Does the protonation of superhalogen anions always lead to superacids?

Highlights: • Systematic search for novel Lewis/Brønsted superacids is presented. • Small deprotonation energies for HMX_k+1 (M = Be, Mg, Ca, B, Al, Ga; X = F, Cl) are predicted. • The route of forming superacids via superhalogen anions protonation is discussed. - Abstract: The results of a thorough theoretical search for novel superacids are presented. The thermodynamic stability and the expected acidity strength of Lewis/Brønsted superacids (considered here as consisting of superhalogen anions and the additional protons) are examined for the systems containing selected alkali metals, alkali earth metals, metalloids and non-metals. The acidities of such designed systems involving alkali earth metals (Be, Mg, Ca) and 13th group elements (B, Al, Ga) evaluated by the estimation of Gibbs free energies of deprotonation reactions were found significant whereas the analogous species utilizing remaining elements as central atoms are not expected to exhibit superacidic properties.