Er2S3 crystallizes in the monoclinic P2_1/m space group. There are six inequivalent Er sites. In the first Er site, Er(1) is bonded to one S(3), one S(4), two equivalent S(2), and three equivalent S(8) atoms to form distorted ErS7 pentagonal bipyramids that share  a cornercorner with one Er(6)S6 octahedra, corners with four equivalent Er(4)S6 octahedra, edges with two equivalent Er(5)S6 octahedra, edges with two equivalent Er(6)S6 octahedra, edges with four equivalent Er(1)S7 pentagonal bipyramids, and  a faceface with one Er(4)S6 octahedra. The corner-sharing octahedral tilt angles range from 33-49°. In the second Er site, Er(2) is bonded to one S(5), one S(9), two equivalent S(6), and three equivalent S(1) atoms to form distorted ErS7 pentagonal bipyramids that share  a cornercorner with one Er(4)S6 octahedra, corners with two equivalent Er(5)S6 octahedra, corners with two equivalent Er(3)S7 pentagonal bipyramids, edges with two equivalent Er(6)S6 octahedra, edges with two equivalent Er(3)S7 pentagonal bipyramids, edges with four equivalent Er(2)S7 pentagonal bipyramids, and  a faceface with one Er(3)S7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 49-51°. In the third Er site, Er(3) is bonded to one S(6), one S(9), two equivalent S(1), and three equivalent S(7) atoms to form distorted ErS7 pentagonal bipyramids that share  a cornercorner with one Er(5)S6 octahedra,  a cornercorner with one Er(6)S6 octahedra, corners with two equivalent Er(2)S7 pentagonal bipyramids, edges with two equivalent Er(5)S6 octahedra, edges with two equivalent Er(2)S7 pentagonal bipyramids, edges with four equivalent Er(3)S7 pentagonal bipyramids, and  a faceface with one Er(2)S7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 33-34°. In the fourth Er site, Er(4) is bonded to one S(5), two equivalent S(2), and three equivalent S(4) atoms to form ErS6 octahedra that share corners with two equivalent Er(5)S6 octahedra, corners with two equivalent Er(6)S6 octahedra,  a cornercorner with one Er(2)S7 pentagonal bipyramid, corners with four equivalent Er(1)S7 pentagonal bipyramids, edges with four equivalent Er(4)S6 octahedra, and  a faceface with one Er(1)S7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 62-67°. In the fifth Er site, Er(5) is bonded to one S(2), one S(7), two equivalent S(3), and two equivalent S(9) atoms to form ErS6 octahedra that share corners with two equivalent Er(4)S6 octahedra, corners with two equivalent Er(6)S6 octahedra,  a cornercorner with one Er(3)S7 pentagonal bipyramid, corners with two equivalent Er(2)S7 pentagonal bipyramids,  an edgeedge with one Er(6)S6 octahedra, edges with two equivalent Er(5)S6 octahedra, edges with two equivalent Er(1)S7 pentagonal bipyramids, and edges with two equivalent Er(3)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 14-67°. In the sixth Er site, Er(6) is bonded to one S(6), one S(8), two equivalent S(3), and two equivalent S(5) atoms to form ErS6 octahedra that share corners with two equivalent Er(4)S6 octahedra, corners with two equivalent Er(5)S6 octahedra,  a cornercorner with one Er(1)S7 pentagonal bipyramid,  a cornercorner with one Er(3)S7 pentagonal bipyramid,  an edgeedge with one Er(5)S6 octahedra, edges with two equivalent Er(6)S6 octahedra, edges with two equivalent Er(1)S7 pentagonal bipyramids, and edges with two equivalent Er(2)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 14-62°. There