CuYSe2 crystallizes in the trigonal P3m1 space group. Y(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form YSe6 octahedra that share corners with six equivalent Cu(1)Se4 tetrahedra, edges with six equivalent Y(1)Se6 octahedra, and edges with three equivalent Cu(1)Se4 tetrahedra. Cu(1) is bonded to one Se(2) and three equivalent Se(1) atoms to form CuSe4 tetrahedra that share corners with six equivalent Y(1)Se6 octahedra, corners with six equivalent Cu(1)Se4 tetrahedra, and edges with three equivalent Y(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 20-57°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Y(1) and three equivalent Cu(1) atoms to form distorted edge-sharing SeY3Cu3 octahedra. In the second Se site, Se(2) is bonded in a distorted rectangular see-saw-like geometry to three equivalent Y(1) and one Cu(1) atom.
CuYSe2 crystallizes in the trigonal P3m1 space group. Y(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form YSe6 octahedra that share corners with six equivalent Cu(1)Se4 tetrahedra, edges with six equivalent Y(1)Se6 octahedra, and edges with three equivalent Cu(1)Se4 tetrahedra. All Y(1)-Se(1) bond lengths are 2.93 Å. All Y(1)-Se(2) bond lengths are 2.80 Å. Cu(1) is bonded to one Se(2) and three equivalent Se(1) atoms to form CuSe4 tetrahedra that share corners with six equivalent Y(1)Se6 octahedra, corners with six equivalent Cu(1)Se4 tetrahedra, and edges with three equivalent Y(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 20-57°. The Cu(1)-Se(2) bond length is 2.42 Å. All Cu(1)-Se(1) bond lengths are 2.46 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Y(1) and three equivalent Cu(1) atoms to form distorted edge-sharing SeY3Cu3 octahedra. In the second Se site, Se(2) is bonded in a distorted rectangular see-saw-like geometry to three equivalent Y(1) and one Cu(1) atom.