X–ray Single Crystal Structure and Raman Spectrum of Ammonium Hexafluoroarsenate

The structure of ammonium hexafluoroarsenate, NH 4 AsF 6 , has been determined by X‐ray diffraction using a single crystal grown from saturated solution in anhydrous HF. NH 4 AsF 6 crystallizes rhombohedral with the KOsF 6 structure type, with a = 7.459(3) Å, c = 7.543(3) Å (at 200 K), Z = 3, space group $R{\bar 3}$ (No. 148). No phase transition was observed in the 100 K–296 K temperature range. The structure is dominated by regular AsF 6 octahedra and disordered NH 4 + cations. Raman spectrum of a single crystal of NH 4 AsF 6 shows the bands at 372 cm −1 , 572 cm −1 , 687 cm −1 (AsF 6 − ) and at 3240 cm −1 and 3360 cm −1 (NH 4 + ).