Mg5Si6 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 8-coordinate geometry to two equivalent Mg(2), two equivalent Mg(3), and four equivalent Si(1) atoms. In the second Mg site, Mg(2) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Si(1), three equivalent Si(2), and three equivalent Si(3) atoms. In the third Mg site, Mg(3) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Si(2), two equivalent Si(3), and four equivalent Si(1) atoms. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 10-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), four equivalent Mg(3), one Si(1), and one Si(3) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to two equivalent Mg(3), three equivalent Mg(2), and three equivalent Si(3) atoms. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to two equivalent Mg(3), three equivalent Mg(2), one Si(1), and three equivalent Si(2) atoms.
Mg5Si6 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 8-coordinate geometry to two equivalent Mg(2), two equivalent Mg(3), and four equivalent Si(1) atoms. Both Mg(1)-Mg(2) bond lengths are 2.84 Å. Both Mg(1)-Mg(3) bond lengths are 2.89 Å. All Mg(1)-Si(1) bond lengths are 3.00 Å. In the second Mg site, Mg(2) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Si(1), three equivalent Si(2), and three equivalent Si(3) atoms. Both Mg(2)-Si(1) bond lengths are 3.04 Å. There is one shorter (2.84 Å) and two longer (2.85 Å) Mg(2)-Si(2) bond lengths. There are two shorter (2.85 Å) and one longer (2.86 Å) Mg(2)-Si(3) bond length. In the third Mg site, Mg(3) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Si(2), two equivalent Si(3), and four equivalent Si(1) atoms. Both Mg(3)-Si(2) bond lengths are 2.89 Å. Both Mg(3)-Si(3) bond lengths are 2.80 Å. There are two shorter (2.85 Å) and two longer (2.92 Å) Mg(3)-Si(1) bond lengths. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 10-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), four equivalent Mg(3), one Si(1), and one Si(3) atom. The Si(1)-Si(1) bond length is 2.65 Å. The Si(1)-Si(3) bond length is 2.56 Å. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to two equivalent Mg(3), three equivalent Mg(2), and three equivalent Si(3) atoms. There is one shorter (2.52 Å) and two longer (2.55 Å) Si(2)-Si(3) bond lengths. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to two equivalent Mg(3), three equivalent Mg(2), one Si(1), and three equivalent Si(2) atoms.