Diammonium tricadmium tris-(sulfate) dihydroxide dihydrate.

The title compound, (NH(4))(2)Cd(3)(SO(4))(3)(OH)(2)(H(2)O)(2), has been obtained serendipitously. It is isotypic with the heavier alkali analogues M(2)Cd(3)(SO(4))(3)(OH)(2)(H(2)O)(2) (M = K, Rb, Cs). The structure contains two Cd(2+) ions, one in a general position and one with site symmetry m. The former Cd(2+) ion is coordinated by three O atoms of three SO(4) groups, two hydroxide O atoms and one water O atom, the latter Cd(2+) ion by four O atoms of four SO(4) groups and two hydroxide O atoms, both in a distorted octa-hedral coordination geometry. This arrangement leads to the formation of a layered framework extending parallel to (100), with the ammonium cations situated in the voids. O-H⋯O hydrogen bonds involving the water mol-ecules, hydroxide groups and sulfate O atoms, as well as N-H⋯O hydrogen bonds between ammonium cations and sulfate O atoms consolidate the crystal packing.