Structures, Stabilities and Electronic Properties of Endo- and Exohedral Dodecahedral Silsesquioxane (T 12 -POSS) Nanosized Complexes with Atomic and Ionic Species

The structures of endohedral complexes of the polyhedral oligomeric silsesquioxane (POSS) cage molecule (HSiO 3/2 ) 12 , with both D 2d and D 6h starting cage symmetries, containing the atomic or ionic species: Li 0 , Li + , Li − , Na 0 , Na + , Na − , K 0 , K + , K − , F − , Cl − , Br − , He, Ne, Ar were optimized by density functional theory using B3LYP and the 6-311G(d,p) and 6-311 ++G(2d,2p) basis sets. The exohedral Li + , Na + , K + , K − , F − , Cl − , Br − , He, Ne, Ar complexes, were also optimized. The properties of these complexes depend on the nature of the species encapsulated in, or bound to, the (HSiO 3/2 ) 12 cage. Noble gas (He, Ne and Ar) encapsulation in (HSiO 3/2 ) 12 has almost no effect on the cage geometry. Alkali metal cation encapsulation, in contrast, exhibits attractive interactions with cage oxygen atoms, leading to cage shrinkage. Halide ion encapsulation expands the cage. The endohedral X@(HSiO 3/2 ) 12 (X = Li + , Na + , K + , F − , Cl − , Br − , He and Ne) complexes form exothermically from the isolated species. The very low ionization potentials of endohedral Li 0 , Na 0 , K 0 complexes suggest that they behave like “superalkalis”. Several endohedral complexes with small guests appear to be viable synthetic targets. The D 2d symmetry of the empty cage was the minimum energy structure in accord with experiment. An exohedral fluoride penetrates the D 6h cage to form the endohedral complex without a barrier.