Na8Mg(NiO4)2 crystallizes in the triclinic P1 space group. There are eight inequivalent Na sites. In the first Na site, Na(1) is bonded in a rectangular see-saw-like geometry to one O(1), one O(2), one O(4), and one O(7) atom. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and one O(7) atom. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and one O(5) atom. In the fourth Na site, Na(4) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(2), one O(3), and one O(4) atom. In the fifth Na site, Na(5) is bonded in a 4-coordinate geometry to one O(3), one O(4), one O(5), one O(6), and one O(8) atom. In the sixth Na site, Na(6) is bonded in a 4-coordinate geometry to one O(1), one O(5), one O(6), one O(7), and one O(8) atom. In the seventh Na site, Na(7) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form distorted NaO4 tetrahedra that share corners with two equivalent Ni(1)O4 tetrahedra, corners with two equivalent Ni(2)O4 tetrahedra, corners with three equivalent Mg(1)O4 tetrahedra, and corners with two equivalent Na(8)O4 trigonal pyramids. In the eighth Na site, Na(8) is bonded to one O(1), one O(2), one O(6), and one O(7) atom to form distorted NaO4 trigonal pyramids that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Ni(1)O4 tetrahedra, corners with two equivalent Na(7)O4 tetrahedra, and corners with three equivalent Ni(2)O4 tetrahedra. Mg(1) is bonded to one O(3), one O(5), one O(6), and one O(8) atom to form distorted MgO4 tetrahedra that share  a cornercorner with one Ni(1)O4 tetrahedra,  a cornercorner with one Ni(2)O4 tetrahedra, corners with three equivalent Na(7)O4 tetrahedra,  a cornercorner with one Na(8)O4 trigonal pyramid, and  an edgeedge with one Ni(1)O4 tetrahedra. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form NiO4 tetrahedra that share  a cornercorner with one Mg(1)O4 tetrahedra, corners with two equivalent Na(7)O4 tetrahedra,  a cornercorner with one Na(8)O4 trigonal pyramid, and  an edgeedge with one Mg(1)O4 tetrahedra. In the second Ni site, Ni(2) is bonded to one O(1), one O(2), one O(7), and one O(8) atom to form NiO4 tetrahedra that share  a cornercorner with one Mg(1)O4 tetrahedra, corners with two equivalent Na(7)O4 tetrahedra, and corners with three equivalent Na(8)O4 trigonal pyramids. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 7-coordinate geometry to one Na(1), one Na(2), one Na(3), one Na(4), one Na(6), one Na(8), and one Ni(2) atom. In the second O site, O(2) is bonded to one Na(1), one Na(2), one Na(3), one Na(4), one Na(8), and one Ni(2) atom to form edge-sharing ONa5Ni octahedra. In the third O site, O(3) is bonded in a 6-coordinate geometry to one Na(2), one Na(3), one Na(4), one Na(5), one Mg(1), and one Ni(1) atom. In the fourth O site, O(4) is bonded to one Na(1), one Na(2), one Na(3), one Na(4), one Na(5), and one Ni(1) atom to form a mixture of corner and edge-sharing ONa5Ni octahedra. The corner-sharing octahedral tilt angles range from 10-11°. In the fifth O site, O(5) is bonded in a 6-coordinate geometry to one Na(3), one Na(5), one Na(6), one Na(7), one Mg(1), and one Ni(1) atom. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to one Na(5), one Na(6), one Na(7), one Na(8), one Mg(1), and one Ni(1) atom. In the seventh O site, O(7) is bonded to one Na(1), one Na(2), one Na(6), one Na(7), one Na(8), and one Ni(2) atom to form a mixture of corner and edge-sharing ONa5Ni octahedra. The corner-sharing octahedral tilt angles range from 10-11°. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to one Na(5), one Na(6), one Na(7), one Mg(1), and one Ni(2) atom.
