Na3MgNi2SbO6 crystallizes in the monoclinic Cm space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 4-coordinate geometry to one Sb(1), one O(2), one O(3), and two equivalent O(1) atoms. In the second Na site, Na(2) is bonded to one O(2), two equivalent O(1), and two equivalent O(4) atoms to form distorted NaO5 trigonal bipyramids that share corners with four equivalent Ni(1)O4 tetrahedra,  a cornercorner with one Na(2)O5 trigonal bipyramid,  an edgeedge with one Ni(1)O4 tetrahedra, and edges with two equivalent Na(2)O5 trigonal bipyramids. Mg(1) is bonded in a 4-coordinate geometry to one O(2), one O(3), and two equivalent O(4) atoms. Ni(1) is bonded to one O(3), one O(4), and two equivalent O(1) atoms to form distorted NiO4 tetrahedra that share corners with three equivalent Ni(1)O4 tetrahedra, corners with four equivalent Na(2)O5 trigonal bipyramids, and  an edgeedge with one Na(2)O5 trigonal bipyramid. Sb(1) is bonded in a 5-coordinate geometry to one Na(1), one O(2), one O(3), and two equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), two equivalent Na(2), and two equivalent Ni(1) atoms to form distorted ONa3Ni2 trigonal bipyramids that share  a cornercorner with one O(2)Na3MgSb square pyramid,  a cornercorner with one O(1)Na3Ni2 trigonal bipyramid,  a cornercorner with one O(3)NaMgNi2Sb trigonal bipyramid, corners with four equivalent O(4)Na2MgNiSb trigonal bipyramids,  an edgeedge with one O(2)Na3MgSb square pyramid,  an edgeedge with one O(4)Na2MgNiSb trigonal bipyramid,  an edgeedge with one O(3)NaMgNi2Sb trigonal bipyramid, and edges with two equivalent O(1)Na3Ni2 trigonal bipyramids. In the second O site, O(2) is bonded to one Na(1), two equivalent Na(2), one Mg(1), and one Sb(1) atom to form distorted ONa3MgSb square pyramids that share corners with two equivalent O(4)Na2MgNiSb trigonal bipyramids, corners with two equivalent O(1)Na3Ni2 trigonal bipyramids, corners with three equivalent O(3)NaMgNi2Sb trigonal bipyramids, edges with two equivalent O(1)Na3Ni2 trigonal bipyramids, and faces with two equivalent O(4)Na2MgNiSb trigonal bipyramids. In the third O site, O(3) is bonded to one Na(1), one Mg(1), two equivalent Ni(1), and one Sb(1) atom to form distorted ONaMgNi2Sb trigonal bipyramids that share corners with three equivalent O(2)Na3MgSb square pyramids, corners with two equivalent O(4)Na2MgNiSb trigonal bipyramids, corners with two equivalent O(1)Na3Ni2 trigonal bipyramids, edges with two equivalent O(4)Na2MgNiSb trigonal bipyramids, and edges with two equivalent O(1)Na3Ni2 trigonal bipyramids. In the fourth O site, O(4) is bonded to two equivalent Na(2), one Mg(1), one Ni(1), and one Sb(1) atom to form distorted ONa2MgNiSb trigonal bipyramids that share  a cornercorner with one O(2)Na3MgSb square pyramid,  a cornercorner with one O(3)NaMgNi2Sb trigonal bipyramid, corners with two equivalent O(4)Na2MgNiSb trigonal bipyramids, corners with four equivalent O(1)Na3Ni2 trigonal bipyramids,  an edgeedge with one O(4)Na2MgNiSb trigonal bipyramid,  an edgeedge with one O(1)Na3Ni2 trigonal bipyramid,  an edgeedge with one O(3)NaMgNi2Sb trigonal bipyramid, and  a faceface with one O(2)Na3MgSb square pyramid.
