Hydrogen bonding in the crystalline state. Crystal structure and twinning of NaNH₄HPO₄.4H₂O (stercorite)

Abstract

Sodium ammonium hydrogen phosphate tetrahydrate (NaNH4HPO4.4H20, stercorite) crystallizes in the space group P1 with a= 10.636 (2), b=6.9187 (14), c=6.4359 (13) ,&, c¢=90.46 (3), fl=97.87 (3), y= 109.20 (3) °, Z= 2. The structure was solved by direct methods and refined anisotropically (R = 0.087) with 1582 reflexions collected from a twinned crystal on a diffractometer (Cu K~t radiation). Corrections for absorption and anomalous scattering were applied. C2/m pseudo-symmetry, which accounts for easy {010} twinning, is obeyed by nearly the whole structure with the exception of the two positions occupied by a water molecule and NH + respectively. A (100) layered structure is built up by [010] rows of Na octahedra sandwiched between P tetrahedra; NH + and its pseudo-equivalent water molecule, which have tetrahedral environments, intercalate the layers and link them through hydrogen bonds. The bond strengths and the geometry of the tetrahedral anion are discussed.

Crystal structure of Ca5(HAsO4)2(AsO4)2.9H2O (guérinite)

“…A structure determination of gu6rinite has been carried out as part of a research programme on acidic and hydrated compounds [the last paper in the series is Ferraris & Franchini-Angela (1974)].…”