A hollow tetrahedral cage of hexadecagold dianion provides a robust backbone for a tuneable sub-nanometer oxidation and reduction agent via endohedral doping

We show, via density functional theory calculations, that dianionic Au-16(2-) cluster has a stable, hollow, T-d symmetric cage structure, stabilized by 18 delocalized valence electrons. The cage maintains its robust geometry, with a minor Jahn-Teller deformation, over several charge states (q = -1,0,+ 1), forming spin doublet, triplet and quadruplet states according to the Hund's rules. Endohedral doping of the Au-16 cage by Al or Si yields a geometrically robust, tuneable oxidation and reduction agent. Si@ Au16 is a magic species with 20 delocalized electrons. We calculate a significant binding energy for the anionic Si@ Au-16/O-2(-) complex and show that the adsorbed O-2 is activated to a superoxo-species, a result which is at variance with the experimentally well-documented inertness of Au-16(-) anion towards oxygen uptake.