Er4FeS7 crystallizes in the monoclinic Cm space group. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to one S(4), two equivalent S(1), two equivalent S(3), and two equivalent S(6) atoms. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one S(3), two equivalent S(2), two equivalent S(4), and two equivalent S(5) atoms. In the third Er site, Er(3) is bonded to one S(2), one S(6), two equivalent S(5), and two equivalent S(7) atoms to form ErS6 octahedra that share  a cornercorner with one Er(4)S6 octahedra, corners with two equivalent Fe(1)S6 octahedra, edges with two equivalent Er(3)S6 octahedra, and edges with three equivalent Fe(1)S6 octahedra. The corner-sharing octahedral tilt angles range from 4-51°. In the fourth Er site, Er(4) is bonded to one S(1), one S(2), two equivalent S(3), and two equivalent S(4) atoms to form ErS6 octahedra that share  a cornercorner with one Er(3)S6 octahedra,  a cornercorner with one Fe(1)S6 octahedra, and edges with two equivalent Er(4)S6 octahedra. The corner-sharing octahedral tilt angles range from 51-53°. Fe(1) is bonded to one S(1), one S(5), two equivalent S(6), and two equivalent S(7) atoms to form FeS6 octahedra that share  a cornercorner with one Er(4)S6 octahedra, corners with two equivalent Er(3)S6 octahedra, edges with two equivalent Fe(1)S6 octahedra, and edges with three equivalent Er(3)S6 octahedra. The corner-sharing octahedral tilt angles range from 4-53°. There are seven inequivalent S sites. In the first S site, S(1) is bonded to one Er(4), two equivalent Er(1), and one Fe(1) atom to form distorted SEr3Fe tetrahedra that share  a cornercorner with one S(2)Er4 tetrahedra, corners with two equivalent S(1)Er3Fe tetrahedra,  a cornercorner with one S(5)Er4Fe trigonal bipyramid, corners with four equivalent S(6)Er3Fe2 trigonal bipyramids, corners with four equivalent S(3)Er5 trigonal bipyramids,  an edgeedge with one S(6)Er3Fe2 trigonal bipyramid,  an edgeedge with one S(3)Er5 trigonal bipyramid, and edges with two equivalent S(4)Er5 trigonal bipyramids. In the second S site, S(2) is bonded to one Er(3), one Er(4), and two equivalent Er(2) atoms to form SEr4 tetrahedra that share  a cornercorner with one S(1)Er3Fe tetrahedra, corners with two equivalent S(2)Er4 tetrahedra,  a cornercorner with one S(6)Er3Fe2 trigonal bipyramid, corners with four equivalent S(5)Er4Fe trigonal bipyramids, corners with four equivalent S(4)Er5 trigonal bipyramids,  an edgeedge with one S(5)Er4Fe trigonal bipyramid,  an edgeedge with one S(4)Er5 trigonal bipyramid, and edges with two equivalent S(3)Er5 trigonal bipyramids. In the third S site, S(3) is bonded to one Er(2), two equivalent Er(1), and two equivalent Er(4) atoms to form distorted SEr5 trigonal bipyramids that share corners with four equivalent S(1)Er3Fe tetrahedra, corners with two equivalent S(6)Er3Fe2 trigonal bipyramids, corners with two equivalent S(5)Er4Fe trigonal bipyramids, corners with two equivalent S(4)Er5 trigonal bipyramids,  an edgeedge with one S(1)Er3Fe tetrahedra, edges with two equivalent S(2)Er4 tetrahedra,  an edgeedge with one S(6)Er3Fe2 trigonal bipyramid, edges with two equivalent S(3)Er5 trigonal bipyramids, and edges with three equivalent S(4)Er5 trigonal bipyramids. In the fourth S site, S(4) is bonded to one Er(1), two equivalent Er(2), and two equivalent Er(4) atoms to form distorted SEr5 trigonal bipyramids that share corners with four equivalent S(2)Er4 tetrahedra, corners with two equivalent S(6)Er3Fe2 trigonal bipyramids, corners with two equivalent S(5)Er4Fe trigonal bipyramids, corners with two equivalent S(3)Er5 trigonal bipyramids,  an edgeedge with one S(2)Er4 tetrahedra, edges with two equivalent S(1)Er3Fe