(CuBr)₃P₄Se₄: A low symmetric variant of the (CuI)₃P₄Se₄ structure type

Bright orange (CuBr)₃P₄Se₄ is obtained from the reaction of CuBr, P, and Se in stoichiometric amounts (CuBr:P:Se = 3:4:4). The composition and the crystal structure of the compound were determined from single crystal X-ray diffraction data. Lattice constants are a = 33.627(2) Å, b = 6.402(1) Å, c = 19.059(1) Å, β = 90.19(3) °, V = 4103.2(3) ų, and Z = 12. The compound crystallizes in a structure that is related to (CuI)₃P₄Se₄. Cages of β-P₄Se₄ are stacked along the b-axis and are separated by columns of copper(I) bromide. However, the coordination of the β-P₄Se₄ cage molecules to the copper atoms in the CuBr columns in (CuBr)₃P₄Se₄ is quite different from (CuI)₃P₄Se₄. The monoclinic compound (space group: P2₁, no. 4) has an almost orthorhombic metric in combination with a threefold superstructure in [100]. Structural aspects of (CuBr)₃P₄Se₄ are discussed with respect to the heavier homologue (CuI)₃P₄Se₄.