Na6Sn2Se7 crystallizes in the monoclinic C2/c space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 4-coordinate geometry to two equivalent Se(1) and two equivalent Se(3) atoms. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one Se(2), one Se(3), two equivalent Se(1), and two equivalent Se(4) atoms. In the third Na site, Na(3) is bonded in a 6-coordinate geometry to one Se(1), one Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. In the fourth Na site, Na(4) is bonded to two equivalent Se(1), two equivalent Se(3), and two equivalent Se(4) atoms to form NaSe6 octahedra that share corners with two equivalent Sn(1)Se4 tetrahedra and edges with two equivalent Sn(1)Se4 tetrahedra. Sn(1) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form SnSe4 tetrahedra that share  a cornercorner with one Na(4)Se6 octahedra,  a cornercorner with one Sn(1)Se4 tetrahedra, and  an edgeedge with one Na(4)Se6 octahedra. The corner-sharing octahedral tilt angles are 22°. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to one Na(1), one Na(3), one Na(4), two equivalent Na(2), and one Sn(1) atom to form a mixture of distorted corner and edge-sharing SeNa5Sn octahedra. The corner-sharing octahedral tilt angles range from 0-74°. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent Na(2), two equivalent Na(3), and two equivalent Sn(1) atoms. In the third Se site, Se(3) is bonded to one Na(1), one Na(2), one Na(4), two equivalent Na(3), and one Sn(1) atom to form a mixture of distorted corner, edge, and face-sharing SeNa5Sn octahedra. The corner-sharing octahedral tilt angles range from 0-71°. In the fourth Se site, Se(4) is bonded to one Na(4), two equivalent Na(2), two equivalent Na(3), and one Sn(1) atom to form a mixture of corner and edge-sharing SeNa5Sn octahedra. The corner-sharing octahedral tilt angles range from 0-58°.
Na6Sn2Se7 crystallizes in the monoclinic C2/c space group. There are four inequivalent Na sites. In the first Na site, Na(1) is bonded in a 4-coordinate geometry to two equivalent Se(1) and two equivalent Se(3) atoms. Both Na(1)-Se(1) bond lengths are 2.87 Å. Both Na(1)-Se(3) bond lengths are 2.92 Å. In the second Na site, Na(2) is bonded in a 6-coordinate geometry to one Se(2), one Se(3), two equivalent Se(1), and two equivalent Se(4) atoms. The Na(2)-Se(2) bond length is 3.43 Å. The Na(2)-Se(3) bond length is 2.99 Å. There is one shorter (3.06 Å) and one longer (3.45 Å) Na(2)-Se(1) bond length. There is one shorter (3.01 Å) and one longer (3.04 Å) Na(2)-Se(4) bond length. In the third Na site, Na(3) is bonded in a 6-coordinate geometry to one Se(1), one Se(2), two equivalent Se(3), and two equivalent Se(4) atoms. The Na(3)-Se(1) bond length is 3.01 Å. The Na(3)-Se(2) bond length is 3.50 Å. There is one shorter (3.03 Å) and one longer (3.39 Å) Na(3)-Se(3) bond length. There is one shorter (3.00 Å) and one longer (3.06 Å) Na(3)-Se(4) bond length. In the fourth Na site, Na(4) is bonded to two equivalent Se(1), two equivalent Se(3), and two equivalent Se(4) atoms to form NaSe6 octahedra that share corners with two equivalent Sn(1)Se4 tetrahedra and edges with two equivalent Sn(1)Se4 tetrahedra. Both Na(4)-Se(1) bond lengths are 3.11 Å. Both Na(4)-Se(3) bond lengths are 3.18 Å. Both Na(4)-Se(4) bond lengths are 2.93 Å. Sn(1) is bonded to one Se(1), one Se(2), one Se(3), and one Se(4) atom to form SnSe4 tetrahedra that share  a cornercorner with one Na(4)Se6 octahedra,  a cornercorner with one Sn(1)Se4 tetrahedra, and  an edgeedge with one Na(4)Se6 octahedra. The corner-sharing octahedral tilt angles are 22°. The Sn(1)-Se(1) bond length is 2.50 Å. The Sn(1)-Se(2) bond length is 2.57 Å. The Sn(1)-Se(3) bond length is 2.51 Å. The Sn(1)-Se(4) bond length is 2.53 Å. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to one Na(1), one Na(3), one Na(4), two equivalent Na(2), and one Sn(1) atom to form a mixture of distorted corner and edge-sharing SeNa5Sn octahedra. The corner-sharing octahedral tilt angles range from 0-74°. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to two equivalent Na(2), two equivalent Na(3), and two equivalent Sn(1) atoms. In the third Se site, Se(3) is bonded to one Na(1), one Na(2), one Na(4), two equivalent Na(3), and one Sn(1) atom to form a mixture of distorted corner, edge, and face-sharing SeNa5Sn octahedra. The corner-sharing octahedral tilt angles range from 0-71°. In the fourth Se site, Se(4) is bonded to one Na(4), two equivalent Na(2), two equivalent Na(3), and one Sn(1) atom to form a mixture of corner and edge-sharing SeNa5Sn octahedra. The corner-sharing octahedral tilt angles range from 0-58°.