The invention relates to boron-containing acids of the general formula (I) [B(RF)4-x-y(CN)xFy]−H+ (I), where x=0, 1, 2, 3 or 4, y=0, 1, 2 or 3 x+y≦4, and in which the ligands RF may be identical or different and RF stands for a perfluorinated or partially fluorinated C1-12-alkyl group and where the CN group is bonded to the B atom via the C atom, and complexes thereof with a solvent, to salts comprising a cation and the anion of a selection of the acids according to the invention, and to processes for the preparation of the salts.