MgMnBiO5 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with four equivalent Mn(1)O4 tetrahedra and  an edgeedge with one Mg(1)O6 octahedra. Mn(1) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form MnO4 tetrahedra that share corners with four equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 26-52°. Bi(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(1), and one Bi(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(1), and one Bi(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(1), and one Bi(1) atom. In the fourth O site, O(4) is bonded to two equivalent Mg(1) and two equivalent Bi(1) atoms to form edge-sharing OMg2Bi2 tetrahedra. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(1), and one Bi(1) atom.
MgMnBiO5 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms to form MgO6 octahedra that share corners with four equivalent Mn(1)O4 tetrahedra and  an edgeedge with one Mg(1)O6 octahedra. The Mg(1)-O(1) bond length is 2.18 Å. The Mg(1)-O(2) bond length is 2.14 Å. The Mg(1)-O(3) bond length is 2.06 Å. The Mg(1)-O(5) bond length is 2.11 Å. There is one shorter (2.10 Å) and one longer (2.15 Å) Mg(1)-O(4) bond length. Mn(1) is bonded to one O(1), one O(2), one O(3), and one O(5) atom to form MnO4 tetrahedra that share corners with four equivalent Mg(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 26-52°. The Mn(1)-O(1) bond length is 1.71 Å. The Mn(1)-O(2) bond length is 1.72 Å. The Mn(1)-O(3) bond length is 1.72 Å. The Mn(1)-O(5) bond length is 1.74 Å. Bi(1) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(3), one O(5), and two equivalent O(4) atoms. The Bi(1)-O(1) bond length is 2.43 Å. The Bi(1)-O(2) bond length is 2.43 Å. The Bi(1)-O(3) bond length is 2.64 Å. The Bi(1)-O(5) bond length is 2.38 Å. There is one shorter (2.20 Å) and one longer (2.25 Å) Bi(1)-O(4) bond length. There are five inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(1), and one Bi(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(1), and one Bi(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(1), and one Bi(1) atom. In the fourth O site, O(4) is bonded to two equivalent Mg(1) and two equivalent Bi(1) atoms to form edge-sharing OMg2Bi2 tetrahedra. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(1), and one Bi(1) atom.