Press Release

Angew. Chem. Int. Ed. 2004, 43 (20), 2678—2681

No. 20/2004

Thought Experiment with Golden Balls

Computer calculations predict an unusual gold cluster: a fullerene made of 32 gold atoms

Golden balls are not just for spoiled princesses—chemists like to play with them too. Particularly in theory: computer calculations at the University of Helsinki, Finland, now predict the existence of a surprising cluster of 32 gold atoms, which are bound into a tiny, cage-like sphere.

Initially, the proposed molecule (Au₃₂) was considered to be just another, somewhat uninteresting gold cluster. However, Mikael Johansson, Dage Sundholm, and Juha Vaara carried out further calculations and determined that, aside from the usual space-filling "clump", there seems to be a second stable Au₃₂ isomer. This isomer is a hollow sphere with a diameter a little under one nanometer, and would be the first fullerene made of gold atoms. The term fullerene comes from a form of carbon discovered in 1985: molecules consisting of 60 carbon atoms bound into a spherical cage containing 15 pentagons and 20 hexagons—built just like a soccer ball. This structure reminded the discoverers of the giant domes made of hexagons and pentagons developed by architect Buckminster Fuller for the 1967 Expo, and they thus named the molecules after him. Now back to the spheres of gold. Their predicted structure can be derived from that of the C₆₀ fullerene by swapping the vertices and planes of the "soccer ball". Just imagine a gold atom at the center of each "leather patch". This results in a ball of gold with triangular surfaces, in which each gold atom is bound to five or six neighbors.

Johansson and his co-workers explain that without effects arising from Einstein's famous theory of relativity, Au₃₂ would not be stable, and they predict unusual electronic properties for these golden fullerenes. The outer electrons of the gold atoms should be able to move almost freely over the entire cluster—to a considerably greater extent than is the case in carbon fullerenes. The mobile electrons shield the interior cavity from external magnetic fields, like a tiny magnetic Faraday cage. The magnetic shielding inside the gold spheres is predicted to be of record-breaking magnitude.

The researchers imagine a possible application for the gold spheres—should it ever prove to be possible to make them—in the area of pharmaceuticals. The required agent would be enclosed within the cavity, special biomolecules, or even entire viruses, could be attached to the outside (which works very well with gold clusters) to lead the transporter to its target.