How are small endohedral silicon clusters stabilized?

Clusters in the (Be, B, C)@Si-n((0,1,2+)) (n = 6-10) series, isoelectronic to Si-n(2-), present multiple symmetric structures, including rings, cages and open structures, which the doping atom stabilizes using contrasting bonding mechanisms. The most striking feature of these clusters is the absence of electron transfer (for Be) or even the inversion (for B and C) in comparison to classic endohedral metallofullerenes (e.g. from the outer frameworks towards the enclosed atom). The relatively small cavity of the highly symmetric Si-8 cubic cage benefits more strongly from the encapsulation of a boron atom than from the insertion of a too large beryllium atom. Overall, the maximization of multicenter-type bonding, as visualized by the Localized Orbital Locator (LOL), is the key to the stabilization of the small Sin cages. Boron offers the best balance between size, electronegativity and delocalized bonding pattern when compared to beryllium and carbon.