Na4Mg(Ni2O5)2 crystallizes in the triclinic P1 space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(10), one O(2), one O(4), one O(5), one O(7), and one O(9) atom to form distorted NaO6 pentagonal pyramids that share  an edgeedge with one Ni(2)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Ni(4)O6 octahedra. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(10), one O(3), one O(4), one O(5), one O(7), and one O(9) atom. In the third Na site, Na(3) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(5), one O(6), one O(7), and one O(8) atom. In the fourth Na site, Na(4) is bonded in a 5-coordinate geometry to one O(10), one O(3), one O(4), one O(8), and one O(9) atom. Mg(1) is bonded in a 5-coordinate geometry to one O(10), one O(2), one O(3), one O(6), and one O(8) atom. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a distorted see-saw-like geometry to one O(1), one O(2), one O(5), and one O(8) atom. In the second Ni site, Ni(2) is bonded to one O(1), one O(10), one O(3), one O(4), one O(6), and one O(8) atom to form NiO6 octahedra that share  an edgeedge with one Ni(3)O6 octahedra, edges with two equivalent Ni(4)O6 octahedra, and  an edgeedge with one Na(1)O6 pentagonal pyramid. In the third Ni site, Ni(3) is bonded to one O(1), one O(2), one O(5), one O(6), one O(7), and one O(9) atom to form NiO6 octahedra that share  an edgeedge with one Ni(2)O6 octahedra,  an edgeedge with one Ni(4)O6 octahedra, and edges with two equivalent Na(1)O6 pentagonal pyramids. In the fourth Ni site, Ni(4) is bonded to one O(10), one O(3), one O(4), one O(7), one O(8), and one O(9) atom to form distorted NiO6 octahedra that share  an edgeedge with one Ni(3)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, and edges with two equivalent Na(1)O6 pentagonal pyramids. There are ten inequivalent O sites. In the first O site, O(1) is bonded to one Na(3), one Ni(1), one Ni(2), and one Ni(3) atom to form ONaNi3 trigonal pyramids that share  a cornercorner with one O(10)Na3MgNi2 octahedra,  a cornercorner with one O(4)Na3Ni2 square pyramid,  a cornercorner with one O(9)Na3Ni2 square pyramid,  a cornercorner with one O(2)Na2MgNi2 trigonal bipyramid,  a cornercorner with one O(5)Na3Ni2 trigonal bipyramid, corners with two equivalent O(7)Na3Ni2 trigonal bipyramids,  an edgeedge with one O(2)Na2MgNi2 trigonal bipyramid, and  an edgeedge with one O(5)Na3Ni2 trigonal bipyramid. The corner-sharing octahedral tilt angles are 15°. In the second O site, O(2) is bonded to one Na(1), one Na(3), one Mg(1), one Ni(1), and one Ni(3) atom to form distorted ONa2MgNi2 trigonal bipyramids that share corners with two equivalent O(10)Na3MgNi2 octahedra,  a cornercorner with one O(4)Na3Ni2 square pyramid,  a cornercorner with one O(7)Na3Ni2 trigonal bipyramid, corners with two equivalent O(5)Na3Ni2 trigonal bipyramids,  a cornercorner with one O(1)NaNi3 trigonal pyramid,  an edgeedge with one O(9)Na3Ni2 square pyramid,  an edgeedge with one O(5)Na3Ni2 trigonal bipyramid,  an edgeedge with one O(7)Na3Ni2 trigonal bipyramid, and  an edgeedge with one O(1)NaNi3 trigonal pyramid. The corner-sharing octahedral tilt angles range from 14-64°. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(2), one Na(4), one Mg(1), one Ni(2), and one Ni(4) atom. In the fourth O site, O(4) is bonded to one Na(1), one Na(2), one Na(4), one Ni(2), and one Ni(4) atom to form ONa3Ni2 square pyramids that share corners with three equivalent O(10)Na3MgNi2 octahedra,  a cornercorner with one O(2)Na2MgNi2 trigonal bipyramid,  a cornercorner with one O(7)Na3Ni2 trigonal bipyramid,  a cornercorner with one O(1)NaNi3 trigonal pyramid,  an edgeedge with one O(10)Na3MgNi2 octahedra, edges with two equivalent O(9)Na3Ni2 square pyramids,  an edgeedge with one O(5)Na3Ni2 trigonal bipyramid, and  an edgeedge with one O(7)Na3Ni2 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 