Mg3(Cu2Al)2 crystallizes in the monoclinic C2/m space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 16-coordinate geometry to one Mg(2), three equivalent Mg(1), three equivalent Cu(1), six equivalent Cu(3), and three equivalent Al(2) atoms. In the second Mg site, Mg(2) is bonded in a 16-coordinate geometry to one Mg(1), three equivalent Mg(3), two equivalent Cu(1), two equivalent Cu(2), four equivalent Cu(3), one Al(3), and three equivalent Al(1) atoms. In the third Mg site, Mg(3) is bonded in a 16-coordinate geometry to one Mg(3), three equivalent Mg(2), one Cu(1), two equivalent Cu(3), four equivalent Cu(2), two equivalent Al(3), and three equivalent Al(1) atoms. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one Mg(3), two equivalent Mg(2), three equivalent Mg(1), four equivalent Cu(3), one Al(1), and one Al(2) atom to form distorted CuMg6Al2Cu4 cuboctahedra that share  a cornercorner with one Al(3)Mg6Al2Cu4 cuboctahedra, corners with two equivalent Al(1)Mg6AlCu5 cuboctahedra, corners with two equivalent Al(2)Mg6Cu6 cuboctahedra, corners with four equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, corners with four equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, corners with five equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, edges with two equivalent Al(3)Mg6Al2Cu4 cuboctahedra, edges with four equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, faces with two equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, faces with three equivalent Al(1)Mg6AlCu5 cuboctahedra, faces with three equivalent Al(2)Mg6Cu6 cuboctahedra, and faces with ten equivalent Cu(3)Mg6Al2Cu4 cuboctahedra. In the second Cu site, Cu(2) is bonded to two equivalent Mg(2), four equivalent Mg(3), two equivalent Cu(2), two equivalent Al(1), and two equivalent Al(3) atoms to form CuMg6Al4Cu2 cuboctahedra that share corners with four equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, corners with four equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, corners with four equivalent Al(1)Mg6AlCu5 cuboctahedra, corners with six equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, edges with two equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, edges with four equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, faces with two equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, faces with two equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, faces with four equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, faces with four equivalent Al(3)Mg6Al2Cu4 cuboctahedra, and faces with six equivalent Al(1)Mg6AlCu5 cuboctahedra. In the third Cu site, Cu(3) is bonded to one Mg(3), two equivalent Mg(2), three equivalent Mg(1), two equivalent Cu(1), two equivalent Cu(3), one Al(1), and one Al(2) atom to form distorted CuMg6Al2Cu4 cuboctahedra that share corners with two equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, corners with two equivalent Al(3)Mg6Al2Cu4 cuboctahedra, corners with two equivalent Al(1)Mg6AlCu5 cuboctahedra, corners with two equivalent Al(2)Mg6Cu6 cuboctahedra, corners with three equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, corners with seven equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, edges with two equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, edges with four equivalent Cu(3)Mg6Al2Cu4 cuboctahedra,  a faceface with one Cu(2)Mg6Al4Cu2 cuboctahedra,  a faceface with one Al(3)Mg6Al2Cu4 cuboctahedra, faces with three equivalent Al(1)Mg6AlCu5 cuboctahedra, faces with three equivalent Al(2)Mg6Cu6 cuboctahedra, faces with five equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, and faces with five equivalent Cu(3)Mg6Al2Cu4 cuboctahedra. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to three equivalent Mg(2), three equivalent Mg(3), one Cu(1), two equivalent Cu(2), two equivalent Cu(3), and one Al(3) atom to form distorted AlMg6AlCu5 cuboctahedra that share corners with two equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, corners with two equivalent Al(3)Mg6Al2Cu4 cuboctahedra, corners with three equivalent Al(1)Mg6AlCu5 cuboctahedra, corners with three equivalent Al(2)Mg6Cu6 cuboctahedra, corners with four equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, corners with four equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, edges with six equivalent Al(1)Mg6AlCu5 cuboctahedra, faces with three equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, faces