CaAl4O7 crystallizes in the monoclinic C2/c space group. Ca(1) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(2), and two equivalent O(3) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2), one O(4), and two equivalent O(1) atoms to form corner-sharing AlO4 tetrahedra. In the second Al site, Al(2) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form corner-sharing AlO4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Al(2) and two equivalent Al(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Al(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1) and two equivalent Al(2) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Al(1) atoms.
CaAl4O7 crystallizes in the monoclinic C2/c space group. Ca(1) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(2), and two equivalent O(3) atoms. The Ca(1)-O(4) bond length is 2.44 Å. Both Ca(1)-O(2) bond lengths are 2.34 Å. Both Ca(1)-O(3) bond lengths are 2.36 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(2), one O(4), and two equivalent O(1) atoms to form corner-sharing AlO4 tetrahedra. The Al(1)-O(2) bond length is 1.73 Å. The Al(1)-O(4) bond length is 1.75 Å. There is one shorter (1.79 Å) and one longer (1.80 Å) Al(1)-O(1) bond length. In the second Al site, Al(2) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form corner-sharing AlO4 tetrahedra. The Al(2)-O(1) bond length is 1.79 Å. The Al(2)-O(2) bond length is 1.73 Å. There is one shorter (1.75 Å) and one longer (1.76 Å) Al(2)-O(3) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Al(2) and two equivalent Al(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Al(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1) and two equivalent Al(2) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Al(1) atoms.