K3Er is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. K(1) is bonded to eight equivalent K(1) and four equivalent Er(1) atoms to form distorted KK8Er4 cuboctahedra that share corners with four equivalent Er(1)K12 cuboctahedra, corners with fourteen equivalent K(1)K8Er4 cuboctahedra, edges with six equivalent Er(1)K12 cuboctahedra, edges with twelve equivalent K(1)K8Er4 cuboctahedra, faces with four equivalent Er(1)K12 cuboctahedra, and faces with sixteen equivalent K(1)K8Er4 cuboctahedra. Er(1) is bonded to twelve equivalent K(1) atoms to form ErK12 cuboctahedra that share corners with six equivalent Er(1)K12 cuboctahedra, corners with twelve equivalent K(1)K8Er4 cuboctahedra, edges with eighteen equivalent K(1)K8Er4 cuboctahedra, faces with eight equivalent Er(1)K12 cuboctahedra, and faces with twelve equivalent K(1)K8Er4 cuboctahedra.
K3Er is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. K(1) is bonded to eight equivalent K(1) and four equivalent Er(1) atoms to form distorted KK8Er4 cuboctahedra that share corners with four equivalent Er(1)K12 cuboctahedra, corners with fourteen equivalent K(1)K8Er4 cuboctahedra, edges with six equivalent Er(1)K12 cuboctahedra, edges with twelve equivalent K(1)K8Er4 cuboctahedra, faces with four equivalent Er(1)K12 cuboctahedra, and faces with sixteen equivalent K(1)K8Er4 cuboctahedra. There are a spread of K(1)-K(1) bond distances ranging from 4.15-4.44 Å. There are two shorter (4.27 Å) and two longer (4.30 Å) K(1)-Er(1) bond lengths. Er(1) is bonded to twelve equivalent K(1) atoms to form ErK12 cuboctahedra that share corners with six equivalent Er(1)K12 cuboctahedra, corners with twelve equivalent K(1)K8Er4 cuboctahedra, edges with eighteen equivalent K(1)K8Er4 cuboctahedra, faces with eight equivalent Er(1)K12 cuboctahedra, and faces with twelve equivalent K(1)K8Er4 cuboctahedra.