Compounds of the formula I Kt z+ z[P(R f) n F 5-n X] - I, where R f in each case, independently of one another, denotes a straight-chain or branched perfluoroalkyl group having 2 to 4 C atoms, X denotes OR, Alk denotes a straight-chain or branched alkyl group having 1 to 12 C atoms, R denotes H, a straight-chain or branched alkyl group having 1 to 20 C atoms, which may be partially substituted by Hal, NH 2, NHAlk, NAlk 2, OH, NO 2, CN or SO 3 H, or denotes a straight-chain or branched alkenyl group having 2 to 20 C atoms, which may contain a plurality of double bonds, where one or two carbon atoms of the alkyl or alkenyl group which are not adjacent and not bonded to the heteroatom may be replaced by atoms and/or atom groups selected from the group -O-, -S-, -S -, -SO 2 -, NH, -C -, -O-C - or -C -O- and Kt denotes a stabilised proton, a metal cation or an organic cation, Hal denotes F, Cl, Br or I, z denotes 1, 2, 3 or 4 and n denotes 1, 2 or 3, and/or tautomers or stereoisomers thereof, including mixtures thereof in all ratios, where the organic cation is selected from ammonium cations of the formula, sulfonium cations of the formula or oxonium cations of the formula [N(R 0) 4] + [S(R 0) 3] + or [O(R 0) 3] + where R 0 in each case, independently of one another, denotes - H, where all substituents R 0 in formula cannot simultaneously be H - straight-chain or branched alkyl having 1-20 C atoms, - saturated cycloalkyl having 3-7 C atoms, which may be substituted by straight-chain or branched alkyl groups having 1-6 C atoms, - phenyl, which may be substituted by straight-chain or branched C 1 - to C 6 -alkyl groups, or phosphonium cations of the formula [P(R 2) 4] +, where R 2 in each case, independently of one another, denotes - straight-chain or branched alkyl having 1-20 C atoms, - saturated cycloalkyl having 3-7 C atoms, which may be substituted by straight-chain or branched alkyl groups having 1-6 C atoms, - phenyl, which may be substituted by straight-chain or branched C 1 - to C 6 -alkyl groups, or uronium cations of the formula or thiouronium cations of the formula [C(NR 3 R 4)(OR 5)(NR 6 R 7)] + or [C(NR 3 R 4)(SR 5)(NR 6 R 7)] +, where R 3 to R 7 each, independently of one another, denote - H, - straight-chain or branched alkyl having 1 to 20 C atoms, - saturated cycloalkyl having 3-7 C atoms, which may be substituted by straight-chain or branched alkyl groups having 1-6 C atoms, - phenyl, which may be substituted by straight-chain or branched C 1 - to C 6 -alkyl groups, or guanidinium cations of the formula [C(NR 8 R 9)(NR 10 R 11)(NR 12 R 13)] +, where R 8 to R 13 each, independently of one another, denote - H, - straight-chain or branched alkyl having 1 to 20 C atoms, - saturated cycloalkyl having 3-7 C atoms, which may be substituted by straight-chain or branched alkyl groups having 1-6 C atoms, - phenyl, which may be substituted by straight-chain or branched C 1 - to C 6 -alkyl groups, or heterocyclic cations of the formula [HetN] +, where [HetN] + is a heterocyclic cation selected from the group comprising where the substituents R 1' and R 4' each, independently of one another, denote - straight-chain or branched alkyl having 1-20 C atoms, which may also be fluorinated or perfluorinated, - saturated cycloalkyl having 3-7 C atoms, which may be substituted by straight-chain or branched alkyl groups having 1-6 C atoms, - phenyl, which may be substituted by straight-chain or branched C 1 - to C 6 -alkyl groups, and where the substituents R 2' and R 3' each, independently of one another, denote H or a straight-chain or branched alkyl group having 1-20 C atoms, and where the metal cation is selected from the cations Li +, Na +, K +, Mg 2+, Ca 2+, Ag +, Cu +, Y 3+, Yb 3+, La 3+, Sc 3+, Ce 2+, Pt 2+ or Pd 2+. - H, where all substituents R 0 in formula cannot simultaneously be H - straight-chain or branched alkyl having 1-20 C atoms, - saturated cycloalkyl having 3-7 C atoms, which may be substituted by straight-chain or branched alkyl groups having 1-6 C atoms, - phenyl, which may be substituted by straight-chain or branched C 1 - to C 6 -alkyl groups, or - straight-chain or branched alkyl having 1-20 C atoms, - saturated cycloalkyl having 3-7 C atoms, which may be substituted by straight-chain or branched alkyl groups having 1-6 C atoms, - phenyl, which may be substituted by straight-chain or branched C 1 - to C 6 -alkyl groups, - H, - straight-chain or branched alkyl having 1 to 20 C atoms, - saturated cycloalkyl having 3-7 C atoms, which may be substituted by straight-chain or branched alkyl groups having 1-6 C atoms, - phenyl, which may be substituted by straight-chain or branched C 1 - to C 6 -alkyl groups, - H, - straight-chain or branched alkyl having 1 to 20 C atoms, - saturated cycloalkyl having 3-7 C atoms, which may be substituted by straight-chain or branched alkyl groups having 1-6 C atoms, - phenyl, which may be substituted by straight-chain or branched C 1 - to C 6 -alkyl groups, - straight-chain or branched alkyl having 1-20 C atoms, which may also be fluorinated or perfluorinated, - saturated cycloalkyl having 3-7 C atoms, which may be substituted by straight-chain or branched alkyl groups having 1-6 C atoms, - phenyl, which may be substituted by straight-chain or branched C 1 - to C 6 -alkyl groups,