Ba2CaI6 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to one I(5), two equivalent I(1), two equivalent I(2), and two equivalent I(6) atoms to form distorted BaI7 pentagonal bipyramids that share  a cornercorner with one Ca(1)I6 octahedra,  a cornercorner with one Ba(2)I7 pentagonal bipyramid, corners with two equivalent Ba(1)I7 pentagonal bipyramids, edges with two equivalent Ca(1)I6 octahedra, edges with two equivalent Ba(1)I7 pentagonal bipyramids, and edges with three equivalent Ba(2)I7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 63°. In the second Ba site, Ba(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 BaI7 pentagonal bipyramids that share corners with five equivalent Ca(1)I6 octahedra,  a cornercorner with one Ba(1)I7 pentagonal bipyramid,  an edgeedge with one Ca(1)I6 octahedra,  an edgeedge with one Ba(2)I7 pentagonal bipyramid, and edges with three equivalent Ba(1)I7 pentagonal bipyramids. 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  a cornercorner with one Ba(1)I7 pentagonal bipyramid, corners with five equivalent Ba(2)I7 pentagonal bipyramids,  an edgeedge with one Ca(1)I6 octahedra,  an edgeedge with one Ba(2)I7 pentagonal bipyramid, and edges with two equivalent Ba(1)I7 pentagonal bipyramids. There are six inequivalent I sites. In the first I site, I(1) is bonded to one Ba(2), two equivalent Ba(1), and one Ca(1) atom to form a mixture of corner and edge-sharing IBa3Ca tetrahedra. In the second I site, I(2) is bonded to one Ba(2), two equivalent Ba(1), and one Ca(1) atom to form a mixture of distorted corner and edge-sharing IBa3Ca tetrahedra. In the third I site, I(3) is bonded in a distorted trigonal non-coplanar geometry to one Ba(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 Ba(2) and one Ca(1) atom. In the fifth I site, I(5) is bonded in a trigonal non-coplanar geometry to one Ba(1), one Ba(2), and one Ca(1) atom. In the sixth I site, I(6) is bonded in a trigonal non-coplanar geometry to one Ba(2) and two equivalent Ba(1) atoms.
Ba2CaI6 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to one I(5), two equivalent I(1), two equivalent I(2), and two equivalent I(6) atoms to form distorted BaI7 pentagonal bipyramids that share  a cornercorner with one Ca(1)I6 octahedra,  a cornercorner with one Ba(2)I7 pentagonal bipyramid, corners with two equivalent Ba(1)I7 pentagonal bipyramids, edges with two equivalent Ca(1)I6 octahedra, edges with two equivalent Ba(1)I7 pentagonal bipyramids, and edges with three equivalent Ba(2)I7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 63°. The Ba(1)-I(5) bond length is 3.48 Å. There is one shorter (3.51 Å) and one longer (3.52 Å) Ba(1)-I(1) bond length. There is one shorter (3.67 Å) and one longer (3.75 Å) Ba(1)-I(2) bond length. There is one shorter (3.50 Å) and one longer (3.51 Å) Ba(1)-I(6) bond length. In the second Ba site, Ba(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 BaI7 pentagonal bipyramids that share corners with five equivalent Ca(1)I6 octahedra,  a cornercorner with one Ba(1)I7 pentagonal bipyramid,  an edgeedge with one Ca(1)I6 octahedra,  an edgeedge with one Ba(2)I7 pentagonal bipyramid, and edges with three equivalent Ba(1)I7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 35-60°. The Ba(2)-I(1) bond length is 3.64 Å. The Ba(2)-I(2) bond length is 3.70 Å. The Ba(2)-I(3) bond length is 3.51 Å. The Ba(2)-I(5) bond length is 3.53 Å. The Ba(2)-I(6) bond length is 3.54 Å. There is one shorter (3.49 Å) and one longer (3.53 Å) Ba(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  a cornercorner with one Ba(1)I7 pentagonal bipyramid, corners with five equivalent Ba(2)I7 pentagonal bipyramids,  an edgeedge with one Ca(1)I6 octahedra,  an edgeedge with one Ba(2)I7 pentagonal bipyramid, and edges with two equivalent Ba(1)I7 pentagonal bipyramids. The Ca(1)-I(1) bond length is 3.28 Å. The Ca(1)-I(2) bond length is 3.30 Å. The Ca(1)-I(4) bond length is 3.16 Å. The Ca(1)-I(5) bond length is 3.24 Å. There is one shorter (3.12 Å) and one longer (3.23 Å) Ca(1)-I(3) bond length. There are six inequivalent I sites. In the first I site, I(1) is bonded to one Ba(2), two equivalent Ba(1), and one Ca(1) atom to form a mixture of corner and edge-sharing IBa3Ca tetrahedra. In the second I site, I(2) is bonded to one Ba(2), two equivalent Ba(1), and one Ca(1) atom to form a mixture of distorted corner and edge-sharing IBa3Ca tetrahedra. In the third I site, I(3) is bonded in a distorted trigonal non-coplanar geometry to one Ba(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 Ba(2) and one Ca(1) atom. In the fifth I site, I(5) is bonded in a trigonal non-coplanar geometry to one Ba(1), one Ba(2), and one Ca(1) atom. In the sixth I site, I(6) is bonded in a trigonal non-coplanar geometry to one Ba(2) and two equivalent Ba(1) atoms.