Na2MgMn2O8 crystallizes in the monoclinic C2/m space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form NaO6 octahedra that share corners with six equivalent Mn(1)O4 tetrahedra and edges with two equivalent Na(2)O6 octahedra. In the second Na site, Na(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form NaO6 octahedra that share corners with six equivalent Mn(1)O4 tetrahedra and edges with two equivalent Na(1)O6 octahedra. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. Mn(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form distorted MnO4 tetrahedra that share corners with three equivalent Na(1)O6 octahedra and corners with three equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 40-62°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Mg(1), and one Mn(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(2), one Mg(1), and one Mn(1) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Na(1) and one Mn(1) atom.
Na2MgMn2O8 crystallizes in the monoclinic C2/m space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form NaO6 octahedra that share corners with six equivalent Mn(1)O4 tetrahedra and edges with two equivalent Na(2)O6 octahedra. Both Na(1)-O(3) bond lengths are 2.32 Å. All Na(1)-O(1) bond lengths are 2.59 Å. In the second Na site, Na(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form NaO6 octahedra that share corners with six equivalent Mn(1)O4 tetrahedra and edges with two equivalent Na(1)O6 octahedra. Both Na(2)-O(2) bond lengths are 2.36 Å. All Na(2)-O(1) bond lengths are 2.51 Å. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. Both Mg(1)-O(2) bond lengths are 2.25 Å. All Mg(1)-O(1) bond lengths are 2.20 Å. Mn(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form distorted MnO4 tetrahedra that share corners with three equivalent Na(1)O6 octahedra and corners with three equivalent Na(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 40-62°. The Mn(1)-O(2) bond length is 1.69 Å. The Mn(1)-O(3) bond length is 1.61 Å. Both Mn(1)-O(1) bond lengths are 1.70 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Mg(1), and one Mn(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Na(2), one Mg(1), and one Mn(1) atom. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to one Na(1) and one Mn(1) atom.