Transition from covalent to metallic behavior in group-14 clusters

We have probed the structures of Pbn cations up to n=32 using ion mobility measurements. These species assume compact near-spherical morphologies for all sizes studied. This behavior is characteristic of clusters of the metallic elements. Silicon, germanium, and tin clusters in the same size range have previously been found to adopt prolate geometries produced by stacking tricapped trigonal prism units. So the transition to `normalʹ metal cluster growth in the group-14 elements occurs between tin and lead, one row lower than the transition from covalent to metallic bonding in the bulk solids under ambient conditions.