Tl2B2Se7 crystallizes in the monoclinic C2/c space group. Tl(1) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms. B(1) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form corner-sharing BSe4 tetrahedra. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted single-bond geometry to two equivalent Tl(1) and one B(1) atom. In the second Se site, Se(2) is bonded in a distorted single-bond geometry to two equivalent Tl(1) and one B(1) atom. In the third Se site, Se(3) is bonded in a distorted single-bond geometry to two equivalent Tl(1) and one B(1) atom. In the fourth Se site, Se(4) is bonded in a water-like geometry to two equivalent B(1) atoms.
Tl2B2Se7 crystallizes in the monoclinic C2/c space group. Tl(1) is bonded in a 6-coordinate geometry to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms. There is one shorter (3.41 Å) and one longer (3.46 Å) Tl(1)-Se(1) bond length. There is one shorter (3.30 Å) and one longer (3.37 Å) Tl(1)-Se(2) bond length. There is one shorter (3.42 Å) and one longer (3.46 Å) Tl(1)-Se(3) bond length. B(1) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form corner-sharing BSe4 tetrahedra. The B(1)-Se(1) bond length is 2.04 Å. The B(1)-Se(2) bond length is 2.05 Å. The B(1)-Se(3) bond length is 2.05 Å. The B(1)-Se(4) bond length is 2.07 Å. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted single-bond geometry to two equivalent Tl(1) and one B(1) atom. In the second Se site, Se(2) is bonded in a distorted single-bond geometry to two equivalent Tl(1) and one B(1) atom. In the third Se site, Se(3) is bonded in a distorted single-bond geometry to two equivalent Tl(1) and one B(1) atom. In the fourth Se site, Se(4) is bonded in a water-like geometry to two equivalent B(1) atoms.