title: Arsenic trifluoride
text: # Arsenic trifluoride
  
  Arsenic trifluoride is a chemical compound of arsenic and fluorine with the chemical formula $AsF_3.$ 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 + $As_2O_3$ → $2AsF_3$ + $3H_2O$
  
  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°.
  
  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 $SbF_3.$
  
  Salts containing $AsF_4^−$ anion can be prepared for example $CsAsF_4.$ the potassium salt $KAs_2F_7$ prepared from KF and $AsF_3$ contains $AsF_4^−$ and $AsF_3$ molecules with evidence of interaction between the $AsF_3$ molecule and the anion.
  
  $AsF_3$ reacts with $SbF_5.$ The product obtained could be described as the ionic compound $AsF_2^+$ $SbF_6^−.$ However, the authors conclude the formed product cannot be viewed only as an ionic compound nor entirely as the neutral adduct $AsF_3SbF_5.$ The crystal structure displays characteristics of both an ionic pair, and a neutral adduct, taking the middle ground in between both models.
  
  