Mg16Al12Si crystallizes in the trigonal R3m space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 12-coordinate geometry to one Mg(3), two equivalent Mg(4), four equivalent Mg(5), one Al(1), and four equivalent Al(3) atoms. In the second Mg site, Mg(2) is bonded in a distorted single-bond geometry to three equivalent Mg(3), three equivalent Al(1), three equivalent Al(2), six equivalent Al(3), and one Si(1) atom. In the third Mg site, Mg(3) is bonded in a 10-coordinate geometry to one Mg(1), one Mg(2), two equivalent Mg(5), two equivalent Al(1), two equivalent Al(2), and two equivalent Al(3) atoms. In the fourth Mg site, Mg(4) is bonded in a 12-coordinate geometry to two equivalent Mg(1), four equivalent Mg(5), one Al(2), two equivalent Al(1), two equivalent Al(3), and one Si(1) atom. In the fifth Mg site, Mg(5) is bonded in a 5-coordinate geometry to one Mg(3), two equivalent Mg(1), two equivalent Mg(4), one Al(1), two equivalent Al(2), and two equivalent Al(3) atoms. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded in a distorted q6 geometry to one Mg(1), one Mg(2), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(5), one Al(2), and two equivalent Al(1) atoms. In the second Al site, Al(2) is bonded in a 11-coordinate geometry to one Mg(2), one Mg(4), two equivalent Mg(3), four equivalent Mg(5), one Al(1), and two equivalent Al(3) atoms. In the third Al site, Al(3) is bonded in a 11-coordinate geometry to one Mg(2), one Mg(3), one Mg(4), two equivalent Mg(1), two equivalent Mg(5), one Al(2), two equivalent Al(3), and one Si(1) atom. Si(1) is bonded in a 10-coordinate geometry to one Mg(2), three equivalent Mg(4), and six equivalent Al(3) atoms.
Mg16Al12Si crystallizes in the trigonal R3m space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 12-coordinate geometry to one Mg(3), two equivalent Mg(4), four equivalent Mg(5), one Al(1), and four equivalent Al(3) atoms. The Mg(1)-Mg(3) bond length is 3.01 Å. Both Mg(1)-Mg(4) bond lengths are 3.09 Å. There are two shorter (3.09 Å) and two longer (3.15 Å) Mg(1)-Mg(5) bond lengths. The Mg(1)-Al(1) bond length is 2.95 Å. There are two shorter (3.00 Å) and two longer (3.13 Å) Mg(1)-Al(3) bond lengths. In the second Mg site, Mg(2) is bonded in a distorted single-bond geometry to three equivalent Mg(3), three equivalent Al(1), three equivalent Al(2), six equivalent Al(3), and one Si(1) atom. All Mg(2)-Mg(3) bond lengths are 3.14 Å. All Mg(2)-Al(1) bond lengths are 3.11 Å. All Mg(2)-Al(2) bond lengths are 3.26 Å. All Mg(2)-Al(3) bond lengths are 3.23 Å. The Mg(2)-Si(1) bond length is 2.77 Å. In the third Mg site, Mg(3) is bonded in a 10-coordinate geometry to one Mg(1), one Mg(2), two equivalent Mg(5), two equivalent Al(1), two equivalent Al(2), and two equivalent Al(3) atoms. Both Mg(3)-Mg(5) bond lengths are 3.04 Å. Both Mg(3)-Al(1) bond lengths are 3.07 Å. Both Mg(3)-Al(2) bond lengths are 3.14 Å. Both Mg(3)-Al(3) bond lengths are 3.11 Å. In the fourth Mg site, Mg(4) is bonded in a 12-coordinate geometry to two equivalent Mg(1), four equivalent Mg(5), one Al(2), two equivalent Al(1), two equivalent Al(3), and one Si(1) atom. There are two shorter (3.19 Å) and two longer (3.29 Å) Mg(4)-Mg(5) bond lengths. The Mg(4)-Al(2) bond length is 3.04 Å. Both Mg(4)-Al(1) bond lengths are 2.95 Å. Both Mg(4)-Al(3) bond lengths are 3.10 Å. The Mg(4)-Si(1) bond length is 3.04 Å. In the fifth Mg site, Mg(5) is bonded in a 5-coordinate geometry to one Mg(3), two equivalent Mg(1), two equivalent Mg(4), one Al(1), two equivalent Al(2), and two equivalent Al(3) atoms. The Mg(5)-Al(1) bond length is 3.10 Å. There is one shorter (2.95 Å) and one longer (3.12 Å) Mg(5)-Al(2) bond length. There is one shorter (2.88 Å) and one longer (2.99 Å) Mg(5)-Al(3) bond length. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded in a distorted q6 geometry to one Mg(1), one Mg(2), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(5), one Al(2), and two equivalent Al(1) atoms. The Al(1)-Al(2) bond length is 2.69 Å. Both Al(1)-Al(1) bond lengths are 2.79 Å. In the second Al site, Al(2) is bonded in a 11-coordinate geometry to one Mg(2), one Mg(4), two equivalent Mg(3), four equivalent Mg(5), one Al(1), and two equivalent Al(3) atoms. Both Al(2)-Al(3) bond lengths are 2.77 Å. In the third Al site, Al(3) is bonded in a 11-coordinate geometry to one Mg(2), one Mg(3), one Mg(4), two equivalent Mg(1), two equivalent Mg(5), one Al(2), two equivalent Al(3), and one Si(1) atom. There is one shorter (2.71 Å) and one longer (2.73 Å) Al(3)-Al(3) bond length. The Al(3)-Si(1) bond length is 2.91 Å. Si(1) is bonded in a 10-coordinate geometry to one Mg(2), three equivalent Mg(4), and six equivalent Al(3) atoms.