The crystal structure of gianellaite, [(NHg2)2](SO4)(H2O)x, cubic, F4̄3m, a = 9.521(6) Å V = 863.1(1.6) Å3, Z = 4, was solved by direct methods and refined to an R 1 index of 2.1% based on 167 unique observed reflections collected on a three-circle rotating-anode (MoKα X-radiation) diffractometer equipped with multilayer optics and an APEX-II detector. In the structure of gianellaite, nitrogen-centred (NHg4)5+ tetrahedra share all corners to form a framework of tetrahedra with an ordered arrangement of interstitial (SO4)2– tetrahedra that show strong orientational disorder. Infrared spectroscopy in the principal O–H stretching region shows peaks at ∼3300 and 1600 cm–1, indicating the presence of (H2O), the position(s) of which could not be discerned in difference-Fourier maps.