with three equivalent Al(3)Mg6Al2Cu4 cuboctahedra, faces with six equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, and faces with six equivalent Cu(2)Mg6Al4Cu2 cuboctahedra. In the second Al site, Al(2) is bonded to six equivalent Mg(1), two equivalent Cu(1), and four equivalent Cu(3) atoms to form distorted AlMg6Cu6 cuboctahedra that share corners with four equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, corners with six equivalent Al(1)Mg6AlCu5 cuboctahedra, corners with eight equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, edges with six equivalent Al(2)Mg6Cu6 cuboctahedra, faces with six equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, and faces with twelve equivalent Cu(3)Mg6Al2Cu4 cuboctahedra. In the third Al site, Al(3) is bonded to two equivalent Mg(2), four equivalent Mg(3), four equivalent Cu(2), and two equivalent Al(1) atoms to form distorted AlMg6Al2Cu4 cuboctahedra that share corners with two equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, corners with four equivalent Al(3)Mg6Al2Cu4 cuboctahedra, corners with four equivalent Al(1)Mg6AlCu5 cuboctahedra, corners with eight equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, edges with two equivalent Al(3)Mg6Al2Cu4 cuboctahedra, edges with four equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, faces with four equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, faces with six equivalent Al(1)Mg6AlCu5 cuboctahedra, and faces with eight equivalent Cu(2)Mg6Al4Cu2 cuboctahedra.
Mg3(Cu2Al)2 crystallizes in the monoclinic C2/m space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 16-coordinate geometry to one Mg(2), three equivalent Mg(1), three equivalent Cu(1), six equivalent Cu(3), and three equivalent Al(2) atoms. The Mg(1)-Mg(2) bond length is 2.95 Å. All Mg(1)-Mg(1) bond lengths are 3.07 Å. There is one shorter (2.84 Å) and two longer (2.94 Å) Mg(1)-Cu(1) bond lengths. There are a spread of Mg(1)-Cu(3) bond distances ranging from 2.90-2.97 Å. There is one shorter (2.94 Å) and two longer (2.96 Å) Mg(1)-Al(2) bond lengths. In the second Mg site, Mg(2) is bonded in a 16-coordinate geometry to one Mg(1), three equivalent Mg(3), two equivalent Cu(1), two equivalent Cu(2), four equivalent Cu(3), one Al(3), and three equivalent Al(1) atoms. There is one shorter (3.08 Å) and two longer (3.12 Å) Mg(2)-Mg(3) bond lengths. Both Mg(2)-Cu(1) bond lengths are 2.92 Å. Both Mg(2)-Cu(2) bond lengths are 3.03 Å. There are two shorter (2.89 Å) and two longer (2.90 Å) Mg(2)-Cu(3) bond lengths. The Mg(2)-Al(3) bond length is 2.99 Å. There are two shorter (2.95 Å) and one longer (3.02 Å) Mg(2)-Al(1) bond length. In the third Mg site, Mg(3) is bonded in a 16-coordinate geometry to one Mg(3), three equivalent Mg(2), one Cu(1), two equivalent Cu(3), four equivalent Cu(2), two equivalent Al(3), and three equivalent Al(1) atoms. The Mg(3)-Mg(3) bond length is 3.15 Å. The Mg(3)-Cu(1) bond length is 2.92 Å. Both Mg(3)-Cu(3) bond lengths are 2.88 Å. There are two shorter (2.92 Å) and two longer (3.03 Å) Mg(3)-Cu(2) bond lengths. Both Mg(3)-Al(3) bond lengths are 2.98 Å. There is one shorter (2.91 Å) and two longer (2.99 Å) Mg(3)-Al(1) bond lengths. There are three inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one Mg(3), two equivalent Mg(2), three equivalent Mg(1), four equivalent Cu(3), one Al(1), and one Al(2) atom to form distorted CuMg6Al2Cu4 cuboctahedra that share  a cornercorner with one Al(3)Mg6Al2Cu4 cuboctahedra, corners with two equivalent Al(1)Mg6AlCu5 cuboctahedra, corners with two equivalent Al(2)Mg6Cu6 cuboctahedra, corners with four equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, corners with four equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, corners with five equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, edges with two equivalent Al(3)Mg6Al2Cu4 cuboctahedra, edges with four equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, faces with two equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, faces with three equivalent Al(1)Mg6AlCu5 cuboctahedra, faces with three equivalent Al(2)Mg6Cu6 cuboctahedra, and faces with ten equivalent Cu(3)Mg6Al2Cu4 cuboctahedra. There are two shorter (2.52 Å) and two longer (2.53 Å) Cu(1)-Cu(3) bond lengths. The Cu(1)-Al(1) bond length is 2.44 Å. The Cu(1)-Al(2) bond length is 2.46 Å. In the second Cu site, Cu(2) is bonded to two equivalent Mg(2), four equivalent Mg(3), two equivalent