ErGdAl6 crystallizes in the trigonal R3m space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to three equivalent Al(2), three equivalent Al(3), and six equivalent Al(5) atoms to form ErAl12 cuboctahedra that share corners with six equivalent Er(1)Al12 cuboctahedra,  a faceface with one Gd(1)Al12 cuboctahedra,  a faceface with one Gd(2)Al12 cuboctahedra, faces with three equivalent Er(3)Al12 cuboctahedra, and faces with three equivalent Gd(3)Al12 cuboctahedra. In the second Er site, Er(2) is bonded to three equivalent Al(1), three equivalent Al(4), and six equivalent Al(6) atoms to form ErAl12 cuboctahedra that share corners with six equivalent Er(2)Al12 cuboctahedra,  a faceface with one Er(3)Al12 cuboctahedra,  a faceface with one Gd(3)Al12 cuboctahedra, faces with three equivalent Gd(1)Al12 cuboctahedra, and faces with three equivalent Gd(2)Al12 cuboctahedra. In the third Er site, Er(3) is bonded to three equivalent Al(1), three equivalent Al(5), and six equivalent Al(3) atoms to form ErAl12 cuboctahedra that share corners with three equivalent Gd(3)Al12 cuboctahedra, corners with six equivalent Er(3)Al12 cuboctahedra,  a faceface with one Er(2)Al12 cuboctahedra, faces with three equivalent Er(1)Al12 cuboctahedra, and faces with three equivalent Gd(2)Al12 cuboctahedra. There are three inequivalent Gd sites. In the first Gd site, Gd(1) is bonded to three equivalent Al(2), three equivalent Al(6), and six equivalent Al(4) atoms to form GdAl12 cuboctahedra that share corners with three equivalent Gd(2)Al12 cuboctahedra, corners with six equivalent Gd(1)Al12 cuboctahedra,  a faceface with one Er(1)Al12 cuboctahedra, faces with three equivalent Er(2)Al12 cuboctahedra, and faces with three equivalent Gd(3)Al12 cuboctahedra. In the second Gd site, Gd(2) is bonded to three equivalent Al(3), three equivalent Al(6), and six equivalent Al(1) atoms to form GdAl12 cuboctahedra that share corners with three equivalent Gd(1)Al12 cuboctahedra, corners with six equivalent Gd(2)Al12 cuboctahedra,  a faceface with one Er(1)Al12 cuboctahedra, faces with three equivalent Er(2)Al12 cuboctahedra, and faces with three equivalent Er(3)Al12 cuboctahedra. In the third Gd site, Gd(3) is bonded to three equivalent Al(4), three equivalent Al(5), and six equivalent Al(2) atoms to form GdAl12 cuboctahedra that share corners with three equivalent Er(3)Al12 cuboctahedra, corners with six equivalent Gd(3)Al12 cuboctahedra,  a faceface with one Er(2)Al12 cuboctahedra, faces with three equivalent Er(1)Al12 cuboctahedra, and faces with three equivalent Gd(1)Al12 cuboctahedra. There are six inequivalent Al sites. In the first Al site, Al(1) is bonded in a 10-coordinate geometry to one Er(2), one Er(3), two equivalent Gd(2), two equivalent Al(1), two equivalent Al(3), and two equivalent Al(6) atoms. In the second Al site, Al(2) is bonded in a 10-coordinate geometry to one Er(1), one Gd(1), two equivalent Gd(3), two equivalent Al(2), two equivalent Al(4), and two equivalent Al(5) atoms. In the third Al site, Al(3) is bonded in a 10-coordinate geometry to one Er(1), two equivalent Er(3), one Gd(2), two equivalent Al(1), two equivalent Al(3), and two equivalent Al(5) atoms. In the fourth Al site, Al(4) is bonded in a 10-coordinate geometry to one Er(2), one Gd(3), two equivalent Gd(1), two equivalent Al(2), two equivalent Al(4), and two equivalent Al(6) atoms. In the fifth Al site, Al(5) is bonded in a 12-coordinate geometry to one Er(3), two equivalent Er(1), one Gd(3), two equivalent Al(2), two equivalent Al(3), and four equivalent Al(5) atoms. In the sixth Al site, Al(6) is bonded in a 12-coordinate geometry to two equivalent Er(2), one Gd(1), one Gd(2), two equivalent Al(1), two equivalent Al(4), and four equivalent Al(6) atoms.
