Endohedral and Exohedral Complexes of T8-Polyhedral Oligomeric Silsesquioxane (POSS) with Transition Metal Atoms and Ions

The equilibrium geometries of the exohedral and endohedral complexes of the polyhedral oligomeric silsesquioxane (POSS) cage (HSiO3/2)8 containing the transition metal atoms or ions Sc0,+, Cr0,+, Fe0,+, Co0,+, Ni0,+, Cu0,+, Zn0,+, Mo0,+, W0,+, Ru0,+, Os0,+ have been investigated at the B3LYP/LanL2DZ levels. All these species form endohedral complexes with the T8-POSS cage except Sc0,+, Mo0, and W0,+. The Mo0 and W0,+ species as well as Cr0,+, Fe0,+, Co0,+, Ni0,+, Cu+, Zn+, Ru0,+, Os0 form stable exohedral complexes. Geometries, electronic properties and ionization potentials were computed. The Si−O and Si−H bond lengths in the cationic endohedral complexes are shorter than in the corresponding complexes of neutral transition metal atoms. The zero-point corrected inclusion energies of the endohedral species X@(SiHO3/2)8 (X = Fe+, Co+, Ni+, Cu+, Os+) are all negative, suggesting that these complexes are more stable than their isolated components. All exohedral complexes have energies that are lower than their corresponding endohedral analogs. Transition metal atom encapsulation raised the HOMO and lowered the LUMO energies, reducing the HOMO−LUMO gaps of every complex compared to that of the pure cage. The HOMO−LUMO gap of the empty cage is 8.1 eV while the endohedral complexes exhibit gaps between 1.2 and 4.96 eV. Insertion of Cr, Fe, Co, Ni, Cu, or Zn into the POSS cage is more favorable in water than in the gas phase. However, insertion of Co+, Ni+, Cu+, or Zn+ into the POSS cage is less favorable in water than in the gas phase. Overall, both the neutral and ionic endohedral transition metal complexes, X@(SiHO3/2)10, (X = Cr0,+, Fe0,+, Co0,+, Ni0,+, Cu0,+, Zn0,+, Ru0,+, Os0,+) appear to be viable synthetic targets.