Na3MgNi2SbO6 crystallizes in the monoclinic Cm space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded in a 4-coordinate geometry to one Sb(1), one O(2), one O(3), and two equivalent O(1) atoms. The Na(1)-Sb(1) bond length is 3.12 Å. The Na(1)-O(2) bond length is 2.25 Å. The Na(1)-O(3) bond length is 2.32 Å. Both Na(1)-O(1) bond lengths are 2.41 Å. In the second Na site, Na(2) is bonded to one O(2), two equivalent O(1), and two equivalent O(4) atoms to form distorted NaO5 trigonal bipyramids that share corners with four equivalent Ni(1)O4 tetrahedra,  a cornercorner with one Na(2)O5 trigonal bipyramid,  an edgeedge with one Ni(1)O4 tetrahedra, and edges with two equivalent Na(2)O5 trigonal bipyramids. The Na(2)-O(2) bond length is 2.34 Å. There is one shorter (2.39 Å) and one longer (2.41 Å) Na(2)-O(1) bond length. There is one shorter (2.35 Å) and one longer (2.60 Å) Na(2)-O(4) bond length. Mg(1) is bonded in a 4-coordinate geometry to one O(2), one O(3), and two equivalent O(4) atoms. The Mg(1)-O(2) bond length is 2.00 Å. The Mg(1)-O(3) bond length is 1.93 Å. Both Mg(1)-O(4) bond lengths are 2.12 Å. Ni(1) is bonded to one O(3), one O(4), and two equivalent O(1) atoms to form distorted NiO4 tetrahedra that share corners with three equivalent Ni(1)O4 tetrahedra, corners with four equivalent Na(2)O5 trigonal bipyramids, and  an edgeedge with one Na(2)O5 trigonal bipyramid. The Ni(1)-O(3) bond length is 2.09 Å. The Ni(1)-O(4) bond length is 2.07 Å. There is one shorter (1.94 Å) and one longer (1.99 Å) Ni(1)-O(1) bond length. Sb(1) is bonded in a 5-coordinate geometry to one Na(1), one O(2), one O(3), and two equivalent O(4) atoms. The Sb(1)-O(2) bond length is 2.06 Å. The Sb(1)-O(3) bond length is 2.33 Å. Both Sb(1)-O(4) bond lengths are 2.03 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Na(1), two equivalent Na(2), and two equivalent Ni(1) atoms to form distorted ONa3Ni2 trigonal bipyramids that share  a cornercorner with one O(2)Na3MgSb square pyramid,  a cornercorner with one O(1)Na3Ni2 trigonal bipyramid,  a cornercorner with one O(3)NaMgNi2Sb trigonal bipyramid, corners with four equivalent O(4)Na2MgNiSb trigonal bipyramids,  an edgeedge with one O(2)Na3MgSb square pyramid,  an edgeedge with one O(4)Na2MgNiSb trigonal bipyramid,  an edgeedge with one O(3)NaMgNi2Sb trigonal bipyramid, and edges with two equivalent O(1)Na3Ni2 trigonal bipyramids. In the second O site, O(2) is bonded to one Na(1), two equivalent Na(2), one Mg(1), and one Sb(1) atom to form distorted ONa3MgSb square pyramids that share corners with two equivalent O(4)Na2MgNiSb trigonal bipyramids, corners with two equivalent O(1)Na3Ni2 trigonal bipyramids, corners with three equivalent O(3)NaMgNi2Sb trigonal bipyramids, edges with two equivalent O(1)Na3Ni2 trigonal bipyramids, and faces with two equivalent O(4)Na2MgNiSb trigonal bipyramids. In the third O site, O(3) is bonded to one Na(1), one Mg(1), two equivalent Ni(1), and one Sb(1) atom to form distorted ONaMgNi2Sb trigonal bipyramids that share corners with three equivalent O(2)Na3MgSb square pyramids, corners with two equivalent O(4)Na2MgNiSb trigonal bipyramids, corners with two equivalent O(1)Na3Ni2 trigonal bipyramids, edges with two equivalent O(4)Na2MgNiSb trigonal bipyramids, and edges with two equivalent O(1)Na3Ni2 trigonal bipyramids. In the fourth O site, O(4) is bonded to two equivalent Na(2), one Mg(1), one Ni(1), and one Sb(1) atom to form distorted ONa2MgNiSb trigonal bipyramids that share  a cornercorner with one O(2)Na3MgSb square pyramid,  a cornercorner with one O(3)NaMgNi2Sb trigonal bipyramid, corners with two equivalent O(4)Na2MgNiSb trigonal bipyramids, corners with four equivalent O(1)Na3Ni2 trigonal bipyramids,  an edgeedge with one O(4)Na2MgNiSb trigonal bipyramid,  an edgeedge with one O(1)Na3Ni2 trigonal bipyramid,  an edgeedge with one O(3)NaMgNi2Sb trigonal bipyramid, and  a faceface with one O(2)Na3MgSb square pyramid.