RbEu3 is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. Rb(1) is bonded to four equivalent Eu(2) and eight equivalent Eu(1) atoms to form RbEu12 cuboctahedra that share corners with four equivalent Rb(1)Eu12 cuboctahedra, corners with eight equivalent Eu(2)Rb4Eu8 cuboctahedra, edges with eight equivalent Rb(1)Eu12 cuboctahedra, edges with sixteen equivalent Eu(1)Rb4Eu8 cuboctahedra, faces with four equivalent Rb(1)Eu12 cuboctahedra, faces with six equivalent Eu(2)Rb4Eu8 cuboctahedra, and faces with eight equivalent Eu(1)Rb4Eu8 cuboctahedra. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded to four equivalent Rb(1), four equivalent Eu(1), and four equivalent Eu(2) atoms to form EuRb4Eu8 cuboctahedra that share corners with twelve equivalent Eu(1)Rb4Eu8 cuboctahedra, edges with eight equivalent Rb(1)Eu12 cuboctahedra, edges with eight equivalent Eu(1)Rb4Eu8 cuboctahedra, edges with eight equivalent Eu(2)Rb4Eu8 cuboctahedra, faces with four equivalent Rb(1)Eu12 cuboctahedra, faces with four equivalent Eu(2)Rb4Eu8 cuboctahedra, and faces with ten equivalent Eu(1)Rb4Eu8 cuboctahedra. In the second Eu site, Eu(2) is bonded to four equivalent Rb(1) and eight equivalent Eu(1) atoms to form distorted EuRb4Eu8 cuboctahedra that share corners with four equivalent Eu(2)Rb4Eu8 cuboctahedra, corners with eight equivalent Rb(1)Eu12 cuboctahedra, edges with eight equivalent Eu(2)Rb4Eu8 cuboctahedra, edges with sixteen equivalent Eu(1)Rb4Eu8 cuboctahedra, faces with four equivalent Eu(2)Rb4Eu8 cuboctahedra, faces with six equivalent Rb(1)Eu12 cuboctahedra, and faces with eight equivalent Eu(1)Rb4Eu8 cuboctahedra.
RbEu3 is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. Rb(1) is bonded to four equivalent Eu(2) and eight equivalent Eu(1) atoms to form RbEu12 cuboctahedra that share corners with four equivalent Rb(1)Eu12 cuboctahedra, corners with eight equivalent Eu(2)Rb4Eu8 cuboctahedra, edges with eight equivalent Rb(1)Eu12 cuboctahedra, edges with sixteen equivalent Eu(1)Rb4Eu8 cuboctahedra, faces with four equivalent Rb(1)Eu12 cuboctahedra, faces with six equivalent Eu(2)Rb4Eu8 cuboctahedra, and faces with eight equivalent Eu(1)Rb4Eu8 cuboctahedra. All Rb(1)-Eu(2) bond lengths are 4.22 Å. All Rb(1)-Eu(1) bond lengths are 4.25 Å. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded to four equivalent Rb(1), four equivalent Eu(1), and four equivalent Eu(2) atoms to form EuRb4Eu8 cuboctahedra that share corners with twelve equivalent Eu(1)Rb4Eu8 cuboctahedra, edges with eight equivalent Rb(1)Eu12 cuboctahedra, edges with eight equivalent Eu(1)Rb4Eu8 cuboctahedra, edges with eight equivalent Eu(2)Rb4Eu8 cuboctahedra, faces with four equivalent Rb(1)Eu12 cuboctahedra, faces with four equivalent Eu(2)Rb4Eu8 cuboctahedra, and faces with ten equivalent Eu(1)Rb4Eu8 cuboctahedra. All Eu(1)-Eu(1) bond lengths are 4.22 Å. All Eu(1)-Eu(2) bond lengths are 4.25 Å. In the second Eu site, Eu(2) is bonded to four equivalent Rb(1) and eight equivalent Eu(1) atoms to form distorted EuRb4Eu8 cuboctahedra that share corners with four equivalent Eu(2)Rb4Eu8 cuboctahedra, corners with eight equivalent Rb(1)Eu12 cuboctahedra, edges with eight equivalent Eu(2)Rb4Eu8 cuboctahedra, edges with sixteen equivalent Eu(1)Rb4Eu8 cuboctahedra, faces with four equivalent Eu(2)Rb4Eu8 cuboctahedra, faces with six equivalent Rb(1)Eu12 cuboctahedra, and faces with eight equivalent Eu(1)Rb4Eu8 cuboctahedra.