Icosahedral clusters point group

The boron hydrides, including the polyhedral boranes, heteroboranes, and their metaUa derivatives, encompass an amazingly diverse area of chemistry. This class contains the most extensive array of structurally characterized cluster compounds known. Included here are many novel clusters possessing idealized molecular geometries ranging over every point group symmetry from identity (C[) to icosahedral (I[). Because boron hydride clusters may be considered in some respects to be progenitorial models of metal clusters, their development has provided a framework for the development of cluster chemistry in... 

The data for the larger clusters (10 to 10" atoms) have been obtained by the T. P. Martin group [18]. From the structure in their mass spectra it is deduced that these large clusters have either icosahedral or fee symmetry. Bulk sodium is bcc, on the other hand, so that a structural phase transition must occur between n = and the bulk. An alternative interpretation would be large sodium clusters near their melting point show the same icosahedral precursor as calculated in Ref. [73] for gold clusters. In this case the ground state could already be bcc-like. 

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