Na3Ti8O16 crystallizes in the monoclinic Pm space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded in a 8-coordinate geometry to one O(13), one O(14), two equivalent O(11), two equivalent O(3), and two equivalent O(7) atoms. In the second Na site, Na(2) is bonded in a 8-coordinate geometry to one O(15), one O(16), two equivalent O(10), two equivalent O(2), and two equivalent O(6) atoms. In the third Na site, Na(3) is bonded in a 8-coordinate geometry to one O(15), one O(16), two equivalent O(1), two equivalent O(5), and two equivalent O(9) atoms. There are eight inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(14), one O(9), two equivalent O(11), and two equivalent O(4) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 48-52°. In the second Ti site, Ti(2) is bonded to one O(10), one O(13), two equivalent O(12), and two equivalent O(3) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 49-52°. In the third Ti site, Ti(3) is bonded to one O(11), one O(16), two equivalent O(2), and two equivalent O(9) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 46-54°. In the fourth Ti site, Ti(4) is bonded to one O(12), one O(15), two equivalent O(1), and two equivalent O(10) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 48-56°. In the fifth Ti site, Ti(5) is bonded to one O(1), one O(6), two equivalent O(16), and two equivalent O(8) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 46-56°. In the sixth Ti site, Ti(6) is bonded to one O(2), one O(5), two equivalent O(15), and two equivalent O(7) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 48-54°. In the seventh Ti site, Ti(7) is bonded to one O(3), one O(8), two equivalent O(14), and two equivalent O(6) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 48-52°. In the eighth Ti site, Ti(8) is bonded to one O(4), one O(7), two equivalent O(13), and two equivalent O(5) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 49-52°. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Na(3), one Ti(5), and two equivalent Ti(4) atoms. In the second O site, O(2) is bonded in a 5-coordinate geometry to two equivalent Na(2), one Ti(6), and two equivalent Ti(3) atoms. In the third O site, O(3) is bonded in a 5-coordinate geometry to two equivalent Na(1), one Ti(7), and two equivalent Ti(2) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ti(8) and two equivalent Ti(1) atoms. In the fifth O site, O(5) is bonded to two equivalent Na(3), one Ti(6), and two equivalent Ti(8) atoms to form distorted ONa2Ti3 square pyramids that share corners with two equivalent O(16)Na2Ti3 trigonal bipyramids, corners with two equivalent O(9)Na2Ti3 trigonal bipyramids, corners with two equivalent O(13)NaTi3 trigonal pyramids, edges with two equivalent O(5)Na2Ti3 square pyramids, edges with two equivalent O(7)Na2Ti3 square pyramids,  an edgeedge with one O(9)Na2Ti3 trigonal bipyramid, edges with two equivalent O(15)Na2Ti3 trigonal bipyramids, and  an edgeedge with one O(13)NaTi3 trigonal pyramid. In the sixth O site, O(6) is bonded to two equivalent Na(2), one Ti(5), and two equivalent Ti(7) atoms to form distorted ONa2Ti3 square pyramids that share corners with two equivalent O(10)Na2Ti3 trigonal bipyramids, corners with two equivalent O(15)Na2Ti3 trigonal bipyramids, corners with two equivalent O(14)NaTi3 trigonal pyramids, edges with two equivalent O(6)Na2Ti3 square pyramids,  