Credit: © 2007 Wiley

The physical and chemical characteristics of small gold clusters are largely determined by their structure, which, in turn, depends on the number of atoms they contain. Those comprising 12 atoms or fewer adopt planar structures, whereas larger numbers congregate into three-dimensional assemblies. Detailed knowledge of cluster geometries, as well as the ability to tailor them, may have significant implications for the application of gold nanoparticles in chemical catalysis.

A team led by Xiao-Cheng Zeng from the University of Nebraska and Lai-Sheng Wang at the Pacific Northwest National Laboratory in the US have shown that gold cages comprising either 16 or 17 atoms can be doped with a copper atom in their hollow interiors1. These bimetallic clusters were observed in photoelectron spectroscopy experiments, and theoretical studies confirm that the most likely atomic structure is one with the copper atom on the inside. In a related study, researchers in Germany from Universität Freiburg, Universität Karlsruhe and the Institut für Nanotechnologie in Karlsruhe led by Detlef Schooss have identified a 34-atom gold cluster with a chiral (non-superimposable mirror-image) structure2. Both theory and experiment suggest a helical arrangement of atoms, similar to that observed in some suspended gold nanowires.

These studies not only increase our fundamental understanding of nanosized gold clusters, but could also have practical consequences. Fine-tuning the properties of gold nanoparticles by doping, and the development of chiral assemblies could have significant implications for catalytic processes, including asymmetric reactions in which one mirror-image product is favoured over the other.