A new crystal modification of diammonium hydrogen phosphate, (NH 4)2(HPO4)

Abstract

The addition of hexa-fluorido-phosphate salts (ammonium, silver, thallium or potassium) is usually used to precipitate complex cations from aqueous solutions. It has long been known that PF6- 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 hexa-fluorido-phosphate in order to crystallize [Ag(diphos-phine)2]PF6 complexes. From these solutions we always obtained needle-like crystals which turned out to be the title compound, 2NH4+·HPO42-. It was received as the hydrolysis product of NH4PF6. 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 mol-ecules of (NH4)2(HPO4) in the unit cell. The structure consists of PO3OH and NH4 tetra-hedra, held together by O - H⋯O and N - H⋯O hydrogen bonds.