The acid strength of the HClO4/n(AlF3) and HClO4/n(SbF5) (n=1-3) Lewis-Bronsted superacids containing the excess of the Lewis acid component

The acidic strength of selected Lewis-Bronsted superacids consisting of HClO4 Bronsted acid and containing the excess of either AlF3 or SbF5 Lewis acid component is evaluated on the basis of theoretical calculations employing ab initio methods. The Gibbs free energies of deprotonation processes for HClO4/n(AlF3) and HClO4/n(SbF5) (n = 1-3) are found to depend on the number (n) of AlF3 or SbF5 molecules (playing Lewis acid role) surrounding the HClO4 system. The successive attachment of either AlF3 or SbF5 molecules to HClO4 gradually increases the acidity strength of the resulting superacid which leads to the saturation achieved for 2-3 AlF3 molecules interacting with Bronsted acid. The preference of formation of the Lewis acid aggregates is observed during the analysis of the most stable HClO4/n(AlF3) and HClO4/n(SbF5) isomeric structures. The mixing ratios of HClO4 and either AlF3 or SbF5 compounds that should likely maximize their resulting acid strength are proposed and discussed.