an edgeedge with one O(10)Na2Ti3 trigonal bipyramid, edges with two equivalent O(16)Na2Ti3 trigonal bipyramids, and  an edgeedge with one O(14)NaTi3 trigonal pyramid. In the seventh O site, O(7) is bonded to two equivalent Na(1), one Ti(8), and two equivalent Ti(6) atoms to form distorted ONa2Ti3 square pyramids that share corners with two equivalent O(11)Na2Ti3 trigonal bipyramids, corners with two equivalent O(15)Na2Ti3 trigonal bipyramids, corners with two equivalent O(14)NaTi3 trigonal pyramids, edges with two equivalent O(5)Na2Ti3 square pyramids, edges with two equivalent O(7)Na2Ti3 square pyramids,  an edgeedge with one O(11)Na2Ti3 trigonal bipyramid,  an edgeedge with one O(15)Na2Ti3 trigonal bipyramid, and edges with two equivalent O(13)NaTi3 trigonal pyramids. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Ti(7) and two equivalent Ti(5) atoms. In the ninth O site, O(9) is bonded to two equivalent Na(3), one Ti(1), and two equivalent Ti(3) atoms to form distorted ONa2Ti3 trigonal bipyramids that share corners with two equivalent O(5)Na2Ti3 square pyramids, corners with two equivalent O(15)Na2Ti3 trigonal bipyramids,  a cornercorner with one O(14)NaTi3 trigonal pyramid,  an edgeedge with one O(5)Na2Ti3 square pyramid, edges with two equivalent O(11)Na2Ti3 trigonal bipyramids, edges with two equivalent O(16)Na2Ti3 trigonal bipyramids, and edges with two equivalent O(9)Na2Ti3 trigonal bipyramids. In the tenth O site, O(10) is bonded to two equivalent Na(2), one Ti(2), and two equivalent Ti(4) atoms to form distorted ONa2Ti3 trigonal bipyramids that share corners with two equivalent O(6)Na2Ti3 square pyramids, corners with two equivalent O(16)Na2Ti3 trigonal bipyramids,  a cornercorner with one O(13)NaTi3 trigonal pyramid,  an edgeedge with one O(6)Na2Ti3 square pyramid, edges with two equivalent O(10)Na2Ti3 trigonal bipyramids, and edges with two equivalent O(15)Na2Ti3 trigonal bipyramids. In the eleventh O site, O(11) is bonded to two equivalent Na(1), one Ti(3), and two equivalent Ti(1) atoms to form distorted ONa2Ti3 trigonal bipyramids that share corners with two equivalent O(7)Na2Ti3 square pyramids,  a cornercorner with one O(16)Na2Ti3 trigonal bipyramid, corners with two equivalent O(13)NaTi3 trigonal pyramids,  an edgeedge with one O(7)Na2Ti3 square pyramid, edges with two equivalent O(11)Na2Ti3 trigonal bipyramids, edges with two equivalent O(9)Na2Ti3 trigonal bipyramids, and edges with two equivalent O(14)NaTi3 trigonal pyramids. In the twelfth O site, O(12) is bonded in a trigonal non-coplanar geometry to one Ti(4) and two equivalent Ti(2) atoms. In the thirteenth O site, O(13) is bonded to one Na(1), one Ti(2), and two equivalent Ti(8) atoms to form distorted ONaTi3 trigonal pyramids that share corners with two equivalent O(5)Na2Ti3 square pyramids,  a cornercorner with one O(10)Na2Ti3 trigonal bipyramid, corners with two equivalent O(11)Na2Ti3 trigonal bipyramids,  a cornercorner with one O(14)NaTi3 trigonal pyramid, corners with two equivalent O(13)NaTi3 trigonal pyramids,  an edgeedge with one O(5)Na2Ti3 square pyramid, and edges with two equivalent O(7)Na2Ti3 square pyramids. In the fourteenth O site, O(14) is bonded to one Na(1), one Ti(1), and two equivalent Ti(7) atoms to form distorted ONaTi3 trigonal pyramids that share corners with two equivalent O(6)Na2Ti3 square pyramids, corners with