Mg16CoAl12 crystallizes in the trigonal R3m space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 10-coordinate geometry to one Mg(2), one Mg(3), two equivalent Mg(5), two equivalent Al(1), two equivalent Al(2), and two equivalent Al(3) atoms. In the second Mg site, Mg(2) is bonded to one Mg(1), two equivalent Mg(4), four equivalent Mg(5), one Al(2), and four equivalent Al(3) atoms to form a mixture of distorted corner and edge-sharing MgMg7Al5 cuboctahedra. In the third Mg site, Mg(3) is bonded in a distorted single-bond geometry to three equivalent Mg(1), one Co(1), three equivalent Al(2), and six equivalent Al(3) atoms. In the fourth Mg site, Mg(4) is bonded in a 6-coordinate geometry to two equivalent Mg(2), one Co(1), one Al(1), two equivalent Al(2), and two equivalent Al(3) atoms. In the fifth Mg site, Mg(5) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Mg(2), one Al(2), two equivalent Al(1), and two equivalent Al(3) atoms. Co(1) is bonded in a 10-coordinate geometry to one Mg(3), three equivalent Mg(4), and six equivalent Al(3) atoms. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded in a 10-coordinate geometry to one Mg(4), two equivalent Mg(1), four equivalent Mg(5), one Al(2), and two equivalent Al(3) atoms. In the second Al site, Al(2) is bonded in a 11-coordinate geometry to one Mg(2), one Mg(3), two equivalent Mg(1), two equivalent Mg(4), two equivalent Mg(5), one Al(1), and two equivalent Al(2) atoms. In the third Al site, Al(3) is bonded in a 11-coordinate geometry to one Mg(1), one Mg(3), one Mg(4), two equivalent Mg(2), two equivalent Mg(5), one Co(1), one Al(1), and two equivalent Al(3) atoms.
Mg16CoAl12 crystallizes in the trigonal R3m space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 10-coordinate geometry to one Mg(2), one Mg(3), two equivalent Mg(5), two equivalent Al(1), two equivalent Al(2), and two equivalent Al(3) atoms. The Mg(1)-Mg(2) bond length is 2.98 Å. The Mg(1)-Mg(3) bond length is 3.13 Å. Both Mg(1)-Mg(5) bond lengths are 3.03 Å. Both Mg(1)-Al(1) bond lengths are 3.17 Å. Both Mg(1)-Al(2) bond lengths are 3.04 Å. Both Mg(1)-Al(3) bond lengths are 3.15 Å. In the second Mg site, Mg(2) is bonded to one Mg(1), two equivalent Mg(4), four equivalent Mg(5), one Al(2), and four equivalent Al(3) atoms to form a mixture of distorted corner and edge-sharing MgMg7Al5 cuboctahedra. Both Mg(2)-Mg(4) bond lengths are 3.05 Å. There are two shorter (3.07 Å) and two longer (3.09 Å) Mg(2)-Mg(5) bond lengths. The Mg(2)-Al(2) bond length is 3.00 Å. There are two shorter (3.03 Å) and two longer (3.11 Å) Mg(2)-Al(3) bond lengths. In the third Mg site, Mg(3) is bonded in a distorted single-bond geometry to three equivalent Mg(1), one Co(1), three equivalent Al(2), and six equivalent Al(3) atoms. The Mg(3)-Co(1) bond length is 2.54 Å. All Mg(3)-Al(2) bond lengths are 3.02 Å. All Mg(3)-Al(3) bond lengths are 3.18 Å. In the fourth Mg site, Mg(4) is bonded in a 6-coordinate geometry to two equivalent Mg(2), one Co(1), one Al(1), two equivalent Al(2), and two equivalent Al(3) atoms. The Mg(4)-Co(1) bond length is 3.02 Å. The Mg(4)-Al(1) bond length is 3.15 Å. Both Mg(4)-Al(2) bond lengths are 2.91 Å. Both Mg(4)-Al(3) bond lengths are 3.04 Å. In the fifth Mg site, Mg(5) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Mg(2), one Al(2), two equivalent Al(1), and two equivalent Al(3) atoms. The Mg(5)-Al(2) bond length is 3.09 Å. There is one shorter (2.92 Å) and one longer (3.10 Å) Mg(5)-Al(1) bond length. There is one shorter (2.90 Å) and one longer (3.05 Å) Mg(5)-Al(3) bond length. Co(1) is bonded in a 10-coordinate geometry to one Mg(3), three equivalent Mg(4), and six equivalent Al(3) atoms. All Co(1)-Al(3) bond lengths are 2.72 Å. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded in a 10-coordinate geometry to one Mg(4), two equivalent Mg(1), four equivalent Mg(5), one Al(2), and two equivalent Al(3) atoms. The Al(1)-Al(2) bond length is 2.68 Å. Both Al(1)-Al(3) bond lengths are 2.80 Å. In the second Al site, Al(2) is bonded in a 11-coordinate geometry to one Mg(2), one Mg(3), two equivalent Mg(1), two equivalent Mg(4), two equivalent Mg(5), one Al(1), and two equivalent Al(2) atoms. Both Al(2)-Al(2) bond lengths are 2.78 Å. In the third Al site, Al(3) is bonded in a 11-coordinate geometry to one Mg(1), one Mg(3), one Mg(4), two equivalent Mg(2), two equivalent Mg(5), one Co(1), one Al(1), and two equivalent Al(3) atoms. There is one shorter (2.60 Å) and one longer (2.63 Å) Al(3)-Al(3) bond length.