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 6-coordinate geometry to one I(5), two equivalent I(1), two equivalent I(2), and two equivalent I(6) atoms. In the second Sr site, Sr(2) is bonded to one I(1), one I(2), one I(3), one I(5), one I(6), and two equivalent I(4) atoms to form distorted SrI7 pentagonal bipyramids that share corners with five equivalent Ca(1)I6 octahedra,  an edgeedge with one Ca(1)I6 octahedra, and  an edgeedge with one Sr(2)I7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 35-60°. Ca(1) is bonded to one I(1), one I(2), one I(4), one I(5), and two equivalent I(3) atoms to form CaI6 octahedra that share corners with five equivalent Sr(2)I7 pentagonal bipyramids,  an edgeedge with one Ca(1)I6 octahedra, and  an edgeedge with one Sr(2)I7 pentagonal bipyramid. There are six inequivalent I sites. In the first I site, I(1) is bonded to one Sr(2), two equivalent Sr(1), and one Ca(1) atom to form corner-sharing ISr3Ca tetrahedra. In the second I site, I(2) is bonded in a 4-coordinate geometry to one Sr(2), two equivalent Sr(1), and one Ca(1) atom. In the third I site, I(3) is bonded in a distorted trigonal non-coplanar geometry to one Sr(2) and two equivalent Ca(1) atoms. In the fourth I site, I(4) is bonded in a distorted trigonal planar geometry to two equivalent Sr(2) and one Ca(1) atom. In the fifth I site, I(5) is bonded in a distorted trigonal non-coplanar geometry to one Sr(1), one Sr(2), and one Ca(1) atom. In the sixth I site, I(6) is bonded in a trigonal non-coplanar geometry to one Sr(2) and two equivalent Sr(1) atoms.
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 6-coordinate geometry to one I(5), two equivalent I(1), two equivalent I(2), and two equivalent I(6) atoms. The Sr(1)-I(5) bond length is 3.29 Å. Both Sr(1)-I(1) bond lengths are 3.35 Å. There is one shorter (3.42 Å) and one longer (3.99 Å) Sr(1)-I(2) bond length. There is one shorter (3.36 Å) and one longer (3.37 Å) Sr(1)-I(6) bond length. In the second Sr site, Sr(2) is bonded to one I(1), one I(2), one I(3), one I(5), one I(6), and two equivalent I(4) atoms to form distorted SrI7 pentagonal bipyramids that share corners with five equivalent Ca(1)I6 octahedra,  an edgeedge with one Ca(1)I6 octahedra, and  an edgeedge with one Sr(2)I7 pentagonal bipyramid. The corner-sharing octahedral tilt angles range from 35-60°. The Sr(2)-I(1) bond length is 3.66 Å. The Sr(2)-I(2) bond length is 3.53 Å. The Sr(2)-I(3) bond length is 3.32 Å. The Sr(2)-I(5) bond length is 3.37 Å. The Sr(2)-I(6) bond length is 3.37 Å. There is one shorter (3.35 Å) and one longer (3.39 Å) Sr(2)-I(4) bond length. Ca(1) is bonded to one I(1), one I(2), one I(4), one I(5), and two equivalent I(3) atoms to form CaI6 octahedra that share corners with five equivalent Sr(2)I7 pentagonal bipyramids,  an edgeedge with one Ca(1)I6 octahedra, and  an edgeedge with one Sr(2)I7 pentagonal bipyramid. The Ca(1)-I(1) bond length is 3.27 Å. The Ca(1)-I(2) bond length is 3.25 Å. The Ca(1)-I(4) bond length is 3.14 Å. The Ca(1)-I(5) bond length is 3.21 Å. There is one shorter (3.12 Å) and one longer (3.18 Å) Ca(1)-I(3) bond length. There are six inequivalent I sites. In the first I site, I(1) is bonded to one Sr(2), two equivalent Sr(1), and one Ca(1) atom to form corner-sharing ISr3Ca tetrahedra. In the second I site, I(2) is bonded in a 4-coordinate geometry to one Sr(2), two equivalent Sr(1), and one Ca(1) atom. In the third I site, I(3) is bonded in a distorted trigonal non-coplanar geometry to one Sr(2) and two equivalent Ca(1) atoms. In the fourth I site, I(4) is bonded in a distorted trigonal planar geometry to two equivalent Sr(2) and one Ca(1) atom. In the fifth I site, I(5) is bonded in a distorted trigonal non-coplanar geometry to one Sr(1), one Sr(2), and one Ca(1) atom. In the sixth I site, I(6) is bonded in a trigonal non-coplanar geometry to one Sr(2) and two equivalent Sr(1) atoms.