MgHg2(BiO3)4 crystallizes in the monoclinic Pm space group. Mg(1) is bonded in a 4-coordinate geometry to one O(2), one O(7), and two equivalent O(5) atoms. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded to one O(3), one O(6), two equivalent O(1), and two equivalent O(8) atoms to form HgO6 octahedra that share corners with eight equivalent Bi(2)O6 octahedra and edges with two equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-54°. In the second Hg site, Hg(2) is bonded in a 4-coordinate geometry to one O(2), one O(7), and two equivalent O(4) atoms. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one O(1), one O(2), one O(4), one O(5), one O(7), and one O(8) atom to form BiO6 octahedra that share corners with four equivalent Bi(2)O6 octahedra,  an edgeedge with one Hg(1)O6 octahedra, and  an edgeedge with one Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-50°. In the second Bi site, Bi(2) is bonded to one O(1), one O(3), one O(4), one O(5), one O(6), and one O(8) atom to form BiO6 octahedra that share corners with four equivalent Hg(1)O6 octahedra, corners with four equivalent Bi(1)O6 octahedra, and  an edgeedge with one Bi(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-54°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Hg(1), one Bi(1), and one Bi(2) atom. In the second O site, O(2) is bonded to one Mg(1), one Hg(2), and two equivalent Bi(1) atoms to form a mixture of distorted corner and face-sharing OMgHgBi2 trigonal pyramids. In the third O site, O(3) is bonded in a trigonal planar geometry to one Hg(1) and two equivalent Bi(2) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Hg(2), one Bi(1), and one Bi(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Bi(1), and one Bi(2) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Hg(1) and two equivalent Bi(2) atoms. In the seventh O site, O(7) is bonded to one Mg(1), one Hg(2), and two equivalent Bi(1) atoms to form a mixture of distorted corner and face-sharing OMgHgBi2 trigonal pyramids. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Hg(1), one Bi(1), and one Bi(2) atom.
MgHg2(BiO3)4 crystallizes in the monoclinic Pm space group. Mg(1) is bonded in a 4-coordinate geometry to one O(2), one O(7), and two equivalent O(5) atoms. The Mg(1)-O(2) bond length is 2.24 Å. The Mg(1)-O(7) bond length is 2.17 Å. Both Mg(1)-O(5) bond lengths are 1.96 Å. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded to one O(3), one O(6), two equivalent O(1), and two equivalent O(8) atoms to form HgO6 octahedra that share corners with eight equivalent Bi(2)O6 octahedra and edges with two equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 51-54°. The Hg(1)-O(3) bond length is 2.40 Å. The Hg(1)-O(6) bond length is 2.44 Å. Both Hg(1)-O(1) bond lengths are 2.33 Å. Both Hg(1)-O(8) bond lengths are 2.32 Å. In the second Hg site, Hg(2) is bonded in a 4-coordinate geometry to one O(2), one O(7), and two equivalent O(4) atoms. The Hg(2)-O(2) bond length is 2.47 Å. The Hg(2)-O(7) bond length is 2.47 Å. Both Hg(2)-O(4) bond lengths are 2.11 Å. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one O(1), one O(2), one O(4), one O(5), one O(7), and one O(8) atom to form BiO6 octahedra that share corners with four equivalent Bi(2)O6 octahedra,  an edgeedge with one Hg(1)O6 octahedra, and  an edgeedge with one Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-50°. The Bi(1)-O(1) bond length is 2.14 Å. The Bi(1)-O(2) bond length is 2.38 Å. The Bi(1)-O(4) bond length is 2.23 Å. The Bi(1)-O(5) bond length is 2.26 Å. The Bi(1)-O(7) bond length is 2.38 Å. The Bi(1)-O(8) bond length is 2.14 Å. In the second Bi site, Bi(2) is bonded to one O(1), one O(3), one O(4), one O(5), one O(6), and one O(8) atom to form BiO6 octahedra that share corners with four equivalent Hg(1)O6 octahedra, corners with four equivalent Bi(1)O6 octahedra, and  an edgeedge with one Bi(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-54°. The Bi(2)-O(1) bond length is 2.16 Å. The Bi(2)-O(3) bond length is 2.20 Å. The Bi(2)-O(4) bond length is 2.27 Å. The Bi(2)-O(5) bond length is 2.23 Å. The Bi(2)-O(6) bond length is 2.19 Å. The Bi(2)-O(8) bond length is 2.16 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Hg(1), one Bi(1), and one Bi(2) atom. In the second O site, O(2) is bonded to one Mg(1), one Hg(2), and two equivalent Bi(1) atoms to form a mixture of distorted corner and face-sharing OMgHgBi2 trigonal pyramids. In the third O site, O(3) is bonded in a trigonal planar geometry to one Hg(1) and two equivalent Bi(2) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Hg(2), one Bi(1), and one Bi(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Bi(1), and one Bi(2) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to one Hg(1) and two equivalent Bi(2) atoms. In the seventh O site, O(7) is bonded to one Mg(1), one Hg(2), and two equivalent Bi(1) atoms to form a mixture of distorted corner and face-sharing OMgHgBi2 trigonal pyramids. In the eighth O site, O(8) is bonded in a distorted trigonal planar geometry to one Hg(1), one Bi(1), and one Bi(2) atom.