ErCoAl crystallizes in the orthorhombic Amm2 space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 12-coordinate geometry to three equivalent Er(2), one Co(3), two equivalent Co(1), two equivalent Co(2), three equivalent Al(1), and four equivalent Al(2) atoms. In the second Er site, Er(2) is bonded in a 16-coordinate geometry to one Er(2), three equivalent Er(1), one Co(1), two equivalent Co(3), four equivalent Co(2), two equivalent Al(2), and three equivalent Al(1) atoms. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent Er(2), four equivalent Er(1), two equivalent Al(1), and four equivalent Al(2) atoms to form CoEr6Al6 cuboctahedra that share corners with four equivalent Co(1)Er6Al6 cuboctahedra, corners with four equivalent Al(1)Er6Al2Co4 cuboctahedra, edges with two equivalent Co(1)Er6Al6 cuboctahedra, faces with six equivalent Al(1)Er6Al2Co4 cuboctahedra, and faces with eight equivalent Al(2)Er6Al4Co2 cuboctahedra. In the second Co site, Co(2) is bonded in a 12-coordinate geometry to two equivalent Er(1), four equivalent Er(2), two equivalent Co(2), two equivalent Co(3), and two equivalent Al(1) atoms. In the third Co site, Co(3) is bonded in a 12-coordinate geometry to two equivalent Er(1), four equivalent Er(2), four equivalent Co(2), and two equivalent Al(1) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to three equivalent Er(1), three equivalent Er(2), one Co(1), one Co(3), two equivalent Co(2), and two equivalent Al(2) atoms to form distorted AlEr6Al2Co4 cuboctahedra that share corners with two equivalent Co(1)Er6Al6 cuboctahedra, corners with four equivalent Al(2)Er6Al4Co2 cuboctahedra, edges with six equivalent Al(1)Er6Al2Co4 cuboctahedra, faces with two equivalent Al(1)Er6Al2Co4 cuboctahedra, faces with three equivalent Co(1)Er6Al6 cuboctahedra, and faces with six equivalent Al(2)Er6Al4Co2 cuboctahedra. In the second Al site, Al(2) is bonded to two equivalent Er(2), four equivalent Er(1), two equivalent Co(1), two equivalent Al(1), and two equivalent Al(2) atoms to form distorted AlEr6Al4Co2 cuboctahedra that share corners with four equivalent Al(1)Er6Al2Co4 cuboctahedra, corners with four equivalent Al(2)Er6Al4Co2 cuboctahedra, edges with two equivalent Al(2)Er6Al4Co2 cuboctahedra, faces with four equivalent Co(1)Er6Al6 cuboctahedra, faces with four equivalent Al(2)Er6Al4Co2 cuboctahedra, and faces with six equivalent Al(1)Er6Al2Co4 cuboctahedra.
ErCoAl crystallizes in the orthorhombic Amm2 space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 12-coordinate geometry to three equivalent Er(2), one Co(3), two equivalent Co(1), two equivalent Co(2), three equivalent Al(1), and four equivalent Al(2) atoms. There are two shorter (3.23 Å) and one longer (3.24 Å) Er(1)-Er(2) bond length. The Er(1)-Co(3) bond length is 2.88 Å. Both Er(1)-Co(1) bond lengths are 3.17 Å. Both Er(1)-Co(2) bond lengths are 2.86 Å. There are two shorter (3.12 Å) and one longer (3.13 Å) Er(1)-Al(1) bond length. There are two shorter (3.13 Å) and two longer (3.16 Å) Er(1)-Al(2) bond lengths. In the second Er site, Er(2) is bonded in a 16-coordinate geometry to one Er(2), three equivalent Er(1), one Co(1), two equivalent Co(3), four equivalent Co(2), two equivalent Al(2), and three equivalent Al(1) atoms. The Er(2)-Er(2) bond length is 2.92 Å. The Er(2)-Co(1) bond length is 3.10 Å. Both Er(2)-Co(3) bond lengths are 3.05 Å. There are two shorter (2.98 Å) and two longer (3.07 Å) Er(2)-Co(2) bond lengths. Both Er(2)-Al(2) bond lengths are 3.12 Å. There is one shorter (3.01 Å) and two longer (3.15 Å) Er(2)-Al(1) bond lengths. There are three inequivalent Co sites. In the first Co site, Co(1) is bonded to two equivalent Er(2), four equivalent Er(1), two equivalent Al(1), and four equivalent Al(2) atoms to form CoEr6Al6 cuboctahedra that share corners with four equivalent Co(1)Er6Al6 cuboctahedra, corners with four equivalent Al(1)Er6Al2Co4 cuboctahedra, edges with two equivalent Co(1)Er6Al6 cuboctahedra, faces with six equivalent Al(1)Er6Al2Co4 cuboctahedra, and faces with eight equivalent Al(2)Er6Al4Co2 cuboctahedra. Both Co(1)-Al(1) bond lengths are 2.72 Å. There are two shorter (2.61 Å) and two longer (2.68 Å) Co(1)-Al(2) bond lengths. In the second Co site, Co(2) is bonded in a 12-coordinate geometry to two equivalent Er(1), four equivalent Er(2), two equivalent Co(2), two equivalent Co(3), and two equivalent Al(1) atoms. There is one shorter (2.51 Å) and one longer (2.85 Å) Co(2)-Co(2) bond length. There is one shorter (2.48 Å) and one longer (2.81 Å) Co(2)-Co(3) bond length. Both Co(2)-Al(1) bond lengths are 2.51 Å. In the third Co site, Co(3) is bonded in a 12-coordinate geometry to two equivalent Er(1), four equivalent Er(2), four equivalent Co(2), and two equivalent Al(1) atoms. Both Co(3)-Al(1) bond lengths are 2.50 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to three equivalent Er(1), three equivalent Er(2), one Co(1), one Co(3), two equivalent Co(2), and two equivalent Al(2) atoms to form distorted AlEr6Al2Co4 cuboctahedra that share corners with two equivalent Co(1)Er6Al6 cuboctahedra, corners with four equivalent Al(2)Er6Al4Co2 cuboctahedra, edges with six equivalent Al(1)Er6Al2Co4 cuboctahedra, faces with two equivalent Al(1)Er6Al2Co4 cuboctahedra, faces with three equivalent Co(1)Er6Al6 cuboctahedra, and faces with six equivalent Al(2)Er6Al4Co2 cuboctahedra. Both Al(1)-Al(2) bond lengths are 2.77 Å. In the second Al site, Al(2) is bonded to two equivalent Er(2), four equivalent Er(1), two equivalent Co(1), two equivalent Al(1), and two equivalent Al(2) atoms to form distorted AlEr6Al4Co2 cuboctahedra that share corners with four equivalent Al(1)Er6Al2Co4 cuboctahedra, corners with four equivalent Al(2)Er6Al4Co2 cuboctahedra, edges with two equivalent Al(2)Er6Al4Co2 cuboctahedra, faces with four equivalent Co(1)Er6Al6 cuboctahedra, faces with four equivalent Al(2)Er6Al4Co2 cuboctahedra, and faces with six equivalent Al(1)Er6Al2Co4 cuboctahedra. There is one shorter (2.65 Å) and one longer (2.71 Å) Al(2)-Al(2) bond length.