Fe7Se3 crystallizes in the orthorhombic Pnma space group. There are five inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 2-coordinate geometry to one Se(1) and two equivalent Se(2) atoms. In the second Fe site, Fe(2) is bonded in a 3-coordinate geometry to two equivalent Se(1) and two equivalent Se(2) atoms. In the third Fe site, Fe(3) is bonded in a 2-coordinate geometry to two equivalent Se(2) atoms. In the fourth Fe site, Fe(4) is bonded in a 4-coordinate geometry to two equivalent Se(1) and two equivalent Se(2) atoms. In the fifth Fe site, Fe(5) is bonded in a 3-coordinate geometry to one Se(1) and two equivalent Se(2) atoms. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 9-coordinate geometry to one Fe(5), two equivalent Fe(1), two equivalent Fe(4), and four equivalent Fe(2) atoms. In the second Se site, Se(2) is bonded in a 7-coordinate geometry to one Fe(3), one Fe(4), one Fe(5), two equivalent Fe(1), and two equivalent Fe(2) atoms.
Fe7Se3 crystallizes in the orthorhombic Pnma space group. There are five inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 2-coordinate geometry to one Se(1) and two equivalent Se(2) atoms. The Fe(1)-Se(1) bond length is 2.41 Å. There is one shorter (2.34 Å) and one longer (2.65 Å) Fe(1)-Se(2) bond length. In the second Fe site, Fe(2) is bonded in a 3-coordinate geometry to two equivalent Se(1) and two equivalent Se(2) atoms. There is one shorter (2.53 Å) and one longer (2.93 Å) Fe(2)-Se(1) bond length. There is one shorter (2.45 Å) and one longer (2.54 Å) Fe(2)-Se(2) bond length. In the third Fe site, Fe(3) is bonded in a 2-coordinate geometry to two equivalent Se(2) atoms. Both Fe(3)-Se(2) bond lengths are 2.57 Å. In the fourth Fe site, Fe(4) is bonded in a 4-coordinate geometry to two equivalent Se(1) and two equivalent Se(2) atoms. There is one shorter (2.70 Å) and one longer (2.71 Å) Fe(4)-Se(1) bond length. Both Fe(4)-Se(2) bond lengths are 2.55 Å. In the fifth Fe site, Fe(5) is bonded in a 3-coordinate geometry to one Se(1) and two equivalent Se(2) atoms. The Fe(5)-Se(1) bond length is 2.49 Å. Both Fe(5)-Se(2) bond lengths are 2.47 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 9-coordinate geometry to one Fe(5), two equivalent Fe(1), two equivalent Fe(4), and four equivalent Fe(2) atoms. In the second Se site, Se(2) is bonded in a 7-coordinate geometry to one Fe(3), one Fe(4), one Fe(5), two equivalent Fe(1), and two equivalent Fe(2) atoms.