CsSr2I5 crystallizes in the monoclinic P2_1/c space group. Cs(1) is bonded in a 9-coordinate geometry to two equivalent I(2), two equivalent I(3), two equivalent I(4), and three equivalent I(1) atoms. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 8-coordinate geometry to two equivalent I(2), two equivalent I(3), two equivalent I(4), and two equivalent I(5) atoms. In the second Sr site, Sr(2) is bonded to one I(2), one I(3), one I(4), two equivalent I(1), and two equivalent I(5) atoms to form distorted edge-sharing SrI7 pentagonal bipyramids. There are five inequivalent I sites. In the first I site, I(1) is bonded in a 5-coordinate geometry to three equivalent Cs(1) and two equivalent Sr(2) atoms. In the second I site, I(2) is bonded in a 5-coordinate geometry to two equivalent Cs(1), one Sr(2), and two equivalent Sr(1) atoms. In the third I site, I(3) is bonded to two equivalent Cs(1), one Sr(2), and two equivalent Sr(1) atoms to form distorted ICs2Sr3 trigonal bipyramids that share corners with four equivalent I(4)Cs2Sr3 square pyramids, corners with four equivalent I(3)Cs2Sr3 trigonal bipyramids, corners with two equivalent I(5)Sr4 trigonal pyramids,  an edgeedge with one I(4)Cs2Sr3 square pyramid, edges with two equivalent I(5)Sr4 trigonal pyramids, and  a faceface with one I(4)Cs2Sr3 square pyramid. In the fourth I site, I(4) is bonded to two equivalent Cs(1), one Sr(2), and two equivalent Sr(1) atoms to form distorted ICs2Sr3 square pyramids that share corners with four equivalent I(3)Cs2Sr3 trigonal bipyramids, corners with four equivalent I(5)Sr4 trigonal pyramids, edges with two equivalent I(4)Cs2Sr3 square pyramids,  an edgeedge with one I(3)Cs2Sr3 trigonal bipyramid,  an edgeedge with one I(5)Sr4 trigonal pyramid, and  a faceface with one I(3)Cs2Sr3 trigonal bipyramid. In the fifth I site, I(5) is bonded to two equivalent Sr(1) and two equivalent Sr(2) atoms to form distorted ISr4 trigonal pyramids that share corners with four equivalent I(4)Cs2Sr3 square pyramids, corners with two equivalent I(3)Cs2Sr3 trigonal bipyramids, corners with two equivalent I(5)Sr4 trigonal pyramids,  an edgeedge with one I(4)Cs2Sr3 square pyramid, edges with two equivalent I(3)Cs2Sr3 trigonal bipyramids, and  an edgeedge with one I(5)Sr4 trigonal pyramid.
CsSr2I5 crystallizes in the monoclinic P2_1/c space group. Cs(1) is bonded in a 9-coordinate geometry to two equivalent I(2), two equivalent I(3), two equivalent I(4), and three equivalent I(1) atoms. There is one shorter (3.89 Å) and one longer (4.22 Å) Cs(1)-I(2) bond length. There is one shorter (3.84 Å) and one longer (3.99 Å) Cs(1)-I(3) bond length. There is one shorter (3.89 Å) and one longer (3.98 Å) Cs(1)-I(4) bond length. There are a spread of Cs(1)-I(1) bond distances ranging from 3.78-4.34 Å. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 8-coordinate geometry to two equivalent I(2), two equivalent I(3), two equivalent I(4), and two equivalent I(5) atoms. There is one shorter (3.42 Å) and one longer (3.66 Å) Sr(1)-I(2) bond length. There is one shorter (3.40 Å) and one longer (3.52 Å) Sr(1)-I(3) bond length. There is one shorter (3.40 Å) and one longer (3.44 Å) Sr(1)-I(4) bond length. There is one shorter (3.47 Å) and one longer (3.59 Å) Sr(1)-I(5) bond length. In the second Sr site, Sr(2) is bonded to one I(2), one I(3), one I(4), two equivalent I(1), and two equivalent I(5) atoms to form distorted edge-sharing SrI7 pentagonal bipyramids. The Sr(2)-I(2) bond length is 3.37 Å. The Sr(2)-I(3) bond length is 3.40 Å. The Sr(2)-I(4) bond length is 3.56 Å. There is one shorter (3.31 Å) and one longer (3.42 Å) Sr(2)-I(1) bond length. Both Sr(2)-I(5) bond lengths are 3.37 Å. There are five inequivalent I sites. In the first I site, I(1) is bonded in a 5-coordinate geometry to three equivalent Cs(1) and two equivalent Sr(2) atoms. In the second I site, I(2) is bonded in a 5-coordinate geometry to two equivalent Cs(1), one Sr(2), and two equivalent Sr(1) atoms. In the third I site, I(3) is bonded to two equivalent Cs(1), one Sr(2), and two equivalent Sr(1) atoms to form distorted ICs2Sr3 trigonal bipyramids that share corners with four equivalent I(4)Cs2Sr3 square pyramids, corners with four equivalent I(3)Cs2Sr3 trigonal bipyramids, corners with two equivalent I(5)Sr4 trigonal pyramids,  an edgeedge with one I(4)Cs2Sr3 square pyramid, edges with two equivalent I(5)Sr4 trigonal pyramids, and  a faceface with one I(4)Cs2Sr3 square pyramid. In the fourth I site, I(4) is bonded to two equivalent Cs(1), one Sr(2), and two equivalent Sr(1) atoms to form distorted ICs2Sr3 square pyramids that share corners with four equivalent I(3)Cs2Sr3 trigonal bipyramids, corners with four equivalent I(5)Sr4 trigonal pyramids, edges with two equivalent I(4)Cs2Sr3 square pyramids,  an edgeedge with one I(3)Cs2Sr3 trigonal bipyramid,  an edgeedge with one I(5)Sr4 trigonal pyramid, and  a faceface with one I(3)Cs2Sr3 trigonal bipyramid. In the fifth I site, I(5) is bonded to two equivalent Sr(1) and two equivalent Sr(2) atoms to form distorted ISr4 trigonal pyramids that share corners with four equivalent I(4)Cs2Sr3 square pyramids, corners with two equivalent I(3)Cs2Sr3 trigonal bipyramids, corners with two equivalent I(5)Sr4 trigonal pyramids,  an edgeedge with one I(4)Cs2Sr3 square pyramid, edges with two equivalent I(3)Cs2Sr3 trigonal bipyramids, and  an edgeedge with one I(5)Sr4 trigonal pyramid.