Na4Mg(FeO2)4 crystallizes in the monoclinic C2 space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded in a 4-coordinate geometry to two equivalent O(2) and two equivalent O(4) atoms. In the second Na site, Na(2) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), and one O(4) atom. In the third Na site, Na(3) is bonded to two equivalent O(1) and two equivalent O(3) atoms to form distorted NaO4 tetrahedra that share corners with two equivalent Fe(3)O4 tetrahedra and  an edgeedge with one Fe(1)O4 tetrahedra. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1) and two equivalent O(4) atoms to form FeO4 tetrahedra that share  an edgeedge with one Na(3)O4 tetrahedra. In the second Fe site, Fe(2) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(2), one O(3), and one O(4) atom. In the third Fe site, Fe(3) is bonded to two equivalent O(2) and two equivalent O(3) atoms to form FeO4 tetrahedra that share corners with two equivalent Na(3)O4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Na(2), one Na(3), one Mg(1), one Fe(1), and one Fe(2) atom to form a mixture of distorted edge and corner-sharing ONa2MgFe2 trigonal bipyramids. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Fe(2), and one Fe(3) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(2), one Na(3), one Mg(1), one Fe(2), and one Fe(3) atom. In the fourth O site, O(4) is bonded to one Na(1), one Na(2), one Mg(1), one Fe(1), and one Fe(2) atom to form a mixture of distorted edge and corner-sharing ONa2MgFe2 trigonal bipyramids.
Na4Mg(FeO2)4 crystallizes in the monoclinic C2 space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded in a 4-coordinate geometry to two equivalent O(2) and two equivalent O(4) atoms. Both Na(1)-O(2) bond lengths are 2.81 Å. Both Na(1)-O(4) bond lengths are 2.46 Å. In the second Na site, Na(2) is bonded in a 4-coordinate geometry to one O(1), one O(2), one O(3), and one O(4) atom. The Na(2)-O(1) bond length is 2.26 Å. The Na(2)-O(2) bond length is 2.11 Å. The Na(2)-O(3) bond length is 2.37 Å. The Na(2)-O(4) bond length is 2.35 Å. In the third Na site, Na(3) is bonded to two equivalent O(1) and two equivalent O(3) atoms to form distorted NaO4 tetrahedra that share corners with two equivalent Fe(3)O4 tetrahedra and  an edgeedge with one Fe(1)O4 tetrahedra. Both Na(3)-O(1) bond lengths are 2.35 Å. Both Na(3)-O(3) bond lengths are 2.40 Å. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms. Both Mg(1)-O(1) bond lengths are 2.45 Å. Both Mg(1)-O(3) bond lengths are 2.21 Å. Both Mg(1)-O(4) bond lengths are 2.12 Å. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1) and two equivalent O(4) atoms to form FeO4 tetrahedra that share  an edgeedge with one Na(3)O4 tetrahedra. Both Fe(1)-O(1) bond lengths are 1.96 Å. Both Fe(1)-O(4) bond lengths are 1.90 Å. In the second Fe site, Fe(2) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(2), one O(3), and one O(4) atom. The Fe(2)-O(1) bond length is 2.02 Å. The Fe(2)-O(2) bond length is 1.90 Å. The Fe(2)-O(3) bond length is 2.11 Å. The Fe(2)-O(4) bond length is 2.15 Å. In the third Fe site, Fe(3) is bonded to two equivalent O(2) and two equivalent O(3) atoms to form FeO4 tetrahedra that share corners with two equivalent Na(3)O4 tetrahedra. Both Fe(3)-O(2) bond lengths are 1.88 Å. Both Fe(3)-O(3) bond lengths are 1.98 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Na(2), one Na(3), one Mg(1), one Fe(1), and one Fe(2) atom to form a mixture of distorted edge and corner-sharing ONa2MgFe2 trigonal bipyramids. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Fe(2), and one Fe(3) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(2), one Na(3), one Mg(1), one Fe(2), and one Fe(3) atom. In the fourth O site, O(4) is bonded to one Na(1), one Na(2), one Mg(1), one Fe(1), and one Fe(2) atom to form a mixture of distorted edge and corner-sharing ONa2MgFe2 trigonal bipyramids.