Zn3 and Ga3 Triangles as Building Units in Sr2Au6Zn3 and Sr2Au6Ga3

The intermetallic compounds Sr2Au6.52Zn2.48, Sr2Au6Zn3, and Sr2Au6Ga3 were obtained by induction melting of the elements in sealed tantalum tubes. Their structures were studied by X-ray diffraction on powders and refined from single crystal diffraction data: R http://www.w3.org/1999/xlinkc, a = 844.5(2), c = 2187.7(5) pm, wR(2) = 0.0411, 936 F-2 values and 20 variables for Sr2Au6.52Zn2.48; a = 841.6(2), c = 2191.5(7) pm, wR(2) = 0.0126, 587 F-2 values and 19 variables for Sr2Au6Zn3; and a = 841.9(2), c = 2191.1(7) pm, wR(2) = 0.0199, 660 F-2 values and 19 variables for Sr2Au6Ga3. The gold substructures of Sr2Au6Zn3 and Sr2Au6Ga3 can be considered as diamond polytypes with 6R stacking sequences (287-304 pm Au-Au in Sr2Au6Zn3). The cavities formed by this network are filled in an ordered manner by strontium atoms and Zn-3 (281 pm Zn-Zn), respectively Ga-3 (286 pm Ga-Ga) triangles in a 2:1 ratio. Consequently one can describe the Sr2Au6Zn3 and Sr2Au6Ga3 structures as ordered substitution variants of the Zintl phase CaIn2. This structural relationship is discussed on the basis of a group-subgroup Scheme. Sr2Au6.52Zn2.48 shows Zn/Au mixing on the triangle.