Na2Mg(NiO2)2 crystallizes in the hexagonal P-6m2 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 9-coordinate geometry to three equivalent Mg(1) and six equivalent O(1) atoms. In the second Na site, Na(2) is bonded to six equivalent O(2) atoms to form distorted edge-sharing NaO6 pentagonal pyramids. Mg(1) is bonded in a 9-coordinate geometry to three equivalent Na(1) and six equivalent O(1) atoms. Ni(1) is bonded in a distorted trigonal non-coplanar geometry to three equivalent O(1) and three equivalent O(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 9-coordinate geometry to three equivalent Na(1), three equivalent Mg(1), and three equivalent Ni(1) atoms. In the second O site, O(2) is bonded to three equivalent Na(2) and three equivalent Ni(1) atoms to form a mixture of distorted corner, edge, and face-sharing ONa3Ni3 octahedra. The corner-sharing octahedral tilt angles are 45°.
Na2Mg(NiO2)2 crystallizes in the hexagonal P-6m2 space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 9-coordinate geometry to three equivalent Mg(1) and six equivalent O(1) atoms. All Na(1)-Mg(1) bond lengths are 1.93 Å. All Na(1)-O(1) bond lengths are 2.28 Å. In the second Na site, Na(2) is bonded to six equivalent O(2) atoms to form distorted edge-sharing NaO6 pentagonal pyramids. All Na(2)-O(2) bond lengths are 2.55 Å. Mg(1) is bonded in a 9-coordinate geometry to three equivalent Na(1) and six equivalent O(1) atoms. All Mg(1)-O(1) bond lengths are 2.28 Å. Ni(1) is bonded in a distorted trigonal non-coplanar geometry to three equivalent O(1) and three equivalent O(2) atoms. All Ni(1)-O(1) bond lengths are 2.56 Å. All Ni(1)-O(2) bond lengths are 2.07 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 9-coordinate geometry to three equivalent Na(1), three equivalent Mg(1), and three equivalent Ni(1) atoms. In the second O site, O(2) is bonded to three equivalent Na(2) and three equivalent Ni(1) atoms to form a mixture of distorted corner, edge, and face-sharing ONa3Ni3 octahedra. The corner-sharing octahedral tilt angles are 45°.