Sr2Bi2Se3O2 crystallizes in the monoclinic P2_1/c space group. Sr(1) is bonded in a 3-coordinate geometry to one Se(1), four equivalent Se(2), and three equivalent O(1) atoms. Bi(1) is bonded in a distorted single-bond geometry to two equivalent Se(1), two equivalent Se(2), and one O(1) atom. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Sr(1) and four equivalent Bi(1) atoms to form SeSr2Bi4 octahedra that share corners with two equivalent O(1)Sr3Bi tetrahedra, edges with two equivalent Se(1)Sr2Bi4 octahedra, and edges with four equivalent O(1)Sr3Bi tetrahedra. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to four equivalent Sr(1) and two equivalent Bi(1) atoms. O(1) is bonded to three equivalent Sr(1) and one Bi(1) atom to form OSr3Bi tetrahedra that share  a cornercorner with one Se(1)Sr2Bi4 octahedra, corners with two equivalent O(1)Sr3Bi tetrahedra, edges with two equivalent Se(1)Sr2Bi4 octahedra, and edges with two equivalent O(1)Sr3Bi tetrahedra. The corner-sharing octahedral tilt angles are 48°.
Sr2Bi2Se3O2 crystallizes in the monoclinic P2_1/c space group. Sr(1) is bonded in a 3-coordinate geometry to one Se(1), four equivalent Se(2), and three equivalent O(1) atoms. The Sr(1)-Se(1) bond length is 3.27 Å. There are a spread of Sr(1)-Se(2) bond distances ranging from 3.46-3.63 Å. There is one shorter (2.47 Å) and two longer (2.50 Å) Sr(1)-O(1) bond lengths. Bi(1) is bonded in a distorted single-bond geometry to two equivalent Se(1), two equivalent Se(2), and one O(1) atom. There is one shorter (3.00 Å) and one longer (3.01 Å) Bi(1)-Se(1) bond length. There is one shorter (2.91 Å) and one longer (2.92 Å) Bi(1)-Se(2) bond length. The Bi(1)-O(1) bond length is 2.13 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Sr(1) and four equivalent Bi(1) atoms to form SeSr2Bi4 octahedra that share corners with two equivalent O(1)Sr3Bi tetrahedra, edges with two equivalent Se(1)Sr2Bi4 octahedra, and edges with four equivalent O(1)Sr3Bi tetrahedra. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to four equivalent Sr(1) and two equivalent Bi(1) atoms. O(1) is bonded to three equivalent Sr(1) and one Bi(1) atom to form OSr3Bi tetrahedra that share  a cornercorner with one Se(1)Sr2Bi4 octahedra, corners with two equivalent O(1)Sr3Bi tetrahedra, edges with two equivalent Se(1)Sr2Bi4 octahedra, and edges with two equivalent O(1)Sr3Bi tetrahedra. The corner-sharing octahedral tilt angles are 48°.