Theoretical Studies of Monosubstituted and Higher Phenyl-Substituted Octahydrosilsesquioxanes

The electronic and structural properties of molecules (octahydrosilsesquioxane, H 8 Si 8 O 12 ), the monosubstituted and higher phenyl-substituted octahydrosilsesquioxanes (PhH 7 Si 8 O 12, Ph 2 H 6 Si 8 O 12, (Ph-Ph)H 7 Si 8 O 12, and Ph 8 Si 8 O 12 ), and crystals (H 8 Si 8 O 12 and octa(phenylsilsesquioxane) acetone solvate (C 48 H 40 O 12 Si 8 ·C 3 H 6 O)) have been studied using plane-wave (PW), pseudo-potential (PP), and density functional theory and the generalized gradient approximation (DFT-GGA) methods. The results show that the orbitals near the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) (inclusive) for the phenyl-substituted polyhedral oligomeric silsesquioxane clusters and crystal are localized on the phenyl functional groups, whereas for both isolated molecular and crystalline H 8 Si 8 O 12, the HOMO is that with the lone pair on the O atoms.