ThCuTlSe3 crystallizes in the orthorhombic Cmcm space group. Th(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form ThSe6 octahedra that share corners with two equivalent Th(1)Se6 octahedra, edges with two equivalent Th(1)Se6 octahedra, and edges with four equivalent Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 39°. 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 Cu(1)Se4 tetrahedra and edges with four equivalent Th(1)Se6 octahedra. Tl(1) is bonded in a 6-coordinate geometry to two equivalent Se(2) and four equivalent Se(1) atoms. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 3-coordinate geometry to two equivalent Th(1), one Cu(1), and two equivalent Tl(1) atoms. In the second Se site, Se(2) is bonded in a 4-coordinate geometry to two equivalent Th(1), two equivalent Cu(1), and two equivalent Tl(1) atoms.
ThCuTlSe3 crystallizes in the orthorhombic Cmcm space group. Th(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form ThSe6 octahedra that share corners with two equivalent Th(1)Se6 octahedra, edges with two equivalent Th(1)Se6 octahedra, and edges with four equivalent Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles are 39°. Both Th(1)-Se(2) bond lengths are 2.91 Å. All Th(1)-Se(1) bond lengths are 2.92 Å. 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 Cu(1)Se4 tetrahedra and edges with four equivalent Th(1)Se6 octahedra. Both Cu(1)-Se(1) bond lengths are 2.46 Å. Both Cu(1)-Se(2) bond lengths are 2.57 Å. Tl(1) is bonded in a 6-coordinate geometry to two equivalent Se(2) and four equivalent Se(1) atoms. Both Tl(1)-Se(2) bond lengths are 3.38 Å. All Tl(1)-Se(1) bond lengths are 3.41 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 3-coordinate geometry to two equivalent Th(1), one Cu(1), and two equivalent Tl(1) atoms. In the second Se site, Se(2) is bonded in a 4-coordinate geometry to two equivalent Th(1), two equivalent Cu(1), and two equivalent Tl(1) atoms.