Structure analysis of [(NH4)(1-x)Rb-x]H-3(SO4)(2) mixed crystals, with
x = 0.57, was carried out by X-ray diffraction at 295 and 180 K in or
der to study the hydrogen-bond character. At room temperature and 180
K, the crystals are isostructural and belong to the monoclinic system,
C2/c. The proton in the short hydrogen bond O(2a)... H(7)... O(2b) is
disordered at 180 and 295 K.