Ba3MgMn2O8 crystallizes in the trigonal R-3m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 10-coordinate geometry to one O(1) and nine equivalent O(2) atoms. In the second Ba site, Ba(2) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form BaO12 cuboctahedra that share corners with six equivalent Mg(1)O6 octahedra and edges with six equivalent Ba(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 9°. Mg(1) is bonded to six equivalent O(2) atoms to form distorted MgO6 octahedra that share corners with six equivalent Ba(2)O12 cuboctahedra. Mn(1) is bonded in a distorted rectangular see-saw-like geometry to one O(1) and three equivalent O(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Ba(1), three equivalent Ba(2), and one Mn(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Ba(2), three equivalent Ba(1), one Mg(1), and one Mn(1) atom.
Ba3MgMn2O8 crystallizes in the trigonal R-3m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 10-coordinate geometry to one O(1) and nine equivalent O(2) atoms. The Ba(1)-O(1) bond length is 2.53 Å. There are six shorter (2.96 Å) and three longer (2.98 Å) Ba(1)-O(2) bond lengths. In the second Ba site, Ba(2) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form BaO12 cuboctahedra that share corners with six equivalent Mg(1)O6 octahedra and edges with six equivalent Ba(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 9°. All Ba(2)-O(1) bond lengths are 3.38 Å. All Ba(2)-O(2) bond lengths are 3.00 Å. Mg(1) is bonded to six equivalent O(2) atoms to form distorted MgO6 octahedra that share corners with six equivalent Ba(2)O12 cuboctahedra. All Mg(1)-O(2) bond lengths are 2.11 Å. Mn(1) is bonded in a distorted rectangular see-saw-like geometry to one O(1) and three equivalent O(2) atoms. The Mn(1)-O(1) bond length is 1.76 Å. All Mn(1)-O(2) bond lengths are 1.84 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Ba(1), three equivalent Ba(2), and one Mn(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Ba(2), three equivalent Ba(1), one Mg(1), and one Mn(1) atom.