Formation and decomposition of hydroxysiliconates in the gas phase

This work describes studies of the formation, structure, and dissociation of hydroxy-siliconate ions. Hydroxide adduct ions can be formed in the reaction of halogenated and oxygenated silanes with hydrated hydroxide, OH-(H2O)(n). Experiments with mass-selected ions indicate that at least two water solvent molecules are required in order to form a hydroxide adduct of fluorotrimethylsilane. Collision-induced dissociation, ion formation, and ion reactivity studies suggest pentavalent siliconate structures for hydroxide adducts of halogenated silanes but solvated siloxides for the oxygenated species. Electronic structure calculations find three types of hydroxide adduct ions, including the hydroxysiliconate and two forms of solvated siloxides. The relative energies of the ions and the barriers that separate them depend on the substituents on the silanes. Empirical modeling of the cross sections for collision-induced dissociation indicates that loss of HF from fluorinated hydroxide adducts occurs through a loose transition state, whereas loss of alkane/arene occurs through a tight transition state at low activation energies.