Sr2CaI6 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 8-coordinate geometry to one I(1), one I(2), one I(4), one I(5), two equivalent I(3), and two equivalent I(6) atoms. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to one I(1), one I(4), one I(5), one I(6), two equivalent I(2), and two equivalent I(3) atoms. Ca(1) is bonded to one I(2), one I(4), one I(5), one I(6), and two equivalent I(1) atoms to form edge-sharing CaI6 octahedra. There are six inequivalent I sites. In the first I site, I(1) is bonded in a distorted see-saw-like geometry to one Sr(1), one Sr(2), and two equivalent Ca(1) atoms. In the second I site, I(2) is bonded to one Sr(1), two equivalent Sr(2), and one Ca(1) atom to form distorted ISr3Ca trigonal pyramids that share corners with two equivalent I(2)Sr3Ca trigonal pyramids, corners with two equivalent I(3)Sr4 trigonal pyramids, and edges with two equivalent I(3)Sr4 trigonal pyramids. In the third I site, I(3) is bonded to two equivalent Sr(1) and two equivalent Sr(2) atoms to form distorted ISr4 trigonal pyramids that share corners with two equivalent I(2)Sr3Ca trigonal pyramids, corners with two equivalent I(3)Sr4 trigonal pyramids,  an edgeedge with one I(3)Sr4 trigonal pyramid, and edges with two equivalent I(2)Sr3Ca trigonal pyramids. In the fourth I site, I(4) is bonded in a distorted trigonal planar geometry to one Sr(1), one Sr(2), and one Ca(1) atom. In the fifth I site, I(5) is bonded in a 3-coordinate geometry to one Sr(1), one Sr(2), and one Ca(1) atom. In the sixth I site, I(6) is bonded in a 4-coordinate geometry to one Sr(2), two equivalent Sr(1), and one Ca(1) atom.
Sr2CaI6 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 8-coordinate geometry to one I(1), one I(2), one I(4), one I(5), two equivalent I(3), and two equivalent I(6) atoms. The Sr(1)-I(1) bond length is 3.60 Å. The Sr(1)-I(2) bond length is 3.47 Å. The Sr(1)-I(4) bond length is 3.38 Å. The Sr(1)-I(5) bond length is 3.61 Å. There is one shorter (3.53 Å) and one longer (3.55 Å) Sr(1)-I(3) bond length. There is one shorter (3.91 Å) and one longer (3.92 Å) Sr(1)-I(6) bond length. In the second Sr site, Sr(2) is bonded in a 8-coordinate geometry to one I(1), one I(4), one I(5), one I(6), two equivalent I(2), and two equivalent I(3) atoms. The Sr(2)-I(1) bond length is 3.73 Å. The Sr(2)-I(4) bond length is 3.39 Å. The Sr(2)-I(5) bond length is 3.47 Å. The Sr(2)-I(6) bond length is 3.43 Å. There is one shorter (3.48 Å) and one longer (3.52 Å) Sr(2)-I(2) bond length. There is one shorter (3.68 Å) and one longer (3.72 Å) Sr(2)-I(3) bond length. Ca(1) is bonded to one I(2), one I(4), one I(5), one I(6), and two equivalent I(1) atoms to form edge-sharing CaI6 octahedra. The Ca(1)-I(2) bond length is 3.19 Å. The Ca(1)-I(4) bond length is 3.04 Å. The Ca(1)-I(5) bond length is 3.17 Å. The Ca(1)-I(6) bond length is 3.07 Å. There is one shorter (3.12 Å) and one longer (3.13 Å) Ca(1)-I(1) bond length. There are six inequivalent I sites. In the first I site, I(1) is bonded in a distorted see-saw-like geometry to one Sr(1), one Sr(2), and two equivalent Ca(1) atoms. In the second I site, I(2) is bonded to one Sr(1), two equivalent Sr(2), and one Ca(1) atom to form distorted ISr3Ca trigonal pyramids that share corners with two equivalent I(2)Sr3Ca trigonal pyramids, corners with two equivalent I(3)Sr4 trigonal pyramids, and edges with two equivalent I(3)Sr4 trigonal pyramids. In the third I site, I(3) is bonded to two equivalent Sr(1) and two equivalent Sr(2) atoms to form distorted ISr4 trigonal pyramids that share corners with two equivalent I(2)Sr3Ca trigonal pyramids, corners with two equivalent I(3)Sr4 trigonal pyramids,  an edgeedge with one I(3)Sr4 trigonal pyramid, and edges with two equivalent I(2)Sr3Ca trigonal pyramids. In the fourth I site, I(4) is bonded in a distorted trigonal planar geometry to one Sr(1), one Sr(2), and one Ca(1) atom. In the fifth I site, I(5) is bonded in a 3-coordinate geometry to one Sr(1), one Sr(2), and one Ca(1) atom. In the sixth I site, I(6) is bonded in a 4-coordinate geometry to one Sr(2), two equivalent Sr(1), and one Ca(1) atom.