University of Bielefeld, Germany

A chemist finds beauty in molecules that resemble an early model of the Solar System.

Since Plato’s time, people have been fascinated by the beauty of highly symmetrical objects. The symmetry of the C60 buckyball surely contributed to scientists’ tremendous interest in this spherical molecule. Indeed, I was convinced that the discovery of C60 would induce a rush among chemists to search for other symmetrical structures.

That rush may not have happened, but scientists have still turned up some surprising highly symmetrical structures. A recent report from researchers at Xiamen University in China (X.-J. Kong et al. J. Am. Chem. Soc. 129, 7016–7017; 2007) describes a cluster in which beauty cages beauty; it consists of an icosidodecahedron of nickel ions, having 20 triangular faces and 12 pentagonal faces, inside of which sits a dodecahedron of lanthanum ions.

The team describes the magnificent structure as ‘Keplerate’, a term that I and my colleagues first used around ten years ago to describe structures that contain Platonic and Archimedean solids (regular polyhedra, and polyhedra with two types of face, respectively) one inside another, like Russian dolls. It honours Johannes Kepler, who in the sixteenth century developed a model of the cosmos in which “the radii of the successive planetary orbits are proportional to the radii of spheres that are successively circumscribed around and inscribed within the five Platonic solids”.

Another recent report found these same shapes — the icosidodecahedron and dodecahedron — in Keplerate-type arrangements in quasicrystals (H. Takakura et al. Nature Mater. 6, 58–63; 2007). Such crystals are still poorly understood. I hope that future work will correlate these materials’ properties with their beauty.