Rb4Fe2S5 crystallizes in the triclinic P-1 space group. There are four inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 7-coordinate geometry to one S(2), one S(4), one S(5), two equivalent S(1), and two equivalent S(3) atoms. In the second Rb site, Rb(2) is bonded in a 5-coordinate geometry to one S(4), two equivalent S(1), and two equivalent S(2) atoms. In the third Rb site, Rb(3) is bonded in a 6-coordinate geometry to two equivalent S(2), two equivalent S(3), and two equivalent S(5) atoms. In the fourth Rb site, Rb(4) is bonded in a 5-coordinate geometry to one S(2), one S(4), one S(5), and two equivalent S(1) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one S(1), one S(2), one S(3), and one S(4) atom to form edge-sharing FeS4 tetrahedra. In the second Fe site, Fe(2) is bonded to one S(3), one S(4), and two equivalent S(5) atoms to form edge-sharing FeS4 tetrahedra. There are five inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Rb(1), two equivalent Rb(2), two equivalent Rb(4), and one Fe(1) atom to form distorted SRb6Fe pentagonal bipyramids that share corners with two equivalent S(5)Rb4Fe2 octahedra,  a cornercorner with one S(2)Rb6Fe pentagonal bipyramid,  an edgeedge with one S(5)Rb4Fe2 octahedra,  an edgeedge with one S(2)Rb6Fe pentagonal bipyramid, edges with three equivalent S(1)Rb6Fe pentagonal bipyramids, and faces with two equivalent S(2)Rb6Fe pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 12-65°. In the second S site, S(2) is bonded to one Rb(1), one Rb(4), two equivalent Rb(2), two equivalent Rb(3), and one Fe(1) atom to form distorted SRb6Fe pentagonal bipyramids that share corners with two equivalent S(5)Rb4Fe2 octahedra,  a cornercorner with one S(1)Rb6Fe pentagonal bipyramid, edges with two equivalent S(5)Rb4Fe2 octahedra,  an edgeedge with one S(1)Rb6Fe pentagonal bipyramid, edges with two equivalent S(2)Rb6Fe pentagonal bipyramids, and faces with two equivalent S(1)Rb6Fe pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 29-72°. In the third S site, S(3) is bonded in a 2-coordinate geometry to two equivalent Rb(1), two equivalent Rb(3), one Fe(1), and one Fe(2) atom. In the fourth S site, S(4) is bonded in a 3-coordinate geometry to one Rb(1), one Rb(2), one Rb(4), one Fe(1), and one Fe(2) atom. In the fifth S site, S(5) is bonded to one Rb(1), one Rb(4), two equivalent Rb(3), and two equivalent Fe(2) atoms to form distorted SRb4Fe2 octahedra that share corners with two equivalent S(1)Rb6Fe pentagonal bipyramids, corners with two equivalent S(2)Rb6Fe pentagonal bipyramids, edges with two equivalent S(5)Rb4Fe2 octahedra,  an edgeedge with one S(1)Rb6Fe pentagonal bipyramid, and edges with two equivalent S(2)Rb6Fe pentagonal bipyramids.
