The acid strength of the datively bound X -> AlF3 complexes (X = HF, HCl, H2S, AsH3, PH3, NF2H, NFH2, NH3, and H2O) is evaluated on the basis of theoretical calculations employing ab initio methods. Significant enhancement of the X acidity upon the formation of X/AlF3 compounds is predicted. It is demonstrated that even the non-acidic molecules X (e. g., H2O, NH3) combined with AlF3 are expected to form the X -> AlF3 complexes characterized by the acid strength comparable or larger than that of H2SO4. (C) 2018 Elsevier B.V. All rights reserved.