Hexafluorophosphate

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Hexafluorophosphate is an anion with chemical formula of [PF₆]⁻. As a non-coordinating anion, it is a poor nucleophile.

Halide anions are easily replaced with [PF₆]⁻ with silver hexafluorophosphate. The precipitation of insoluble silver halide helps drive this reaction to completion. Some room temperature ionic liquids such as bmimPF₆ use [PF₆]⁻ as a counterion.

Also, many imidazolium and formamidinium hexafluorophosphate salts are insoluble in water. The addition of ammonium hexafluorophosphate (NH₄PF₆) to an aqueous solution of the formamdinium/imidazolium salt results in a precipitate of the formamidinium/imidazolium hexafluorophosphate salt which can be gathered by filtration. This method can have advantages over the silver hexafluorophosphate method mentioned above in terms of expense and in systems where contamination with metal ions is strongly discouraged.

[edit] See also

• Non-coordinating anion
• Hexafluorophosphoric acid