An M₁₈L₂₄ stellated cuboctahedron through post-stellation of an M₁₂L₂₄ core.

Platonic and Archimedean polyhedra, well-known to mathematicians, have been recently constructed by chemists at a molecular scale by defining the vertices and the edges with metal ions (M) and organic ligands (L), respectively. Here, we report the first synthesis of a concave-surface 'stellated polyhedron', constructed by extending the faces of its precursor polyhedron until they intersect, forming additional nodes. Our approach involves the formation of an M(12)L(24) cuboctahedron core, the linkers of which each bear a pendant ligand site that is subsequently able to bind an additional metal centre to form the stellated M(18)L(24) cuboctahedron. During this post-stellation process, the square faces of the M(12)L(24) core are closed by coordination of the pendant moieties to the additional metal centres, but they are re-opened on removing these metals ions from the vertices. This behaviour is reminiscent of the analogous metal-triggered gate opening-closing switches found in spherical virus capsids.