Credit: © 2009 Wiley

Fullerenes, formed by hexagonal and pentagonal carbon rings, have many potential isomers and the most stable ones do not have adjacent pentagons. For the non-aromatic C80, the icosahedral form is the least energetically favoured isomer, and although it has not yet been isolated, it has been indirectly observed as a host structure. Fullerene-like inorganic structures have also recently been built around guest molecules, but these have so far remained incomplete shells.

Using a carborane of suitable size and pseudo-five-fold symmetry as a template, Manfred Scheer at the University of Regensburg and colleagues have now prepared1 an 80-atom icosahedral inorganic structure that resembles a fullerene. The fullerene pentagons are defined by the phosphorus atoms in a pentaphosphorus ligand, which forms half of a ferrocene-like structure (Cp*FeP5). These phosphorus atoms take four of the positions in the fullerene hexagons, with the other two positions occupied by copper atoms from copper chloride.

With the chloride ions, iron centres and cyclopentadienyl ligands surrounding this icosahedral core, the complete molecule is about twice as large as a C80 fullerene. Solid-state NMR and infrared spectroscopies revealed electronic interactions between the host and the encapsulated carborane. The structure of the inorganic shell is controlled by that of the guest, which offers the promise of the preparation of other such structures.