A three-dimensional bromo-bridged mixed-valence gold(I,III) compound, Cs₂Au^IAu^IIIBr₆

The title compound, dicaesium gold(I) gold(III) hexa­bromide or dicaesium dibromo­aurate(I) tetra­bromo­aurate(III), Cs₂[Au^IBr₂][Au^IIIBr₄], has a distorted perovskite-type structure which is isotypic with its chloride and iodide analogues, Cs₂Au^IAu^IIIX₆ (X is Cl or I). The structure contains compressed and elongated [AuBr₆] octa­hedra stacked alternately along the [001] and [110] directions by sharing all the corner Br⁻ ions. The compound is also characterized by the assembly of the gold complex ions [Au^IBr₂]⁻ and [Au^IIIBr₄]⁻. Structural parameters indicating the mixed-valence distortion of Au^I and Au^III due to displacement of two crystallographically independent halide (X) ions from the mid-point between the two adjacent Au ions, expressed by (Au—X)/(Au...X), are 0.738 (2) along the c axis and 0.799 (1) in the ab plane. These values show that the mixed-valence distortion of the title bromide is inter­mediate between those of the chloride and the iodide. The distortion of the title bromide from the cubic system to the tetra­gonal system, expressed by 2^1/2a/c = 0.9704 (1), is also inter­mediate between those of the chloride and the iodide.