Mg2(AlSi2)3 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded in a 12-coordinate geometry to two equivalent Mg(1), one Al(1), one Al(2), two equivalent Si(2), three equivalent Si(1), and three equivalent Si(3) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded in a 11-coordinate geometry to one Mg(1), one Al(1), one Al(2), two equivalent Si(1), two equivalent Si(3), and four equivalent Si(2) atoms. In the second Al site, Al(2) is bonded in a 6-coordinate geometry to two equivalent Mg(1), two equivalent Al(1), and four equivalent Si(2) atoms. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to three equivalent Mg(1), two equivalent Al(1), one Si(2), and three equivalent Si(3) atoms. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to two equivalent Mg(1), two equivalent Al(2), four equivalent Al(1), one Si(1), and one Si(2) atom. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to three equivalent Mg(1), two equivalent Al(1), and three equivalent Si(1) atoms.
Mg2(AlSi2)3 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded in a 12-coordinate geometry to two equivalent Mg(1), one Al(1), one Al(2), two equivalent Si(2), three equivalent Si(1), and three equivalent Si(3) atoms. Both Mg(1)-Mg(1) bond lengths are 2.98 Å. The Mg(1)-Al(1) bond length is 3.09 Å. The Mg(1)-Al(2) bond length is 2.73 Å. Both Mg(1)-Si(2) bond lengths are 2.92 Å. There are two shorter (2.77 Å) and one longer (2.94 Å) Mg(1)-Si(1) bond length. There are two shorter (2.90 Å) and one longer (2.95 Å) Mg(1)-Si(3) bond length. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded in a 11-coordinate geometry to one Mg(1), one Al(1), one Al(2), two equivalent Si(1), two equivalent Si(3), and four equivalent Si(2) atoms. The Al(1)-Al(1) bond length is 2.91 Å. The Al(1)-Al(2) bond length is 2.90 Å. Both Al(1)-Si(1) bond lengths are 2.71 Å. Both Al(1)-Si(3) bond lengths are 2.68 Å. There are two shorter (2.70 Å) and two longer (2.84 Å) Al(1)-Si(2) bond lengths. In the second Al site, Al(2) is bonded in a 6-coordinate geometry to two equivalent Mg(1), two equivalent Al(1), and four equivalent Si(2) atoms. All Al(2)-Si(2) bond lengths are 2.82 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to three equivalent Mg(1), two equivalent Al(1), one Si(2), and three equivalent Si(3) atoms. The Si(1)-Si(2) bond length is 2.68 Å. There is one shorter (2.49 Å) and two longer (2.70 Å) Si(1)-Si(3) bond lengths. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to two equivalent Mg(1), two equivalent Al(2), four equivalent Al(1), one Si(1), and one Si(2) atom. The Si(2)-Si(2) bond length is 2.73 Å. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to three equivalent Mg(1), two equivalent Al(1), and three equivalent Si(1) atoms.