α-SrZn5-Type solid solution, BaZn2.6Cu2.4.

Single crystals of the title compound barium zinc copper, BaCu2.6Zn2.4, were obtained from a sample prepared by heating metal chips of Ba, Cu, and Zn in an Ar atmosphere up to 973 K, followed by slow cooling. Single-crystal X-ray structure analysis revealed that BaCu2.6Zn2.4 crystallizes in an ortho-rhom-bic cell [a = 12.9858 (3), b = 5.2162 (1), and c = 6.6804 (2) Å] with an α-SrZn5-type structure (space group Pnma). The three-dimensional framework consists of Cu and Zn atoms, with Ba atoms in the tunnels extending in the b-axis direction. Although the Ba atom is larger than the Sr atom, the cell volume of BaCu2.6Zn2.4 [452.507 (19) Å3] is smaller than that of α-SrZn5 [466.08 Å3]. This decrease in volume can be attributed to the partial substitution of Cu atoms by Zn atoms in the framework because the Cu-Zn and Cu-Cu bonds are shorter than the Zn-Zn bond. The increase in Ba-Zn inter-atomic distances from the Sr-Zn distances is cancelled out by the partial replacement of Zn with Cu atoms, which leads to shorter average Ba-Zn/Cu distances.