FeFeS crystallizes in the monoclinic Cm space group. There are fourteen inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a distorted bent 150 degrees geometry to one S(1) and one S(2) atom. In the second Fe site, Fe(2) is bonded in a 4-coordinate geometry to one S(2), one S(7), and two equivalent S(1) atoms. In the third Fe site, Fe(3) is bonded in a 3-coordinate geometry to one S(4) and two equivalent S(3) atoms. In the fourth Fe site, Fe(4) is bonded in a 3-coordinate geometry to one S(3) and two equivalent S(2) atoms. In the fifth Fe site, Fe(5) is bonded in a 3-coordinate geometry to one S(4) and two equivalent S(3) atoms. In the sixth Fe site, Fe(6) is bonded in a 3-coordinate geometry to one S(3) and two equivalent S(2) atoms. In the seventh Fe site, Fe(7) is bonded in a 3-coordinate geometry to one S(5) and two equivalent S(4) atoms. In the eighth Fe site, Fe(8) is bonded in a 3-coordinate geometry to one S(5) and two equivalent S(4) atoms. In the ninth Fe site, Fe(9) is bonded in a 3-coordinate geometry to one S(6) and two equivalent S(5) atoms. In the tenth Fe site, Fe(10) is bonded in a 3-coordinate geometry to one S(6) and two equivalent S(5) atoms. In the eleventh Fe site, Fe(11) is bonded in a 3-coordinate geometry to one S(7) and two equivalent S(6) atoms. In the twelfth Fe site, Fe(12) is bonded in a 3-coordinate geometry to one S(7) and two equivalent S(6) atoms. In the thirteenth Fe site, Fe(13) is bonded in a rectangular see-saw-like geometry to two equivalent S(1) and two equivalent S(7) atoms. In the fourteenth Fe site, Fe(14) is bonded in a distorted trigonal non-coplanar geometry to one S(1) and two equivalent S(7) atoms. There are seven inequivalent S sites. In the first S site, S(1) is bonded to one Fe(1), one Fe(14), two equivalent Fe(13), and two equivalent Fe(2) atoms to form distorted edge-sharing SFe6 pentagonal pyramids. In the second S site, S(2) is bonded in a 6-coordinate geometry to one Fe(1), one Fe(2), two equivalent Fe(4), and two equivalent Fe(6) atoms. In the third S site, S(3) is bonded to one Fe(4), one Fe(6), two equivalent Fe(3), and two equivalent Fe(5) atoms to form distorted edge-sharing SFe6 pentagonal pyramids. In the fourth S site, S(4) is bonded to one Fe(3), one Fe(5), two equivalent Fe(7), and two equivalent Fe(8) atoms to form distorted edge-sharing SFe6 pentagonal pyramids. In the fifth S site, S(5) is bonded to one Fe(7), one Fe(8), two equivalent Fe(10), and two equivalent Fe(9) atoms to form distorted edge-sharing SFe6 pentagonal pyramids. In the sixth S site, S(6) is bonded to one Fe(10), one Fe(9), two equivalent Fe(11), and two equivalent Fe(12) atoms to form distorted edge-sharing SFe6 pentagonal pyramids. In the seventh S site, S(7) is bonded in a 7-coordinate geometry to one Fe(11), one Fe(12), one Fe(2), two equivalent Fe(13), and two equivalent Fe(14) atoms.