are nine inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Er(3) and three equivalent Er(2) atoms to form distorted SEr5 trigonal bipyramids that share  a cornercorner with one S(9)Er4 trigonal pyramid, corners with two equivalent S(6)Er4 trigonal pyramids, corners with four equivalent S(7)Er4 trigonal pyramids, edges with four equivalent S(1)Er5 trigonal bipyramids,  an edgeedge with one S(7)Er4 trigonal pyramid, edges with two equivalent S(9)Er4 trigonal pyramids, and edges with three equivalent S(6)Er4 trigonal pyramids. In the second S site, S(2) is bonded to one Er(5), two equivalent Er(1), and two equivalent Er(4) atoms to form distorted SEr5 trigonal bipyramids that share corners with four equivalent S(8)Er4 tetrahedra,  a cornercorner with one S(7)Er4 trigonal pyramid, corners with two equivalent S(4)Er4 trigonal pyramids, corners with two equivalent S(9)Er4 trigonal pyramids, edges with two equivalent S(3)Er5 square pyramids,  an edgeedge with one S(8)Er4 tetrahedra, edges with two equivalent S(2)Er5 trigonal bipyramids, and edges with three equivalent S(4)Er4 trigonal pyramids. In the third S site, S(3) is bonded to one Er(1), two equivalent Er(5), and two equivalent Er(6) atoms to form SEr5 square pyramids that share  a cornercorner with one S(8)Er4 tetrahedra,  a cornercorner with one S(4)Er4 trigonal pyramid, corners with two equivalent S(6)Er4 trigonal pyramids, corners with two equivalent S(7)Er4 trigonal pyramids, corners with two equivalent S(9)Er4 trigonal pyramids, edges with two equivalent S(3)Er5 square pyramids, edges with two equivalent S(8)Er4 tetrahedra, edges with two equivalent S(2)Er5 trigonal bipyramids, and  an edgeedge with one S(9)Er4 trigonal pyramid. In the fourth S site, S(4) is bonded to one Er(1) and three equivalent Er(4) atoms to form SEr4 trigonal pyramids that share  a cornercorner with one S(3)Er5 square pyramid, corners with three equivalent S(8)Er4 tetrahedra, corners with two equivalent S(2)Er5 trigonal bipyramids, corners with two equivalent S(4)Er4 trigonal pyramids, edges with three equivalent S(2)Er5 trigonal bipyramids, and edges with two equivalent S(4)Er4 trigonal pyramids. In the fifth S site, S(5) is bonded in a distorted rectangular see-saw-like geometry to one Er(2), one Er(4), and two equivalent Er(6) atoms. In the sixth S site, S(6) is bonded to one Er(3), one Er(6), and two equivalent Er(2) atoms to form distorted SEr4 trigonal pyramids that share corners with two equivalent S(3)Er5 square pyramids,  a cornercorner with one S(8)Er4 tetrahedra, corners with two equivalent S(1)Er5 trigonal bipyramids, corners with two equivalent S(6)Er4 trigonal pyramids, corners with three equivalent S(7)Er4 trigonal pyramids, corners with three equivalent S(9)Er4 trigonal pyramids, and edges with three equivalent S(1)Er5 trigonal bipyramids. In the seventh S site, S(7) is bonded to one Er(5) and three equivalent Er(3) atoms to form distorted SEr4 trigonal pyramids that share corners with two equivalent S(3)Er5 square pyramids,  a cornercorner with one S(2)Er5 trigonal bipyramid, corners with four equivalent S(1)Er5 trigonal bipyramids,  a cornercorner with one S(9)Er4 trigonal pyramid, corners with two equivalent S(7)Er4 trigonal pyramids, corners with three equivalent S(6)Er4 trigonal pyramids,  an edgeedge with one S(1)Er5 trigonal bipyramid, edges with two equivalent S(7)Er4 trigonal pyramids, and edges with two