Self-Assembled M 24 L 48 Polyhedra and Their Sharp Structural Switch upon Subtle Ligand Variation

Viruses form highly symmetrical coat structures, capsids, through the assembly of multiple lower-symmetry protein precursors. Recently, chemists have sought to emulate this process on a smaller scale, relying on the assembly of organic molecular struts and metal ions, rather than proteins. Sun et al. (p. 1144 , published online 29 April; see the Perspective by Stefankiewicz and Sanders ) now demonstrate that a mixture of palladium ions and V-shaped bridging ligands can self-assemble into a hollow, nearly spherical polyhedron with 24 vertices and a central diameter of 4 nanometers. The assembly process was highly sensitive to the ligand angle; a subtle average decrease generated instead a smaller 12-vertex product. A slight change in ligand geometry determines whether a 12- or 24-vertex polyhedron will form. Self-assembly is a powerful technique for the bottom-up construction of discrete, well-defined nanoscale structures. Large multicomponent systems (with more than 50 components) offer mechanistic insights into biological assembly but present daunting synthetic challenges. Here we report the self-assembly of giant M 24 L 48 coordination spheres from 24 palladium ions (M) and 48 curved bridging ligands (L). The structure of this multicomponent system is highly sensitive to the geometry of the bent ligands. Even a slight change in the ligand bend angle critically switches the final structure observed across the entire ensemble of building blocks between M 24 L 48 and M 12 L 24 coordination spheres. The amplification of this small initial difference into an incommensurable difference in the resultant structures is a key mark of emergent behavior.