Rb3Er is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. Rb(1) is bonded to eight equivalent Rb(1) and four equivalent Er(1) atoms to form distorted RbRb8Er4 cuboctahedra that share corners with four equivalent Er(1)Rb12 cuboctahedra, corners with fourteen equivalent Rb(1)Rb8Er4 cuboctahedra, edges with six equivalent Er(1)Rb12 cuboctahedra, edges with twelve equivalent Rb(1)Rb8Er4 cuboctahedra, faces with four equivalent Er(1)Rb12 cuboctahedra, and faces with sixteen equivalent Rb(1)Rb8Er4 cuboctahedra. Er(1) is bonded to twelve equivalent Rb(1) atoms to form ErRb12 cuboctahedra that share corners with six equivalent Er(1)Rb12 cuboctahedra, corners with twelve equivalent Rb(1)Rb8Er4 cuboctahedra, edges with eighteen equivalent Rb(1)Rb8Er4 cuboctahedra, faces with eight equivalent Er(1)Rb12 cuboctahedra, and faces with twelve equivalent Rb(1)Rb8Er4 cuboctahedra.
Rb3Er is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. Rb(1) is bonded to eight equivalent Rb(1) and four equivalent Er(1) atoms to form distorted RbRb8Er4 cuboctahedra that share corners with four equivalent Er(1)Rb12 cuboctahedra, corners with fourteen equivalent Rb(1)Rb8Er4 cuboctahedra, edges with six equivalent Er(1)Rb12 cuboctahedra, edges with twelve equivalent Rb(1)Rb8Er4 cuboctahedra, faces with four equivalent Er(1)Rb12 cuboctahedra, and faces with sixteen equivalent Rb(1)Rb8Er4 cuboctahedra. There are a spread of Rb(1)-Rb(1) bond distances ranging from 4.36-4.74 Å. There are two shorter (4.47 Å) and two longer (4.55 Å) Rb(1)-Er(1) bond lengths. Er(1) is bonded to twelve equivalent Rb(1) atoms to form ErRb12 cuboctahedra that share corners with six equivalent Er(1)Rb12 cuboctahedra, corners with twelve equivalent Rb(1)Rb8Er4 cuboctahedra, edges with eighteen equivalent Rb(1)Rb8Er4 cuboctahedra, faces with eight equivalent Er(1)Rb12 cuboctahedra, and faces with twelve equivalent Rb(1)Rb8Er4 cuboctahedra.