tetrahedra,  an edgeedge with one S(5)Er4Fe trigonal bipyramid, edges with two equivalent S(4)Er5 trigonal bipyramids, and edges with three equivalent S(3)Er5 trigonal bipyramids. In the fifth S site, S(5) is bonded to two equivalent Er(2), two equivalent Er(3), and one Fe(1) atom to form SEr4Fe trigonal bipyramids that share  a cornercorner with one S(1)Er3Fe tetrahedra, corners with four equivalent S(2)Er4 tetrahedra, corners with two equivalent S(3)Er5 trigonal bipyramids, corners with two equivalent S(4)Er5 trigonal bipyramids,  an edgeedge with one S(2)Er4 tetrahedra,  an edgeedge with one S(4)Er5 trigonal bipyramid, edges with two equivalent S(6)Er3Fe2 trigonal bipyramids, and edges with two equivalent S(5)Er4Fe trigonal bipyramids. In the sixth S site, S(6) is bonded to one Er(3), two equivalent Er(1), and two equivalent Fe(1) atoms to form SEr3Fe2 trigonal bipyramids that share  a cornercorner with one S(2)Er4 tetrahedra, corners with four equivalent S(1)Er3Fe tetrahedra, corners with two equivalent S(3)Er5 trigonal bipyramids, corners with two equivalent S(4)Er5 trigonal bipyramids,  an edgeedge with one S(1)Er3Fe tetrahedra,  an edgeedge with one S(3)Er5 trigonal bipyramid, edges with two equivalent S(6)Er3Fe2 trigonal bipyramids, and edges with two equivalent S(5)Er4Fe trigonal bipyramids. In the seventh S site, S(7) is bonded in a rectangular see-saw-like geometry to two equivalent Er(3) and two equivalent Fe(1) atoms.
Er4FeS7 crystallizes in the monoclinic Cm space group. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to one S(4), two equivalent S(1), two equivalent S(3), and two equivalent S(6) atoms. The Er(1)-S(4) bond length is 3.06 Å. Both Er(1)-S(1) bond lengths are 2.71 Å. Both Er(1)-S(3) bond lengths are 2.86 Å. Both Er(1)-S(6) bond lengths are 2.83 Å. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one S(3), two equivalent S(2), two equivalent S(4), and two equivalent S(5) atoms. The Er(2)-S(3) bond length is 2.97 Å. Both Er(2)-S(2) bond lengths are 2.69 Å. Both Er(2)-S(4) bond lengths are 2.84 Å. Both Er(2)-S(5) bond lengths are 2.87 Å. In the third Er site, Er(3) is bonded to one S(2), one S(6), two equivalent S(5), and two equivalent S(7) atoms to form ErS6 octahedra that share  a cornercorner with one Er(4)S6 octahedra, corners with two equivalent Fe(1)S6 octahedra, edges with two equivalent Er(3)S6 octahedra, and edges with three equivalent Fe(1)S6 octahedra. The corner-sharing octahedral tilt angles range from 4-51°. The Er(3)-S(2) bond length is 2.70 Å. The Er(3)-S(6) bond length is 2.68 Å. Both Er(3)-S(5) bond lengths are 2.76 Å. Both Er(3)-S(7) bond lengths are 2.66 Å. In the fourth Er site, Er(4) is bonded to one S(1), one S(2), two equivalent S(3), and two equivalent S(4) atoms to form ErS6 octahedra that share  a cornercorner with one Er(3)S6 octahedra,  a cornercorner with one Fe(1)S6 octahedra, and edges with two equivalent Er(4)S6 octahedra. The corner-sharing octahedral tilt angles range from 51-53°. The Er(4)-S(1) bond length is 2.65 Å. The Er(4)-S(2) bond length is 2.67 Å. Both Er(4)-S(3) bond lengths are 2.69 Å. Both Er(4)-S(4) bond lengths are 2.69 Å. Fe(1) is bonded to one S(1), one S(5), two equivalent S(6), and two equivalent S(7) atoms to form FeS6 octahedra that share  a cornercorner with one Er(4)S6 octahedra, corners with two equivalent Er(3)S6 octahedra, edges with two equivalent Fe(1)S6 octahedra, and edges with three equivalent Er(3)S6 octahedra. The corner-sharing octahedral tilt angles range from 4-53°. The Fe(1)-S(1) bond length is 2.48 Å. The Fe(1)-S(5) bond length is 2.65 Å. Both Fe(1)-S(6) bond lengths are 2.63 Å. Both Fe(1)-S(7) bond lengths are 2.50 Å. There are seven