Rb3Os2Br9 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded to three equivalent Br(1) and nine equivalent Br(2) atoms to form distorted RbBr12 cuboctahedra that share corners with three equivalent Rb(2)Br12 cuboctahedra, corners with six equivalent Rb(1)Br12 cuboctahedra, corners with three equivalent Os(1)Br6 octahedra, faces with three equivalent Rb(2)Br12 cuboctahedra, faces with four equivalent Rb(1)Br12 cuboctahedra, and faces with four equivalent Os(1)Br6 octahedra. The corner-sharing octahedral tilt angles are 25°. In the second Rb site, Rb(2) is bonded to six equivalent Br(1) and six equivalent Br(2) atoms to form RbBr12 cuboctahedra that share corners with six equivalent Rb(1)Br12 cuboctahedra, corners with six equivalent Rb(2)Br12 cuboctahedra, faces with six equivalent Rb(1)Br12 cuboctahedra, and faces with six equivalent Os(1)Br6 octahedra. Os(1) is bonded to three equivalent Br(1) and three equivalent Br(2) atoms to form OsBr6 octahedra that share corners with three equivalent Rb(1)Br12 cuboctahedra, faces with three equivalent Rb(2)Br12 cuboctahedra, faces with four equivalent Rb(1)Br12 cuboctahedra, and  a faceface with one Os(1)Br6 octahedra. There are two inequivalent Br sites. In the first Br site, Br(1) is bonded in a 2-coordinate geometry to two equivalent Rb(1), two equivalent Rb(2), and two equivalent Os(1) atoms. In the second Br site, Br(2) is bonded to one Rb(2), three equivalent Rb(1), and one Os(1) atom to form a mixture of distorted corner, edge, and face-sharing BrRb4Os square pyramids.
Rb3Os2Br9 crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded to three equivalent Br(1) and nine equivalent Br(2) atoms to form distorted RbBr12 cuboctahedra that share corners with three equivalent Rb(2)Br12 cuboctahedra, corners with six equivalent Rb(1)Br12 cuboctahedra, corners with three equivalent Os(1)Br6 octahedra, faces with three equivalent Rb(2)Br12 cuboctahedra, faces with four equivalent Rb(1)Br12 cuboctahedra, and faces with four equivalent Os(1)Br6 octahedra. The corner-sharing octahedral tilt angles are 25°. All Rb(1)-Br(1) bond lengths are 4.02 Å. There are three shorter (3.56 Å) and six longer (3.79 Å) Rb(1)-Br(2) bond lengths. In the second Rb site, Rb(2) is bonded to six equivalent Br(1) and six equivalent Br(2) atoms to form RbBr12 cuboctahedra that share corners with six equivalent Rb(1)Br12 cuboctahedra, corners with six equivalent Rb(2)Br12 cuboctahedra, faces with six equivalent Rb(1)Br12 cuboctahedra, and faces with six equivalent Os(1)Br6 octahedra. All Rb(2)-Br(1) bond lengths are 3.74 Å. All Rb(2)-Br(2) bond lengths are 3.62 Å. Os(1) is bonded to three equivalent Br(1) and three equivalent Br(2) atoms to form OsBr6 octahedra that share corners with three equivalent Rb(1)Br12 cuboctahedra, faces with three equivalent Rb(2)Br12 cuboctahedra, faces with four equivalent Rb(1)Br12 cuboctahedra, and  a faceface with one Os(1)Br6 octahedra. All Os(1)-Br(1) bond lengths are 2.54 Å. All Os(1)-Br(2) bond lengths are 2.51 Å. There are two inequivalent Br sites. In the first Br site, Br(1) is bonded in a 2-coordinate geometry to two equivalent Rb(1), two equivalent Rb(2), and two equivalent Os(1) atoms. In the second Br site, Br(2) is bonded to one Rb(2), three equivalent Rb(1), and one Os(1) atom to form a mixture of distorted corner, edge, and face-sharing BrRb4Os square pyramids.