FeFeS crystallizes in the monoclinic Cm space group. There are fourteen inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a distorted bent 150 degrees geometry to one S(1) and one S(2) atom. The Fe(1)-S(1) bond length is 2.14 Å. The Fe(1)-S(2) bond length is 2.18 Å. In the second Fe site, Fe(2) is bonded in a 4-coordinate geometry to one S(2), one S(7), and two equivalent S(1) atoms. The Fe(2)-S(2) bond length is 2.31 Å. The Fe(2)-S(7) bond length is 2.42 Å. Both Fe(2)-S(1) bond lengths are 2.21 Å. In the third Fe site, Fe(3) is bonded in a 3-coordinate geometry to one S(4) and two equivalent S(3) atoms. The Fe(3)-S(4) bond length is 2.24 Å. Both Fe(3)-S(3) bond lengths are 2.32 Å. In the fourth Fe site, Fe(4) is bonded in a 3-coordinate geometry to one S(3) and two equivalent S(2) atoms. The Fe(4)-S(3) bond length is 2.22 Å. Both Fe(4)-S(2) bond lengths are 2.56 Å. In the fifth Fe site, Fe(5) is bonded in a 3-coordinate geometry to one S(4) and two equivalent S(3) atoms. The Fe(5)-S(4) bond length is 2.18 Å. Both Fe(5)-S(3) bond lengths are 2.19 Å. In the sixth Fe site, Fe(6) is bonded in a 3-coordinate geometry to one S(3) and two equivalent S(2) atoms. The Fe(6)-S(3) bond length is 2.18 Å. Both Fe(6)-S(2) bond lengths are 2.23 Å. In the seventh Fe site, Fe(7) is bonded in a 3-coordinate geometry to one S(5) and two equivalent S(4) atoms. The Fe(7)-S(5) bond length is 2.20 Å. Both Fe(7)-S(4) bond lengths are 2.19 Å. In the eighth Fe site, Fe(8) is bonded in a 3-coordinate geometry to one S(5) and two equivalent S(4) atoms. The Fe(8)-S(5) bond length is 2.22 Å. Both Fe(8)-S(4) bond lengths are 2.21 Å. In the ninth Fe site, Fe(9) is bonded in a 3-coordinate geometry to one S(6) and two equivalent S(5) atoms. The Fe(9)-S(6) bond length is 2.26 Å. Both Fe(9)-S(5) bond lengths are 2.27 Å. In the tenth Fe site, Fe(10) is bonded in a 3-coordinate geometry to one S(6) and two equivalent S(5) atoms. The Fe(10)-S(6) bond length is 2.25 Å. Both Fe(10)-S(5) bond lengths are 2.25 Å. In the eleventh Fe site, Fe(11) is bonded in a 3-coordinate geometry to one S(7) and two equivalent S(6) atoms. The Fe(11)-S(7) bond length is 2.26 Å. Both Fe(11)-S(6) bond lengths are 2.21 Å. In the twelfth Fe site, Fe(12) is bonded in a 3-coordinate geometry to one S(7) and two equivalent S(6) atoms. The Fe(12)-S(7) bond length is 2.31 Å. Both Fe(12)-S(6) bond lengths are 2.28 Å. In the thirteenth Fe site, Fe(13) is bonded in a rectangular see-saw-like geometry to two equivalent S(1) and two equivalent S(7) atoms. Both Fe(13)-S(1) bond lengths are 2.35 Å. Both Fe(13)-S(7) bond lengths are 2.21 Å. In the fourteenth Fe site, Fe(14) is bonded in a distorted trigonal non-coplanar geometry to one S(1) and two equivalent S(7) atoms. The Fe(14)-S(1) bond length is 2.20 Å. Both Fe(14)-S(7) bond lengths are 2.18 Å. There are seven inequivalent S sites. In the first S site, S(1) is bonded to one Fe(1), one Fe(14), two equivalent Fe(13), and two equivalent Fe(2) atoms to form distorted edge-sharing SFe6 pentagonal pyramids. In the second S site, S(2) is bonded in a 6-coordinate geometry to one Fe(1), one Fe(2), two equivalent Fe(4), and two equivalent Fe(6) atoms. In the third S site, S(3) is bonded to one Fe(4), one Fe(6), two equivalent Fe(3), and two equivalent Fe(5) atoms to form distorted edge-sharing SFe6 pentagonal pyramids. In the fourth S site, S(4) is bonded to one Fe(3), one Fe(5), two equivalent Fe(7), and two equivalent Fe(8) atoms to form distorted edge-sharing SFe6 pentagonal pyramids. In the fifth S site, S(5) is bonded to one Fe(7), one Fe(8), two equivalent Fe(10), and two equivalent Fe(9) atoms to form distorted edge-sharing SFe6 pentagonal pyramids. In the sixth S site, S(6) is bonded to one Fe(10), one Fe(9), two equivalent Fe(11), and two equivalent Fe(12) atoms to form distorted edge-sharing SFe6 pentagonal pyramids. In the seventh S site, S(7) is bonded in a 7-coordinate geometry to one Fe(11), one Fe(12), one Fe(2), two equivalent Fe(13), and two equivalent Fe(14) atoms.