19-59°. In the fifth O site, O(5) is bonded to one Na(1), one Na(2), one Na(3), one Ni(1), and one Ni(3) atom to form ONa3Ni2 trigonal bipyramids that share corners with two equivalent O(10)Na3MgNi2 octahedra,  a cornercorner with one O(9)Na3Ni2 square pyramid, corners with two equivalent O(2)Na2MgNi2 trigonal bipyramids,  a cornercorner with one O(1)NaNi3 trigonal pyramid,  an edgeedge with one O(4)Na3Ni2 square pyramid,  an edgeedge with one O(9)Na3Ni2 square pyramid,  an edgeedge with one O(2)Na2MgNi2 trigonal bipyramid, edges with two equivalent O(7)Na3Ni2 trigonal bipyramids, and  an edgeedge with one O(1)NaNi3 trigonal pyramid. The corner-sharing octahedral tilt angles range from 23-28°. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Na(3), one Mg(1), one Ni(2), and one Ni(3) atom. In the seventh O site, O(7) is bonded to one Na(1), one Na(2), one Na(3), one Ni(3), and one Ni(4) atom to form distorted ONa3Ni2 trigonal bipyramids that share  a cornercorner with one O(10)Na3MgNi2 octahedra,  a cornercorner with one O(4)Na3Ni2 square pyramid, corners with two equivalent O(9)Na3Ni2 square pyramids,  a cornercorner with one O(2)Na2MgNi2 trigonal bipyramid, corners with two equivalent O(1)NaNi3 trigonal pyramids,  an edgeedge with one O(10)Na3MgNi2 octahedra,  an edgeedge with one O(4)Na3Ni2 square pyramid,  an edgeedge with one O(9)Na3Ni2 square pyramid,  an edgeedge with one O(2)Na2MgNi2 trigonal bipyramid, and edges with two equivalent O(5)Na3Ni2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 63°. In the eighth O site, O(8) is bonded in a 6-coordinate geometry to one Na(3), one Na(4), one Mg(1), one Ni(1), one Ni(2), and one Ni(4) atom. In the ninth O site, O(9) is bonded to one Na(1), one Na(2), one Na(4), one Ni(3), and one Ni(4) atom to form ONa3Ni2 square pyramids that share  a cornercorner with one O(5)Na3Ni2 trigonal bipyramid, corners with two equivalent O(7)Na3Ni2 trigonal bipyramids,  a cornercorner with one O(1)NaNi3 trigonal pyramid, edges with two equivalent O(10)Na3MgNi2 octahedra, edges with two equivalent O(4)Na3Ni2 square pyramids,  an edgeedge with one O(2)Na2MgNi2 trigonal bipyramid,  an edgeedge with one O(5)Na3Ni2 trigonal bipyramid, and  an edgeedge with one O(7)Na3Ni2 trigonal bipyramid. In the tenth O site, O(10) is bonded to one Na(1), one Na(2), one Na(4), one Mg(1), one Ni(2), and one Ni(4) atom to form distorted ONa3MgNi2 octahedra that share corners with three equivalent O(4)Na3Ni2 square pyramids,  a cornercorner with one O(7)Na3Ni2 trigonal bipyramid, corners with two equivalent O(2)Na2MgNi2 trigonal bipyramids, corners with two equivalent O(5)Na3Ni2 trigonal bipyramids,  a cornercorner with one O(1)NaNi3 trigonal pyramid,  an edgeedge with one O(4)Na3Ni2 square pyramid, edges with two equivalent O(9)Na3Ni2 square pyramids, and  an edgeedge with one O(7)Na3Ni2 trigonal bipyramid.
Na4Mg(Ni2O5)2 crystallizes in the triclinic P1 space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded to one O(10), one O(2), one O(4), one O(5), one O(7), and one O(9) atom to form distorted NaO6 pentagonal pyramids that share  an edgeedge with one Ni(2)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Ni(4)O6 octahedra. The Na(1)-O(10) bond length is 2.28 Å. The Na(1)-O(2) bond length is 2.21 Å. The Na(1)-O(4) bond length is 2.30 Å. The Na(1)-O(5) bond length is 2.42 Å. The Na(1)-O(7) bond length is 2.29 Å. The Na(1)-O(9) bond length is 2.50 Å. