Abstract

Three complexes (A)-(C), M^I₄ [Zr₆Cr₄O₈(OH)₈(SO₄)₈(H₂O)₄].yH₂O, where M^I₄ is Cs_2.78- Na_1.22 (A), Na₄ (B) or not present (C), in which (A) and (B) contain the same Zr^IV-Cr^III heteropolyanion and (C) contains a structural isomer of it, have been crystallographically characterized with varying degrees of refinement. A fourth complex (D), [Zr₆Cr₄O₈(OH)₈(SO₄)₅(DL-α-Ala)₄(H₂O)4]ⁿ⁺ hydrate, in which some of the sulfate groups that form part of the heteropolyanion have been replaced by alanine (Ala) molecules, is also described.

The heteropolyanion [it has 4 crystallographic symmetry in (A), no symmetry in (B)] is best described as an octahedron of eight-coordinate Zr^IV ions (intermediate between square-antiprismatic and dodecahedral stereochemistry) with Cr^III octahedra and sulfate tetrahedra bound to it. In (C), two Cr^III octahedra and two sulfate groups have been rotated with respect to the octahedron of zirconium ions leaving an unsymmetrical heteropolyanion, while in (D) the heteropolyanion has twofold symmetry and is similar to that in (A) and (B) except for the presence of alanine in place of some sulfate groups.