CsEr2Cu3S5 crystallizes in the orthorhombic Cmcm space group. Cs(1) is bonded in a 10-coordinate geometry to two equivalent Cu(2), two equivalent S(1), two equivalent S(3), and four equivalent S(2) atoms. Er(1) is bonded to one S(3), two equivalent S(2), and three equivalent S(1) atoms to form ErS6 octahedra that share  a cornercorner with one Er(1)S6 octahedra, corners with four equivalent Cu(1)S4 tetrahedra, edges with four equivalent Er(1)S6 octahedra, and edges with three equivalent Cu(1)S4 tetrahedra. The corner-sharing octahedral tilt angles are 24°. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form CuS4 tetrahedra that share corners with four equivalent Er(1)S6 octahedra, corners with two equivalent Cu(1)S4 tetrahedra, edges with three equivalent Er(1)S6 octahedra, and  an edgeedge with one Cu(1)S4 tetrahedra. The corner-sharing octahedral tilt angles range from 14-58°. In the second Cu site, Cu(2) is bonded in a 4-coordinate geometry to two equivalent Cs(1), two equivalent S(2), and two equivalent S(3) atoms. There are three inequivalent S sites. In the first S site, S(1) is bonded to one Cs(1), three equivalent Er(1), and two equivalent Cu(1) atoms to form a mixture of distorted edge and corner-sharing SCsEr3Cu2 octahedra. The corner-sharing octahedral tilt angles are 52°. In the second S site, S(2) is bonded in a 7-coordinate geometry to two equivalent Cs(1), two equivalent Er(1), one Cu(2), and two equivalent Cu(1) atoms. In the third S site, S(3) is bonded in a 6-coordinate geometry to two equivalent Cs(1), two equivalent Er(1), and two equivalent Cu(2) atoms.
CsEr2Cu3S5 crystallizes in the orthorhombic Cmcm space group. Cs(1) is bonded in a 10-coordinate geometry to two equivalent Cu(2), two equivalent S(1), two equivalent S(3), and four equivalent S(2) atoms. Both Cs(1)-Cu(2) bond lengths are 3.67 Å. Both Cs(1)-S(1) bond lengths are 3.38 Å. Both Cs(1)-S(3) bond lengths are 3.49 Å. All Cs(1)-S(2) bond lengths are 3.56 Å. Er(1) is bonded to one S(3), two equivalent S(2), and three equivalent S(1) atoms to form ErS6 octahedra that share  a cornercorner with one Er(1)S6 octahedra, corners with four equivalent Cu(1)S4 tetrahedra, edges with four equivalent Er(1)S6 octahedra, and edges with three equivalent Cu(1)S4 tetrahedra. The corner-sharing octahedral tilt angles are 24°. The Er(1)-S(3) bond length is 2.70 Å. Both Er(1)-S(2) bond lengths are 2.70 Å. There is one shorter (2.69 Å) and two longer (2.79 Å) Er(1)-S(1) bond lengths. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form CuS4 tetrahedra that share corners with four equivalent Er(1)S6 octahedra, corners with two equivalent Cu(1)S4 tetrahedra, edges with three equivalent Er(1)S6 octahedra, and  an edgeedge with one Cu(1)S4 tetrahedra. The corner-sharing octahedral tilt angles range from 14-58°. Both Cu(1)-S(1) bond lengths are 2.37 Å. There is one shorter (2.39 Å) and one longer (2.43 Å) Cu(1)-S(2) bond length. In the second Cu site, Cu(2) is bonded in a 4-coordinate geometry to two equivalent Cs(1), two equivalent S(2), and two equivalent S(3) atoms. Both Cu(2)-S(2) bond lengths are 2.70 Å. Both Cu(2)-S(3) bond lengths are 2.24 Å. There are three inequivalent S sites. In the first S site, S(1) is bonded to one Cs(1), three equivalent Er(1), and two equivalent Cu(1) atoms to form a mixture of distorted edge and corner-sharing SCsEr3Cu2 octahedra. The corner-sharing octahedral tilt angles are 52°. In the second S site, S(2) is bonded in a 7-coordinate geometry to two equivalent Cs(1), two equivalent Er(1), one Cu(2), and two equivalent Cu(1) atoms. In the third S site, S(3) is bonded in a 6-coordinate geometry to two equivalent Cs(1), two equivalent Er(1), and two equivalent Cu(2) atoms.