CsEr10(C2I9)2 crystallizes in the triclinic P-1 space group. Cs(1) is bonded to two equivalent I(2), two equivalent I(4), two equivalent I(5), two equivalent I(6), two equivalent I(7), and two equivalent I(8) atoms to form distorted CsI12 cuboctahedra that share corners with two equivalent Er(1)CI5 octahedra, corners with four equivalent Er(4)CI5 octahedra, and faces with two equivalent Er(1)CI5 octahedra. The corner-sharing octahedral tilt angles range from 41-46°. There are five inequivalent Er sites. In the first Er site, Er(1) is bonded to one C(1), one I(1), one I(2), one I(6), and two equivalent I(4) atoms to form distorted ErCI5 octahedra that share  a cornercorner with one Cs(1)I12 cuboctahedra,  an edgeedge with one Er(1)CI5 octahedra,  an edgeedge with one Er(4)CI5 octahedra, and  a faceface with one Cs(1)I12 cuboctahedra. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one C(1), one C(2), one I(3), one I(5), one I(7), and two equivalent I(2) atoms. In the third Er site, Er(3) is bonded in a 8-coordinate geometry to two equivalent C(1), two equivalent C(2), one I(1), one I(3), one I(6), and one I(8) atom. In the fourth Er site, Er(4) is bonded to one C(2), one I(1), one I(5), one I(6), and two equivalent I(9) atoms to form distorted ErCI5 octahedra that share corners with two equivalent Cs(1)I12 cuboctahedra,  an edgeedge with one Er(1)CI5 octahedra, and  an edgeedge with one Er(4)CI5 octahedra. In the fifth Er site, Er(5) is bonded in a 7-coordinate geometry to one C(1), one C(2), one I(4), one I(8), one I(9), and two equivalent I(7) atoms. There are two inequivalent C sites. In the first C site, C(1) is bonded in a 6-coordinate geometry to one Er(1), one Er(2), one Er(5), two equivalent Er(3), and one C(2) atom. In the second C site, C(2) is bonded in a 6-coordinate geometry to one Er(2), one Er(4), one Er(5), two equivalent Er(3), and one C(1) atom. There are nine inequivalent I sites. In the first I site, I(1) is bonded in a distorted T-shaped geometry to one Er(1), one Er(3), and one Er(4) atom. In the second I site, I(2) is bonded in a distorted rectangular see-saw-like geometry to one Cs(1), one Er(1), and two equivalent Er(2) atoms. In the third I site, I(3) is bonded in a 2-coordinate geometry to one Er(2) and one Er(3) atom. In the fourth I site, I(4) is bonded in a distorted rectangular see-saw-like geometry to one Cs(1), one Er(5), and two equivalent Er(1) atoms. In the fifth I site, I(5) is bonded in a 3-coordinate geometry to one Cs(1), one Er(2), and one Er(4) atom. In the sixth I site, I(6) is bonded in a 4-coordinate geometry to one Cs(1), one Er(1), one Er(3), and one Er(4) atom. In the seventh I site, I(7) is bonded in a 4-coordinate geometry to one Cs(1), one Er(2), and two equivalent Er(5) atoms. In the eighth I site, I(8) is bonded in a 2-coordinate geometry to one Cs(1), one Er(3), and one Er(5) atom. In the ninth I site, I(9) is bonded in a distorted T-shaped geometry to one Er(5) and two equivalent Er(4) atoms.
