Na4Mg(CuO2)2 crystallizes in the monoclinic Cm space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a distorted L-shaped geometry to two equivalent O(3) atoms. In the second Na site, Na(2) is bonded in a 4-coordinate geometry to one O(2), one O(3), and two equivalent O(4) atoms. In the third Na site, Na(3) is bonded in a rectangular see-saw-like geometry to one O(1), one O(4), and two equivalent O(2) atoms. In the fourth Na site, Na(4) is bonded in a 3-coordinate geometry to one O(3) and two equivalent O(1) atoms. Mg(1) is bonded to one O(2), one O(4), and two equivalent O(1) atoms to form distorted corner-sharing MgO4 tetrahedra. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 4-coordinate geometry to two equivalent O(2) and two equivalent O(4) atoms. In the second Cu site, Cu(2) is bonded in a water-like geometry to two equivalent O(3) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Na(3), two equivalent Na(4), and two equivalent Mg(1) atoms to form distorted ONa3Mg2 trigonal bipyramids that share corners with two equivalent O(3)Na4Cu2 octahedra, edges with two equivalent O(2)Na3MgCu2 pentagonal pyramids, and edges with two equivalent O(1)Na3Mg2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 44°. In the second O site, O(2) is bonded to one Na(2), two equivalent Na(3), one Mg(1), and two equivalent Cu(1) atoms to form distorted ONa3MgCu2 pentagonal pyramids that share  a cornercorner with one O(3)Na4Cu2 octahedra, edges with two equivalent O(2)Na3MgCu2 pentagonal pyramids, and edges with two equivalent O(1)Na3Mg2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 71°. In the third O site, O(3) is bonded to one Na(2), one Na(4), two equivalent Na(1), and two equivalent Cu(2) atoms to form ONa4Cu2 octahedra that share  a cornercorner with one O(2)Na3MgCu2 pentagonal pyramid, corners with two equivalent O(1)Na3Mg2 trigonal bipyramids, and edges with two equivalent O(3)Na4Cu2 octahedra. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to one Na(3), two equivalent Na(2), one Mg(1), and two equivalent Cu(1) atoms.
Na4Mg(CuO2)2 crystallizes in the monoclinic Cm space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a distorted L-shaped geometry to two equivalent O(3) atoms. Both Na(1)-O(3) bond lengths are 2.38 Å. In the second Na site, Na(2) is bonded in a 4-coordinate geometry to one O(2), one O(3), and two equivalent O(4) atoms. The Na(2)-O(2) bond length is 2.26 Å. The Na(2)-O(3) bond length is 2.42 Å. Both Na(2)-O(4) bond lengths are 2.40 Å. In the third Na site, Na(3) is bonded in a rectangular see-saw-like geometry to one O(1), one O(4), and two equivalent O(2) atoms. The Na(3)-O(1) bond length is 2.46 Å. The Na(3)-O(4) bond length is 2.28 Å. Both Na(3)-O(2) bond lengths are 2.37 Å. In the fourth Na site, Na(4) is bonded in a 3-coordinate geometry to one O(3) and two equivalent O(1) atoms. The Na(4)-O(3) bond length is 2.33 Å. Both Na(4)-O(1) bond lengths are 2.31 Å. Mg(1) is bonded to one O(2), one O(4), and two equivalent O(1) atoms to form distorted corner-sharing MgO4 tetrahedra. The Mg(1)-O(2) bond length is 2.13 Å. The Mg(1)-O(4) bond length is 2.04 Å. Both Mg(1)-O(1) bond lengths are 1.96 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a 4-coordinate geometry to two equivalent O(2) and two equivalent O(4) atoms. Both Cu(1)-O(2) bond lengths are 2.03 Å. Both Cu(1)-O(4) bond lengths are 2.13 Å. In the second Cu site, Cu(2) is bonded in a water-like geometry to two equivalent O(3) atoms. Both Cu(2)-O(3) bond lengths are 1.95 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Na(3), two equivalent Na(4), and two equivalent Mg(1) atoms to form distorted ONa3Mg2 trigonal bipyramids that share corners with two equivalent O(3)Na4Cu2 octahedra, edges with two equivalent O(2)Na3MgCu2 pentagonal pyramids, and edges with two equivalent O(1)Na3Mg2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 44°. In the second O site, O(2) is bonded to one Na(2), two equivalent Na(3), one Mg(1), and two equivalent Cu(1) atoms to form distorted ONa3MgCu2 pentagonal pyramids that share  a cornercorner with one O(3)Na4Cu2 octahedra, edges with two equivalent O(2)Na3MgCu2 pentagonal pyramids, and edges with two equivalent O(1)Na3Mg2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 71°. In the third O site, O(3) is bonded to one Na(2), one Na(4), two equivalent Na(1), and two equivalent Cu(2) atoms to form ONa4Cu2 octahedra that share  a cornercorner with one O(2)Na3MgCu2 pentagonal pyramid, corners with two equivalent O(1)Na3Mg2 trigonal bipyramids, and edges with two equivalent O(3)Na4Cu2 octahedra. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to one Na(3), two equivalent Na(2), one Mg(1), and two equivalent Cu(1) atoms.