A new crystal modification of diammonium hydrogen phosphate, (NH(4))(2)(HPO(4))

The addition of hexa­fluorido­phosphate salts (ammonium, silver, thallium or potassium) is usually used to precipitate complex cations from aqueous solutions. It has long been known that PF(6) (−) is sensitive towards hydrolysis under acidic conditions [Gebala & Jones (1969 ▶). J. Inorg. Nucl. Chem. 31, 771–776; Plakhotnyk et al. (2005 ▶). J. Fluorine Chem. 126, 27–31]. During the course of our investigation into coinage metal complexes of diphosphine ligands, we used ammonium hexa­fluorido­phosphate in order to crystallize [Ag(diphos­phine)(2)]PF(6) complexes. From these solutions we always obtained needle-like crystals which turned out to be the title compound, 2NH(4) (+)·HPO(4) (2−). It was received as the hydrolysis product of NH(4)PF(6). The crystals are a new modification of diammonium hydrogen phosphate. In contrast to the previously published polymorph [Khan et al. (1972 ▶). Acta Cryst. B28, 2065–2069], Z′ of the title compound is 2. In the new modification of the title compound, there are eight mol­ecules of (NH(4))(2)(HPO(4)) in the unit cell. The structure consists of PO(3)OH and NH(4) tetra­hedra, held together by O—H⋯O and N—H⋯O hydrogen bonds.