RbSeBr3 crystallizes in the monoclinic P2_1/m space group. Rb(1) is bonded in a 8-coordinate geometry to two equivalent Se(1) and six equivalent Br(1) atoms. Se(1) is bonded to two equivalent Rb(1), two equivalent Br(1), and two equivalent Br(2) atoms to form distorted SeRb2Br4 octahedra that share corners with twelve equivalent Br(1)Rb3Se trigonal pyramids and edges with two equivalent Se(1)Rb2Br4 octahedra. There are two inequivalent Br sites. In the first Br site, Br(2) is bonded in a bent 120 degrees geometry to two equivalent Se(1) atoms. In the second Br site, Br(1) is bonded to three equivalent Rb(1) and one Se(1) atom to form distorted BrRb3Se trigonal pyramids that share corners with six equivalent Se(1)Rb2Br4 octahedra, corners with ten equivalent Br(1)Rb3Se trigonal pyramids, and edges with three equivalent Br(1)Rb3Se trigonal pyramids. The corner-sharing octahedral tilt angles range from 9-138°.
RbSeBr3 crystallizes in the monoclinic P2_1/m space group. Rb(1) is bonded in a 8-coordinate geometry to two equivalent Se(1) and six equivalent Br(1) atoms. Both Rb(1)-Se(1) bond lengths are 3.74 Å. There are a spread of Rb(1)-Br(1) bond distances ranging from 3.47-3.50 Å. Se(1) is bonded to two equivalent Rb(1), two equivalent Br(1), and two equivalent Br(2) atoms to form distorted SeRb2Br4 octahedra that share corners with twelve equivalent Br(1)Rb3Se trigonal pyramids and edges with two equivalent Se(1)Rb2Br4 octahedra. Both Se(1)-Br(1) bond lengths are 2.60 Å. Both Se(1)-Br(2) bond lengths are 2.62 Å. There are two inequivalent Br sites. In the first Br site, Br(2) is bonded in a bent 120 degrees geometry to two equivalent Se(1) atoms. In the second Br site, Br(1) is bonded to three equivalent Rb(1) and one Se(1) atom to form distorted BrRb3Se trigonal pyramids that share corners with six equivalent Se(1)Rb2Br4 octahedra, corners with ten equivalent Br(1)Rb3Se trigonal pyramids, and edges with three equivalent Br(1)Rb3Se trigonal pyramids. The corner-sharing octahedral tilt angles range from 9-138°.