Na3(FeSe2)2 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent Se(1) and four equivalent Se(3) atoms to form NaSe6 octahedra that share corners with eight equivalent Fe(1)Se4 tetrahedra, edges with two equivalent Fe(1)Se4 tetrahedra, and faces with two equivalent Na(1)Se6 octahedra. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one Se(1), two equivalent Se(2), and two equivalent Se(3) atoms. Fe(1) is bonded to one Se(1), one Se(2), and two equivalent Se(3) atoms to form FeSe4 tetrahedra that share corners with four equivalent Na(1)Se6 octahedra,  an edgeedge with one Na(1)Se6 octahedra, and edges with two equivalent Fe(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 14-63°. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent Na(1), two equivalent Na(2), and two equivalent Fe(1) atoms. In the second Se site, Se(2) is bonded to four equivalent Na(2) and two equivalent Fe(1) atoms to form distorted edge-sharing SeNa4Fe2 pentagonal pyramids. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to two equivalent Na(1), two equivalent Na(2), and two equivalent Fe(1) atoms.
Na3(FeSe2)2 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Na sites. In the first Na site, Na(1) is bonded to two equivalent Se(1) and four equivalent Se(3) atoms to form NaSe6 octahedra that share corners with eight equivalent Fe(1)Se4 tetrahedra, edges with two equivalent Fe(1)Se4 tetrahedra, and faces with two equivalent Na(1)Se6 octahedra. There is one shorter (2.94 Å) and one longer (2.96 Å) Na(1)-Se(1) bond length. There are two shorter (3.07 Å) and two longer (3.11 Å) Na(1)-Se(3) bond lengths. In the second Na site, Na(2) is bonded in a 5-coordinate geometry to one Se(1), two equivalent Se(2), and two equivalent Se(3) atoms. The Na(2)-Se(1) bond length is 3.20 Å. There is one shorter (2.95 Å) and one longer (3.04 Å) Na(2)-Se(2) bond length. There is one shorter (3.04 Å) and one longer (3.15 Å) Na(2)-Se(3) bond length. Fe(1) is bonded to one Se(1), one Se(2), and two equivalent Se(3) atoms to form FeSe4 tetrahedra that share corners with four equivalent Na(1)Se6 octahedra,  an edgeedge with one Na(1)Se6 octahedra, and edges with two equivalent Fe(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 14-63°. The Fe(1)-Se(1) bond length is 2.41 Å. The Fe(1)-Se(2) bond length is 2.39 Å. There is one shorter (2.41 Å) and one longer (2.42 Å) Fe(1)-Se(3) bond length. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent Na(1), two equivalent Na(2), and two equivalent Fe(1) atoms. In the second Se site, Se(2) is bonded to four equivalent Na(2) and two equivalent Fe(1) atoms to form distorted edge-sharing SeNa4Fe2 pentagonal pyramids. In the third Se site, Se(3) is bonded in a 6-coordinate geometry to two equivalent Na(1), two equivalent Na(2), and two equivalent Fe(1) atoms.