Ba2GdCu2(HgO4)2 crystallizes in the tetragonal I4/mmm space group. Ba(1) is bonded in a 9-coordinate geometry to one O(2), four equivalent O(1), and four equivalent O(3) atoms. Gd(1) is bonded in a body-centered cubic geometry to eight equivalent O(1) atoms. Cu(1) is bonded to one O(3) and four equivalent O(1) atoms to form corner-sharing CuO5 square pyramids. Hg(1) is bonded in a linear geometry to one O(2) and one O(3) atom. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to two equivalent Ba(1), two equivalent Gd(1), and two equivalent Cu(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to one Ba(1) and one Hg(1) atom. In the third O site, O(3) is bonded to four equivalent Ba(1), one Cu(1), and one Hg(1) atom to form a mixture of corner and edge-sharing OBa4CuHg octahedra. The corner-sharing octahedral tilt angles are 16°.
Ba2GdCu2(HgO4)2 crystallizes in the tetragonal I4/mmm space group. Ba(1) is bonded in a 9-coordinate geometry to one O(2), four equivalent O(1), and four equivalent O(3) atoms. The Ba(1)-O(2) bond length is 2.68 Å. All Ba(1)-O(1) bond lengths are 3.00 Å. All Ba(1)-O(3) bond lengths are 2.79 Å. Gd(1) is bonded in a body-centered cubic geometry to eight equivalent O(1) atoms. All Gd(1)-O(1) bond lengths are 2.45 Å. Cu(1) is bonded to one O(3) and four equivalent O(1) atoms to form corner-sharing CuO5 square pyramids. The Cu(1)-O(3) bond length is 2.46 Å. All Cu(1)-O(1) bond lengths are 1.96 Å. Hg(1) is bonded in a linear geometry to one O(2) and one O(3) atom. The Hg(1)-O(2) bond length is 2.08 Å. The Hg(1)-O(3) bond length is 2.11 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to two equivalent Ba(1), two equivalent Gd(1), and two equivalent Cu(1) atoms. In the second O site, O(2) is bonded in a distorted linear geometry to one Ba(1) and one Hg(1) atom. In the third O site, O(3) is bonded to four equivalent Ba(1), one Cu(1), and one Hg(1) atom to form a mixture of corner and edge-sharing OBa4CuHg octahedra. The corner-sharing octahedral tilt angles are 16°.