Na2Mg(CuO2)2 crystallizes in the monoclinic C2/m space group. Na(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted edge-sharing NaO6 pentagonal pyramids. Mg(1) is bonded in a distorted square co-planar geometry to four equivalent O(1) atoms. Cu(1) is bonded in a distorted T-shaped geometry to one O(1) and two equivalent O(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Na(1), two equivalent Mg(1), and one Cu(1) atom to form distorted ONa3Mg2Cu octahedra that share corners with two equivalent O(1)Na3Mg2Cu octahedra, corners with eight equivalent O(2)Na3Cu2 trigonal bipyramids, edges with five equivalent O(1)Na3Mg2Cu octahedra, and  a faceface with one O(2)Na3Cu2 trigonal bipyramid. The corner-sharing octahedra are not tilted. In the second O site, O(2) is bonded to three equivalent Na(1) and two equivalent Cu(1) atoms to form distorted ONa3Cu2 trigonal bipyramids that share corners with eight equivalent O(1)Na3Mg2Cu octahedra, corners with two equivalent O(2)Na3Cu2 trigonal bipyramids, edges with three equivalent O(2)Na3Cu2 trigonal bipyramids, and  a faceface with one O(1)Na3Mg2Cu octahedra. The corner-sharing octahedral tilt angles range from 19-82°.
Na2Mg(CuO2)2 crystallizes in the monoclinic C2/m space group. Na(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted edge-sharing NaO6 pentagonal pyramids. There is one shorter (2.56 Å) and two longer (2.62 Å) Na(1)-O(1) bond lengths. There are two shorter (2.40 Å) and one longer (2.57 Å) Na(1)-O(2) bond length. Mg(1) is bonded in a distorted square co-planar geometry to four equivalent O(1) atoms. All Mg(1)-O(1) bond lengths are 2.10 Å. Cu(1) is bonded in a distorted T-shaped geometry to one O(1) and two equivalent O(2) atoms. The Cu(1)-O(1) bond length is 1.87 Å. There is one shorter (1.80 Å) and one longer (1.95 Å) Cu(1)-O(2) bond length. There are two inequivalent O sites. In the first O site, O(1) is bonded to three equivalent Na(1), two equivalent Mg(1), and one Cu(1) atom to form distorted ONa3Mg2Cu octahedra that share corners with two equivalent O(1)Na3Mg2Cu octahedra, corners with eight equivalent O(2)Na3Cu2 trigonal bipyramids, edges with five equivalent O(1)Na3Mg2Cu octahedra, and  a faceface with one O(2)Na3Cu2 trigonal bipyramid. The corner-sharing octahedra are not tilted. In the second O site, O(2) is bonded to three equivalent Na(1) and two equivalent Cu(1) atoms to form distorted ONa3Cu2 trigonal bipyramids that share corners with eight equivalent O(1)Na3Mg2Cu octahedra, corners with two equivalent O(2)Na3Cu2 trigonal bipyramids, edges with three equivalent O(2)Na3Cu2 trigonal bipyramids, and  a faceface with one O(1)Na3Mg2Cu octahedra. The corner-sharing octahedral tilt angles range from 19-82°.