Elusive icosahedral symmetry

Credit: © 2009 WILEY

Fullerenes have many potential isomers and the most stable ones do not have adjacent pentagons. For 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 as a template, Manfred Scheer at the University of Regensburg and colleagues have now prepared an 80-atom icosahedral inorganic structure that resembles the unstable C₈₀ cage (pictured; Angew. Chem. Int. Ed. doi:10.1002/anie.200900342; 2009). The fullerene pentagons are defined by the phosphorus atoms (purple) 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 (blue).

With the chloride ions (light green), iron centres (dark green) and cyclopentadienyl ligands (grey) surrounding this icosahedral core (orange), the complete molecule is about twice as large as a C₈₀ fullerene.