Penta-potassium μ-arsenato-bis-(hy-droxy-tetra-molybdate) dihydrate.

The title arsenatomolybdate, K(5)[Mo(8)O(24)(OH)(2)(AsO(4))]·2H(2)O, which was obtained hydro-thermally, features an [AsMo(8)O(28)(OH)(2)](5-) anion, which is formed by two Mo(4)O(14)(OH) units that are linked by As in a sandwich-like fashion. The overall symmetry of the anion is m2m. The {Mo(4)O(14)(OH)} core is composed of two pairs of confacial biocta-hedral {Mo(2)O(9)} units with two μ(4)-O atoms which have been characterized as hydroxyl groups. The anions are further inter-connected by potassium cations, forming a three-dimensional network structure with the uncoordinated water mol-ecules occupying the channels. The structure is further stabilized by O-H⋯O hydrogen bonding.