inequivalent S sites. In the first S site, S(1) is bonded to one Er(4), two equivalent Er(1), and one Fe(1) atom to form distorted SEr3Fe tetrahedra that share  a cornercorner with one S(2)Er4 tetrahedra, corners with two equivalent S(1)Er3Fe tetrahedra,  a cornercorner with one S(5)Er4Fe trigonal bipyramid, corners with four equivalent S(6)Er3Fe2 trigonal bipyramids, corners with four equivalent S(3)Er5 trigonal bipyramids,  an edgeedge with one S(6)Er3Fe2 trigonal bipyramid,  an edgeedge with one S(3)Er5 trigonal bipyramid, and edges with two equivalent S(4)Er5 trigonal bipyramids. In the second S site, S(2) is bonded to one Er(3), one Er(4), and two equivalent Er(2) atoms to form SEr4 tetrahedra that share  a cornercorner with one S(1)Er3Fe tetrahedra, corners with two equivalent S(2)Er4 tetrahedra,  a cornercorner with one S(6)Er3Fe2 trigonal bipyramid, corners with four equivalent S(5)Er4Fe trigonal bipyramids, corners with four equivalent S(4)Er5 trigonal bipyramids,  an edgeedge with one S(5)Er4Fe trigonal bipyramid,  an edgeedge with one S(4)Er5 trigonal bipyramid, and edges with two equivalent S(3)Er5 trigonal bipyramids. In the third S site, S(3) is bonded to one Er(2), two equivalent Er(1), and two equivalent Er(4) atoms to form distorted SEr5 trigonal bipyramids that share corners with four equivalent S(1)Er3Fe tetrahedra, corners with two equivalent S(6)Er3Fe2 trigonal bipyramids, corners with two equivalent S(5)Er4Fe trigonal bipyramids, corners with two equivalent S(4)Er5 trigonal bipyramids,  an edgeedge with one S(1)Er3Fe tetrahedra, edges with two equivalent S(2)Er4 tetrahedra,  an edgeedge with one S(6)Er3Fe2 trigonal bipyramid, edges with two equivalent S(3)Er5 trigonal bipyramids, and edges with three equivalent S(4)Er5 trigonal bipyramids. In the fourth S site, S(4) is bonded to one Er(1), two equivalent Er(2), and two equivalent Er(4) atoms to form distorted SEr5 trigonal bipyramids that share corners with four equivalent S(2)Er4 tetrahedra, corners with two equivalent S(6)Er3Fe2 trigonal bipyramids, corners with two equivalent S(5)Er4Fe trigonal bipyramids, corners with two equivalent S(3)Er5 trigonal bipyramids,  an edgeedge with one S(2)Er4 tetrahedra, edges with two equivalent S(1)Er3Fe tetrahedra,  an edgeedge with one S(5)Er4Fe trigonal bipyramid, edges with two equivalent S(4)Er5 trigonal bipyramids, and edges with three equivalent S(3)Er5 trigonal bipyramids. In the fifth S site, S(5) is bonded to two equivalent Er(2), two equivalent Er(3), and one Fe(1) atom to form SEr4Fe trigonal bipyramids that share  a cornercorner with one S(1)Er3Fe tetrahedra, corners with four equivalent S(2)Er4 tetrahedra, corners with two equivalent S(3)Er5 trigonal bipyramids, corners with two equivalent S(4)Er5 trigonal bipyramids,  an edgeedge with one S(2)Er4 tetrahedra,  an edgeedge with one S(4)Er5 trigonal bipyramid, edges with two equivalent S(6)Er3Fe2 trigonal bipyramids, and edges with two equivalent S(5)Er4Fe trigonal bipyramids. In the sixth S site, S(6) is bonded to one Er(3), two equivalent Er(1), and two equivalent Fe(1) atoms to form SEr3Fe2 trigonal bipyramids that share  a cornercorner with one S(2)Er4 tetrahedra, corners with four equivalent S(1)Er3Fe tetrahedra, corners with two equivalent S(3)Er5 trigonal bipyramids, corners with two equivalent S(4)Er5 trigonal bipyramids,  an edgeedge with one S(1)Er3Fe tetrahedra,  an edgeedge with one S(3)Er5 trigonal bipyramid, edges with two equivalent S(6)Er3Fe2 trigonal bipyramids, and edges with two equivalent S(5)Er4Fe trigonal bipyramids. In the seventh S site, S(7) is bonded in a rectangular see-saw-like geometry to two equivalent Er(3) and two equivalent Fe(1) atoms.