X-Ray crystallographic determination of the structure of the isopolyanion [Mo ₃₆ O ₁₁₂ (H ₂ O) ₁₆ ] ⁸– in the compound K ₈ [Mo ₃₆ O ₁₁₂ (H ₂ O) ₁₆ ]·36H ₂ O

X-Ray structure determination of K8[Mo36O112(H2O)16]·36H2O which crystallises from medium-acidified aqueous molybdate solutions (mole ratio added [H+]: added [MoO42–], ca. 1·8–2·0) shows that the largest isopolyanion known to date reflects the conditions of its formation and contains structural features typical of both the isopolymolybdates which precipitate from slightly acidified molybdate solutions (i.e., compact groups of mainly edge-sharing MoO6 octahedra) and the polymeric compounds which precipitate from strongly acidic solutions (i.e., groups of corner-sharing MoO6 octahedra forming three- and four-membered ‘rings’, and H2O molecules co-ordinated to Mo atoms); the H2O molecules in the compound which are simultaneously co-ordinated to two Mo atoms and the MoO7 polyhedra are hitherto unknown features of the structure.