Cu(2), two equivalent Al(1), and two equivalent Al(3) atoms to form CuMg6Al4Cu2 cuboctahedra that share corners with four equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, corners with four equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, corners with four equivalent Al(1)Mg6AlCu5 cuboctahedra, corners with six equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, edges with two equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, edges with four equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, faces with two equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, faces with two equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, faces with four equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, faces with four equivalent Al(3)Mg6Al2Cu4 cuboctahedra, and faces with six equivalent Al(1)Mg6AlCu5 cuboctahedra. Both Cu(2)-Cu(2) bond lengths are 2.53 Å. Both Cu(2)-Al(1) bond lengths are 2.52 Å. Both Cu(2)-Al(3) bond lengths are 2.52 Å. In the third Cu site, Cu(3) is bonded to one Mg(3), two equivalent Mg(2), three equivalent Mg(1), two equivalent Cu(1), two equivalent Cu(3), one Al(1), and one Al(2) atom to form distorted CuMg6Al2Cu4 cuboctahedra that share corners with two equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, corners with two equivalent Al(3)Mg6Al2Cu4 cuboctahedra, corners with two equivalent Al(1)Mg6AlCu5 cuboctahedra, corners with two equivalent Al(2)Mg6Cu6 cuboctahedra, corners with three equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, corners with seven equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, edges with two equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, edges with four equivalent Cu(3)Mg6Al2Cu4 cuboctahedra,  a faceface with one Cu(2)Mg6Al4Cu2 cuboctahedra,  a faceface with one Al(3)Mg6Al2Cu4 cuboctahedra, faces with three equivalent Al(1)Mg6AlCu5 cuboctahedra, faces with three equivalent Al(2)Mg6Cu6 cuboctahedra, faces with five equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, and faces with five equivalent Cu(3)Mg6Al2Cu4 cuboctahedra. Both Cu(3)-Cu(3) bond lengths are 2.53 Å. The Cu(3)-Al(1) bond length is 2.47 Å. The Cu(3)-Al(2) bond length is 2.48 Å. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to three equivalent Mg(2), three equivalent Mg(3), one Cu(1), two equivalent Cu(2), two equivalent Cu(3), and one Al(3) atom to form distorted AlMg6AlCu5 cuboctahedra that share corners with two equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, corners with two equivalent Al(3)Mg6Al2Cu4 cuboctahedra, corners with three equivalent Al(1)Mg6AlCu5 cuboctahedra, corners with three equivalent Al(2)Mg6Cu6 cuboctahedra, corners with four equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, corners with four equivalent Cu(2)Mg6Al4Cu2 cuboctahedra, edges with six equivalent Al(1)Mg6AlCu5 cuboctahedra, faces with three equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, faces with three equivalent Al(3)Mg6Al2Cu4 cuboctahedra, faces with six equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, and faces with six equivalent Cu(2)Mg6Al4Cu2 cuboctahedra. The Al(1)-Al(3) bond length is 2.62 Å. In the second Al site, Al(2) is bonded to six equivalent Mg(1), two equivalent Cu(1), and four equivalent Cu(3) atoms to form distorted AlMg6Cu6 cuboctahedra that share corners with four equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, corners with six equivalent Al(1)Mg6AlCu5 cuboctahedra, corners with eight equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, edges with six equivalent Al(2)Mg6Cu6 cuboctahedra, faces with six equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, and faces with twelve equivalent Cu(3)Mg6Al2Cu4 cuboctahedra. In the third Al site, Al(3) is bonded to two equivalent Mg(2), four equivalent Mg(3), four equivalent Cu(2), and two equivalent Al(1) atoms to form distorted AlMg6Al2Cu4 cuboctahedra that share corners with two equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, corners with four equivalent Al(3)Mg6Al2Cu4 cuboctahedra, corners with four equivalent Al(1)Mg6AlCu5 cuboctahedra, corners with eight equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, edges with two equivalent Al(3)Mg6Al2Cu4 cuboctahedra, edges with four equivalent Cu(1)Mg6Al2Cu4 cuboctahedra, faces with four equivalent Cu(3)Mg6Al2Cu4 cuboctahedra, faces with six equivalent Al(1)Mg6AlCu5 cuboctahedra, and faces with eight equivalent Cu(2)Mg6Al4Cu2 cuboctahedra.