Alkali-metal heptafluorodiarsenates(III): their preparation and the crystal structure of the potassium salt

Abstract

Heptafluorodiarsenates(III), MAs₂F₇(M = K, Rb, or Cs), have been prepared by the dissolution of the alkalimetal fluoride in arsenic trifluoride and crystallisation from the solvent at room temperatue. Loss of arsenic trifluoride and formation of the tetrafluoroarsenate(III) occurs on heating to 100 °C under vacuum. The structure of the potassium salt has been determined by the heavy-atom method from 799 reflections, and refined by full-matrix least-squares methods to R 0.070. Crystals are monoclinic, space group P2₁/c, with a= 10.99(1), b= 7.39(1), c= 8.75(1)Å, and β= 110.8(2)°. The structure consists of potassium ions, tetrafluoroarsenate(III) ions, and arsenic trifluoride molecules, with some interaction between anions and molecules to form a complex chain arrangement.