Ba2Bi2Se3O2 crystallizes in the monoclinic P2_1/c space group. Ba(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 Ba(1) and four equivalent Bi(1) atoms to form SeBa2Bi4 octahedra that share corners with two equivalent O(1)Ba3Bi tetrahedra, edges with two equivalent Se(1)Ba2Bi4 octahedra, and edges with four equivalent O(1)Ba3Bi tetrahedra. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to four equivalent Ba(1) and two equivalent Bi(1) atoms. O(1) is bonded to three equivalent Ba(1) and one Bi(1) atom to form OBa3Bi tetrahedra that share  a cornercorner with one Se(1)Ba2Bi4 octahedra, corners with two equivalent O(1)Ba3Bi tetrahedra, edges with two equivalent Se(1)Ba2Bi4 octahedra, and edges with two equivalent O(1)Ba3Bi tetrahedra. The corner-sharing octahedral tilt angles are 51°.
Ba2Bi2Se3O2 crystallizes in the monoclinic P2_1/c space group. Ba(1) is bonded in a 3-coordinate geometry to one Se(1), four equivalent Se(2), and three equivalent O(1) atoms. The Ba(1)-Se(1) bond length is 3.38 Å. There are a spread of Ba(1)-Se(2) bond distances ranging from 3.55-3.75 Å. There are a spread of Ba(1)-O(1) bond distances ranging from 2.62-2.69 Å. 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 (3.03 Å) and one longer (3.06 Å) Bi(1)-Se(1) bond length. Both Bi(1)-Se(2) bond lengths are 2.93 Å. The Bi(1)-O(1) bond length is 2.12 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to two equivalent Ba(1) and four equivalent Bi(1) atoms to form SeBa2Bi4 octahedra that share corners with two equivalent O(1)Ba3Bi tetrahedra, edges with two equivalent Se(1)Ba2Bi4 octahedra, and edges with four equivalent O(1)Ba3Bi tetrahedra. In the second Se site, Se(2) is bonded in a 6-coordinate geometry to four equivalent Ba(1) and two equivalent Bi(1) atoms. O(1) is bonded to three equivalent Ba(1) and one Bi(1) atom to form OBa3Bi tetrahedra that share  a cornercorner with one Se(1)Ba2Bi4 octahedra, corners with two equivalent O(1)Ba3Bi tetrahedra, edges with two equivalent Se(1)Ba2Bi4 octahedra, and edges with two equivalent O(1)Ba3Bi tetrahedra. The corner-sharing octahedral tilt angles are 51°.