Na4MgTi3O8 crystallizes in the monoclinic Cm space group. There are three 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(5), and two equivalent O(4) atoms. In the second Na site, Na(2) is bonded in a 3-coordinate geometry to one O(1), one O(2), and one O(5) atom. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(5), two equivalent O(3), and two equivalent O(4) atoms. Mg(1) is bonded in a 3-coordinate geometry to one O(5) and two equivalent O(3) atoms. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(6) atom to form a mixture of distorted corner and edge-sharing TiO5 trigonal bipyramids. In the second Ti site, Ti(2) is bonded in a 5-coordinate geometry to one O(6), two equivalent O(3), and two equivalent O(4) atoms. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Na(1), two equivalent Na(2), and two equivalent Ti(1) atoms. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Na(2) and two equivalent Ti(1) atoms. In the third O site, O(3) is bonded to one Na(3), one Mg(1), one Ti(1), and one Ti(2) atom to form ONaMgTi2 tetrahedra that share  a cornercorner with one O(3)NaMgTi2 tetrahedra, corners with two equivalent O(5)Na4Mg trigonal bipyramids, corners with three equivalent O(4)Na2Ti2 trigonal pyramids,  an edgeedge with one O(3)NaMgTi2 tetrahedra, and  an edgeedge with one O(4)Na2Ti2 trigonal pyramid. In the fourth O site, O(4) is bonded to one Na(1), one Na(3), one Ti(1), and one Ti(2) atom to form distorted ONa2Ti2 trigonal pyramids that share corners with three equivalent O(3)NaMgTi2 tetrahedra, corners with two equivalent O(5)Na4Mg trigonal bipyramids,  a cornercorner with one O(4)Na2Ti2 trigonal pyramid,  an edgeedge with one O(3)NaMgTi2 tetrahedra, and  an edgeedge with one O(4)Na2Ti2 trigonal pyramid. In the fifth O site, O(5) is bonded to one Na(1), one Na(3), two equivalent Na(2), and one Mg(1) atom to form ONa4Mg trigonal bipyramids that share corners with four equivalent O(3)NaMgTi2 tetrahedra and corners with four equivalent O(4)Na2Ti2 trigonal pyramids. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ti(2) and two equivalent Ti(1) atoms.
Na4MgTi3O8 crystallizes in the monoclinic Cm space group. There are three 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(5), and two equivalent O(4) atoms. The Na(1)-O(1) bond length is 2.58 Å. The Na(1)-O(5) bond length is 2.29 Å. Both Na(1)-O(4) bond lengths are 2.31 Å. In the second Na site, Na(2) is bonded in a 3-coordinate geometry to one O(1), one O(2), and one O(5) atom. The Na(2)-O(1) bond length is 2.78 Å. The Na(2)-O(2) bond length is 2.54 Å. The Na(2)-O(5) bond length is 2.20 Å. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(5), two equivalent O(3), and two equivalent O(4) atoms. The Na(3)-O(5) bond length is 2.41 Å. Both Na(3)-O(3) bond lengths are 2.30 Å. Both Na(3)-O(4) bond lengths are 2.53 Å. Mg(1) is bonded in a 3-coordinate geometry to one O(5) and two equivalent O(3) atoms. The Mg(1)-O(5) bond length is 1.88 Å. Both Mg(1)-O(3) bond lengths are 1.98 Å. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(1), one O(2), one O(3), one O(4), and one O(6) atom to form a mixture of distorted corner and edge-sharing TiO5 trigonal bipyramids. The Ti(1)-O(1) bond length is 1.97 Å. The Ti(1)-O(2) bond length is 1.92 Å. The Ti(1)-O(3) bond length is 1.95 Å. The Ti(1)-O(4) bond length is 1.90 Å. The Ti(1)-O(6) bond length is 2.18 Å. In the second Ti site, Ti(2) is bonded in a 5-coordinate geometry to one O(6), two equivalent O(3), and two equivalent O(4) atoms. The Ti(2)-O(6) bond length is 1.83 Å. Both Ti(2)-O(3) bond lengths are 2.05 Å. Both Ti(2)-O(4) bond lengths are 1.93 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Na(1), two equivalent Na(2), and two equivalent Ti(1) atoms. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Na(2) and two equivalent Ti(1) atoms. In the third O site, O(3) is bonded to one Na(3), one Mg(1), one Ti(1), and one Ti(2) atom to form ONaMgTi2 tetrahedra that share  a cornercorner with one O(3)NaMgTi2 tetrahedra, corners with two equivalent O(5)Na4Mg trigonal bipyramids, corners with three equivalent O(4)Na2Ti2 trigonal pyramids,  an edgeedge with one O(3)NaMgTi2 tetrahedra, and  an edgeedge with one O(4)Na2Ti2 trigonal pyramid. In the fourth O site, O(4) is bonded to one Na(1), one Na(3), one Ti(1), and one Ti(2) atom to form distorted ONa2Ti2 trigonal pyramids that share corners with three equivalent O(3)NaMgTi2 tetrahedra, corners with two equivalent O(5)Na4Mg trigonal bipyramids,  a cornercorner with one O(4)Na2Ti2 trigonal pyramid,  an edgeedge with one O(3)NaMgTi2 tetrahedra, and  an edgeedge with one O(4)Na2Ti2 trigonal pyramid. In the fifth O site, O(5) is bonded to one Na(1), one Na(3), two equivalent Na(2), and one Mg(1) atom to form ONa4Mg trigonal bipyramids that share corners with four equivalent O(3)NaMgTi2 tetrahedra and corners with four equivalent O(4)Na2Ti2 trigonal pyramids. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ti(2) and two equivalent Ti(1) atoms.