Ammonium bifluoride

Ammonium hydrogen fluoride, NH₄HF₂, is a chemical compound which can be produced from ammonia and hydrogen fluoride. It is the major constituent in glass-etching fluid (though sometimes replaced by potassium hydrogen fluoride), etching occurring due to the fluorination of silicon:

SiO_{2 (s)} + 4[NH₄][HF₂] _(aq) → SiF_{4 (l)} + 4[NH₄]F _(aq) + 2H₂O _(l)

The structure of [NH₄][HF₂] contains tetrahedral [NH₄]⁺ cations and linear [HF₂]⁻ anions. Each cation is surrounded by four fluorine atoms in a tetrahedron, with hydrogen - fluorine hydrogen bonds present between the hydrogen atoms of the ammonium ion and the fluorine atoms.

References

1. A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, UK, 1984.

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