Na4Mg(CuO2)2 crystallizes in the monoclinic Pm space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 3-coordinate geometry to one O(4) and two equivalent O(3) atoms. In the second Na site, Na(2) is bonded in a 2-coordinate geometry to two equivalent O(2) and two equivalent O(4) atoms. In the third Na site, Na(3) is bonded in a distorted rectangular see-saw-like geometry to one O(2), one O(4), and two equivalent O(1) atoms. In the fourth Na site, Na(4) is bonded in a 3-coordinate geometry to one O(1) and two equivalent O(2) atoms. Mg(1) is bonded in a distorted square co-planar geometry to two equivalent O(1) and two equivalent O(3) atoms. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a distorted L-shaped geometry to two equivalent O(3) atoms. In the second Cu site, Cu(2) is bonded in a distorted square co-planar geometry to two equivalent O(2) and two equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Na(4), two equivalent Na(3), and two equivalent Mg(1) atoms to form distorted ONa3Mg2 trigonal bipyramids that share corners with two equivalent O(4)Na4Cu2 octahedra, corners with two equivalent O(3)Na2Mg2Cu2 pentagonal pyramids,  an edgeedge with one O(3)Na2Mg2Cu2 pentagonal pyramid, and edges with two equivalent O(1)Na3Mg2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 51°. In the second O site, O(2) is bonded in a 7-coordinate geometry to one Na(3), two equivalent Na(2), two equivalent Na(4), and two equivalent Cu(2) atoms. In the third O site, O(3) is bonded to two equivalent Na(1), two equivalent Mg(1), and two equivalent Cu(1) atoms to form distorted ONa2Mg2Cu2 pentagonal pyramids that share corners with two equivalent O(4)Na4Cu2 octahedra, corners with two equivalent O(1)Na3Mg2 trigonal bipyramids,  an edgeedge with one O(1)Na3Mg2 trigonal bipyramid, and faces with two equivalent O(3)Na2Mg2Cu2 pentagonal pyramids. The corner-sharing octahedral tilt angles are 61°. In the fourth O site, O(4) is bonded to one Na(1), one Na(3), two equivalent Na(2), and two equivalent Cu(2) atoms to form ONa4Cu2 octahedra that share corners with two equivalent O(3)Na2Mg2Cu2 pentagonal pyramids, corners with two equivalent O(1)Na3Mg2 trigonal bipyramids, and edges with two equivalent O(4)Na4Cu2 octahedra.
Na4Mg(CuO2)2 crystallizes in the monoclinic Pm space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 3-coordinate geometry to one O(4) and two equivalent O(3) atoms. The Na(1)-O(4) bond length is 2.25 Å. Both Na(1)-O(3) bond lengths are 2.43 Å. In the second Na site, Na(2) is bonded in a 2-coordinate geometry to two equivalent O(2) and two equivalent O(4) atoms. Both Na(2)-O(2) bond lengths are 2.81 Å. Both Na(2)-O(4) bond lengths are 2.27 Å. In the third Na site, Na(3) is bonded in a distorted rectangular see-saw-like geometry to one O(2), one O(4), and two equivalent O(1) atoms. The Na(3)-O(2) bond length is 2.32 Å. The Na(3)-O(4) bond length is 2.41 Å. Both Na(3)-O(1) bond lengths are 2.26 Å. In the fourth Na site, Na(4) is bonded in a 3-coordinate geometry to one O(1) and two equivalent O(2) atoms. The Na(4)-O(1) bond length is 2.34 Å. Both Na(4)-O(2) bond lengths are 2.44 Å. Mg(1) is bonded in a distorted square co-planar geometry to two equivalent O(1) and two equivalent O(3) atoms. Both Mg(1)-O(1) bond lengths are 1.97 Å. Both Mg(1)-O(3) bond lengths are 2.14 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded in a distorted L-shaped geometry to two equivalent O(3) atoms. Both Cu(1)-O(3) bond lengths are 2.09 Å. In the second Cu site, Cu(2) is bonded in a distorted square co-planar geometry to two equivalent O(2) and two equivalent O(4) atoms. Both Cu(2)-O(2) bond lengths are 1.98 Å. Both Cu(2)-O(4) bond lengths are 1.98 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Na(4), two equivalent Na(3), and two equivalent Mg(1) atoms to form distorted ONa3Mg2 trigonal bipyramids that share corners with two equivalent O(4)Na4Cu2 octahedra, corners with two equivalent O(3)Na2Mg2Cu2 pentagonal pyramids,  an edgeedge with one O(3)Na2Mg2Cu2 pentagonal pyramid, and edges with two equivalent O(1)Na3Mg2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 51°. In the second O site, O(2) is bonded in a 7-coordinate geometry to one Na(3), two equivalent Na(2), two equivalent Na(4), and two equivalent Cu(2) atoms. In the third O site, O(3) is bonded to two equivalent Na(1), two equivalent Mg(1), and two equivalent Cu(1) atoms to form distorted ONa2Mg2Cu2 pentagonal pyramids that share corners with two equivalent O(4)Na4Cu2 octahedra, corners with two equivalent O(1)Na3Mg2 trigonal bipyramids,  an edgeedge with one O(1)Na3Mg2 trigonal bipyramid, and faces with two equivalent O(3)Na2Mg2Cu2 pentagonal pyramids. The corner-sharing octahedral tilt angles are 61°. In the fourth O site, O(4) is bonded to one Na(1), one Na(3), two equivalent Na(2), and two equivalent Cu(2) atoms to form ONa4Cu2 octahedra that share corners with two equivalent O(3)Na2Mg2Cu2 pentagonal pyramids, corners with two equivalent O(1)Na3Mg2 trigonal bipyramids, and edges with two equivalent O(4)Na4Cu2 octahedra.