Re-refinement of sodium ammonium sulfate dihydrate at 170 K

Abstract

The title compound, sodium ammonium sulfate dihydrate (SASD), NaNH4SO4·2H2O, a synthetic analogue of the mineral lecontite, is a well known ferroelectric. The crystal structure of the paraelectric phase has been re-refined at 170 K on the basis of single-crystal X-ray data, improving the previous study [Arzt & Glazer (1994). Acta Cryst. B50, 425–431] in terms of accuracy regarding hydrogen-atom positions and thus details of the hydrogen bonding. O—H...O and N—H...O hydrogen bonds between the principal building units [Na(OH2)4O2 octahedra, SO4 tetrahedra and ammonium cations] constitute a three-dimensional network structure.