Arsenic trifluoride explained

Arsenic trifluoride is a chemical compound of arsenic and fluorine with the chemical formula AsF₃. It is a colorless liquid which reacts readily with water.

Preparation and properties

It can be prepared by reacting hydrogen fluoride, HF, with arsenic trioxide:

6HF + As₂O₃ → 2AsF₃ + 3H₂O

It has a pyramidal molecular structure in the gas phase which is also present in the solid. In the gas phase the As-F bond length is 170.6 pm and the F-As-F bond angle 96.2°.^[1]

Arsenic trifluoride is used as a fluorinating agent for the conversion of non-metal chlorides to fluorides, in this respect it is less reactive than SbF₃.

Salts containing AsF₄^− anion can be prepared for example CsAsF₄.^[2] the potassium salt KAs₂F₇ prepared from KF and AsF₃ contains AsF₄^− and AsF₃ molecules with evidence of interaction between the AsF₃ molecule and the anion.^[3]

AsF₃ reacts with SbF₅. The product obtained could be described as the ionic compound AsF₂⁺ SbF₆^−. However, the authors conclude the formed product cannot be viewed only as an ionic compound nor entirely as the neutral adduct AsF₃SbF₅. The crystal structure displays characteristics of both an ionic pair, and a neutral adduct, taking the middle ground in between both models. ^[4]

Notes and References

1. Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications
2. New alkali metal and tetramethylammonium tetrafluoroarsenates(III), their vibrational spectra and crystal structure of caesium tetrafluoroarsenate(III) Klampfer P, Benkič P, Lesar A, Volavšek B, Ponikvar M, Jesih A., Collect. Czech. Chem. Commun. 2004, 69, 339-350
3. Alkali-metal heptafluorodiarsenates(III): their preparation and the crystal structure of the potassium salt, Edwards A.J., Patel S.N., J. Chem. Soc., Dalton Trans., 1980, 1630-1632,
4. Fluoride crystal structures. Part XV. Arsenic trifluoride–antimony pentafluoride, Edwards A. J., Sills R. J. C. J. Chem. Soc. A, 1971, 942 - 945,