two equivalent O(7)Na2Ti3 square pyramids,  a cornercorner with one O(9)Na2Ti3 trigonal bipyramid,  a cornercorner with one O(13)NaTi3 trigonal pyramid, corners with two equivalent O(14)NaTi3 trigonal pyramids,  an edgeedge with one O(6)Na2Ti3 square pyramid, and edges with two equivalent O(11)Na2Ti3 trigonal bipyramids. In the fifteenth O site, O(15) is bonded to one Na(2), one Na(3), one Ti(4), and two equivalent Ti(6) atoms to form a mixture of distorted corner and edge-sharing ONa2Ti3 trigonal bipyramids. In the sixteenth O site, O(16) is bonded to one Na(2), one Na(3), one Ti(3), and two equivalent Ti(5) atoms to form a mixture of distorted corner and edge-sharing ONa2Ti3 trigonal bipyramids.
Na3Ti8O16 crystallizes in the monoclinic Pm space group. There are three inequivalent Na sites. In the first Na site, Na(1) is bonded in a 8-coordinate geometry to one O(13), one O(14), two equivalent O(11), two equivalent O(3), and two equivalent O(7) atoms. The Na(1)-O(13) bond length is 2.50 Å. The Na(1)-O(14) bond length is 2.55 Å. Both Na(1)-O(11) bond lengths are 2.41 Å. Both Na(1)-O(3) bond lengths are 2.64 Å. Both Na(1)-O(7) bond lengths are 2.40 Å. In the second Na site, Na(2) is bonded in a 8-coordinate geometry to one O(15), one O(16), two equivalent O(10), two equivalent O(2), and two equivalent O(6) atoms. The Na(2)-O(15) bond length is 2.59 Å. The Na(2)-O(16) bond length is 2.56 Å. Both Na(2)-O(10) bond lengths are 2.39 Å. Both Na(2)-O(2) bond lengths are 2.63 Å. Both Na(2)-O(6) bond lengths are 2.39 Å. In the third Na site, Na(3) is bonded in a 8-coordinate geometry to one O(15), one O(16), two equivalent O(1), two equivalent O(5), and two equivalent O(9) atoms. The Na(3)-O(15) bond length is 2.56 Å. The Na(3)-O(16) bond length is 2.60 Å. Both Na(3)-O(1) bond lengths are 2.61 Å. Both Na(3)-O(5) bond lengths are 2.40 Å. Both Na(3)-O(9) bond lengths are 2.40 Å. There are eight inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(14), one O(9), two equivalent O(11), and two equivalent O(4) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 48-52°. The Ti(1)-O(14) bond length is 1.98 Å. The Ti(1)-O(9) bond length is 2.01 Å. Both Ti(1)-O(11) bond lengths are 2.06 Å. Both Ti(1)-O(4) bond lengths are 2.00 Å. In the second Ti site, Ti(2) is bonded to one O(10), one O(13), two equivalent O(12), and two equivalent O(3) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 49-52°. The Ti(2)-O(10) bond length is 2.00 Å. The Ti(2)-O(13) bond length is 1.99 Å. Both Ti(2)-O(12) bond lengths are 1.98 Å. Both Ti(2)-O(3) bond lengths are 2.07 Å. In the third Ti site, Ti(3) is bonded to one O(11), one O(16), two equivalent O(2), and two equivalent O(9) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 46-54°. The Ti(3)-O(11) bond length is 1.97 Å. The Ti(3)-O(16) bond length is 2.02 Å. Both Ti(3)-O(2) bond lengths are 2.05 Å. Both Ti(3)-O(9) bond lengths are 2.03 Å. In the fourth Ti site, Ti(4) is bonded to one O(12), one O(15), two equivalent O(1), and two equivalent O(10) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 48-56°. The Ti(4)-O(12) bond length is 1.93 Å. The Ti(4)-O(15) bond length is 2.05 Å. Both Ti(4)-O(1) bond lengths are 2.04 Å. Both Ti(4)-O(10) bond lengths are 2.04 Å. In the fifth Ti site, Ti(5) is bonded to one O(1), one O(6), two equivalent O(16), and two equivalent O(8) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 