Fe7Se8 crystallizes in the trigonal P3_121 space group. There are five inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form a mixture of face, corner, and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles range from 48-54°. In the second Fe site, Fe(2) is bonded to one Se(1), one Se(3), two equivalent Se(2), and two equivalent Se(4) atoms to form a mixture of face, corner, and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. In the third Fe site, Fe(3) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form a mixture of distorted face, corner, and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles range from 51-58°. In the fourth Fe site, Fe(4) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(4) atoms to form a mixture of distorted face, corner, and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles range from 51-56°. In the fifth Fe site, Fe(5) is bonded to one Se(1), one Se(2), two equivalent Se(3), and two equivalent Se(4) atoms to form a mixture of distorted face, corner, and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-53°. There are four inequivalent Se sites. In the first Se site, Se(4) is bonded to one Fe(4), two equivalent Fe(2), and two equivalent Fe(5) atoms to form a mixture of distorted corner and edge-sharing SeFe5 trigonal bipyramids. In the second Se site, Se(1) is bonded to one Fe(1), one Fe(2), one Fe(3), one Fe(4), and one Fe(5) atom to form a mixture of distorted corner and edge-sharing SeFe5 square pyramids. In the third Se site, Se(2) is bonded in a 6-coordinate geometry to one Fe(1), one Fe(3), one Fe(4), one Fe(5), and two equivalent Fe(2) atoms. In the fourth Se site, Se(3) is bonded to one Fe(1), one Fe(2), one Fe(3), and two equivalent Fe(5) atoms to form a mixture of distorted corner and edge-sharing SeFe5 trigonal bipyramids.
Fe7Se8 crystallizes in the trigonal P3_121 space group. There are five inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form a mixture of face, corner, and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles range from 48-54°. Both Fe(1)-Se(1) bond lengths are 2.55 Å. Both Fe(1)-Se(2) bond lengths are 2.60 Å. Both Fe(1)-Se(3) bond lengths are 2.49 Å. In the second Fe site, Fe(2) is bonded to one Se(1), one Se(3), two equivalent Se(2), and two equivalent Se(4) atoms to form a mixture of face, corner, and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-58°. The Fe(2)-Se(1) bond length is 2.51 Å. The Fe(2)-Se(3) bond length is 2.43 Å. There is one shorter (2.52 Å) and one longer (2.58 Å) Fe(2)-Se(2) bond length. There is one shorter (2.51 Å) and one longer (2.52 Å) Fe(2)-Se(4) bond length. In the third Fe site, Fe(3) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms to form a mixture of distorted face, corner, and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles range from 51-58°. Both Fe(3)-Se(1) bond lengths are 2.44 Å. Both Fe(3)-Se(2) bond lengths are 2.61 Å. Both Fe(3)-Se(3) bond lengths are 2.48 Å. In the fourth Fe site, Fe(4) is bonded to two equivalent Se(1), two equivalent Se(2), and two equivalent Se(4) atoms to form a mixture of distorted face, corner, and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles range from 51-56°. Both Fe(4)-Se(1) bond lengths are 2.36 Å. Both Fe(4)-Se(2) bond lengths are 2.54 Å. Both Fe(4)-Se(4) bond lengths are 2.42 Å. In the fifth Fe site, Fe(5) is bonded to one Se(1), one Se(2), two equivalent Se(3), and two equivalent Se(4) atoms to form a mixture of distorted face, corner, and edge-sharing FeSe6 octahedra. The corner-sharing octahedral tilt angles range from 47-53°. The Fe(5)-Se(1) bond length is 2.41 Å. The Fe(5)-Se(2) bond length is 2.54 Å. Both Fe(5)-Se(3) bond lengths are 2.43 Å. There is one shorter (2.47 Å) and one longer (2.48 Å) Fe(5)-Se(4) bond length. There are four inequivalent Se sites. In the first Se site, Se(4) is bonded to one Fe(4), two equivalent Fe(2), and two equivalent Fe(5) atoms to form a mixture of distorted corner and edge-sharing SeFe5 trigonal bipyramids. In the second Se site, Se(1) is bonded to one Fe(1), one Fe(2), one Fe(3), one Fe(4), and one Fe(5) atom to form a mixture of distorted corner and edge-sharing SeFe5 square pyramids. In the third Se site, Se(2) is bonded in a 6-coordinate geometry to one Fe(1), one Fe(3), one Fe(4), one Fe(5), and two equivalent Fe(2) atoms. In the fourth Se site, Se(3) is bonded to one Fe(1), one Fe(2), one Fe(3), and two equivalent Fe(5) atoms to form a mixture of distorted corner and edge-sharing SeFe5 trigonal bipyramids.