Pentapotassium dodecatungsto­borate(III) hexadecahydrate

The title compound, K₅BW₁₂O₄₀]·16H₂O, contains a BW₁₂O₄₀]^5? polyanion of 222 crystallographic symmetry, with a central tetrahedrally coordinated B^III atom surrounded by four groups of three edge‐sharing octahedra (W₃O₁₃ subunits), which are linked in turn to each other and to the central BO₄ tetrahedron by shared O atoms at the vertices. There is a crystallographically unique B—O bond of 1.554 (10) Å, while the average W—O distances are 2.344 (17) Å for four coordinate O atoms, 1.917 (12) and 1.89 (2) Å for two coordinate O atoms within and connecting the W₃O₁₃ subunits, respectively, and 1.709 (8) Å for terminal O atoms. Not all of the K⁺ ions and H₂O groups were located.