Structure of ammonium difluorophosphate

Abstract

Crystals of ammonium difluorophosphate are orthorhombic, with a= 8·13, b= 6·43, c= 7·86 Å, and Z= 4, in space group Pnma. The structure was determined with data from a Mo-K_α scintillation counter by comparison with that for the potassium salt, and refined by least-squares methods, the hydrogen atoms of the ammonium ion being located from difference syntheses. The final R is 0·065 for 387 observed reflexions.

The structure is similar to that of the potassium, rubidium, and caesium difluorophosphates, but with some interesting differences as a result of hydrogen bonding. There are two N–H ⋯ O hydrogen bonds of 2·86 Å, and possibly two bifurcated hydrogen bonds N–H[graphic omitted] with N ⋯ O, 3·18 and 3·07 Å. The fluorine atoms are not involved in the hydrogen bonding. The difluorophosphate anion has dimensions: P–O 1·457(σ 0·008), P–F 1·541 (σ 0·007)Å; F–P–F 98·6(σ 0·5), and O–P–O 118·7(σ 0·5)°, after correction for rotational oscillation effects. These dimensions differ slightly from those of the potassium salt, probably as a result of the hydrogen bonding.