Er4CeS7 crystallizes in the monoclinic Cm space group. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded to one S(4), two equivalent S(1), two equivalent S(3), and two equivalent S(6) atoms to form distorted ErS7 pentagonal bipyramids that share corners with two equivalent Er(3)S6 octahedra, corners with two equivalent Er(4)S6 octahedra, corners with four equivalent Ce(1)S6 octahedra,  an edgeedge with one Ce(1)S6 octahedra, edges with three equivalent Er(4)S6 octahedra, edges with two equivalent Er(2)S7 pentagonal bipyramids, and faces with two equivalent Er(1)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 22-65°. In the second Er site, Er(2) is bonded to one S(3), two equivalent S(2), two equivalent S(4), and two equivalent S(5) atoms to form distorted ErS7 pentagonal bipyramids that share corners with two equivalent Er(4)S6 octahedra, corners with two equivalent Ce(1)S6 octahedra, corners with four equivalent Er(3)S6 octahedra,  an edgeedge with one Er(3)S6 octahedra, edges with three equivalent Er(4)S6 octahedra, edges with two equivalent Er(1)S7 pentagonal bipyramids, and faces with two equivalent Er(2)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 22-69°. 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 Ce(1)S6 octahedra, corners with two equivalent Er(1)S7 pentagonal bipyramids, corners with four equivalent Er(2)S7 pentagonal bipyramids, edges with two equivalent Er(3)S6 octahedra, edges with three equivalent Ce(1)S6 octahedra, and  an edgeedge with one Er(2)S7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 2-58°. 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 Ce(1)S6 octahedra, corners with two equivalent Er(1)S7 pentagonal bipyramids, corners with two equivalent Er(2)S7 pentagonal bipyramids, edges with two equivalent Er(4)S6 octahedra, edges with three equivalent Er(1)S7 pentagonal bipyramids, and edges with three equivalent Er(2)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 58°. Ce(1) is bonded to one S(1), one S(5), two equivalent S(6), and two equivalent S(7) atoms to form CeS6 octahedra that share  a cornercorner with one Er(4)S6 octahedra, corners with two equivalent Er(3)S6 octahedra, corners with two equivalent Er(2)S7 pentagonal bipyramids, corners with four equivalent Er(1)S7 pentagonal bipyramids, edges with two equivalent Ce(1)S6 octahedra, edges with three equivalent Er(3)S6 octahedra, and  an edgeedge with one Er(1)S7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 2-58°. 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 Ce(1) atom to form SCeEr3 tetrahedra that share  a cornercorner with one S(2)Er4 tetrahedra, corners with two equivalent S(1)CeEr3 tetrahedra,  a cornercorner with one S(5)CeEr4 trigonal bipyramid, corners with four equivalent S(6)Ce2Er3 trigonal bipyramids, corners with four equivalent S(3)Er5 trigonal bipyramids,  an edgeedge with one S(6)Ce2Er3 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 distorted SEr4 tetrahedra that share  a cornercorner with one S(1)CeEr3 tetrahedra, corners with two equivalent S(2)Er4 tetrahedra,  a cornercorner with one S(6)Ce2Er3 trigonal bipyramid, corners with four equivalent S(5)CeEr4 trigonal bipyramids, corners with four equivalent S(4)Er5 trigonal bipyramids,  an edgeedge with one S(5)CeEr4 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)CeEr3 tetrahedra, corners with two equivalent S(6)Ce2Er3 trigonal bipyramids, corners with two equivalent S(5)CeEr4 trigonal bipyramids, corners with two equivalent S(4)Er5 trigonal bipyramids,  an edgeedge with one S(1)CeEr3 tetrahedra, edges with two equivalent S(2)Er4 tetrahedra,  an edgeedge with one S(6)Ce2Er3 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)Ce2Er3 trigonal bipyramids, corners with two equivalent S(5)CeEr4 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)CeEr3 tetrahedra,  an edgeedge with one S(5)CeEr4 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 Ce(1) atom to form SCeEr4 trigonal bipyramids that share  a cornercorner with one S(1)CeEr3 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)Ce2Er3 trigonal bipyramids, and edges with two equivalent S(5)CeEr4 trigonal bipyramids. In the sixth S site, S(6) is bonded to one Er(3), two equivalent Er(1), and two equivalent Ce(1) atoms to form SCe2Er3 trigonal bipyramids that share  a cornercorner with one S(2)Er4 tetrahedra, corners with four equivalent S(1)CeEr3 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)CeEr3 tetrahedra,  an edgeedge with one S(3)Er5 trigonal bipyramid, edges with two equivalent S(6)Ce2Er3 trigonal bipyramids, and edges with two equivalent S(5)CeEr4 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 Ce(1) atoms.
