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 to one I(2), one I(4), one I(5), one I(6), and two equivalent I(3) atoms to form distorted SrI6 octahedra that share corners with five equivalent Ca(1)I6 octahedra and  an edgeedge with one Sr(1)I6 octahedra. The corner-sharing octahedral tilt angles range from 55-62°. In the second Sr site, Sr(2) is bonded in a 7-coordinate geometry to one I(1), one I(2), one I(3), one I(4), one I(5), and two equivalent I(6) atoms. Ca(1) is bonded to one I(2), one I(3), one I(4), one I(5), and two equivalent I(1) atoms to form CaI6 octahedra that share corners with five equivalent Sr(1)I6 octahedra and  an edgeedge with one Ca(1)I6 octahedra. The corner-sharing octahedral tilt angles range from 55-62°. There are six inequivalent I sites. In the first I site, I(1) is bonded in a trigonal planar geometry to one Sr(2) and two equivalent Ca(1) atoms. In the second I site, I(2) is bonded in a trigonal non-coplanar geometry to one Sr(1), one Sr(2), and one Ca(1) atom. In the third I site, I(3) is bonded in a 4-coordinate geometry to one Sr(2), two equivalent Sr(1), and one Ca(1) atom. 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 distorted trigonal planar 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(1) and two equivalent Sr(2) 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 to one I(2), one I(4), one I(5), one I(6), and two equivalent I(3) atoms to form distorted SrI6 octahedra that share corners with five equivalent Ca(1)I6 octahedra and  an edgeedge with one Sr(1)I6 octahedra. The corner-sharing octahedral tilt angles range from 55-62°. The Sr(1)-I(2) bond length is 3.29 Å. The Sr(1)-I(4) bond length is 3.39 Å. The Sr(1)-I(5) bond length is 3.27 Å. The Sr(1)-I(6) bond length is 3.29 Å. There is one shorter (3.40 Å) and one longer (3.48 Å) Sr(1)-I(3) bond length. In the second Sr site, Sr(2) is bonded in a 7-coordinate geometry to one I(1), one I(2), one I(3), one I(4), one I(5), and two equivalent I(6) atoms. The Sr(2)-I(1) bond length is 3.26 Å. The Sr(2)-I(2) bond length is 3.33 Å. The Sr(2)-I(3) bond length is 3.87 Å. The Sr(2)-I(4) bond length is 3.54 Å. The Sr(2)-I(5) bond length is 3.79 Å. There is one shorter (3.21 Å) and one longer (3.25 Å) Sr(2)-I(6) bond length. Ca(1) is bonded to one I(2), one I(3), one I(4), one I(5), and two equivalent I(1) atoms to form CaI6 octahedra that share corners with five equivalent Sr(1)I6 octahedra and  an edgeedge with one Ca(1)I6 octahedra. The corner-sharing octahedral tilt angles range from 55-62°. The Ca(1)-I(2) bond length is 3.23 Å. The Ca(1)-I(3) bond length is 3.30 Å. The Ca(1)-I(4) bond length is 3.18 Å. The Ca(1)-I(5) bond length is 3.15 Å. There is one shorter (3.16 Å) and one longer (3.22 Å) Ca(1)-I(1) bond length. There are six inequivalent I sites. In the first I site, I(1) is bonded in a trigonal planar geometry to one Sr(2) and two equivalent Ca(1) atoms. In the second I site, I(2) is bonded in a trigonal non-coplanar geometry to one Sr(1), one Sr(2), and one Ca(1) atom. In the third I site, I(3) is bonded in a 4-coordinate geometry to one Sr(2), two equivalent Sr(1), and one Ca(1) atom. 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 distorted trigonal planar 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(1) and two equivalent Sr(2) atoms.