CsEr10(C2I9)2 crystallizes in the triclinic P-1 space group. Cs(1) is bonded to two equivalent I(2), two equivalent I(4), two equivalent I(5), two equivalent I(6), two equivalent I(7), and two equivalent I(8) atoms to form distorted CsI12 cuboctahedra that share corners with two equivalent Er(1)CI5 octahedra, corners with four equivalent Er(4)CI5 octahedra, and faces with two equivalent Er(1)CI5 octahedra. The corner-sharing octahedral tilt angles range from 41-46°. Both Cs(1)-I(2) bond lengths are 4.40 Å. Both Cs(1)-I(4) bond lengths are 4.28 Å. Both Cs(1)-I(5) bond lengths are 4.07 Å. Both Cs(1)-I(6) bond lengths are 4.26 Å. Both Cs(1)-I(7) bond lengths are 4.43 Å. Both Cs(1)-I(8) bond lengths are 4.49 Å. There are five inequivalent Er sites. In the first Er site, Er(1) is bonded to one C(1), one I(1), one I(2), one I(6), and two equivalent I(4) atoms to form distorted ErCI5 octahedra that share  a cornercorner with one Cs(1)I12 cuboctahedra,  an edgeedge with one Er(1)CI5 octahedra,  an edgeedge with one Er(4)CI5 octahedra, and  a faceface with one Cs(1)I12 cuboctahedra. The Er(1)-C(1) bond length is 2.18 Å. The Er(1)-I(1) bond length is 3.05 Å. The Er(1)-I(2) bond length is 3.04 Å. The Er(1)-I(6) bond length is 3.04 Å. There is one shorter (3.03 Å) and one longer (3.41 Å) Er(1)-I(4) bond length. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one C(1), one C(2), one I(3), one I(5), one I(7), and two equivalent I(2) atoms. The Er(2)-C(1) bond length is 2.46 Å. The Er(2)-C(2) bond length is 2.47 Å. The Er(2)-I(3) bond length is 2.92 Å. The Er(2)-I(5) bond length is 3.07 Å. The Er(2)-I(7) bond length is 3.10 Å. There is one shorter (3.11 Å) and one longer (3.65 Å) Er(2)-I(2) bond length. In the third Er site, Er(3) is bonded in a 8-coordinate geometry to two equivalent C(1), two equivalent C(2), one I(1), one I(3), one I(6), and one I(8) atom. There is one shorter (2.61 Å) and one longer (2.62 Å) Er(3)-C(1) bond length. There is one shorter (2.60 Å) and one longer (2.63 Å) Er(3)-C(2) bond length. The Er(3)-I(1) bond length is 3.21 Å. The Er(3)-I(3) bond length is 3.12 Å. The Er(3)-I(6) bond length is 3.26 Å. The Er(3)-I(8) bond length is 3.20 Å. In the fourth Er site, Er(4) is bonded to one C(2), one I(1), one I(5), one I(6), and two equivalent I(9) atoms to form distorted ErCI5 octahedra that share corners with two equivalent Cs(1)I12 cuboctahedra,  an edgeedge with one Er(1)CI5 octahedra, and  an edgeedge with one Er(4)CI5 octahedra. The Er(4)-C(2) bond length is 2.19 Å. The Er(4)-I(1) bond length is 3.03 Å. The Er(4)-I(5) bond length is 3.00 Å. The Er(4)-I(6) bond length is 3.08 Å. There is one shorter (3.01 Å) and one longer (3.40 Å) Er(4)-I(9) bond length. In the fifth Er site, Er(5) is bonded in a 7-coordinate geometry to one C(1), one C(2), one I(4), one I(8), one I(9), and two equivalent I(7) atoms. The Er(5)-C(1) bond length is 2.44 Å. The Er(5)-C(2) bond length is 2.44 Å. The Er(5)-I(4) bond length is 3.20 Å. The Er(5)-I(8) bond length is 2.91 Å. The Er(5)-I(9) bond length is 3.14 Å. There is one shorter (3.04 Å) and one longer (3.78 Å) Er(5)-I(7) bond length. There are two inequivalent C sites. In the first C site, C(1) is bonded in a 6-coordinate geometry to one Er(1), one Er(2), one Er(5), two equivalent Er(3), and one C(2) atom. The C(1)-C(2) bond length is 1.44 Å. In the second C site, C(2) is bonded in a 6-coordinate geometry to one Er(2), one Er(4), one Er(5), two equivalent Er(3), and one C(1) atom. There are nine inequivalent I sites. In the first I site, I(1) is bonded in a distorted T-shaped geometry to one Er(1), one Er(3), and one Er(4) atom. In the second I site, I(2) is bonded in a distorted rectangular see-saw-like geometry to one Cs(1), one Er(1), and two equivalent Er(2) atoms. In the third I site, I(3) is bonded in a 2-coordinate geometry to one Er(2) and one Er(3) atom. In the fourth I site, I(4) is bonded in a distorted rectangular see-saw-like geometry to one Cs(1), one Er(5), and two equivalent Er(1) atoms. In the fifth I site, I(5) is bonded in a 3-coordinate geometry to one Cs(1), one Er(2), and one Er(4) atom. In the sixth I site, I(6) is bonded in a 4-coordinate geometry to one Cs(1), one Er(1), one Er(3), and one Er(4) atom. In the seventh I site, I(7) is bonded in a 4-coordinate geometry to one Cs(1), one Er(2), and two equivalent Er(5) atoms. In the eighth I site, I(8) is bonded in a 2-coordinate geometry to one Cs(1), one Er(3), and one Er(5) atom. In the ninth I site, I(9) is bonded in a distorted T-shaped geometry to one Er(5) and two equivalent Er(4) atoms.