Mg(BiO2)4 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(2), one O(4), two equivalent O(6), and two equivalent O(7) atoms to form distorted MgO6 octahedra that share  a cornercorner with one Bi(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with two equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles are 35°. There are four inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form BiO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with two equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles are 35°. In the second Bi site, Bi(2) is bonded in a 3-coordinate geometry to one O(8), two equivalent O(3), and two equivalent O(6) atoms. In the third Bi site, Bi(3) is bonded in a 6-coordinate geometry to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms. In the fourth Bi site, Bi(4) is bonded in a distorted see-saw-like geometry to one O(3), one O(5), and two equivalent O(1) atoms. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Bi(3) and two equivalent Bi(4) atoms. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Bi(1), and two equivalent Bi(3) atoms. In the third O site, O(3) is bonded in a trigonal non-coplanar geometry to one Bi(4) and two equivalent Bi(2) atoms. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Mg(1) and two equivalent Bi(1) atoms. In the fifth O site, O(5) is bonded in a trigonal non-coplanar geometry to one Bi(4) and two equivalent Bi(1) atoms. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to two equivalent Mg(1), one Bi(3), and two equivalent Bi(2) atoms. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to two equivalent Mg(1) and one Bi(1) atom. In the eighth O site, O(8) is bonded in a trigonal non-coplanar geometry to one Bi(2) and two equivalent Bi(3) atoms.
Mg(BiO2)4 crystallizes in the monoclinic Cm space group. Mg(1) is bonded to one O(2), one O(4), two equivalent O(6), and two equivalent O(7) atoms to form distorted MgO6 octahedra that share  a cornercorner with one Bi(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with two equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles are 35°. The Mg(1)-O(2) bond length is 2.15 Å. The Mg(1)-O(4) bond length is 2.20 Å. Both Mg(1)-O(6) bond lengths are 2.22 Å. Both Mg(1)-O(7) bond lengths are 2.24 Å. There are four inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form BiO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with two equivalent Bi(1)O6 octahedra. The corner-sharing octahedral tilt angles are 35°. The Bi(1)-O(2) bond length is 2.13 Å. The Bi(1)-O(7) bond length is 2.16 Å. Both Bi(1)-O(4) bond lengths are 2.24 Å. Both Bi(1)-O(5) bond lengths are 2.21 Å. In the second Bi site, Bi(2) is bonded in a 3-coordinate geometry to one O(8), two equivalent O(3), and two equivalent O(6) atoms. The Bi(2)-O(8) bond length is 2.17 Å. Both Bi(2)-O(3) bond lengths are 2.24 Å. Both Bi(2)-O(6) bond lengths are 2.64 Å. In the third Bi site, Bi(3) is bonded in a 6-coordinate geometry to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms. The Bi(3)-O(1) bond length is 2.70 Å. The Bi(3)-O(6) bond length is 2.17 Å. Both Bi(3)-O(2) bond lengths are 2.58 Å. Both Bi(3)-O(8) bond lengths are 2.25 Å. In the fourth Bi site, Bi(4) is bonded in a distorted see-saw-like geometry to one O(3), one O(5), and two equivalent O(1) atoms. The Bi(4)-O(3) bond length is 2.27 Å. The Bi(4)-O(5) bond length is 2.60 Å. Both Bi(4)-O(1) bond lengths are 2.19 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Bi(3) and two equivalent Bi(4) atoms. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Mg(1), one Bi(1), and two equivalent Bi(3) atoms. In the third O site, O(3) is bonded in a trigonal non-coplanar geometry to one Bi(4) and two equivalent Bi(2) atoms. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Mg(1) and two equivalent Bi(1) atoms. In the fifth O site, O(5) is bonded in a trigonal non-coplanar geometry to one Bi(4) and two equivalent Bi(1) atoms. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to two equivalent Mg(1), one Bi(3), and two equivalent Bi(2) atoms. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to two equivalent Mg(1) and one Bi(1) atom. In the eighth O site, O(8) is bonded in a trigonal non-coplanar geometry to one Bi(2) and two equivalent Bi(3) atoms.