Rb4Fe2S5 crystallizes in the triclinic P-1 space group. There are four inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 7-coordinate geometry to one S(2), one S(4), one S(5), two equivalent S(1), and two equivalent S(3) atoms. The Rb(1)-S(2) bond length is 3.19 Å. The Rb(1)-S(4) bond length is 3.74 Å. The Rb(1)-S(5) bond length is 3.35 Å. There is one shorter (3.38 Å) and one longer (3.45 Å) Rb(1)-S(1) bond length. There is one shorter (3.42 Å) and one longer (3.58 Å) Rb(1)-S(3) bond length. In the second Rb site, Rb(2) is bonded in a 5-coordinate geometry to one S(4), two equivalent S(1), and two equivalent S(2) atoms. The Rb(2)-S(4) bond length is 3.22 Å. There is one shorter (3.31 Å) and one longer (3.36 Å) Rb(2)-S(1) bond length. There is one shorter (3.31 Å) and one longer (3.32 Å) Rb(2)-S(2) bond length. In the third Rb site, Rb(3) is bonded in a 6-coordinate geometry to two equivalent S(2), two equivalent S(3), and two equivalent S(5) atoms. There is one shorter (3.24 Å) and one longer (3.47 Å) Rb(3)-S(2) bond length. There is one shorter (3.60 Å) and one longer (3.78 Å) Rb(3)-S(3) bond length. There is one shorter (3.39 Å) and one longer (3.43 Å) Rb(3)-S(5) bond length. In the fourth Rb site, Rb(4) is bonded in a 5-coordinate geometry to one S(2), one S(4), one S(5), and two equivalent S(1) atoms. The Rb(4)-S(2) bond length is 3.50 Å. The Rb(4)-S(4) bond length is 3.69 Å. The Rb(4)-S(5) bond length is 3.30 Å. There is one shorter (3.25 Å) and one longer (3.42 Å) Rb(4)-S(1) bond length. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one S(1), one S(2), one S(3), and one S(4) atom to form edge-sharing FeS4 tetrahedra. The Fe(1)-S(1) bond length is 2.22 Å. The Fe(1)-S(2) bond length is 2.22 Å. The Fe(1)-S(3) bond length is 2.27 Å. The Fe(1)-S(4) bond length is 2.28 Å. In the second Fe site, Fe(2) is bonded to one S(3), one S(4), and two equivalent S(5) atoms to form edge-sharing FeS4 tetrahedra. The Fe(2)-S(3) bond length is 2.20 Å. The Fe(2)-S(4) bond length is 2.22 Å. There is one shorter (2.23 Å) and one longer (2.24 Å) Fe(2)-S(5) bond length. There are five inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Rb(1), two equivalent Rb(2), two equivalent Rb(4), and one Fe(1) atom to form distorted SRb6Fe pentagonal bipyramids that share corners with two equivalent S(5)Rb4Fe2 octahedra,  a cornercorner with one S(2)Rb6Fe pentagonal bipyramid,  an edgeedge with one S(5)Rb4Fe2 octahedra,  an edgeedge with one S(2)Rb6Fe pentagonal bipyramid, edges with three equivalent S(1)Rb6Fe pentagonal bipyramids, and faces with two equivalent S(2)Rb6Fe pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 12-65°. In the second S site, S(2) is bonded to one Rb(1), one Rb(4), two equivalent Rb(2), two equivalent Rb(3), and one Fe(1) atom to form distorted SRb6Fe pentagonal bipyramids that share corners with two equivalent S(5)Rb4Fe2 octahedra,  a cornercorner with one S(1)Rb6Fe pentagonal bipyramid, edges with two equivalent S(5)Rb4Fe2 octahedra,  an edgeedge with one S(1)Rb6Fe pentagonal bipyramid, edges with two equivalent S(2)Rb6Fe pentagonal bipyramids, and faces with two equivalent S(1)Rb6Fe pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 29-72°. In the third S site, S(3) is bonded in a 2-coordinate geometry to two equivalent Rb(1), two equivalent Rb(3), one Fe(1), and one Fe(2) atom. In the fourth S site, S(4) is bonded in a 3-coordinate geometry to one Rb(1), one Rb(2), one Rb(4), one Fe(1), and one Fe(2) atom. In the fifth S site, S(5) is bonded to one Rb(1), one Rb(4), two equivalent Rb(3), and two equivalent Fe(2) atoms to form distorted SRb4Fe2 octahedra that share corners with two equivalent S(1)Rb6Fe pentagonal bipyramids, corners with two equivalent S(2)Rb6Fe pentagonal bipyramids, edges with two equivalent S(5)Rb4Fe2 octahedra,  an edgeedge with one S(1)Rb6Fe pentagonal bipyramid, and edges with two equivalent S(2)Rb6Fe pentagonal bipyramids.