoelectron spectroscopic experiment.3 Stannaspherene has a diameter of 6.1 Å, which is large enough to entrap a foreign atom and suggests possibilities to create endohedral stannaspherenes analogous to the endohedral fullerenes. Indeed, we have shown recently that stannaspherene can trap all transition-metal atoms, as well as f-block elements, giving rise to a whole new class of endohedral clusters.4 The endohedral stannaspherenes may even rival the fullerenes, which cannot trap transition-metal atoms other than the rare-earth and f-block atoms,5 and be used as building blocks for novel cluster-assembled materials with tunable magnetic and electronic properties. We have found further that Pb12 2- (plumbaspherene)6 is also a highly stable icosahedral cage cluster in the gas phase with a diameter (6.3 Å) slightly larger than that of stannaspherene and should also be able to trap a variety of foreign atoms. Indeed, an endohedral AlPb12 + cluster has been observed as a stable gaseous species,7 which can be formulated as Al3+@Pb12 2-. Very interestingly, Eichhorn and co-workers have synthesized a series of endohedral cage compounds, M@Pb12 2- (M ) Ni, Pd, Pt), through chemical reactions of K4Pb9 and ML4 (M ) Pt, Pd, L ) PPh3) in ethylenediamine (ED) and crystallized them as (2,2,2-crypt)K+ salts.