Er2CoAl3 crystallizes in the hexagonal P6_3/mmc space group. Er(1) is bonded in a 16-coordinate geometry to four equivalent Er(1), three equivalent Co(1), and nine equivalent Al(1) atoms. Co(1) is bonded to six equivalent Er(1) and six equivalent Al(1) atoms to form CoEr6Al6 cuboctahedra that share corners with twelve equivalent Al(1)Er6Al4Co2 cuboctahedra, edges with six equivalent Co(1)Er6Al6 cuboctahedra, faces with two equivalent Co(1)Er6Al6 cuboctahedra, and faces with eighteen equivalent Al(1)Er6Al4Co2 cuboctahedra. Al(1) is bonded to six equivalent Er(1), two equivalent Co(1), and four equivalent Al(1) atoms to form distorted AlEr6Al4Co2 cuboctahedra that share corners with four equivalent Co(1)Er6Al6 cuboctahedra, corners with fourteen equivalent Al(1)Er6Al4Co2 cuboctahedra, edges with six equivalent Al(1)Er6Al4Co2 cuboctahedra, faces with six equivalent Co(1)Er6Al6 cuboctahedra, and faces with twelve equivalent Al(1)Er6Al4Co2 cuboctahedra.
Er2CoAl3 crystallizes in the hexagonal P6_3/mmc space group. Er(1) is bonded in a 16-coordinate geometry to four equivalent Er(1), three equivalent Co(1), and nine equivalent Al(1) atoms. There is one shorter (3.28 Å) and three longer (3.29 Å) Er(1)-Er(1) bond lengths. All Er(1)-Co(1) bond lengths are 3.17 Å. There are three shorter (3.09 Å) and six longer (3.17 Å) Er(1)-Al(1) bond lengths. Co(1) is bonded to six equivalent Er(1) and six equivalent Al(1) atoms to form CoEr6Al6 cuboctahedra that share corners with twelve equivalent Al(1)Er6Al4Co2 cuboctahedra, edges with six equivalent Co(1)Er6Al6 cuboctahedra, faces with two equivalent Co(1)Er6Al6 cuboctahedra, and faces with eighteen equivalent Al(1)Er6Al4Co2 cuboctahedra. All Co(1)-Al(1) bond lengths are 2.63 Å. Al(1) is bonded to six equivalent Er(1), two equivalent Co(1), and four equivalent Al(1) atoms to form distorted AlEr6Al4Co2 cuboctahedra that share corners with four equivalent Co(1)Er6Al6 cuboctahedra, corners with fourteen equivalent Al(1)Er6Al4Co2 cuboctahedra, edges with six equivalent Al(1)Er6Al4Co2 cuboctahedra, faces with six equivalent Co(1)Er6Al6 cuboctahedra, and faces with twelve equivalent Al(1)Er6Al4Co2 cuboctahedra. There are two shorter (2.66 Å) and two longer (2.77 Å) Al(1)-Al(1) bond lengths.