ABSTRACT
This chapter examines experimental data on clusters of different metals and valency, before looking at how these complexities affect the idea of metal clusters as being ‘superatomic’. Monovalent metals – in particular, those that appear in the first group of the periodic table, with a single valence s-electron per atom – have been very well studied. Indeed, sodium clusters are often considered the prototypical example of electronic shell structure in clusters, due to the early and influential work of Knight and others, which first demonstrated the size-dependence of cluster abundance in mass spectra. With two valence electrons per atom, one might worry that the divalent metals would exhibit less clear electronic shell structure. The simplest trivalent metals are those with electronic configuration s2p1, which occur in group 13, and include aluminium, gallium, and indium. Of these, the lightest congener has the most simple metallic behaviour, and for this reason, aluminium clusters have been studied the most extensively.
