The present invention relates to acids of the general formula [I], [R.sub.yPF.sub.6-y].sup.-H.sup.+ [I], where y=1, 2 or 3, and in which the ligands R may be identical or different and R is a perfluorinated C.sub.1-8-alkyl or aryl group or R is a partially fluorinated C.sub.1-8-alkyl or aryl group, in which some of the F or H may have been substituted by chlorine. The present invention furthermore relates to a process for the preparation of the acids according to the invention, to salts comprising a cation and the anion of the acid according to the invention, and to a process for the preparation of the salts. The invention furthermore relates to the use of the acids and salts according to the invention.