Na6FeSe4 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one Se(1) and three equivalent Se(2) atoms to form distorted NaSe4 tetrahedra that share corners with two equivalent Fe(1)Se4 tetrahedra, corners with eight equivalent Na(1)Se4 tetrahedra, and  an edgeedge with one Fe(1)Se4 tetrahedra. In the second Na site, Na(2) is bonded in a 3-coordinate geometry to one Se(1) and four equivalent Se(2) atoms. Fe(1) is bonded to one Se(1) and three equivalent Se(2) atoms to form distorted FeSe4 tetrahedra that share corners with six equivalent Na(1)Se4 tetrahedra and edges with three equivalent Na(1)Se4 tetrahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 7-coordinate geometry to three equivalent Na(1), three equivalent Na(2), and one Fe(1) atom. In the second Se site, Se(2) is bonded in a 8-coordinate geometry to three equivalent Na(1), four equivalent Na(2), and one Fe(1) atom.
Na6FeSe4 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to one Se(1) and three equivalent Se(2) atoms to form distorted NaSe4 tetrahedra that share corners with two equivalent Fe(1)Se4 tetrahedra, corners with eight equivalent Na(1)Se4 tetrahedra, and  an edgeedge with one Fe(1)Se4 tetrahedra. The Na(1)-Se(1) bond length is 3.03 Å. There are two shorter (2.88 Å) and one longer (2.94 Å) Na(1)-Se(2) bond length. In the second Na site, Na(2) is bonded in a 3-coordinate geometry to one Se(1) and four equivalent Se(2) atoms. The Na(2)-Se(1) bond length is 2.97 Å. There are two shorter (3.03 Å) and two longer (3.29 Å) Na(2)-Se(2) bond lengths. Fe(1) is bonded to one Se(1) and three equivalent Se(2) atoms to form distorted FeSe4 tetrahedra that share corners with six equivalent Na(1)Se4 tetrahedra and edges with three equivalent Na(1)Se4 tetrahedra. The Fe(1)-Se(1) bond length is 2.48 Å. All Fe(1)-Se(2) bond lengths are 2.48 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 7-coordinate geometry to three equivalent Na(1), three equivalent Na(2), and one Fe(1) atom. In the second Se site, Se(2) is bonded in a 8-coordinate geometry to three equivalent Na(1), four equivalent Na(2), and one Fe(1) atom.