Ca4OCl6 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to one O(1), three equivalent Cl(1), and four equivalent Cl(2) atoms. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one O(1), three equivalent Cl(1), and three equivalent Cl(2) atoms. O(1) is bonded to one Ca(2) and three equivalent Ca(1) atoms to form OCa4 tetrahedra that share corners with six equivalent Cl(1)Ca4 trigonal pyramids and edges with three equivalent Cl(1)Ca4 trigonal pyramids. There are two inequivalent Cl sites. In the first Cl site, Cl(1) is bonded to one Ca(2) and three equivalent Ca(1) atoms to form distorted ClCa4 trigonal pyramids that share corners with two equivalent O(1)Ca4 tetrahedra, corners with eight equivalent Cl(1)Ca4 trigonal pyramids, and  an edgeedge with one O(1)Ca4 tetrahedra. In the second Cl site, Cl(2) is bonded in a 5-coordinate geometry to one Ca(2) and four equivalent Ca(1) atoms.
Ca4OCl6 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 8-coordinate geometry to one O(1), three equivalent Cl(1), and four equivalent Cl(2) atoms. The Ca(1)-O(1) bond length is 2.24 Å. There is one shorter (2.81 Å) and two longer (2.87 Å) Ca(1)-Cl(1) bond lengths. There are two shorter (2.89 Å) and two longer (3.16 Å) Ca(1)-Cl(2) bond lengths. In the second Ca site, Ca(2) is bonded in a 7-coordinate geometry to one O(1), three equivalent Cl(1), and three equivalent Cl(2) atoms. The Ca(2)-O(1) bond length is 2.21 Å. All Ca(2)-Cl(1) bond lengths are 3.09 Å. All Ca(2)-Cl(2) bond lengths are 2.82 Å. O(1) is bonded to one Ca(2) and three equivalent Ca(1) atoms to form OCa4 tetrahedra that share corners with six equivalent Cl(1)Ca4 trigonal pyramids and edges with three equivalent Cl(1)Ca4 trigonal pyramids. There are two inequivalent Cl sites. In the first Cl site, Cl(1) is bonded to one Ca(2) and three equivalent Ca(1) atoms to form distorted ClCa4 trigonal pyramids that share corners with two equivalent O(1)Ca4 tetrahedra, corners with eight equivalent Cl(1)Ca4 trigonal pyramids, and  an edgeedge with one O(1)Ca4 tetrahedra. In the second Cl site, Cl(2) is bonded in a 5-coordinate geometry to one Ca(2) and four equivalent Ca(1) atoms.