equivalent S(9)Er4 trigonal pyramids. In the eighth S site, S(8) is bonded to one Er(6) and three equivalent Er(1) atoms to form SEr4 tetrahedra that share  a cornercorner with one S(3)Er5 square pyramid, corners with two equivalent S(8)Er4 tetrahedra, corners with four equivalent S(2)Er5 trigonal bipyramids,  a cornercorner with one S(6)Er4 trigonal pyramid, corners with three equivalent S(4)Er4 trigonal pyramids, edges with two equivalent S(3)Er5 square pyramids, edges with two equivalent S(8)Er4 tetrahedra, and  an edgeedge with one S(2)Er5 trigonal bipyramid. In the ninth S site, S(9) is bonded to one Er(2), one Er(3), and two equivalent Er(5) atoms to form SEr4 trigonal pyramids that share corners with two equivalent S(3)Er5 square pyramids,  a cornercorner with one S(1)Er5 trigonal bipyramid, corners with two equivalent S(2)Er5 trigonal bipyramids,  a cornercorner with one S(7)Er4 trigonal pyramid, corners with two equivalent S(9)Er4 trigonal pyramids, corners with three equivalent S(6)Er4 trigonal pyramids,  an edgeedge with one S(3)Er5 square pyramid, edges with two equivalent S(1)Er5 trigonal bipyramids, and edges with two equivalent S(7)Er4 trigonal pyramids.
Er2S3 crystallizes in the monoclinic P2_1/m space group. There are six inequivalent Er sites. In the first Er site, Er(1) is bonded to one S(3), one S(4), two equivalent S(2), and three equivalent S(8) atoms to form distorted ErS7 pentagonal bipyramids that share  a cornercorner with one Er(6)S6 octahedra, corners with four equivalent Er(4)S6 octahedra, edges with two equivalent Er(5)S6 octahedra, edges with two equivalent Er(6)S6 octahedra, edges with four equivalent Er(1)S7 pentagonal bipyramids, and  a faceface with one Er(4)S6 octahedra. The corner-sharing octahedral tilt angles range from 33-49°. The Er(1)-S(3) bond length is 2.90 Å. The Er(1)-S(4) bond length is 2.80 Å. Both Er(1)-S(2) bond lengths are 2.91 Å. There are two shorter (2.66 Å) and one longer (2.74 Å) Er(1)-S(8) bond length. In the second Er site, Er(2) is bonded to one S(5), one S(9), two equivalent S(6), and three equivalent S(1) atoms to form distorted ErS7 pentagonal bipyramids that share  a cornercorner with one Er(4)S6 octahedra, corners with two equivalent Er(5)S6 octahedra, corners with two equivalent Er(3)S7 pentagonal bipyramids, edges with two equivalent Er(6)S6 octahedra, edges with two equivalent Er(3)S7 pentagonal bipyramids, edges with four equivalent Er(2)S7 pentagonal bipyramids, and  a faceface with one Er(3)S7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 49-51°. The Er(2)-S(5) bond length is 2.94 Å. The Er(2)-S(9) bond length is 2.75 Å. Both Er(2)-S(6) bond lengths are 2.69 Å. There is one shorter (2.75 Å) and two longer (2.84 Å) Er(2)-S(1) bond lengths. In the third Er site, Er(3) is bonded to one S(6), one S(9), two equivalent S(1), and three equivalent S(7) atoms to form distorted ErS7 pentagonal bipyramids that share  a cornercorner with one Er(5)S6 octahedra,  a cornercorner with one Er(6)S6 octahedra, corners with two equivalent Er(2)S7 pentagonal bipyramids, edges with two equivalent Er(5)S6 octahedra, edges with two equivalent Er(2)S7 pentagonal bipyramids, edges with four equivalent Er(3)S7 pentagonal bipyramids, and  a faceface with one Er(2)S7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 33-34°. The Er(3)-S(6) bond length is 2.82 Å. The Er(3)-S(9) bond length is 2.92 Å. Both Er(3)-S(1) bond