46-56°. The Ti(5)-O(1) bond length is 2.02 Å. The Ti(5)-O(6) bond length is 2.02 Å. Both Ti(5)-O(16) bond lengths are 2.05 Å. Both Ti(5)-O(8) bond lengths are 1.93 Å. In the sixth Ti site, Ti(6) is bonded to one O(2), one O(5), two equivalent O(15), and two equivalent O(7) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 48-54°. The Ti(6)-O(2) bond length is 2.03 Å. The Ti(6)-O(5) bond length is 2.00 Å. Both Ti(6)-O(15) bond lengths are 2.01 Å. Both Ti(6)-O(7) bond lengths are 2.01 Å. In the seventh Ti site, Ti(7) is bonded to one O(3), one O(8), two equivalent O(14), and two equivalent O(6) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 48-52°. The Ti(7)-O(3) bond length is 2.02 Å. The Ti(7)-O(8) bond length is 2.05 Å. Both Ti(7)-O(14) bond lengths are 2.00 Å. Both Ti(7)-O(6) bond lengths are 2.02 Å. In the eighth Ti site, Ti(8) is bonded to one O(4), one O(7), two equivalent O(13), and two equivalent O(5) atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 49-52°. The Ti(8)-O(4) bond length is 1.97 Å. The Ti(8)-O(7) bond length is 2.07 Å. Both Ti(8)-O(13) bond lengths are 2.00 Å. Both Ti(8)-O(5) bond lengths are 2.04 Å. There are sixteen inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Na(3), one Ti(5), and two equivalent Ti(4) atoms. In the second O site, O(2) is bonded in a 5-coordinate geometry to two equivalent Na(2), one Ti(6), and two equivalent Ti(3) atoms. In the third O site, O(3) is bonded in a 5-coordinate geometry to two equivalent Na(1), one Ti(7), and two equivalent Ti(2) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ti(8) and two equivalent Ti(1) atoms. In the fifth O site, O(5) is bonded to two equivalent Na(3), one Ti(6), and two equivalent Ti(8) atoms to form distorted ONa2Ti3 square pyramids that share corners with two equivalent O(16)Na2Ti3 trigonal bipyramids, corners with two equivalent O(9)Na2Ti3 trigonal bipyramids, corners with two equivalent O(13)NaTi3 trigonal pyramids, edges with two equivalent O(5)Na2Ti3 square pyramids, edges with two equivalent O(7)Na2Ti3 square pyramids,  an edgeedge with one O(9)Na2Ti3 trigonal bipyramid, edges with two equivalent O(15)Na2Ti3 trigonal bipyramids, and  an edgeedge with one O(13)NaTi3 trigonal pyramid. In the sixth O site, O(6) is bonded to two equivalent Na(2), one Ti(5), and two equivalent Ti(7) atoms to form distorted ONa2Ti3 square pyramids that share corners with two equivalent O(10)Na2Ti3 trigonal bipyramids, corners with two equivalent O(15)Na2Ti3 trigonal bipyramids, corners with two equivalent O(14)NaTi3 trigonal pyramids, edges with two equivalent O(6)Na2Ti3 square pyramids,  an edgeedge with one O(10)Na2Ti3 trigonal bipyramid, edges with two equivalent O(16)Na2Ti3 trigonal bipyramids, and  an edgeedge with one O(14)NaTi3 trigonal pyramid. In the seventh O site, O(7) is bonded to two equivalent Na(1), one Ti(8), and two equivalent Ti(6) atoms to form distorted ONa2Ti3 square pyramids that share corners with two equivalent O(11)Na2Ti3 trigonal bipyramids, corners with two equivalent O(15)Na2Ti3 trigonal bipyramids, corners with two equivalent O(14)NaTi3 trigonal pyramids, edges with two equivalent O(5)Na2Ti3 square pyramids, edges with two equivalent O(7)Na2Ti3 square pyramids,  an edgeedge with one O(11)Na2Ti3 trigonal bipyramid,  an edgeedge with one O(15)Na2Ti3 trigonal bipyramid, and edges with two