BaCa2I6 is Hydrophilite-derived structured and crystallizes in the monoclinic C2/c space group. Ba(1) is bonded to two equivalent I(2) and four equivalent I(1) atoms to form distorted BaI6 pentagonal pyramids that share corners with four equivalent Ca(1)I6 octahedra, edges with two equivalent Ca(1)I6 octahedra, and edges with two equivalent Ba(1)I6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 41-62°. Ca(1) is bonded to one I(1), two equivalent I(2), and three equivalent I(3) atoms to form CaI6 octahedra that share corners with six equivalent Ca(1)I6 octahedra, corners with two equivalent Ba(1)I6 pentagonal pyramids,  an edgeedge with one Ca(1)I6 octahedra, and  an edgeedge with one Ba(1)I6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 43-57°. There are three inequivalent I sites. In the first I site, I(1) is bonded in a distorted trigonal planar geometry to two equivalent Ba(1) and one Ca(1) atom. In the second I site, I(2) is bonded in a distorted trigonal planar geometry to one Ba(1) and two equivalent Ca(1) atoms. In the third I site, I(3) is bonded in a distorted T-shaped geometry to three equivalent Ca(1) atoms.
BaCa2I6 is Hydrophilite-derived structured and crystallizes in the monoclinic C2/c space group. Ba(1) is bonded to two equivalent I(2) and four equivalent I(1) atoms to form distorted BaI6 pentagonal pyramids that share corners with four equivalent Ca(1)I6 octahedra, edges with two equivalent Ca(1)I6 octahedra, and edges with two equivalent Ba(1)I6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 41-62°. Both Ba(1)-I(2) bond lengths are 3.64 Å. There are two shorter (3.41 Å) and two longer (3.52 Å) Ba(1)-I(1) bond lengths. Ca(1) is bonded to one I(1), two equivalent I(2), and three equivalent I(3) atoms to form CaI6 octahedra that share corners with six equivalent Ca(1)I6 octahedra, corners with two equivalent Ba(1)I6 pentagonal pyramids,  an edgeedge with one Ca(1)I6 octahedra, and  an edgeedge with one Ba(1)I6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 43-57°. The Ca(1)-I(1) bond length is 3.04 Å. There is one shorter (3.20 Å) and one longer (3.21 Å) Ca(1)-I(2) bond length. There are a spread of Ca(1)-I(3) bond distances ranging from 3.10-3.26 Å. There are three inequivalent I sites. In the first I site, I(1) is bonded in a distorted trigonal planar geometry to two equivalent Ba(1) and one Ca(1) atom. In the second I site, I(2) is bonded in a distorted trigonal planar geometry to one Ba(1) and two equivalent Ca(1) atoms. In the third I site, I(3) is bonded in a distorted T-shaped geometry to three equivalent Ca(1) atoms.