lengths are 2.78 Å. There are two shorter (2.70 Å) and one longer (2.71 Å) Er(3)-S(7) bond length. In the fourth Er site, Er(4) is bonded to one S(5), two equivalent S(2), and three equivalent S(4) atoms to form ErS6 octahedra that share corners with two equivalent Er(5)S6 octahedra, corners with two equivalent Er(6)S6 octahedra,  a cornercorner with one Er(2)S7 pentagonal bipyramid, corners with four equivalent Er(1)S7 pentagonal bipyramids, edges with four equivalent Er(4)S6 octahedra, and  a faceface with one Er(1)S7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 62-67°. The Er(4)-S(5) bond length is 2.72 Å. Both Er(4)-S(2) bond lengths are 2.80 Å. There are two shorter (2.65 Å) and one longer (2.75 Å) Er(4)-S(4) bond length. In the fifth Er site, Er(5) is bonded to one S(2), one S(7), two equivalent S(3), and two equivalent S(9) atoms to form ErS6 octahedra that share corners with two equivalent Er(4)S6 octahedra, corners with two equivalent Er(6)S6 octahedra,  a cornercorner with one Er(3)S7 pentagonal bipyramid, corners with two equivalent Er(2)S7 pentagonal bipyramids,  an edgeedge with one Er(6)S6 octahedra, edges with two equivalent Er(5)S6 octahedra, edges with two equivalent Er(1)S7 pentagonal bipyramids, and edges with two equivalent Er(3)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 14-67°. The Er(5)-S(2) bond length is 2.71 Å. The Er(5)-S(7) bond length is 2.60 Å. Both Er(5)-S(3) bond lengths are 2.80 Å. Both Er(5)-S(9) bond lengths are 2.62 Å. In the sixth Er site, Er(6) is bonded to one S(6), one S(8), two equivalent S(3), and two equivalent S(5) atoms to form ErS6 octahedra that share corners with two equivalent Er(4)S6 octahedra, corners with two equivalent Er(5)S6 octahedra,  a cornercorner with one Er(1)S7 pentagonal bipyramid,  a cornercorner with one Er(3)S7 pentagonal bipyramid,  an edgeedge with one Er(5)S6 octahedra, edges with two equivalent Er(6)S6 octahedra, edges with two equivalent Er(1)S7 pentagonal bipyramids, and edges with two equivalent Er(2)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 14-62°. The Er(6)-S(6) bond length is 2.66 Å. The Er(6)-S(8) bond length is 2.70 Å. Both Er(6)-S(3) bond lengths are 2.82 Å. Both Er(6)-S(5) bond lengths are 2.66 Å. There are nine inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Er(3) and three equivalent Er(2) atoms to form distorted SEr5 trigonal bipyramids that share  a cornercorner with one S(9)Er4 trigonal pyramid, corners with two equivalent S(6)Er4 trigonal pyramids, corners with four equivalent S(7)Er4 trigonal pyramids, edges with four equivalent S(1)Er5 trigonal bipyramids,  an edgeedge with one S(7)Er4 trigonal pyramid, edges with two equivalent S(9)Er4 trigonal pyramids, and edges with three equivalent S(6)Er4 trigonal pyramids. In the second S site, S(2) is bonded to one Er(5), two equivalent Er(1), and two equivalent Er(4) atoms to form distorted SEr5 trigonal bipyramids that share corners with four equivalent S(8)Er4 tetrahedra,  a cornercorner with one S(7)Er4 trigonal pyramid, corners with two equivalent S(4)Er4 trigonal pyramids, corners with two equivalent S(9)Er4 trigonal pyramids, edges with two equivalent S(3)Er5 square pyramids,  an edgeedge with one S(8)Er4 tetrahedra, edges with two equivalent S(2)Er5 trigonal bipyramids, and edges with three equivalent S(4)Er4 trigonal pyramids. In the third S site, S(3) is bonded to one Er(1), two equivalent Er(5), and