equivalent O(13)NaTi3 trigonal pyramids. In the eighth O site, O(8) is bonded in a distorted trigonal non-coplanar geometry to one Ti(7) and two equivalent Ti(5) atoms. In the ninth O site, O(9) is bonded to two equivalent Na(3), one Ti(1), and two equivalent Ti(3) atoms to form distorted ONa2Ti3 trigonal bipyramids that share corners with two equivalent O(5)Na2Ti3 square pyramids, corners with two equivalent O(15)Na2Ti3 trigonal bipyramids,  a cornercorner with one O(14)NaTi3 trigonal pyramid,  an edgeedge with one O(5)Na2Ti3 square pyramid, edges with two equivalent O(11)Na2Ti3 trigonal bipyramids, edges with two equivalent O(16)Na2Ti3 trigonal bipyramids, and edges with two equivalent O(9)Na2Ti3 trigonal bipyramids. In the tenth O site, O(10) is bonded to two equivalent Na(2), one Ti(2), and two equivalent Ti(4) atoms to form distorted ONa2Ti3 trigonal bipyramids that share corners with two equivalent O(6)Na2Ti3 square pyramids, corners with two equivalent O(16)Na2Ti3 trigonal bipyramids,  a cornercorner with one O(13)NaTi3 trigonal pyramid,  an edgeedge with one O(6)Na2Ti3 square pyramid, edges with two equivalent O(10)Na2Ti3 trigonal bipyramids, and edges with two equivalent O(15)Na2Ti3 trigonal bipyramids. In the eleventh O site, O(11) is bonded to two equivalent Na(1), one Ti(3), and two equivalent Ti(1) atoms to form distorted ONa2Ti3 trigonal bipyramids that share corners with two equivalent O(7)Na2Ti3 square pyramids,  a cornercorner with one O(16)Na2Ti3 trigonal bipyramid, corners with two equivalent O(13)NaTi3 trigonal pyramids,  an edgeedge with one O(7)Na2Ti3 square pyramid, edges with two equivalent O(11)Na2Ti3 trigonal bipyramids, edges with two equivalent O(9)Na2Ti3 trigonal bipyramids, and edges with two equivalent O(14)NaTi3 trigonal pyramids. In the twelfth O site, O(12) is bonded in a trigonal non-coplanar geometry to one Ti(4) and two equivalent Ti(2) atoms. In the thirteenth O site, O(13) is bonded to one Na(1), one Ti(2), and two equivalent Ti(8) atoms to form distorted ONaTi3 trigonal pyramids that share corners with two equivalent O(5)Na2Ti3 square pyramids,  a cornercorner with one O(10)Na2Ti3 trigonal bipyramid, corners with two equivalent O(11)Na2Ti3 trigonal bipyramids,  a cornercorner with one O(14)NaTi3 trigonal pyramid, corners with two equivalent O(13)NaTi3 trigonal pyramids,  an edgeedge with one O(5)Na2Ti3 square pyramid, and edges with two equivalent O(7)Na2Ti3 square pyramids. In the fourteenth O site, O(14) is bonded to one Na(1), one Ti(1), and two equivalent Ti(7) atoms to form distorted ONaTi3 trigonal pyramids that share corners with two equivalent O(6)Na2Ti3 square pyramids, corners with two equivalent O(7)Na2Ti3 square pyramids,  a cornercorner with one O(9)Na2Ti3 trigonal bipyramid,  a cornercorner with one O(13)NaTi3 trigonal pyramid, corners with two equivalent O(14)NaTi3 trigonal pyramids,  an edgeedge with one O(6)Na2Ti3 square pyramid, and edges with two equivalent O(11)Na2Ti3 trigonal bipyramids. In the fifteenth O site, O(15) is bonded to one Na(2), one Na(3), one Ti(4), and two equivalent Ti(6) atoms to form a mixture of distorted corner and edge-sharing ONa2Ti3 trigonal bipyramids. In the sixteenth O site, O(16) is bonded to one Na(2), one Na(3), one Ti(3), and two equivalent Ti(5) atoms to form a mixture of distorted corner and edge-sharing ONa2Ti3 trigonal bipyramids.