CsLa2CuSe4 crystallizes in the orthorhombic Cmcm space group. Cs(1) is bonded in a 8-coordinate geometry to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms. La(1) is bonded to one Se(2), two equivalent Se(3), and three equivalent Se(1) atoms to form LaSe6 octahedra that share corners with three equivalent La(1)Se6 octahedra,  a cornercorner with one Cu(1)Se4 tetrahedra, edges with five equivalent La(1)Se6 octahedra, and edges with two equivalent Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 0-33°. Cu(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form CuSe4 tetrahedra that share corners with two equivalent La(1)Se6 octahedra, corners with two equivalent Cu(1)Se4 tetrahedra, and edges with four equivalent La(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 3°. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Cs(1), three equivalent La(1), and one Cu(1) atom to form distorted SeCs2La3Cu octahedra that share corners with two equivalent Se(1)Cs2La3Cu octahedra, corners with four equivalent Se(3)Cs2La4 octahedra, edges with three equivalent Se(3)Cs2La4 octahedra, edges with four equivalent Se(1)Cs2La3Cu octahedra, and  a faceface with one Se(1)Cs2La3Cu octahedra. The corner-sharing octahedral tilt angles range from 3-69°. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent Cs(1), two equivalent La(1), and two equivalent Cu(1) atoms. In the third Se site, Se(3) is bonded to two equivalent Cs(1) and four equivalent La(1) atoms to form distorted SeCs2La4 octahedra that share corners with two equivalent Se(3)Cs2La4 octahedra, corners with eight equivalent Se(1)Cs2La3Cu octahedra, edges with two equivalent Se(3)Cs2La4 octahedra, and edges with six equivalent Se(1)Cs2La3Cu octahedra. The corner-sharing octahedral tilt angles range from 3-46°.
CsLa2CuSe4 crystallizes in the orthorhombic Cmcm space group. Cs(1) is bonded in a 8-coordinate geometry to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms. Both Cs(1)-Se(2) bond lengths are 3.55 Å. Both Cs(1)-Se(3) bond lengths are 4.05 Å. All Cs(1)-Se(1) bond lengths are 3.63 Å. La(1) is bonded to one Se(2), two equivalent Se(3), and three equivalent Se(1) atoms to form LaSe6 octahedra that share corners with three equivalent La(1)Se6 octahedra,  a cornercorner with one Cu(1)Se4 tetrahedra, edges with five equivalent La(1)Se6 octahedra, and edges with two equivalent Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 0-33°. The La(1)-Se(2) bond length is 2.94 Å. Both La(1)-Se(3) bond lengths are 3.12 Å. There are two shorter (2.98 Å) and one longer (3.04 Å) La(1)-Se(1) bond length. Cu(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form CuSe4 tetrahedra that share corners with two equivalent La(1)Se6 octahedra, corners with two equivalent Cu(1)Se4 tetrahedra, and edges with four equivalent La(1)Se6 octahedra. The corner-sharing octahedral tilt angles are 3°. Both Cu(1)-Se(1) bond lengths are 2.50 Å. Both Cu(1)-Se(2) bond lengths are 2.53 Å. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Cs(1), three equivalent La(1), and one Cu(1) atom to form distorted SeCs2La3Cu octahedra that share corners with two equivalent Se(1)Cs2La3Cu octahedra, corners with four equivalent Se(3)Cs2La4 octahedra, edges with three equivalent Se(3)Cs2La4 octahedra, edges with four equivalent Se(1)Cs2La3Cu octahedra, and  a faceface with one Se(1)Cs2La3Cu octahedra. The corner-sharing octahedral tilt angles range from 3-69°. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent Cs(1), two equivalent La(1), and two equivalent Cu(1) atoms. In the third Se site, Se(3) is bonded to two equivalent Cs(1) and four equivalent La(1) atoms to form distorted SeCs2La4 octahedra that share corners with two equivalent Se(3)Cs2La4 octahedra, corners with eight equivalent Se(1)Cs2La3Cu octahedra, edges with two equivalent Se(3)Cs2La4 octahedra, and edges with six equivalent Se(1)Cs2La3Cu octahedra. The corner-sharing octahedral tilt angles range from 3-46°.