Gold as we see it is a non-reactive metal. And it's because it's so inert that it has been used for centuries in jewelry. But at the nanoscale, it's a very different story. Gold clusters containing only a small number of atoms can show very different properties and exhibit chemical reactivity that make them potent catalysts. A team of Georgia Tech has been working on such clusters for several years now. And with the help of other teams around the world, they've unveiled the structures of gold nanoclusters from 13 to 24 atoms. When the cluster reaches 24 atoms, it looks like a capped tubular cigar: pretty surprising!
In fact, now that the various research teams have built all kinds of gold nanoclusters, it's amazing to see the impact of a single atom on the shape of a gold nanocluster.
The teams found that the clusters start out as two-dimensional structures till 13 or 14 atoms in size, changing to three-dimensional hollow cages from about 16 atoms, and developing a face-centered-cubic tetrahedral structure at 20 atoms, resembling the bulk gold crystalline structure. However, at 24 atoms the gold clusters take an unexpected capped tubular cigar shape.
Below is an image showing the "theoretical best-fit electron structure of a gold nanocluster containing 24 atoms" (Credit: Uzi Landman research team, Georgia Tech). And here is a link to similar images.
This research work was published by two different scientific journals. In October 2006, Physical Review B published "Structural evolution of Au nanoclusters: From planar to cage to tubular motifs" (Volume 74, Number 16, Article 165423). Here are the links to the abstract and to the full paper (6 pages).
And in January 2007, ChemPhysChem published "Size-Dependent Evolution of Structures and Chemical Reactivity of Gold Nanosclusters: AuN-, N=15-24" (Volume 8, Issue 1, Pages 157-161, published online on November 28, 2006, and offline in 2007). Here are two links to the abstract and to the full paper (5 pages).
So what will be the next shapes of these gold clusters when they reach 26, 30, or 40 atoms? Time will tell.
Sources: Georgia Institute of Technology news release, January 16, 2007; and various other websites
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