MgBi4O9 crystallizes in the monoclinic P2/c space group. Mg(1) is bonded to two equivalent O(3) and two equivalent O(5) atoms to form distorted MgO4 tetrahedra that share corners with four equivalent Bi(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 64-67°. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded in a 7-coordinate geometry to one O(1), one O(3), one O(4), two equivalent O(2), and two equivalent O(5) atoms. In the second Bi site, Bi(2) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms to form BiO6 octahedra that share  a cornercorner with one Bi(2)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra, and  an edgeedge with one Bi(2)O6 octahedra. The corner-sharing octahedral tilt angles are 48°. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted tetrahedral geometry to two equivalent Bi(1) and two equivalent Bi(2) atoms. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Bi(2) and two equivalent Bi(1) atoms. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Bi(1), and one Bi(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Bi(1) and two equivalent Bi(2) atoms. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Bi(2), and two equivalent Bi(1) atoms.
MgBi4O9 crystallizes in the monoclinic P2/c space group. Mg(1) is bonded to two equivalent O(3) and two equivalent O(5) atoms to form distorted MgO4 tetrahedra that share corners with four equivalent Bi(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 64-67°. Both Mg(1)-O(3) bond lengths are 2.05 Å. Both Mg(1)-O(5) bond lengths are 2.10 Å. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded in a 7-coordinate geometry to one O(1), one O(3), one O(4), two equivalent O(2), and two equivalent O(5) atoms. The Bi(1)-O(1) bond length is 2.65 Å. The Bi(1)-O(3) bond length is 2.47 Å. The Bi(1)-O(4) bond length is 2.30 Å. There is one shorter (2.28 Å) and one longer (2.53 Å) Bi(1)-O(2) bond length. There is one shorter (2.32 Å) and one longer (2.85 Å) Bi(1)-O(5) bond length. In the second Bi site, Bi(2) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms to form BiO6 octahedra that share  a cornercorner with one Bi(2)O6 octahedra, corners with two equivalent Mg(1)O4 tetrahedra, and  an edgeedge with one Bi(2)O6 octahedra. The corner-sharing octahedral tilt angles are 48°. The Bi(2)-O(1) bond length is 2.17 Å. The Bi(2)-O(2) bond length is 2.12 Å. The Bi(2)-O(3) bond length is 2.11 Å. The Bi(2)-O(5) bond length is 2.18 Å. There is one shorter (2.14 Å) and one longer (2.23 Å) Bi(2)-O(4) bond length. There are five inequivalent O sites. In the first O site, O(1) is bonded in a distorted tetrahedral geometry to two equivalent Bi(1) and two equivalent Bi(2) atoms. In the second O site, O(2) is bonded in a distorted trigonal non-coplanar geometry to one Bi(2) and two equivalent Bi(1) atoms. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Bi(1), and one Bi(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Bi(1) and two equivalent Bi(2) atoms. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Bi(2), and two equivalent Bi(1) atoms.