TlCu3Se2 crystallizes in the monoclinic C2/m space group. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 9-coordinate geometry to one Cu(2), two equivalent Cu(1), two equivalent Cu(3), one Se(1), and three equivalent Se(2) atoms. In the second Cu site, Cu(2) is bonded in a distorted trigonal non-coplanar geometry to one Cu(1), one Se(1), and two equivalent Se(2) atoms. In the third Cu site, Cu(3) is bonded in a distorted trigonal planar geometry to two equivalent Cu(1), one Se(2), and two equivalent Se(1) atoms. 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 4-coordinate geometry to one Cu(1), one Cu(2), two equivalent Cu(3), and four equivalent Tl(1) atoms. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to one Cu(3), two equivalent Cu(2), three equivalent Cu(1), and two equivalent Tl(1) atoms.
TlCu3Se2 crystallizes in the monoclinic C2/m space group. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 9-coordinate geometry to one Cu(2), two equivalent Cu(1), two equivalent Cu(3), one Se(1), and three equivalent Se(2) atoms. The Cu(1)-Cu(2) bond length is 2.56 Å. Both Cu(1)-Cu(1) bond lengths are 2.65 Å. Both Cu(1)-Cu(3) bond lengths are 2.71 Å. The Cu(1)-Se(1) bond length is 2.53 Å. There is one shorter (2.42 Å) and two longer (2.76 Å) Cu(1)-Se(2) bond lengths. In the second Cu site, Cu(2) is bonded in a distorted trigonal non-coplanar geometry to one Cu(1), one Se(1), and two equivalent Se(2) atoms. The Cu(2)-Se(1) bond length is 2.40 Å. Both Cu(2)-Se(2) bond lengths are 2.52 Å. In the third Cu site, Cu(3) is bonded in a distorted trigonal planar geometry to two equivalent Cu(1), one Se(2), and two equivalent Se(1) atoms. The Cu(3)-Se(2) bond length is 2.49 Å. Both Cu(3)-Se(1) bond lengths are 2.48 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 3.40 Å. There are two shorter (3.29 Å) and two longer (3.40 Å) Tl(1)-Se(1) bond lengths. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 4-coordinate geometry to one Cu(1), one Cu(2), two equivalent Cu(3), and four equivalent Tl(1) atoms. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to one Cu(3), two equivalent Cu(2), three equivalent Cu(1), and two equivalent Tl(1) atoms.