SrAl2(SiO5)2 crystallizes in the monoclinic P2_1/m space group. Sr(1) is bonded in a 9-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and edges with two equivalent Al(2)O6 octahedra. In the second Al site, Al(2) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and edges with two equivalent Al(1)O6 octahedra. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share corners with two equivalent Al(1)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-58°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Sr(1) and two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Sr(1), one Al(2), and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Sr(1), one Al(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Sr(1), one Al(1), one Al(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a water-like geometry to one Al(1) and one Al(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to two equivalent Sr(1) atoms.
SrAl2(SiO5)2 crystallizes in the monoclinic P2_1/m space group. Sr(1) is bonded in a 9-coordinate geometry to one O(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), and two equivalent O(6) atoms. The Sr(1)-O(1) bond length is 2.74 Å. Both Sr(1)-O(2) bond lengths are 2.55 Å. Both Sr(1)-O(3) bond lengths are 2.51 Å. Both Sr(1)-O(4) bond lengths are 2.89 Å. There is one shorter (2.74 Å) and one longer (3.00 Å) Sr(1)-O(6) bond length. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to two equivalent O(3), two equivalent O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and edges with two equivalent Al(2)O6 octahedra. Both Al(1)-O(3) bond lengths are 1.86 Å. Both Al(1)-O(4) bond lengths are 2.01 Å. Both Al(1)-O(5) bond lengths are 1.90 Å. In the second Al site, Al(2) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms to form AlO6 octahedra that share corners with four equivalent Si(1)O4 tetrahedra and edges with two equivalent Al(1)O6 octahedra. Both Al(2)-O(2) bond lengths are 1.89 Å. Both Al(2)-O(4) bond lengths are 1.99 Å. Both Al(2)-O(5) bond lengths are 1.90 Å. Si(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SiO4 tetrahedra that share corners with two equivalent Al(1)O6 octahedra, corners with two equivalent Al(2)O6 octahedra, and  a cornercorner with one Si(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-58°. The Si(1)-O(1) bond length is 1.67 Å. The Si(1)-O(2) bond length is 1.64 Å. The Si(1)-O(3) bond length is 1.63 Å. The Si(1)-O(4) bond length is 1.65 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one Sr(1) and two equivalent Si(1) atoms. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Sr(1), one Al(2), and one Si(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Sr(1), one Al(1), and one Si(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Sr(1), one Al(1), one Al(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a water-like geometry to one Al(1) and one Al(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to two equivalent Sr(1) atoms.