Ca2Al2Si(HO4)2 crystallizes in the tetragonal I-42m space group. Ca(1) is bonded to one O(1), two equivalent O(2), and three equivalent O(3) atoms to form distorted CaO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Al(1)O4 tetrahedra, and edges with three equivalent Ca(1)O6 octahedra. Al(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form AlO4 tetrahedra that share corners with four equivalent Ca(1)O6 octahedra, corners with two equivalent Al(1)O4 tetrahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 67-68°. Si(1) is bonded to four equivalent O(2) atoms to form SiO4 tetrahedra that share corners with four equivalent Ca(1)O6 octahedra and corners with four equivalent Al(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 63°. H(1) is bonded in a single-bond geometry to one O(3) atom. There are three inequivalent O sites. In the first O site, O(3) is bonded in a distorted single-bond geometry to three equivalent Ca(1) and one H(1) atom. In the second O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Al(1) atoms. In the third O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(1) atom.
Ca2Al2Si(HO4)2 crystallizes in the tetragonal I-42m space group. Ca(1) is bonded to one O(1), two equivalent O(2), and three equivalent O(3) atoms to form distorted CaO6 octahedra that share corners with two equivalent Si(1)O4 tetrahedra, corners with four equivalent Al(1)O4 tetrahedra, and edges with three equivalent Ca(1)O6 octahedra. The Ca(1)-O(1) bond length is 2.42 Å. Both Ca(1)-O(2) bond lengths are 2.47 Å. There are two shorter (2.30 Å) and one longer (2.33 Å) Ca(1)-O(3) bond length. Al(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form AlO4 tetrahedra that share corners with four equivalent Ca(1)O6 octahedra, corners with two equivalent Al(1)O4 tetrahedra, and corners with two equivalent Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 67-68°. Both Al(1)-O(1) bond lengths are 1.74 Å. Both Al(1)-O(2) bond lengths are 1.78 Å. Si(1) is bonded to four equivalent O(2) atoms to form SiO4 tetrahedra that share corners with four equivalent Ca(1)O6 octahedra and corners with four equivalent Al(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 63°. All Si(1)-O(2) bond lengths are 1.63 Å. H(1) is bonded in a single-bond geometry to one O(3) atom. The H(1)-O(3) bond length is 0.96 Å. There are three inequivalent O sites. In the first O site, O(3) is bonded in a distorted single-bond geometry to three equivalent Ca(1) and one H(1) atom. In the second O site, O(1) is bonded in a distorted trigonal planar geometry to one Ca(1) and two equivalent Al(1) atoms. In the third O site, O(2) is bonded in a distorted trigonal planar geometry to one Ca(1), one Al(1), and one Si(1) atom.