Structures and energetics of organosilanes in the gaseous phase: a computational study

The gas-phase conformations and stabilities of neutral and anionic organosilanes with structure ((HO)(3)Si-organic linker-Si(OH)(3)), where the organic linker is benzene, ethene, or ethane, were studied using density functional theory. The calculations were performed at the B3LYP/6-311+G(2d, 2p) level of theory and show that the cis-bis(trihydroxysilyl)-ethene and gauche-bis(trihydroxysilyl)-ethane species are more stable than their trans and anti-counterparts, respectively. The local geometries of the organic and inorganic fragments in these hybrid compounds are similar to those found in the case of pure silicate compounds or in the parent organic molecules. The calculated enthalpies of deprotonation for these species suggest an acid-base behavior for 1,4-bis(trihydroxysilyl)benzene species that is intermediate of those calculated for the silicate monomer and for the silicate dimer, while for the cis-bis(trihydroxysilyl)-ethene and gauche-bis(trihydroxysilyl)-ethane, an acid-base behavior that is intermediate of those calculated for small and for large pure silicates. It was also found that the calculated charges of the Si atoms are almost independent of the type of carbon atom to which they are bonded and that the charge localized on the organic moiety is always negative, even for the neutral species. This information is valuable for the development of molecular force fields for simulating systems involving organosilicates.