ErGdAl6 crystallizes in the trigonal R3m space group. There are three inequivalent Er sites. In the first Er site, Er(1) is bonded to three equivalent Al(2), three equivalent Al(3), and six equivalent Al(5) atoms to form ErAl12 cuboctahedra that share corners with six equivalent Er(1)Al12 cuboctahedra,  a faceface with one Gd(1)Al12 cuboctahedra,  a faceface with one Gd(2)Al12 cuboctahedra, faces with three equivalent Er(3)Al12 cuboctahedra, and faces with three equivalent Gd(3)Al12 cuboctahedra. All Er(1)-Al(2) bond lengths are 3.06 Å. All Er(1)-Al(3) bond lengths are 3.05 Å. All Er(1)-Al(5) bond lengths are 3.10 Å. In the second Er site, Er(2) is bonded to three equivalent Al(1), three equivalent Al(4), and six equivalent Al(6) atoms to form ErAl12 cuboctahedra that share corners with six equivalent Er(2)Al12 cuboctahedra,  a faceface with one Er(3)Al12 cuboctahedra,  a faceface with one Gd(3)Al12 cuboctahedra, faces with three equivalent Gd(1)Al12 cuboctahedra, and faces with three equivalent Gd(2)Al12 cuboctahedra. All Er(2)-Al(1) bond lengths are 3.07 Å. All Er(2)-Al(4) bond lengths are 3.05 Å. All Er(2)-Al(6) bond lengths are 3.10 Å. In the third Er site, Er(3) is bonded to three equivalent Al(1), three equivalent Al(5), and six equivalent Al(3) atoms to form ErAl12 cuboctahedra that share corners with three equivalent Gd(3)Al12 cuboctahedra, corners with six equivalent Er(3)Al12 cuboctahedra,  a faceface with one Er(2)Al12 cuboctahedra, faces with three equivalent Er(1)Al12 cuboctahedra, and faces with three equivalent Gd(2)Al12 cuboctahedra. All Er(3)-Al(1) bond lengths are 3.03 Å. All Er(3)-Al(5) bond lengths are 3.01 Å. All Er(3)-Al(3) bond lengths are 3.11 Å. There are three inequivalent Gd sites. In the first Gd site, Gd(1) is bonded to three equivalent Al(2), three equivalent Al(6), and six equivalent Al(4) atoms to form GdAl12 cuboctahedra that share corners with three equivalent Gd(2)Al12 cuboctahedra, corners with six equivalent Gd(1)Al12 cuboctahedra,  a faceface with one Er(1)Al12 cuboctahedra, faces with three equivalent Er(2)Al12 cuboctahedra, and faces with three equivalent Gd(3)Al12 cuboctahedra. All Gd(1)-Al(2) bond lengths are 3.04 Å. All Gd(1)-Al(6) bond lengths are 3.02 Å. All Gd(1)-Al(4) bond lengths are 3.11 Å. In the second Gd site, Gd(2) is bonded to three equivalent Al(3), three equivalent Al(6), and six equivalent Al(1) atoms to form GdAl12 cuboctahedra that share corners with three equivalent Gd(1)Al12 cuboctahedra, corners with six equivalent Gd(2)Al12 cuboctahedra,  a faceface with one Er(1)Al12 cuboctahedra, faces with three equivalent Er(2)Al12 cuboctahedra, and faces with three equivalent Er(3)Al12 cuboctahedra. All Gd(2)-Al(3) bond lengths are 3.03 Å. All Gd(2)-Al(6) bond lengths are 3.03 Å. All Gd(2)-Al(1) bond lengths are 3.11 Å. In the third Gd site, Gd(3) is bonded to three equivalent Al(4), three equivalent Al(5), and six equivalent Al(2) atoms to form GdAl12 cuboctahedra that share corners with three equivalent Er(3)Al12 cuboctahedra, corners with six equivalent Gd(3)Al12 cuboctahedra,  a faceface with one Er(2)Al12 cuboctahedra, faces with three equivalent Er(1)Al12 cuboctahedra, and faces with three equivalent Gd(1)Al12 cuboctahedra. All Gd(3)-Al(4) bond lengths are 3.04 Å. All Gd(3)-Al(5) bond lengths are 3.04 Å. All Gd(3)-Al(2) bond lengths are 3.11 Å. There are six inequivalent Al sites. In the first Al site, Al(1) is bonded in a 10-coordinate geometry to one Er(2), one Er(3), two equivalent Gd(2), two equivalent Al(1), two equivalent Al(3), and two equivalent Al(6) atoms. Both Al(1)-Al(1) bond lengths are 2.76 Å. Both Al(1)-Al(3) bond lengths are 2.89 Å. Both Al(1)-Al(6) bond lengths are 2.88 Å. In the second Al site, Al(2) is bonded in a 10-coordinate geometry to one Er(1), one Gd(1), two equivalent Gd(3), two equivalent Al(2), two equivalent Al(4), and two equivalent Al(5) atoms. Both Al(2)-Al(2) bond lengths are 2.75 Å. Both Al(2)-Al(4) bond lengths are 2.89 Å. Both Al(2)-Al(5) bond lengths are 2.88 Å. In the third Al site, Al(3) is bonded in a 10-coordinate geometry to one Er(1), two equivalent Er(3), one Gd(2), two equivalent Al(1), two equivalent Al(3), and two equivalent Al(5) atoms. Both Al(3)-Al(3) bond lengths are 2.76 Å. Both Al(3)-Al(5) bond lengths are 2.88 Å. In the fourth Al site, Al(4) is bonded in a 10-coordinate geometry to one Er(2), one Gd(3), two equivalent Gd(1), two equivalent Al(2), two equivalent Al(4), and two equivalent Al(6) atoms. Both Al(4)-Al(4) bond lengths are 2.77 Å. Both Al(4)-Al(6) bond lengths are 2.88 Å. In the fifth Al site, Al(5) is bonded in a 12-coordinate geometry to one Er(3), two equivalent Er(1), one Gd(3), two equivalent Al(2), two equivalent Al(3), and four equivalent Al(5) atoms. There are two shorter (3.08 Å) and two longer (3.12 Å) Al(5)-Al(5) bond lengths. In the sixth Al site, Al(6) is bonded in a 12-coordinate geometry to two equivalent Er(2), one Gd(1), one Gd(2), two equivalent Al(1), two equivalent Al(4), and four equivalent Al(6) atoms. There are two shorter (3.09 Å) and two longer (3.11 Å) Al(6)-Al(6) bond lengths.