Sr2Sb2Se3O2 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. Sb(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 Sb(1) atoms to form SeSr2Sb4 octahedra that share corners with two equivalent O(1)Sr3Sb tetrahedra, edges with two equivalent Se(1)Sr2Sb4 octahedra, and edges with four equivalent O(1)Sr3Sb tetrahedra. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to four equivalent Sr(1) and two equivalent Sb(1) atoms. O(1) is bonded to three equivalent Sr(1) and one Sb(1) atom to form OSr3Sb tetrahedra that share  a cornercorner with one Se(1)Sr2Sb4 octahedra, corners with two equivalent O(1)Sr3Sb tetrahedra, edges with two equivalent Se(1)Sr2Sb4 octahedra, and edges with two equivalent O(1)Sr3Sb tetrahedra. The corner-sharing octahedral tilt angles are 48°.
Sr2Sb2Se3O2 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 3.24 Å. There are a spread of Sr(1)-Se(2) bond distances ranging from 3.38-3.53 Å. There are a spread of Sr(1)-O(1) bond distances ranging from 2.49-2.55 Å. Sb(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 (2.93 Å) and one longer (3.00 Å) Sb(1)-Se(1) bond length. There is one shorter (2.83 Å) and one longer (2.85 Å) Sb(1)-Se(2) bond length. The Sb(1)-O(1) bond length is 2.00 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Sr(1) and four equivalent Sb(1) atoms to form SeSr2Sb4 octahedra that share corners with two equivalent O(1)Sr3Sb tetrahedra, edges with two equivalent Se(1)Sr2Sb4 octahedra, and edges with four equivalent O(1)Sr3Sb tetrahedra. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to four equivalent Sr(1) and two equivalent Sb(1) atoms. O(1) is bonded to three equivalent Sr(1) and one Sb(1) atom to form OSr3Sb tetrahedra that share  a cornercorner with one Se(1)Sr2Sb4 octahedra, corners with two equivalent O(1)Sr3Sb tetrahedra, edges with two equivalent Se(1)Sr2Sb4 octahedra, and edges with two equivalent O(1)Sr3Sb tetrahedra. The corner-sharing octahedral tilt angles are 48°.