Na6Ti2O7 crystallizes in the monoclinic Pc space group. There are six inequivalent Na sites. In the first Na site, Na(1) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(2), one O(6), 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(4), one O(6), and one O(7) atom. In the third Na site, Na(3) is bonded to one O(1), one O(3), one O(4), one O(6), and one O(7) atom to form distorted NaO5 trigonal bipyramids that share  a cornercorner with one Ti(2)O4 tetrahedra, corners with two equivalent Ti(1)O4 tetrahedra,  an edgeedge with one Ti(2)O4 tetrahedra, and edges with two equivalent Na(4)O5 trigonal bipyramids. In the fourth Na site, Na(4) is bonded to one O(1), one O(3), one O(4), one O(5), and one O(7) atom to form distorted NaO5 trigonal bipyramids that share  a cornercorner with one Ti(1)O4 tetrahedra, corners with two equivalent Ti(2)O4 tetrahedra,  an edgeedge with one Ti(1)O4 tetrahedra, and edges with two equivalent Na(3)O5 trigonal bipyramids. In the fifth Na site, Na(5) is bonded in a 3-coordinate geometry to one O(3), one O(4), and one O(5) atom. In the sixth Na site, Na(6) is bonded in a 4-coordinate geometry to one O(1), one O(3), one O(4), and one O(5) atom. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form TiO4 tetrahedra that share  a cornercorner with one Ti(2)O4 tetrahedra,  a cornercorner with one Na(4)O5 trigonal bipyramid, corners with two equivalent Na(3)O5 trigonal bipyramids, and  an edgeedge with one Na(4)O5 trigonal bipyramid. In the second Ti site, Ti(2) is bonded to one O(1), one O(2), one O(6), and one O(7) atom to form TiO4 tetrahedra that share  a cornercorner with one Ti(1)O4 tetrahedra,  a cornercorner with one Na(3)O5 trigonal bipyramid, corners with two equivalent Na(4)O5 trigonal bipyramids, and  an edgeedge with one Na(3)O5 trigonal bipyramid. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to one Na(1), one Na(2), one Na(3), one Na(4), one Na(6), and one Ti(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Ti(1), and one Ti(2) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(3), one Na(4), one Na(5), one Na(6), and one Ti(1) atom. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to one Na(2), one Na(3), one Na(4), one Na(5), one Na(6), and one Ti(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Na(4), one Na(5), one Na(6), and one Ti(1) atom. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Na(3), and one Ti(2) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one Na(1), one Na(2), one Na(3), one Na(4), and one Ti(2) atom.
Na6Ti2O7 crystallizes in the monoclinic Pc space group. There are six inequivalent Na sites. In the first Na site, Na(1) is bonded in a distorted rectangular see-saw-like geometry to one O(1), one O(2), one O(6), and one O(7) atom. The Na(1)-O(1) bond length is 2.53 Å. The Na(1)-O(2) bond length is 2.51 Å. The Na(1)-O(6) bond length is 2.28 Å. The Na(1)-O(7) bond length is 2.63 Å. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(4), one O(6), and one O(7) atom. The Na(2)-O(1) bond length is 2.81 Å. The Na(2)-O(2) bond length is 2.47 Å. The Na(2)-O(4) bond length is 2.88 Å. The Na(2)-O(6) bond length is 2.30 Å. The Na(2)-O(7) bond length is 2.34 Å. In the third Na site, Na(3) is bonded to one O(1), one O(3), one O(4), one O(6), and one O(7) atom to form distorted NaO5 trigonal bipyramids that share  a cornercorner with one Ti(2)O4 tetrahedra, corners with two equivalent Ti(1)O4 tetrahedra,  an edgeedge with one Ti(2)O4 tetrahedra, and edges with two equivalent Na(4)O5 trigonal bipyramids. The Na(3)-O(1) bond length is 2.41 Å. The Na(3)-O(3) bond length is 2.33 Å. The Na(3)-O(4) bond length is 2.44 Å. The Na(3)-O(6) bond length is 2.71 Å. The Na(3)-O(7) bond length is 2.38 Å. In the fourth Na site, Na(4) is bonded to one O(1), one O(3), one O(4), one O(5), and one O(7) atom to form distorted NaO5 trigonal bipyramids that share  a cornercorner with one Ti(1)O4 tetrahedra, corners with two equivalent Ti(2)O4 tetrahedra,  an edgeedge with one Ti(1)O4 tetrahedra, and edges with two equivalent Na(3)O5 trigonal bipyramids. The Na(4)-O(1) bond length is 2.42 Å. The Na(4)-O(3) bond length is 2.37 Å. The Na(4)-O(4) bond length is 2.34 Å. The Na(4)-O(5) bond length is 2.76 Å. The Na(4)-O(7) bond length is 2.33 Å. In the fifth Na site, Na(5) is bonded in a 3-coordinate geometry to one O(3), one O(4), and one O(5) atom. The Na(5)-O(3) bond length is 2.35 Å. The Na(5)-O(4) bond length is 2.33 Å. The Na(5)-O(5) bond length is 2.27 Å. In the sixth Na site, Na(6) is bonded in a 4-coordinate geometry to one O(1), one O(3), one O(4), and one O(5) atom. The Na(6)-O(1) bond length is 2.69 Å. The Na(6)-O(3) bond length is 2.51 Å. The Na(6)-O(4) bond length is 2.55 Å. The Na(6)-O(5) bond length is 2.28 Å. There are two inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(2), one O(3), one O(4), and one O(5) atom to form TiO4 tetrahedra that share  a cornercorner with one Ti(2)O4 tetrahedra,  a cornercorner with one Na(4)O5 trigonal bipyramid, corners with two equivalent Na(3)O5 trigonal bipyramids, and  an edgeedge with one Na(4)O5 trigonal bipyramid. The Ti(1)-O(2) bond length is 1.91 Å. The Ti(1)-O(3) bond length is 1.81 Å. The Ti(1)-O(4) bond length is 1.81 Å. The Ti(1)-O(5) bond length is 1.80 Å. In the second Ti site, Ti(2) is bonded to one O(1), one O(2), one O(6), and one O(7) atom to form TiO4 tetrahedra that share  a cornercorner with one Ti(1)O4 tetrahedra,  a cornercorner with one Na(3)O5 trigonal bipyramid, corners with two equivalent Na(4)O5 trigonal bipyramids, and  an edgeedge with one Na(3)O5 trigonal bipyramid. The Ti(2)-O(1) bond length is 1.82 Å. The Ti(2)-O(2) bond length is 1.91 Å. The Ti(2)-O(6) bond length is 1.81 Å. The Ti(2)-O(7) bond length is 1.80 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to one Na(1), one Na(2), one Na(3), one Na(4), one Na(6), and one Ti(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Na(1), one Na(2), one Ti(1), and one Ti(2) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Na(3), one Na(4), one Na(5), one Na(6), and one Ti(1) atom. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to one Na(2), one Na(3), one Na(4), one Na(5), one Na(6), and one Ti(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Na(4), one Na(5), one Na(6), and one Ti(1) atom. In the sixth O site, O(6) is bonded in a distorted rectangular see-saw-like geometry to one Na(1), one Na(2), one Na(3), and one Ti(2) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one Na(1), one Na(2), one Na(3), one Na(4), and one Ti(2) atom.