Ca(ErS2)2 crystallizes in the orthorhombic Pnma space group. Ca(1) is bonded to two equivalent S(1), two equivalent S(2), and three equivalent S(3) atoms to form distorted CaS7 pentagonal bipyramids that share corners with four equivalent Er(1)S6 octahedra, corners with four equivalent Er(2)S6 octahedra,  an edgeedge with one Er(1)S6 octahedra, edges with four equivalent Er(2)S6 octahedra, edges with two equivalent Ca(1)S7 pentagonal bipyramids, and faces with two equivalent Ca(1)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 14-68°. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one S(1), two equivalent S(2), and three equivalent S(4) atoms to form ErS6 octahedra that share corners with three equivalent Er(2)S6 octahedra, corners with four equivalent Ca(1)S7 pentagonal bipyramids, edges with two equivalent Er(2)S6 octahedra, edges with four equivalent Er(1)S6 octahedra, and  an edgeedge with one Ca(1)S7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 51-60°. In the second Er site, Er(2) is bonded to one S(2), one S(4), two equivalent S(1), and two equivalent S(3) atoms to form ErS6 octahedra that share corners with three equivalent Er(1)S6 octahedra, corners with four equivalent Ca(1)S7 pentagonal bipyramids, edges with two equivalent Er(1)S6 octahedra, edges with two equivalent Er(2)S6 octahedra, and edges with four equivalent Ca(1)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 51-60°. There are four inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Ca(1), one Er(1), and two equivalent Er(2) atoms to form distorted SCa2Er3 trigonal bipyramids that share corners with two equivalent S(2)Ca2Er3 square pyramids, corners with six equivalent S(3)Ca3Er2 square pyramids, edges with two equivalent S(3)Ca3Er2 square pyramids, edges with three equivalent S(2)Ca2Er3 square pyramids, and edges with two equivalent S(1)Ca2Er3 trigonal bipyramids. In the second S site, S(2) is bonded to two equivalent Ca(1), one Er(2), and two equivalent Er(1) atoms to form SCa2Er3 square pyramids that share corners with two equivalent S(3)Ca3Er2 square pyramids, corners with two equivalent S(1)Ca2Er3 trigonal bipyramids, edges with two equivalent S(2)Ca2Er3 square pyramids, edges with three equivalent S(3)Ca3Er2 square pyramids, and edges with three equivalent S(1)Ca2Er3 trigonal bipyramids. In the third S site, S(3) is bonded to three equivalent Ca(1) and two equivalent Er(2) atoms to form SCa3Er2 square pyramids that share corners with two equivalent S(2)Ca2Er3 square pyramids, corners with six equivalent S(1)Ca2Er3 trigonal bipyramids, edges with three equivalent S(2)Ca2Er3 square pyramids, edges with four equivalent S(3)Ca3Er2 square pyramids, and edges with two equivalent S(1)Ca2Er3 trigonal bipyramids. In the fourth S site, S(4) is bonded in a rectangular see-saw-like geometry to one Er(2) and three equivalent Er(1) atoms.
Ca(ErS2)2 crystallizes in the orthorhombic Pnma space group. Ca(1) is bonded to two equivalent S(1), two equivalent S(2), and three equivalent S(3) atoms to form distorted CaS7 pentagonal bipyramids that share corners with four equivalent Er(1)S6 octahedra, corners with four equivalent Er(2)S6 octahedra,  an edgeedge with one Er(1)S6 octahedra, edges with four equivalent Er(2)S6 octahedra, edges with two equivalent Ca(1)S7 pentagonal bipyramids, and faces with two equivalent Ca(1)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 14-68°. Both Ca(1)-S(1) bond lengths are 3.01 Å. Both Ca(1)-S(2) bond lengths are 2.90 Å. There are two shorter (2.87 Å) and one longer (2.92 Å) Ca(1)-S(3) bond length. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one S(1), two equivalent S(2), and three equivalent S(4) atoms to form ErS6 octahedra that share corners with three equivalent Er(2)S6 octahedra, corners with four equivalent Ca(1)S7 pentagonal bipyramids, edges with two equivalent Er(2)S6 octahedra, edges with four equivalent Er(1)S6 octahedra, and  an edgeedge with one Ca(1)S7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 51-60°. The Er(1)-S(1) bond length is 2.73 Å. Both Er(1)-S(2) bond lengths are 2.70 Å. There are two shorter (2.69 Å) and one longer (2.79 Å) Er(1)-S(4) bond length. In the second Er site, Er(2) is bonded to one S(2), one S(4), two equivalent S(1), and two equivalent S(3) atoms to form ErS6 octahedra that share corners with three equivalent Er(1)S6 octahedra, corners with four equivalent Ca(1)S7 pentagonal bipyramids, edges with two equivalent Er(1)S6 octahedra, edges with two equivalent Er(2)S6 octahedra, and edges with four equivalent Ca(1)S7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 51-60°. The Er(2)-S(2) bond length is 2.71 Å. The Er(2)-S(4) bond length is 2.75 Å. Both Er(2)-S(1) bond lengths are 2.72 Å. Both Er(2)-S(3) bond lengths are 2.68 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 two equivalent Er(2) atoms to form distorted SCa2Er3 trigonal bipyramids that share corners with two equivalent S(2)Ca2Er3 square pyramids, corners with six equivalent S(3)Ca3Er2 square pyramids, edges with two equivalent S(3)Ca3Er2 square pyramids, edges with three equivalent S(2)Ca2Er3 square pyramids, and edges with two equivalent S(1)Ca2Er3 trigonal bipyramids. In the second S site, S(2) is bonded to two equivalent Ca(1), one Er(2), and two equivalent Er(1) atoms to form SCa2Er3 square pyramids that share corners with two equivalent S(3)Ca3Er2 square pyramids, corners with two equivalent S(1)Ca2Er3 trigonal bipyramids, edges with two equivalent S(2)Ca2Er3 square pyramids, edges with three equivalent S(3)Ca3Er2 square pyramids, and edges with three equivalent S(1)Ca2Er3 trigonal bipyramids. In the third S site, S(3) is bonded to three equivalent Ca(1) and two equivalent Er(2) atoms to form SCa3Er2 square pyramids that share corners with two equivalent S(2)Ca2Er3 square pyramids, corners with six equivalent S(1)Ca2Er3 trigonal bipyramids, edges with three equivalent S(2)Ca2Er3 square pyramids, edges with four equivalent S(3)Ca3Er2 square pyramids, and edges with two equivalent S(1)Ca2Er3 trigonal bipyramids. In the fourth S site, S(4) is bonded in a rectangular see-saw-like geometry to one Er(2) and three equivalent Er(1) atoms.