Mg5Si6 crystallizes in the triclinic P-1 space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a square co-planar geometry to two equivalent Si(1) and two equivalent Si(2) atoms. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Si(3), two equivalent Si(1), and three equivalent Si(2) atoms. In the third Mg site, Mg(3) is bonded in a 8-coordinate geometry to 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 9-coordinate geometry to one 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 9-coordinate geometry to one Mg(1), 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 7-coordinate geometry to one Mg(2), two equivalent Mg(3), one Si(1), and three equivalent Si(2) atoms.
Mg5Si6 crystallizes in the triclinic P-1 space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a square co-planar geometry to two equivalent Si(1) and two equivalent Si(2) atoms. Both Mg(1)-Si(1) bond lengths are 2.68 Å. Both Mg(1)-Si(2) bond lengths are 2.85 Å. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Si(3), two equivalent Si(1), and three equivalent Si(2) atoms. The Mg(2)-Si(3) bond length is 2.94 Å. Both Mg(2)-Si(1) bond lengths are 2.79 Å. There are a spread of Mg(2)-Si(2) bond distances ranging from 2.93-2.99 Å. In the third Mg site, Mg(3) is bonded in a 8-coordinate geometry to two equivalent Si(2), two equivalent Si(3), and four equivalent Si(1) atoms. There is one shorter (2.96 Å) and one longer (3.00 Å) Mg(3)-Si(2) bond length. There is one shorter (2.96 Å) and one longer (3.00 Å) Mg(3)-Si(3) bond length. There are a spread of Mg(3)-Si(1) bond distances ranging from 2.84-3.07 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one 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 2.37 Å. The Si(1)-Si(3) bond length is 2.36 Å. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(3), three equivalent Mg(2), and three equivalent Si(3) atoms. All Si(2)-Si(3) bond lengths are 2.47 Å. In the third Si site, Si(3) is bonded in a 7-coordinate geometry to one Mg(2), two equivalent Mg(3), one Si(1), and three equivalent Si(2) atoms.