Ba2Cu2HgTl2O8 crystallizes in the tetragonal I4mm space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 9-coordinate geometry to one O(3), four equivalent O(1), and four equivalent O(5) atoms. In the second Ba site, Ba(2) is bonded in a 9-coordinate geometry to one O(4), four equivalent O(2), and four equivalent O(6) atoms. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(5) and four equivalent O(1) atoms to form corner-sharing CuO5 square pyramids. In the second Cu site, Cu(2) is bonded to one O(6) and four equivalent O(2) atoms to form distorted corner-sharing CuO5 square pyramids. Hg(1) is bonded in a linear geometry to one O(4) and one O(5) atom. There are two inequivalent Tl sites. In the first Tl site, Tl(1) is bonded in a distorted linear geometry to one O(3), one O(6), and four equivalent O(4) atoms. In the second Tl site, Tl(2) is bonded in a body-centered cubic geometry to four equivalent O(1) and four equivalent O(2) atoms. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to two equivalent Ba(1), two equivalent Cu(1), and two equivalent Tl(2) atoms. In the second O site, O(2) is bonded to two equivalent Ba(2), two equivalent Cu(2), and two equivalent Tl(2) atoms to form distorted OBa2Tl2Cu2 octahedra that share corners with two equivalent O(2)Ba2Tl2Cu2 octahedra, corners with two equivalent O(4)BaTl4Hg octahedra, edges with two equivalent O(2)Ba2Tl2Cu2 octahedra, and faces with four equivalent O(2)Ba2Tl2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 8-42°. In the third O site, O(3) is bonded in a distorted linear geometry to one Ba(1) and one Tl(1) atom. In the fourth O site, O(4) is bonded to one Ba(2), one Hg(1), and four equivalent Tl(1) atoms to form distorted OBaTl4Hg octahedra that share  a cornercorner with one O(5)Ba4CuHg octahedra, corners with four equivalent O(2)Ba2Tl2Cu2 octahedra, corners with four equivalent O(4)BaTl4Hg octahedra, and edges with four equivalent O(4)BaTl4Hg octahedra. The corner-sharing octahedral tilt angles range from 0-42°. In the fifth O site, O(5) is bonded to four equivalent Ba(1), one Cu(1), and one Hg(1) atom to form OBa4CuHg octahedra that share  a cornercorner with one O(4)BaTl4Hg octahedra, corners with four equivalent O(5)Ba4CuHg octahedra, and edges with four equivalent O(5)Ba4CuHg octahedra. The corner-sharing octahedral tilt angles range from 0-16°. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to four equivalent Ba(2), one Cu(2), and one Tl(1) atom.
Ba2Cu2HgTl2O8 crystallizes in the tetragonal I4mm space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 9-coordinate geometry to one O(3), four equivalent O(1), and four equivalent O(5) atoms. The Ba(1)-O(3) bond length is 2.69 Å. All Ba(1)-O(1) bond lengths are 3.01 Å. All Ba(1)-O(5) bond lengths are 2.79 Å. In the second Ba site, Ba(2) is bonded in a 9-coordinate geometry to one O(4), four equivalent O(2), and four equivalent O(6) atoms. The Ba(2)-O(4) bond length is 2.70 Å. All Ba(2)-O(2) bond lengths are 2.92 Å. All Ba(2)-O(6) bond lengths are 2.83 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(5) and four equivalent O(1) atoms to form corner-sharing CuO5 square pyramids. The Cu(1)-O(5) bond length is 2.45 Å. All Cu(1)-O(1) bond lengths are 1.97 Å. In the second Cu site, Cu(2) is bonded to one O(6) and four equivalent O(2) atoms to form distorted corner-sharing CuO5 square pyramids. The Cu(2)-O(6) bond length is 2.61 Å. All Cu(2)-O(2) bond lengths are 1.96 Å. Hg(1) is bonded in a linear geometry to one O(4) and one O(5) atom. The Hg(1)-O(4) bond length is 2.16 Å. The Hg(1)-O(5) bond length is 2.13 Å. There are two inequivalent Tl sites. In the first Tl site, Tl(1) is bonded in a distorted linear geometry to one O(3), one O(6), and four equivalent O(4) atoms. The Tl(1)-O(3) bond length is 2.03 Å. The Tl(1)-O(6) bond length is 2.08 Å. All Tl(1)-O(4) bond lengths are 2.77 Å. In the second Tl site, Tl(2) is bonded in a body-centered cubic geometry to four equivalent O(1) and four equivalent O(2) atoms. All Tl(2)-O(1) bond lengths are 2.44 Å. All Tl(2)-O(2) bond lengths are 2.48 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to two equivalent Ba(1), two equivalent Cu(1), and two equivalent Tl(2) atoms. In the second O site, O(2) is bonded to two equivalent Ba(2), two equivalent Cu(2), and two equivalent Tl(2) atoms to form distorted OBa2Tl2Cu2 octahedra that share corners with two equivalent O(2)Ba2Tl2Cu2 octahedra, corners with two equivalent O(4)BaTl4Hg octahedra, edges with two equivalent O(2)Ba2Tl2Cu2 octahedra, and faces with four equivalent O(2)Ba2Tl2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 8-42°. In the third O site, O(3) is bonded in a distorted linear geometry to one Ba(1) and one Tl(1) atom. In the fourth O site, O(4) is bonded to one Ba(2), one Hg(1), and four equivalent Tl(1) atoms to form distorted OBaTl4Hg octahedra that share  a cornercorner with one O(5)Ba4CuHg octahedra, corners with four equivalent O(2)Ba2Tl2Cu2 octahedra, corners with four equivalent O(4)BaTl4Hg octahedra, and edges with four equivalent O(4)BaTl4Hg octahedra. The corner-sharing octahedral tilt angles range from 0-42°. In the fifth O site, O(5) is bonded to four equivalent Ba(1), one Cu(1), and one Hg(1) atom to form OBa4CuHg octahedra that share  a cornercorner with one O(4)BaTl4Hg octahedra, corners with four equivalent O(5)Ba4CuHg octahedra, and edges with four equivalent O(5)Ba4CuHg octahedra. The corner-sharing octahedral tilt angles range from 0-16°. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to four equivalent Ba(2), one Cu(2), and one Tl(1) atom.