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one O(10), one O(3), one O(4), one O(5), one O(7), and one O(9) atom. The Na(2)-O(10) bond length is 2.37 Å. The Na(2)-O(3) bond length is 2.51 Å. The Na(2)-O(4) bond length is 2.31 Å. The Na(2)-O(5) bond length is 2.27 Å. The Na(2)-O(7) bond length is 2.35 Å. The Na(2)-O(9) bond length is 2.35 Å. In the third Na site, Na(3) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(5), one O(6), one O(7), and one O(8) atom. The Na(3)-O(1) bond length is 2.22 Å. The Na(3)-O(2) bond length is 2.33 Å. The Na(3)-O(5) bond length is 2.35 Å. The Na(3)-O(6) bond length is 2.27 Å. The Na(3)-O(7) bond length is 2.42 Å. The Na(3)-O(8) bond length is 2.83 Å. In the fourth Na site, Na(4) is bonded in a 5-coordinate geometry to one O(10), one O(3), one O(4), one O(8), and one O(9) atom. The Na(4)-O(10) bond length is 2.45 Å. The Na(4)-O(3) bond length is 2.35 Å. The Na(4)-O(4) bond length is 2.42 Å. The Na(4)-O(8) bond length is 2.41 Å. The Na(4)-O(9) bond length is 2.35 Å. Mg(1) is bonded in a 5-coordinate geometry to one O(10), one O(2), one O(3), one O(6), and one O(8) atom. The Mg(1)-O(10) bond length is 2.11 Å. The Mg(1)-O(2) bond length is 2.04 Å. The Mg(1)-O(3) bond length is 1.97 Å. The Mg(1)-O(6) bond length is 1.98 Å. The Mg(1)-O(8) bond length is 2.27 Å. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a distorted see-saw-like geometry to one O(1), one O(2), one O(5), and one O(8) atom. The Ni(1)-O(1) bond length is 1.86 Å. The Ni(1)-O(2) bond length is 1.94 Å. The Ni(1)-O(5) bond length is 1.82 Å. The Ni(1)-O(8) bond length is 1.93 Å. In the second Ni site, Ni(2) is bonded to one O(1), one O(10), one O(3), one O(4), one O(6), and one O(8) atom to form NiO6 octahedra that share  an edgeedge with one Ni(3)O6 octahedra, edges with two equivalent Ni(4)O6 octahedra, and  an edgeedge with one Na(1)O6 pentagonal pyramid. The Ni(2)-O(1) bond length is 1.99 Å. The Ni(2)-O(10) bond length is 2.03 Å. The Ni(2)-O(3) bond length is 1.97 Å. The Ni(2)-O(4) bond length is 1.88 Å. The Ni(2)-O(6) bond length is 1.89 Å. The Ni(2)-O(8) bond length is 2.17 Å. In the third Ni site, Ni(3) is bonded to one O(1), one O(2), one O(5), one O(6), one O(7), and one O(9) atom to form NiO6 octahedra that share  an edgeedge with one Ni(2)O6 octahedra,  an edgeedge with one Ni(4)O6 octahedra, and edges with two equivalent Na(1)O6 pentagonal pyramids. The Ni(3)-O(1) bond length is 1.92 Å. The Ni(3)-O(2) bond length is 1.94 Å. The Ni(3)-O(5) bond length is 1.89 Å. The Ni(3)-O(6) bond length is 1.91 Å. The Ni(3)-O(7) bond length is 1.86 Å. The Ni(3)-O(9) bond length is 1.94 Å. In the fourth Ni site, Ni(4) is bonded to one O(10), one O(3), one O(4), one O(7), one O(8), and one O(9) atom to form distorted NiO6 octahedra that share  an edgeedge with one Ni(3)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, and edges with two equivalent Na(1)O6 pentagonal pyramids. The Ni(4)-O(10) bond length is 2.04 Å. The Ni(4)-O(3) bond length is 1.90 Å. The Ni(4)-O(4) bond length is 1.98 Å. The Ni(4)-O(7) bond length is 1.94 Å. The Ni(4)-O(8) bond length is 2.23 Å. The Ni(4)-O(9) bond length is 1.94 Å. There are ten inequivalent O sites. In the first O site, O(1) is bonded to one Na(3), one Ni(1), one Ni(2), and one Ni(3) atom to form ONaNi3 trigonal pyramids that share  a cornercorner with one O(10)Na3MgNi2 octahedra,  a cornercorner with one O(4)Na3Ni2 square pyramid,  a cornercorner with one O(9)Na3Ni2 square pyramid,  a cornercorner with one O(2)Na2MgNi2 trigonal bipyramid,  a cornercorner with one O(5)Na3Ni2 trigonal bipyramid, corners with two equivalent O(7)Na3Ni2 trigonal bipyramids,  an edgeedge with one O(2)Na2MgNi2 trigonal bipyramid, and  an edgeedge with one O(5)Na3Ni2 trigonal bipyramid. The corner-sharing octahedral tilt angles are 15°. In the second O site, O(2) is bonded to one Na(1), one Na(3), one Mg(1), one Ni(1), and one Ni(3) atom to form distorted ONa2MgNi2 trigonal bipyramids that share corners with two equivalent O(10)Na3MgNi2 octahedra,  a cornercorner with one O(4)Na3Ni2 square pyramid,  a cornercorner with one O(7)Na3Ni2 trigonal bipyramid, corners with two equivalent O(5)Na3Ni2 trigonal bipyramids,  a cornercorner with one O(1)NaNi3 trigonal pyramid,  an edgeedge with one O(9)Na3Ni2 square pyramid,  an edgeedge with one O(5)Na3Ni2 trigonal bipyramid,  an edgeedge with one O(7)Na3Ni2 trigonal bipyramid, and  an edgeedge with one O(1)NaNi3 trigonal pyramid. The corner-sharing octahedral tilt angles range from 14-64°. