Sighting The Golden Cage

Clusters of 16, 17, or 18 gold atoms produced by laser vaporization of gold form hollow cage structures akin to fullerene molecules, new theoretical and experimental studies suggest (Proc. Natl. Acad. Sci. USA, to be published online this week). These anionic structures are the first experimentally identified hollow cage structures made entirely of metal atoms, according to Lai-Sheng Wang of Washington State University, Richland, and Pacific Northwest National Laboratory and Xiao Cheng Zeng of the University of Nebraska, who jointly led the effort to identify the structures.

Previous theoretical predictions suggested that a hollow cage structure of 32 gold atoms would be highly stable, but experimentally, Wang found that Au₃₂^??? exists as a compact clump. Gold anion clusters of 13 atoms or fewer tend to be planar, while clusters of 20 atoms take on a pyramidal structure. Wang and Zeng???s group therefore speculated that gold clusters with 14 to 19 atoms would be the most likely to assume a hollow cage structure.

Using photoelectron spectroscopy and theoretical calculations, they found that all but one of the lowest energy isomers of Au₁₆^???, Au₁₇^???, and Au₁₈^??? are hollow cages with an empty interior roughly 6 Å across. This space is large enough to imprison a guest atom—something the group hopes to do in the future.