Ca(ErS2)2 crystallizes in the orthorhombic Cmc2_1 space group. Ca(1) is bonded in a 7-coordinate geometry to one S(4), two equivalent S(1), two equivalent S(2), and two equivalent S(3) atoms. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one S(1), one S(2), two equivalent S(3), and two equivalent S(4) atoms to form a mixture of corner and edge-sharing ErS6 octahedra. The corner-sharing octahedral tilt angles range from 5-53°. In the second Er site, Er(2) is bonded to one S(1), one S(3), two equivalent S(2), and two equivalent S(4) atoms to form a mixture of corner and edge-sharing ErS6 octahedra. The corner-sharing octahedral tilt angles range from 5-53°. There are four inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Ca(1), one Er(1), and one Er(2) atom to form SCa2Er2 tetrahedra that share corners with two equivalent S(4)CaEr4 square pyramids, corners with two equivalent S(1)Ca2Er2 tetrahedra, corners with five equivalent S(2)Ca2Er3 trigonal bipyramids, corners with five equivalent S(3)Ca2Er3 trigonal bipyramids, edges with two equivalent S(4)CaEr4 square pyramids,  an edgeedge with one S(2)Ca2Er3 trigonal bipyramid, and  an edgeedge with one S(3)Ca2Er3 trigonal bipyramid. In the second S site, S(2) is bonded to two equivalent Ca(1), one Er(1), and two equivalent Er(2) atoms to form SCa2Er3 trigonal bipyramids that share corners with two equivalent S(4)CaEr4 square pyramids, corners with five equivalent S(1)Ca2Er2 tetrahedra, corners with two equivalent S(3)Ca2Er3 trigonal bipyramids, edges with three equivalent S(4)CaEr4 square pyramids,  an edgeedge with one S(1)Ca2Er2 tetrahedra, edges with two equivalent S(2)Ca2Er3 trigonal bipyramids, and edges with three equivalent S(3)Ca2Er3 trigonal bipyramids. In the third S site, S(3) is bonded to two equivalent Ca(1), one Er(2), and two equivalent Er(1) atoms to form distorted SCa2Er3 trigonal bipyramids that share corners with six equivalent S(4)CaEr4 square pyramids, corners with five equivalent S(1)Ca2Er2 tetrahedra, corners with two equivalent S(2)Ca2Er3 trigonal bipyramids,  an edgeedge with one S(4)CaEr4 square pyramid,  an edgeedge with one S(1)Ca2Er2 tetrahedra, edges with two equivalent S(3)Ca2Er3 trigonal bipyramids, and edges with three equivalent S(2)Ca2Er3 trigonal bipyramids. In the fourth S site, S(4) is bonded to one Ca(1), two equivalent Er(1), and two equivalent Er(2) atoms to form SCaEr4 square pyramids that share corners with two equivalent S(1)Ca2Er2 tetrahedra, corners with two equivalent S(2)Ca2Er3 trigonal bipyramids, corners with six equivalent S(3)Ca2Er3 trigonal bipyramids, edges with two equivalent S(4)CaEr4 square pyramids, edges with two equivalent S(1)Ca2Er2 tetrahedra,  an edgeedge with one S(3)Ca2Er3 trigonal bipyramid, and edges with three equivalent S(2)Ca2Er3 trigonal bipyramids.
Ca(ErS2)2 crystallizes in the orthorhombic Cmc2_1 space group. Ca(1) is bonded in a 7-coordinate geometry to one S(4), two equivalent S(1), two equivalent S(2), and two equivalent S(3) atoms. The Ca(1)-S(4) bond length is 3.34 Å. Both Ca(1)-S(1) bond lengths are 2.77 Å. Both Ca(1)-S(2) bond lengths are 2.97 Å. Both Ca(1)-S(3) bond lengths are 3.03 Å. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one S(1), one S(2), two equivalent S(3), and two equivalent S(4) atoms to form a mixture of corner and edge-sharing ErS6 octahedra. The corner-sharing octahedral tilt angles range from 5-53°. The Er(1)-S(1) bond length is 2.63 Å. The Er(1)-S(2) bond length is 2.74 Å. Both Er(1)-S(3) bond lengths are 2.68 Å. Both Er(1)-S(4) bond lengths are 2.76 Å. In the second Er site, Er(2) is bonded to one S(1), one S(3), two equivalent S(2), and two equivalent S(4) atoms to form a mixture of corner and edge-sharing ErS6 octahedra. The corner-sharing octahedral tilt angles range from 5-53°. The Er(2)-S(1) bond length is 2.63 Å. The Er(2)-S(3) bond length is 2.75 Å. Both Er(2)-S(2) bond lengths are 2.68 Å. Both Er(2)-S(4) bond lengths are 2.74 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Ca(1), one Er(1), and one Er(2) atom to form SCa2Er2 tetrahedra that share corners with two equivalent S(4)CaEr4 square pyramids, corners with two equivalent S(1)Ca2Er2 tetrahedra, corners with five equivalent S(2)Ca2Er3 trigonal bipyramids, corners with five equivalent S(3)Ca2Er3 trigonal bipyramids, edges with two equivalent S(4)CaEr4 square pyramids,  an edgeedge with one S(2)Ca2Er3 trigonal bipyramid, and  an edgeedge with one S(3)Ca2Er3 trigonal bipyramid. In the second S site, S(2) is bonded to two equivalent Ca(1), one Er(1), and two equivalent Er(2) atoms to form SCa2Er3 trigonal bipyramids that share corners with two equivalent S(4)CaEr4 square pyramids, corners with five equivalent S(1)Ca2Er2 tetrahedra, corners with two equivalent S(3)Ca2Er3 trigonal bipyramids, edges with three equivalent S(4)CaEr4 square pyramids,  an edgeedge with one S(1)Ca2Er2 tetrahedra, edges with two equivalent S(2)Ca2Er3 trigonal bipyramids, and edges with three equivalent S(3)Ca2Er3 trigonal bipyramids. In the third S site, S(3) is bonded to two equivalent Ca(1), one Er(2), and two equivalent Er(1) atoms to form distorted SCa2Er3 trigonal bipyramids that share corners with six equivalent S(4)CaEr4 square pyramids, corners with five equivalent S(1)Ca2Er2 tetrahedra, corners with two equivalent S(2)Ca2Er3 trigonal bipyramids,  an edgeedge with one S(4)CaEr4 square pyramid,  an edgeedge with one S(1)Ca2Er2 tetrahedra, edges with two equivalent S(3)Ca2Er3 trigonal bipyramids, and edges with three equivalent S(2)Ca2Er3 trigonal bipyramids. In the fourth S site, S(4) is bonded to one Ca(1), two equivalent Er(1), and two equivalent Er(2) atoms to form SCaEr4 square pyramids that share corners with two equivalent S(1)Ca2Er2 tetrahedra, corners with two equivalent S(2)Ca2Er3 trigonal bipyramids, corners with six equivalent S(3)Ca2Er3 trigonal bipyramids, edges with two equivalent S(4)CaEr4 square pyramids, edges with two equivalent S(1)Ca2Er2 tetrahedra,  an edgeedge with one S(3)Ca2Er3 trigonal bipyramid, and edges with three equivalent S(2)Ca2Er3 trigonal bipyramids.