Na4TiAs2O9 crystallizes in the monoclinic C2/m space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(5) atoms to form distorted NaO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra, edges with two equivalent Na(1)O6 octahedra, and edges with two equivalent As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one O(2), one O(6), one O(7), and two equivalent O(4) atoms. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(3), one O(5), one O(6), and two equivalent O(1) atoms. In the fourth Na site, Na(4) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(7) atoms to form NaO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent As(2)O4 tetrahedra, edges with two equivalent Na(4)O6 octahedra, and edges with two equivalent As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 62°. Ti(1) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(6) atoms to form TiO6 octahedra that share corners with two equivalent Na(1)O6 octahedra, corners with two equivalent Na(4)O6 octahedra, corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra, and corners with two equivalent As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 35-62°. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(3), one O(5), and two equivalent O(4) atoms to form AsO4 tetrahedra that share corners with two equivalent Na(1)O6 octahedra, corners with two equivalent Ti(1)O6 octahedra, and edges with two equivalent Na(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-62°. In the second As site, As(2) is bonded to one O(2), one O(7), and two equivalent O(1) atoms to form AsO4 tetrahedra that share corners with two equivalent Na(4)O6 octahedra, corners with two equivalent Ti(1)O6 octahedra, and edges with two equivalent Na(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-64°. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a 4-coordinate geometry to one Na(2), one Na(4), one Ti(1), and one As(1) atom. In the second O site, O(5) is bonded to one Na(3), two equivalent Na(1), and one As(1) atom to form distorted edge-sharing ONa3As trigonal pyramids. In the third O site, O(6) is bonded in a 4-coordinate geometry to one Na(2), one Na(3), and two equivalent Ti(1) atoms. In the fourth O site, O(7) is bonded in a distorted rectangular see-saw-like geometry to one Na(2), two equivalent Na(4), and one As(2) atom. In the fifth O site, O(1) is bonded in a 4-coordinate geometry to one Na(1), one Na(3), one Ti(1), and one As(2) atom. In the sixth O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Na(2), two equivalent Na(1), and one As(2) atom. In the seventh O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Na(3), two equivalent Na(4), and one As(1) atom.
Na4TiAs2O9 crystallizes in the monoclinic C2/m space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(5) atoms to form distorted NaO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra, edges with two equivalent Na(1)O6 octahedra, and edges with two equivalent As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. Both Na(1)-O(1) bond lengths are 2.55 Å. Both Na(1)-O(2) bond lengths are 2.46 Å. Both Na(1)-O(5) bond lengths are 2.41 Å. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one O(2), one O(6), one O(7), and two equivalent O(4) atoms. The Na(2)-O(2) bond length is 2.21 Å. The Na(2)-O(6) bond length is 2.68 Å. The Na(2)-O(7) bond length is 2.29 Å. Both Na(2)-O(4) bond lengths are 2.42 Å. In the third Na site, Na(3) is bonded in a 5-coordinate geometry to one O(3), one O(5), one O(6), and two equivalent O(1) atoms. The Na(3)-O(3) bond length is 2.20 Å. The Na(3)-O(5) bond length is 2.32 Å. The Na(3)-O(6) bond length is 2.55 Å. Both Na(3)-O(1) bond lengths are 2.43 Å. In the fourth Na site, Na(4) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(7) atoms to form NaO6 octahedra that share corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent As(2)O4 tetrahedra, edges with two equivalent Na(4)O6 octahedra, and edges with two equivalent As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 62°. Both Na(4)-O(3) bond lengths are 2.53 Å. Both Na(4)-O(4) bond lengths are 2.55 Å. Both Na(4)-O(7) bond lengths are 2.42 Å. Ti(1) is bonded to two equivalent O(1), two equivalent O(4), and two equivalent O(6) atoms to form TiO6 octahedra that share corners with two equivalent Na(1)O6 octahedra, corners with two equivalent Na(4)O6 octahedra, corners with two equivalent Ti(1)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra, and corners with two equivalent As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 35-62°. Both Ti(1)-O(1) bond lengths are 2.03 Å. Both Ti(1)-O(4) bond lengths are 2.01 Å. Both Ti(1)-O(6) bond lengths are 1.90 Å. There are two inequivalent As sites. In the first As site, As(1) is bonded to one O(3), one O(5), and two equivalent O(4) atoms to form AsO4 tetrahedra that share corners with two equivalent Na(1)O6 octahedra, corners with two equivalent Ti(1)O6 octahedra, and edges with two equivalent Na(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-62°. The As(1)-O(3) bond length is 1.69 Å. The As(1)-O(5) bond length is 1.70 Å. Both As(1)-O(4) bond lengths are 1.76 Å. In the second As site, As(2) is bonded to one O(2), one O(7), and two equivalent O(1) atoms to form AsO4 tetrahedra that share corners with two equivalent Na(4)O6 octahedra, corners with two equivalent Ti(1)O6 octahedra, and edges with two equivalent Na(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 50-64°. The As(2)-O(2) bond length is 1.70 Å. The As(2)-O(7) bond length is 1.70 Å. Both As(2)-O(1) bond lengths are 1.76 Å. There are seven inequivalent O sites. In the first O site, O(4) is bonded in a 4-coordinate geometry to one Na(2), one Na(4), one Ti(1), and one As(1) atom. In the second O site, O(5) is bonded to one Na(3), two equivalent Na(1), and one As(1) atom to form distorted edge-sharing ONa3As trigonal pyramids. In the third O site, O(6) is bonded in a 4-coordinate geometry to one Na(2), one Na(3), and two equivalent Ti(1) atoms. In the fourth O site, O(7) is bonded in a distorted rectangular see-saw-like geometry to one Na(2), two equivalent Na(4), and one As(2) atom. In the fifth O site, O(1) is bonded in a 4-coordinate geometry to one Na(1), one Na(3), one Ti(1), and one As(2) atom. In the sixth O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Na(2), two equivalent Na(1), and one As(2) atom. In the seventh O site, O(3) is bonded in a distorted rectangular see-saw-like geometry to one Na(3), two equivalent Na(4), and one As(1) atom.