Na4MgMn4O8 crystallizes in the monoclinic Pm space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(2), one O(6), two equivalent O(1), and two equivalent O(5) atoms. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(2), one O(8), two equivalent O(4), and two equivalent O(7) atoms. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(2), and two equivalent O(6) atoms. In the fourth Na site, Na(4) is bonded in a 5-coordinate geometry to one O(7), two equivalent O(3), and two equivalent O(8) atoms. Mg(1) is bonded to one O(1), one O(5), and two equivalent O(3) atoms to form MgO4 tetrahedra that share corners with two equivalent Mn(3)O5 square pyramids, corners with four equivalent Mn(1)O5 square pyramids, corners with two equivalent Mg(1)O4 tetrahedra, and  an edgeedge with one Mn(3)O5 square pyramid. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(6), two equivalent O(1), and two equivalent O(5) atoms to form MnO5 square pyramids that share corners with two equivalent Mn(2)O5 square pyramids, corners with four equivalent Mg(1)O4 tetrahedra, and edges with two equivalent Mn(1)O5 square pyramids. In the second Mn site, Mn(2) is bonded to one O(4), two equivalent O(2), and two equivalent O(6) atoms to form a mixture of corner and edge-sharing MnO5 square pyramids. In the third Mn site, Mn(3) is bonded to one O(7), two equivalent O(3), and two equivalent O(8) atoms to form distorted MnO5 square pyramids that share corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent Mn(3)O5 square pyramids, edges with two equivalent Mn(4)O5 square pyramids, and  an edgeedge with one Mg(1)O4 tetrahedra. In the fourth Mn site, Mn(4) is bonded to one O(8), two equivalent O(4), and two equivalent O(7) atoms to form a mixture of corner and edge-sharing MnO5 square pyramids. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Na(1), one Mg(1), and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded to one Na(1), one Na(2), two equivalent Na(3), and two equivalent Mn(2) atoms to form edge-sharing ONa4Mn2 octahedra. In the third O site, O(3) is bonded in a 6-coordinate geometry to two equivalent Na(4), two equivalent Mg(1), and two equivalent Mn(3) atoms. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to one Na(3), two equivalent Na(2), one Mn(2), and two equivalent Mn(4) atoms. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to two equivalent Na(1), one Mg(1), and two equivalent Mn(1) atoms. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to one Na(1), two equivalent Na(3), one Mn(1), and two equivalent Mn(2) atoms. In the seventh O site, O(7) is bonded in a 6-coordinate geometry to one Na(4), two equivalent Na(2), one Mn(3), and two equivalent Mn(4) atoms. In the eighth O site, O(8) is bonded in a 6-coordinate geometry to one Na(2), two equivalent Na(4), one Mn(4), and two equivalent Mn(3) atoms.
Na4MgMn4O8 crystallizes in the monoclinic Pm space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 6-coordinate geometry to one O(2), one O(6), two equivalent O(1), and two equivalent O(5) atoms. The Na(1)-O(2) bond length is 2.37 Å. The Na(1)-O(6) bond length is 2.69 Å. Both Na(1)-O(1) bond lengths are 2.44 Å. Both Na(1)-O(5) bond lengths are 2.48 Å. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(2), one O(8), two equivalent O(4), and two equivalent O(7) atoms. The Na(2)-O(2) bond length is 2.49 Å. The Na(2)-O(8) bond length is 2.79 Å. Both Na(2)-O(4) bond lengths are 2.45 Å. Both Na(2)-O(7) bond lengths are 2.42 Å. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(2), and two equivalent O(6) atoms. The Na(3)-O(4) bond length is 2.41 Å. Both Na(3)-O(2) bond lengths are 2.32 Å. Both Na(3)-O(6) bond lengths are 2.47 Å. In the fourth Na site, Na(4) is bonded in a 5-coordinate geometry to one O(7), two equivalent O(3), and two equivalent O(8) atoms. The Na(4)-O(7) bond length is 2.67 Å. Both Na(4)-O(3) bond lengths are 2.55 Å. Both Na(4)-O(8) bond lengths are 2.30 Å. Mg(1) is bonded to one O(1), one O(5), and two equivalent O(3) atoms to form MgO4 tetrahedra that share corners with two equivalent Mn(3)O5 square pyramids, corners with four equivalent Mn(1)O5 square pyramids, corners with two equivalent Mg(1)O4 tetrahedra, and  an edgeedge with one Mn(3)O5 square pyramid. The Mg(1)-O(1) bond length is 1.99 Å. The Mg(1)-O(5) bond length is 2.00 Å. Both Mg(1)-O(3) bond lengths are 2.01 Å. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(6), two equivalent O(1), and two equivalent O(5) atoms to form MnO5 square pyramids that share corners with two equivalent Mn(2)O5 square pyramids, corners with four equivalent Mg(1)O4 tetrahedra, and edges with two equivalent Mn(1)O5 square pyramids. The Mn(1)-O(6) bond length is 2.31 Å. Both Mn(1)-O(1) bond lengths are 2.05 Å. Both Mn(1)-O(5) bond lengths are 2.07 Å. In the second Mn site, Mn(2) is bonded to one O(4), two equivalent O(2), and two equivalent O(6) atoms to form a mixture of corner and edge-sharing MnO5 square pyramids. The Mn(2)-O(4) bond length is 2.24 Å. Both Mn(2)-O(2) bond lengths are 2.02 Å. Both Mn(2)-O(6) bond lengths are 2.01 Å. In the third Mn site, Mn(3) is bonded to one O(7), two equivalent O(3), and two equivalent O(8) atoms to form distorted MnO5 square pyramids that share corners with two equivalent Mg(1)O4 tetrahedra, edges with two equivalent Mn(3)O5 square pyramids, edges with two equivalent Mn(4)O5 square pyramids, and  an edgeedge with one Mg(1)O4 tetrahedra. The Mn(3)-O(7) bond length is 2.25 Å. Both Mn(3)-O(3) bond lengths are 2.27 Å. Both Mn(3)-O(8) bond lengths are 2.10 Å. In the fourth Mn site, Mn(4) is bonded to one O(8), two equivalent O(4), and two equivalent O(7) atoms to form a mixture of corner and edge-sharing MnO5 square pyramids. The Mn(4)-O(8) bond length is 2.15 Å. Both Mn(4)-O(4) bond lengths are 2.04 Å. Both Mn(4)-O(7) bond lengths are 2.06 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Na(1), one Mg(1), and two equivalent Mn(1) atoms. In the second O site, O(2) is bonded to one Na(1), one Na(2), two equivalent Na(3), and two equivalent Mn(2) atoms to form edge-sharing ONa4Mn2 octahedra. In the third O site, O(3) is bonded in a 6-coordinate geometry to two equivalent Na(4), two equivalent Mg(1), and two equivalent Mn(3) atoms. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to one Na(3), two equivalent Na(2), one Mn(2), and two equivalent Mn(4) atoms. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to two equivalent Na(1), one Mg(1), and two equivalent Mn(1) atoms. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to one Na(1), two equivalent Na(3), one Mn(1), and two equivalent Mn(2) atoms. In the seventh O site, O(7) is bonded in a 6-coordinate geometry to one Na(4), two equivalent Na(2), one Mn(3), and two equivalent Mn(4) atoms. In the eighth O site, O(8) is bonded in a 6-coordinate geometry to one Na(2), two equivalent Na(4), one Mn(4), and two equivalent Mn(3) atoms.