Supramolecular chemistry: Unexplored territory for self-assembly.

Abstract

Cage-like structures can self-assemble from suitable metal ions and organic linkers, but the size of the assemblies was limited. The surprise discovery of a new series of cages opens up fresh horizons for self-assembly. See Letter p.563 Rational control of self-assembly remains a formidable challenge. It is thought to become increasingly difficult, even impossible, as the number of individual constituents increases. For example, no one has ever been able to design discrete molecules that self-assemble from more than 100 components. When exploring design principles appropriate for dealing with the self-assembly of large numbers of components, Daishi Fujita et al. discovered a spherical structure with a topology not previously reported at the molecular level. Using mathematics describing this class of structures, the authors then targeted and characterized an even larger structure containing 48 palladium ions coordinated by 96 bent organic ligands—by far the largest number of components observed in a self-assembled molecular structure to date. The structure has the topology of a tetravalent Goldberg polyhedron, a type of convex polyhedron made from squares and triangles—a twist on the original Goldberg polyhedra that were first described by Michael Goldberg in 1937.