TlCu5Se3 crystallizes in the tetragonal P4_2/mnm space group. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form distorted corner-sharing CuSe4 tetrahedra. In the second Cu site, Cu(2) is bonded in a 4-coordinate geometry to one Se(1) and three equivalent Se(2) atoms. In the third Cu site, Cu(3) is bonded in a 3-coordinate geometry to three equivalent Se(2) atoms. Tl(1) is bonded in a distorted body-centered cubic geometry to four equivalent Se(1) and four equivalent Se(2) atoms. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to two equivalent Cu(1), two equivalent Cu(2), and four equivalent Tl(1) atoms. In the second Se site, Se(2) is bonded in a 7-coordinate geometry to one Cu(1), three equivalent Cu(2), three equivalent Cu(3), and two equivalent Tl(1) atoms.
TlCu5Se3 crystallizes in the tetragonal P4_2/mnm space group. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form distorted corner-sharing CuSe4 tetrahedra. Both Cu(1)-Se(1) bond lengths are 2.45 Å. Both Cu(1)-Se(2) bond lengths are 2.61 Å. In the second Cu site, Cu(2) is bonded in a 4-coordinate geometry to one Se(1) and three equivalent Se(2) atoms. The Cu(2)-Se(1) bond length is 2.42 Å. There is one shorter (2.60 Å) and two longer (2.63 Å) Cu(2)-Se(2) bond lengths. In the third Cu site, Cu(3) is bonded in a 3-coordinate geometry to three equivalent Se(2) atoms. There is one shorter (2.45 Å) and two longer (2.56 Å) Cu(3)-Se(2) bond lengths. Tl(1) is bonded in a distorted body-centered cubic geometry to four equivalent Se(1) and four equivalent Se(2) atoms. All Tl(1)-Se(1) bond lengths are 3.34 Å. All Tl(1)-Se(2) bond lengths are 3.44 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to two equivalent Cu(1), two equivalent Cu(2), and four equivalent Tl(1) atoms. In the second Se site, Se(2) is bonded in a 7-coordinate geometry to one Cu(1), three equivalent Cu(2), three equivalent Cu(3), and two equivalent Tl(1) atoms.