CsYZnSe3 crystallizes in the orthorhombic Cmcm space group. Cs(1) is bonded in a 8-coordinate geometry to two equivalent Se(2) and six equivalent Se(1) atoms. Y(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form YSe6 octahedra that share corners with two equivalent Y(1)Se6 octahedra, edges with two equivalent Y(1)Se6 octahedra, and edges with four equivalent Zn(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 35°. Zn(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form ZnSe4 tetrahedra that share corners with two equivalent Zn(1)Se4 tetrahedra and edges with four equivalent Y(1)Se6 octahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to three equivalent Cs(1), two equivalent Y(1), and one Zn(1) atom. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent Cs(1), two equivalent Y(1), and two equivalent Zn(1) atoms.
CsYZnSe3 crystallizes in the orthorhombic Cmcm space group. Cs(1) is bonded in a 8-coordinate geometry to two equivalent Se(2) and six equivalent Se(1) atoms. Both Cs(1)-Se(2) bond lengths are 3.69 Å. There are four shorter (3.75 Å) and two longer (3.96 Å) Cs(1)-Se(1) bond lengths. Y(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form YSe6 octahedra that share corners with two equivalent Y(1)Se6 octahedra, edges with two equivalent Y(1)Se6 octahedra, and edges with four equivalent Zn(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 35°. Both Y(1)-Se(2) bond lengths are 2.89 Å. All Y(1)-Se(1) bond lengths are 2.89 Å. Zn(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form ZnSe4 tetrahedra that share corners with two equivalent Zn(1)Se4 tetrahedra and edges with four equivalent Y(1)Se6 octahedra. Both Zn(1)-Se(1) bond lengths are 2.45 Å. Both Zn(1)-Se(2) bond lengths are 2.59 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to three equivalent Cs(1), two equivalent Y(1), and one Zn(1) atom. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent Cs(1), two equivalent Y(1), and two equivalent Zn(1) atoms.