two equivalent Er(6) atoms to form SEr5 square pyramids that share  a cornercorner with one S(8)Er4 tetrahedra,  a cornercorner with one S(4)Er4 trigonal pyramid, corners with two equivalent S(6)Er4 trigonal pyramids, corners with two equivalent S(7)Er4 trigonal pyramids, corners with two equivalent S(9)Er4 trigonal pyramids, edges with two equivalent S(3)Er5 square pyramids, edges with two equivalent S(8)Er4 tetrahedra, edges with two equivalent S(2)Er5 trigonal bipyramids, and  an edgeedge with one S(9)Er4 trigonal pyramid. In the fourth S site, S(4) is bonded to one Er(1) and three equivalent Er(4) atoms to form SEr4 trigonal pyramids that share  a cornercorner with one S(3)Er5 square pyramid, corners with three equivalent S(8)Er4 tetrahedra, corners with two equivalent S(2)Er5 trigonal bipyramids, corners with two equivalent S(4)Er4 trigonal pyramids, edges with three equivalent S(2)Er5 trigonal bipyramids, and edges with two equivalent S(4)Er4 trigonal pyramids. In the fifth S site, S(5) is bonded in a distorted rectangular see-saw-like geometry to one Er(2), one Er(4), and two equivalent Er(6) atoms. In the sixth S site, S(6) is bonded to one Er(3), one Er(6), and two equivalent Er(2) atoms to form distorted SEr4 trigonal pyramids that share corners with two equivalent S(3)Er5 square pyramids,  a cornercorner with one S(8)Er4 tetrahedra, corners with two equivalent S(1)Er5 trigonal bipyramids, corners with two equivalent S(6)Er4 trigonal pyramids, corners with three equivalent S(7)Er4 trigonal pyramids, corners with three equivalent S(9)Er4 trigonal pyramids, and edges with three equivalent S(1)Er5 trigonal bipyramids. In the seventh S site, S(7) is bonded to one Er(5) and three equivalent Er(3) atoms to form distorted SEr4 trigonal pyramids that share corners with two equivalent S(3)Er5 square pyramids,  a cornercorner with one S(2)Er5 trigonal bipyramid, corners with four equivalent S(1)Er5 trigonal bipyramids,  a cornercorner with one S(9)Er4 trigonal pyramid, corners with two equivalent S(7)Er4 trigonal pyramids, corners with three equivalent S(6)Er4 trigonal pyramids,  an edgeedge with one S(1)Er5 trigonal bipyramid, edges with two equivalent S(7)Er4 trigonal pyramids, and edges with two equivalent S(9)Er4 trigonal pyramids. In the eighth S site, S(8) is bonded to one Er(6) and three equivalent Er(1) atoms to form SEr4 tetrahedra that share  a cornercorner with one S(3)Er5 square pyramid, corners with two equivalent S(8)Er4 tetrahedra, corners with four equivalent S(2)Er5 trigonal bipyramids,  a cornercorner with one S(6)Er4 trigonal pyramid, corners with three equivalent S(4)Er4 trigonal pyramids, edges with two equivalent S(3)Er5 square pyramids, edges with two equivalent S(8)Er4 tetrahedra, and  an edgeedge with one S(2)Er5 trigonal bipyramid. In the ninth S site, S(9) is bonded to one Er(2), one Er(3), and two equivalent Er(5) atoms to form SEr4 trigonal pyramids that share corners with two equivalent S(3)Er5 square pyramids,  a cornercorner with one S(1)Er5 trigonal bipyramid, corners with two equivalent S(2)Er5 trigonal bipyramids,  a cornercorner with one S(7)Er4 trigonal pyramid, corners with two equivalent S(9)Er4 trigonal pyramids, corners with three equivalent S(6)Er4 trigonal pyramids,  an edgeedge with one S(3)Er5 square pyramid, edges with two equivalent S(1)Er5 trigonal bipyramids, and edges with two equivalent S(7)Er4 trigonal pyramids.