Dirubidium tricadmium tetra­kis­(sulfate) penta­hydrate

The title compound, Rb₂Cd₃(SO₄)₄·5H₂O, arose as an unexpected product during the attempted synthesis of an Rb₂Cd₂(SO₄)₃ potassium cadmium sulfate langbeinite, It has two layers, layer A containing Cd octa­hedra bridged by sulfate groups and layer B containing edge-shared Cd octa­hedra, with Rb atoms occupying inter­stial positions. The layers are connected by way of Cd-O-S links.