: + HF ·F^-p''K''_a = 3.17This ion pair has been characterized in the crystalline state at very low temperature. Further association has been characterized both in solution and in the solid state.
:HF + F^- log K = 0.6

It is assumed that polymerization occurs as the concentration increases. This assumption is supported by the isolation of a salt of a tetrameric anion and by low-temperature X-ray crystallography.