Ba2CaCu(HgO3)2 crystallizes in the tetragonal P4/mmm space group. Ba(1) is bonded in a 8-coordinate geometry to four equivalent O(1) and four equivalent O(2) atoms. Ca(1) is bonded in a body-centered cubic geometry to eight equivalent O(1) atoms. Cu(1) is bonded in a linear geometry to two equivalent O(2) atoms. Hg(1) is bonded to one O(2) and four equivalent O(1) atoms to form corner-sharing HgO5 square pyramids. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(1), two equivalent Ca(1), and two equivalent Hg(1) atoms to form a mixture of distorted edge, corner, and face-sharing OBa2Ca2Hg2 octahedra. The corner-sharing octahedral tilt angles range from 0-70°. In the second O site, O(2) is bonded in a 6-coordinate geometry to four equivalent Ba(1), one Cu(1), and one Hg(1) atom.
Ba2CaCu(HgO3)2 crystallizes in the tetragonal P4/mmm space group. Ba(1) is bonded in a 8-coordinate geometry to four equivalent O(1) and four equivalent O(2) atoms. All Ba(1)-O(1) bond lengths are 3.01 Å. All Ba(1)-O(2) bond lengths are 3.07 Å. Ca(1) is bonded in a body-centered cubic geometry to eight equivalent O(1) atoms. All Ca(1)-O(1) bond lengths are 2.64 Å. Cu(1) is bonded in a linear geometry to two equivalent O(2) atoms. Both Cu(1)-O(2) bond lengths are 1.80 Å. Hg(1) is bonded to one O(2) and four equivalent O(1) atoms to form corner-sharing HgO5 square pyramids. The Hg(1)-O(2) bond length is 2.56 Å. All Hg(1)-O(1) bond lengths are 2.14 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ba(1), two equivalent Ca(1), and two equivalent Hg(1) atoms to form a mixture of distorted edge, corner, and face-sharing OBa2Ca2Hg2 octahedra. The corner-sharing octahedral tilt angles range from 0-70°. In the second O site, O(2) is bonded in a 6-coordinate geometry to four equivalent Ba(1), one Cu(1), and one Hg(1) atom.