BaMgMn4O8 crystallizes in the monoclinic C2 space group. Ba(1) is bonded in a 10-coordinate geometry to two equivalent O(4), four equivalent O(1), and four equivalent O(3) atoms. Mg(1) is bonded to two equivalent O(4) and four equivalent O(2) atoms to form distorted MgO6 octahedra that share corners with two equivalent Mn(1)O5 trigonal bipyramids, edges with two equivalent Mg(1)O6 octahedra, edges with four equivalent Mn(2)O6 octahedra, and edges with two equivalent Mn(1)O5 trigonal bipyramids. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(4), and three equivalent O(3) atoms to form distorted MnO5 trigonal bipyramids that share  a cornercorner with one Mg(1)O6 octahedra, corners with three equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids,  an edgeedge with one Mg(1)O6 octahedra, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 39-54°. In the second Mn site, Mn(2) is bonded to one O(2), two equivalent O(4), and three equivalent O(1) atoms to form MnO6 octahedra that share corners with three equivalent Mn(1)O5 trigonal bipyramids, edges with two equivalent Mg(1)O6 octahedra, and edges with four equivalent Mn(2)O6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Ba(1) and three equivalent Mn(2) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Mg(1), one Mn(1), and one Mn(2) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Ba(1) and three equivalent Mn(1) atoms. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ba(1), one Mg(1), one Mn(1), and two equivalent Mn(2) atoms.
BaMgMn4O8 crystallizes in the monoclinic C2 space group. Ba(1) is bonded in a 10-coordinate geometry to two equivalent O(4), four equivalent O(1), and four equivalent O(3) atoms. Both Ba(1)-O(4) bond lengths are 3.11 Å. There are two shorter (2.87 Å) and two longer (3.32 Å) Ba(1)-O(1) bond lengths. There are two shorter (2.79 Å) and two longer (3.29 Å) Ba(1)-O(3) bond lengths. Mg(1) is bonded to two equivalent O(4) and four equivalent O(2) atoms to form distorted MgO6 octahedra that share corners with two equivalent Mn(1)O5 trigonal bipyramids, edges with two equivalent Mg(1)O6 octahedra, edges with four equivalent Mn(2)O6 octahedra, and edges with two equivalent Mn(1)O5 trigonal bipyramids. Both Mg(1)-O(4) bond lengths are 2.00 Å. There are two shorter (2.05 Å) and two longer (2.24 Å) Mg(1)-O(2) bond lengths. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(4), and three equivalent O(3) atoms to form distorted MnO5 trigonal bipyramids that share  a cornercorner with one Mg(1)O6 octahedra, corners with three equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids,  an edgeedge with one Mg(1)O6 octahedra, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 39-54°. The Mn(1)-O(2) bond length is 1.96 Å. The Mn(1)-O(4) bond length is 1.96 Å. There are a spread of Mn(1)-O(3) bond distances ranging from 1.95-2.18 Å. In the second Mn site, Mn(2) is bonded to one O(2), two equivalent O(4), and three equivalent O(1) atoms to form MnO6 octahedra that share corners with three equivalent Mn(1)O5 trigonal bipyramids, edges with two equivalent Mg(1)O6 octahedra, and edges with four equivalent Mn(2)O6 octahedra. The Mn(2)-O(2) bond length is 1.97 Å. There is one shorter (2.00 Å) and one longer (2.43 Å) Mn(2)-O(4) bond length. There are a spread of Mn(2)-O(1) bond distances ranging from 1.94-2.24 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Ba(1) and three equivalent Mn(2) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Mg(1), one Mn(1), and one Mn(2) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Ba(1) and three equivalent Mn(1) atoms. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Ba(1), one Mg(1), one Mn(1), and two equivalent Mn(2) atoms.