Na8Mg(NiO4)2 crystallizes in the triclinic P1 space group. There are eight inequivalent Na sites. In the first Na site, Na(1) is bonded in a rectangular see-saw-like geometry to one O(1), one O(2), one O(4), and one O(7) atom. The Na(1)-O(1) bond length is 2.43 Å. The Na(1)-O(2) bond length is 2.36 Å. The Na(1)-O(4) bond length is 2.33 Å. The Na(1)-O(7) bond length is 2.37 Å. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and one O(7) atom. The Na(2)-O(1) bond length is 2.37 Å. The Na(2)-O(2) bond length is 2.37 Å. The Na(2)-O(3) bond length is 2.65 Å. The Na(2)-O(4) bond length is 2.33 Å. The Na(2)-O(7) bond length is 2.36 Å. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(3), one O(4), and one O(5) atom. The Na(3)-O(1) bond length is 2.47 Å. The Na(3)-O(2) bond length is 2.34 Å. The Na(3)-O(3) bond length is 2.70 Å. The Na(3)-O(4) bond length is 2.42 Å. The Na(3)-O(5) bond length is 2.47 Å. In the fourth Na site, Na(4) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(2), one O(3), and one O(4) atom. The Na(4)-O(1) bond length is 2.48 Å. The Na(4)-O(2) bond length is 2.28 Å. The Na(4)-O(3) bond length is 2.48 Å. The Na(4)-O(4) bond length is 2.41 Å. In the fifth Na site, Na(5) is bonded in a 4-coordinate geometry to one O(3), one O(4), one O(5), one O(6), and one O(8) atom. The Na(5)-O(3) bond length is 2.35 Å. The Na(5)-O(4) bond length is 2.21 Å. The Na(5)-O(5) bond length is 2.50 Å. The Na(5)-O(6) bond length is 2.85 Å. The Na(5)-O(8) bond length is 2.50 Å. In the sixth Na site, Na(6) is bonded in a 4-coordinate geometry to one O(1), one O(5), one O(6), one O(7), and one O(8) atom. The Na(6)-O(1) bond length is 2.86 Å. The Na(6)-O(5) bond length is 2.57 Å. The Na(6)-O(6) bond length is 2.48 Å. The Na(6)-O(7) bond length is 2.30 Å. The Na(6)-O(8) bond length is 2.34 Å. In the seventh Na site, Na(7) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form distorted NaO4 tetrahedra that share corners with two equivalent Ni(1)O4 tetrahedra, corners with two equivalent Ni(2)O4 tetrahedra, corners with three equivalent Mg(1)O4 tetrahedra, and corners with two equivalent Na(8)O4 trigonal pyramids. The Na(7)-O(5) bond length is 2.54 Å. The Na(7)-O(6) bond length is 2.46 Å. The Na(7)-O(7) bond length is 2.38 Å. The Na(7)-O(8) bond length is 2.45 Å. In the eighth Na site, Na(8) is bonded to one O(1), one O(2), one O(6), and one O(7) atom to form distorted NaO4 trigonal pyramids that share  a cornercorner with one Mg(1)O4 tetrahedra,  a cornercorner with one Ni(1)O4 tetrahedra, corners with two equivalent Na(7)O4 tetrahedra, and corners with three equivalent Ni(2)O4 tetrahedra. The Na(8)-O(1) bond length is 2.36 Å. The Na(8)-O(2) bond length is 2.23 Å. The Na(8)-O(6) bond length is 2.42 Å. The Na(8)-O(7) bond length is 2.30 Å. Mg(1) is bonded to one O(3), one O(5), one O(6), and one O(8) atom to form distorted MgO4 tetrahedra that share  a cornercorner with one Ni(1)O4 tetrahedra,  a cornercorner with one Ni(2)O4 tetrahedra, corners with three equivalent Na(7)O4 tetrahedra,  a cornercorner with one Na(8)O4 trigonal pyramid, and  an edgeedge with one Ni(1)O4 tetrahedra. The Mg(1)-O(3) bond length is 2.05 Å. The Mg(1)-O(5) bond length is 1.97 Å. The Mg(1)-O(6) bond length is 1.99 Å. The Mg(1)-O(8) bond length is 2.00 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(3), one O(4), one O(5), and one O(6) atom to form NiO4 tetrahedra that share  a cornercorner with one Mg(1)O4 tetrahedra, corners with two equivalent Na(7)O4 tetrahedra,  a cornercorner with one Na(8)O4 trigonal pyramid, and  an edgeedge with one Mg(1)O4 tetrahedra. The Ni(1)-O(3) bond length is 1.89 Å. The Ni(1)-O(4) bond length is 1.82 Å. The Ni(1)-O(5) bond length is 1.86 Å. The Ni(1)-O(6) bond length is 1.96 Å. In the second Ni site, Ni(2) is bonded to one O(1), one O(2), one O(7), and one O(8) atom to form NiO4 tetrahedra that share  a cornercorner with one Mg(1)O4 tetrahedra, corners with two equivalent Na(7)O4 tetrahedra, and corners with three equivalent Na(8)O4 trigonal pyramids. The Ni(2)-O(1) bond length is 1.89 Å. The Ni(2)-O(2) bond length is 1.88 Å. The Ni(2)-O(7) bond length is 1.85 Å. The Ni(2)-O(8) bond length is 1.93 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 7-coordinate geometry to one Na(1), one Na(2), one Na(3), one Na(4), one Na(6), one Na(8), and one Ni(2) atom. In the second O site, O(2) is bonded to one Na(1), one Na(2), one Na(3), one Na(4), one Na(8), and one Ni(2) atom to form edge-sharing ONa5Ni octahedra. In the third O site, O(3) is bonded in a 6-coordinate geometry to one Na(2), one Na(3), one Na(4), one Na(5), one Mg(1), and one Ni(1) atom. In the fourth O site, O(4) is bonded to one Na(1), one Na(2), one Na(3), one Na(4), one Na(5), and one Ni(1) atom to form a mixture of corner and edge-sharing ONa5Ni octahedra. The corner-sharing octahedral tilt angles range from 10-11°. In the fifth O site, O(5) is bonded in a 6-coordinate geometry to one Na(3), one Na(5), one Na(6), one Na(7), one Mg(1), and one Ni(1) atom. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to one Na(5), one Na(6), one Na(7), one Na(8), one Mg(1), and one Ni(1) atom. In the seventh O site, O(7) is bonded to one Na(1), one Na(2), one Na(6), one Na(7), one Na(8), and one Ni(2) atom to form a mixture of corner and edge-sharing ONa5Ni octahedra. The corner-sharing octahedral tilt angles range from 10-11°. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to one Na(5), one Na(6), one Na(7), one Mg(1), and one Ni(2) atom.