(CaAl2(Si2O7)2)4(O2)5 crystallizes in the monoclinic C2/m space group. The structure consists of two tetraoxetane molecules and two water atoms inside a CaAl2(Si2O7)2 framework. In the CaAl2(Si2O7)2 framework, Ca(1) is bonded in a 6-coordinate geometry to two equivalent O(11), two equivalent O(2), and two equivalent O(3) atoms. Al(1) is bonded to one O(2), one O(3), one O(5), and one O(7) atom to form AlO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra and corners with two equivalent Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. In the second Si site, Si(2) is bonded to one O(3), one O(4), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(2) atom. In the second O site, O(4) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the third O site, O(5) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(1) atom. In the fourth O site, O(6) is bonded in a bent 150 degrees geometry to two equivalent Si(2) atoms. In the fifth O site, O(7) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(2) atom. In the sixth O site, O(11) is bonded in a distorted L-shaped geometry to one Ca(1) and one O(11) atom. In the seventh O site, O(1) is bonded in a bent 150 degrees geometry to two equivalent Si(1) atoms. In the eighth O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(1) atom.
(CaAl2(Si2O7)2)4(O2)5 crystallizes in the monoclinic C2/m space group. The structure consists of two tetraoxetane molecules and two water atoms inside a CaAl2(Si2O7)2 framework. In the CaAl2(Si2O7)2 framework, Ca(1) is bonded in a 6-coordinate geometry to two equivalent O(11), two equivalent O(2), and two equivalent O(3) atoms. Both Ca(1)-O(11) bond lengths are 2.61 Å. Both Ca(1)-O(2) bond lengths are 2.29 Å. Both Ca(1)-O(3) bond lengths are 2.28 Å. Al(1) is bonded to one O(2), one O(3), one O(5), and one O(7) atom to form AlO4 tetrahedra that share corners with two equivalent Si(1)O4 tetrahedra and corners with two equivalent Si(2)O4 tetrahedra. The Al(1)-O(2) bond length is 1.81 Å. The Al(1)-O(3) bond length is 1.80 Å. The Al(1)-O(5) bond length is 1.73 Å. The Al(1)-O(7) bond length is 1.73 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(2), one O(4), and one O(5) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. The Si(1)-O(1) bond length is 1.64 Å. The Si(1)-O(2) bond length is 1.65 Å. The Si(1)-O(4) bond length is 1.64 Å. The Si(1)-O(5) bond length is 1.61 Å. In the second Si site, Si(2) is bonded to one O(3), one O(4), one O(6), and one O(7) atom to form SiO4 tetrahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, and corners with two equivalent Al(1)O4 tetrahedra. The Si(2)-O(3) bond length is 1.66 Å. The Si(2)-O(4) bond length is 1.64 Å. The Si(2)-O(6) bond length is 1.64 Å. The Si(2)-O(7) bond length is 1.61 Å. There are eight inequivalent O sites. In the first O site, O(3) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(2) atom. In the second O site, O(4) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom. In the third O site, O(5) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(1) atom. In the fourth O site, O(6) is bonded in a bent 150 degrees geometry to two equivalent Si(2) atoms. In the fifth O site, O(7) is bonded in a bent 150 degrees geometry to one Al(1) and one Si(2) atom. In the sixth O site, O(11) is bonded in a distorted L-shaped geometry to one Ca(1) and one O(11) atom. The O(11)-O(11) bond length is 1.26 Å. In the seventh O site, O(1) is bonded in a bent 150 degrees geometry to two equivalent Si(1) atoms. In the eighth O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(1) atom.