Er4CeS7 crystallizes in the monoclinic Cm space group. There are four inequivalent Er sites. In the first Er site, Er(1) is bonded to one S(4), two equivalent S(1), two equivalent S(3), and two equivalent S(6) atoms to form distorted ErS7 pentagonal bipyramids that share corners with two equivalent Er(3)S6 octahedra, corners with two equivalent Er(4)S6 octahedra, corners with four equivalent Ce(1)S6 octahedra,  an edgeedge with one Ce(1)S6 octahedra, edges with three equivalent Er(4)S6 octahedra, edges with two equivalent Er(2)S7 pentagonal bipyramids, and faces with two equivalent Er(1)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 22-65°. The Er(1)-S(4) bond length is 2.94 Å. Both Er(1)-S(1) bond lengths are 2.72 Å. Both Er(1)-S(3) bond lengths are 2.83 Å. Both Er(1)-S(6) bond lengths are 2.89 Å. In the second Er site, Er(2) is bonded to one S(3), two equivalent S(2), two equivalent S(4), and two equivalent S(5) atoms to form distorted ErS7 pentagonal bipyramids that share corners with two equivalent Er(4)S6 octahedra, corners with two equivalent Ce(1)S6 octahedra, corners with four equivalent Er(3)S6 octahedra,  an edgeedge with one Er(3)S6 octahedra, edges with three equivalent Er(4)S6 octahedra, edges with two equivalent Er(1)S7 pentagonal bipyramids, and faces with two equivalent Er(2)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 22-69°. The Er(2)-S(3) bond length is 2.94 Å. Both Er(2)-S(2) bond lengths are 2.73 Å. Both Er(2)-S(4) bond lengths are 2.83 Å. Both Er(2)-S(5) bond lengths are 2.92 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 Ce(1)S6 octahedra, corners with two equivalent Er(1)S7 pentagonal bipyramids, corners with four equivalent Er(2)S7 pentagonal bipyramids, edges with two equivalent Er(3)S6 octahedra, edges with three equivalent Ce(1)S6 octahedra, and  an edgeedge with one Er(2)S7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 2-58°. The Er(3)-S(2) bond length is 2.70 Å. The Er(3)-S(6) bond length is 2.84 Å. Both Er(3)-S(5) bond lengths are 2.75 Å. Both Er(3)-S(7) bond lengths are 2.64 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 Ce(1)S6 octahedra, corners with two equivalent Er(1)S7 pentagonal bipyramids, corners with two equivalent Er(2)S7 pentagonal bipyramids, edges with two equivalent Er(4)S6 octahedra, edges with three equivalent Er(1)S7 pentagonal bipyramids, and edges with three equivalent Er(2)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 58°. The Er(4)-S(1) bond length is 2.66 Å. The Er(4)-S(2) bond length is 2.67 Å. Both Er(4)-S(3) bond lengths are 2.74 Å. Both Er(4)-S(4) bond lengths are 2.75 Å. Ce(1) is bonded to one S(1), one S(5), two equivalent S(6), and two equivalent S(7) atoms to form CeS6 octahedra that share  a cornercorner with one Er(4)S6 octahedra, corners with two equivalent Er(3)S6 octahedra, corners with two equivalent Er(2)S7 pentagonal bipyramids, corners with four equivalent Er(1)S7 pentagonal bipyramids, edges with two equivalent Ce(1)S6 octahedra, edges with three equivalent Er(3)S6 octahedra, and  an edgeedge with one Er(1)S7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 2-58°. The Ce(1)-S(1) bond length is 2.78 Å. The Ce(1)-S(5) bond length is 2.91 Å. Both Ce(1)-S(6) bond lengths are 2.85 Å. Both Ce(1)-S(7) bond lengths are 2.76 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 Ce(1) atom to form SCeEr3 tetrahedra that share  a cornercorner with one S(2)Er4 tetrahedra, corners with two equivalent S(1)CeEr3 tetrahedra,  a cornercorner with one S(5)CeEr4 trigonal bipyramid, corners with four equivalent S(6)Ce2Er3 trigonal bipyramids, corners with four equivalent S(3)Er5 trigonal bipyramids,  an edgeedge with one S(6)Ce2Er3 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 distorted SEr4 tetrahedra that share  a cornercorner with one S(1)CeEr3 tetrahedra, corners with two equivalent S(2)Er4 tetrahedra,  a cornercorner with one S(6)Ce2Er3 trigonal bipyramid, corners with four equivalent S(5)CeEr4 trigonal bipyramids, corners with four equivalent S(4)Er5 trigonal bipyramids,  an edgeedge with one S(5)CeEr4 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)CeEr3 tetrahedra, corners with two equivalent S(6)Ce2Er3 trigonal bipyramids, corners with two equivalent S(5)CeEr4 trigonal bipyramids, corners with two equivalent S(4)Er5 trigonal bipyramids,  an edgeedge with one S(1)CeEr3 tetrahedra, edges with two equivalent S(2)Er4 tetrahedra,  an edgeedge with one S(6)Ce2Er3 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)Ce2Er3 trigonal bipyramids, corners with two equivalent S(5)CeEr4 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)CeEr3 tetrahedra,  an edgeedge with one S(5)CeEr4 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 Ce(1) atom to form SCeEr4 trigonal bipyramids that share  a cornercorner with one S(1)CeEr3 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)Ce2Er3 trigonal bipyramids, and edges with two equivalent S(5)CeEr4 trigonal bipyramids. In the sixth S site, S(6) is bonded to one Er(3), two equivalent Er(1), and two equivalent Ce(1) atoms to form SCe2Er3 trigonal bipyramids that share  a cornercorner with one S(2)Er4 tetrahedra, corners with four equivalent S(1)CeEr3 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)CeEr3 tetrahedra,  an edgeedge with one S(3)Er5 trigonal bipyramid, edges with two equivalent S(6)Ce2Er3 trigonal bipyramids, and edges with two equivalent S(5)CeEr4 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 Ce(1) atoms.