Disodium zinc bis(sulfate) tetrahydrate (zinc astrakanite) revisited

We present a new low-temperature refinement of disodium zinc bis(sulfate) tetrahydrate {systematic name: poly[tetra-mu-aqua-di-mu-sulfato-zinc(II)disodium(I)]}, [Na2Zn(SO4)(2)-(H2O)(4)](n) or Zn astrakanite, which is an upgrade of previously reported data [Bukin & Nozik (1974). Zh. Strukt. Khim. 15, 712-716]. The compound is part of an isosrtuctural family containing the Mg (the original astrakanite mineral), Co and Ni species. The very regular ZnO(aqua)(4)O(sulfate)(2) octahedra lie on centres of symmetry, while the rather distorted NaO(aqua)(2)O(sulfate)(4) octahedra appear at general positions, linked into a three-dimensional network by the bridging water molecules and the fully coordinated sulfate groups.