The structure of three compounds in the Cu 2 Se-In 2 Se 3 -Cr 2 Se 3 system near CuInCr 2 Se 5 is determined by single-crystal x-ray diffraction: CuInCr 4 Se 8 ( I ), Cu 2 In 2 Se 4 ( II ), and Cu 0.5 In 0.5 Se ( III ). I has a cubic (spinel type) structure: a = 10.606(4) Å, Z = 4, sp. gr.. II has a pseudotetragonal (sphalerite type) structure: a = 5.774(2) Å, c = 11.617(6) Å. The structure of II was solved in a reduced unit cell with a = 5.774 (2) Å, b = 5.774(2) Å, c = 7.095(6) Å, α = 113.95(5)°, β = 113.95(5)°, γ = 90.00(4)°, Z = 1, sp. gr. P1. III has a triclinic cell (disordered structure of II): a = 4.088(1) Å, b = 4.091(2) Å, c = 4.101(1) Å, α = 60.05(1)°, β = 60.08(1)°, γ = 89.98(4)°, Z = 1, sp. gr. P1. The Cu and In atoms in I sit in inequivalent tetrahedral sites, and the Cr atoms reside in octahedral interstices of the close packing of Se atoms. The bond lengths are In-Se = 2.538(6), Cr(1)−Se(1) = 2.514 (7), Cr(1)-Se(2) = 2.576(8), and Cu-Se = 2.437(5) Å. In II, all of the atoms sit in tetrahedral sites; the mean bond lengths are In-Se = 2.578(6) and Cu-Se = 2.44(1) Å. In III, the Cu and In atoms are fully disordered in the same tetrahedral site; the mean Cu(In)-Se bond length is 2.508(6) Å. F43m