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(2), one Na(4), one Mg(1), one Ni(2), and one Ni(4) atom. In the fourth O site, O(4) is bonded to one Na(1), one Na(2), one Na(4), one Ni(2), and one Ni(4) atom to form ONa3Ni2 square pyramids that share corners with three equivalent O(10)Na3MgNi2 octahedra,  a cornercorner with one O(2)Na2MgNi2 trigonal bipyramid,  a cornercorner with one O(7)Na3Ni2 trigonal bipyramid,  a cornercorner with one O(1)NaNi3 trigonal pyramid,  an edgeedge with one O(10)Na3MgNi2 octahedra, edges with two equivalent O(9)Na3Ni2 square pyramids,  an edgeedge with one O(5)Na3Ni2 trigonal bipyramid, and  an edgeedge with one O(7)Na3Ni2 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 19-59°. In the fifth O site, O(5) is bonded to one Na(1), one Na(2), one Na(3), one Ni(1), and one Ni(3) atom to form ONa3Ni2 trigonal bipyramids that share corners with two equivalent O(10)Na3MgNi2 octahedra,  a cornercorner with one O(9)Na3Ni2 square pyramid, corners with two equivalent O(2)Na2MgNi2 trigonal bipyramids,  a cornercorner with one O(1)NaNi3 trigonal pyramid,  an edgeedge with one O(4)Na3Ni2 square pyramid,  an edgeedge with one O(9)Na3Ni2 square pyramid,  an edgeedge with one O(2)Na2MgNi2 trigonal bipyramid, edges with two equivalent O(7)Na3Ni2 trigonal bipyramids, and  an edgeedge with one O(1)NaNi3 trigonal pyramid. The corner-sharing octahedral tilt angles range from 23-28°. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Na(3), one Mg(1), one Ni(2), and one Ni(3) atom. In the seventh O site, O(7) is bonded to one Na(1), one Na(2), one Na(3), one Ni(3), and one Ni(4) atom to form distorted ONa3Ni2 trigonal bipyramids that share  a cornercorner with one O(10)Na3MgNi2 octahedra,  a cornercorner with one O(4)Na3Ni2 square pyramid, corners with two equivalent O(9)Na3Ni2 square pyramids,  a cornercorner with one O(2)Na2MgNi2 trigonal bipyramid, corners with two equivalent O(1)NaNi3 trigonal pyramids,  an edgeedge with one O(10)Na3MgNi2 octahedra,  an edgeedge with one O(4)Na3Ni2 square pyramid,  an edgeedge with one O(9)Na3Ni2 square pyramid,  an edgeedge with one O(2)Na2MgNi2 trigonal bipyramid, and edges with two equivalent O(5)Na3Ni2 trigonal bipyramids. The corner-sharing octahedral tilt angles are 63°. In the eighth O site, O(8) is bonded in a 6-coordinate geometry to one Na(3), one Na(4), one Mg(1), one Ni(1), one Ni(2), and one Ni(4) atom. In the ninth O site, O(9) is bonded to one Na(1), one Na(2), one Na(4), one Ni(3), and one Ni(4) atom to form ONa3Ni2 square pyramids that share  a cornercorner with one O(5)Na3Ni2 trigonal bipyramid, corners with two equivalent O(7)Na3Ni2 trigonal bipyramids,  a cornercorner with one O(1)NaNi3 trigonal pyramid, edges with two equivalent O(10)Na3MgNi2 octahedra, edges with two equivalent O(4)Na3Ni2 square pyramids,  an edgeedge with one O(2)Na2MgNi2 trigonal bipyramid,  an edgeedge with one O(5)Na3Ni2 trigonal bipyramid, and  an edgeedge with one O(7)Na3Ni2 trigonal bipyramid. In the tenth O site, O(10) is bonded to one Na(1), one Na(2), one Na(4), one Mg(1), one Ni(2), and one Ni(4) atom to form distorted ONa3MgNi2 octahedra that share corners with three equivalent O(4)Na3Ni2 square pyramids,  a cornercorner with one O(7)Na3Ni2 trigonal bipyramid, corners with two equivalent O(2)Na2MgNi2 trigonal bipyramids, corners with two equivalent O(5)Na3Ni2 trigonal bipyramids,  a cornercorner with one O(1)NaNi3 trigonal pyramid,  an edgeedge with one O(4)Na3Ni2 square pyramid, edges with two equivalent O(9)Na3Ni2 square pyramids, and  an edgeedge with one O(7)Na3Ni2 trigonal bipyramid.