Mg2Si crystallizes in the triclinic P-1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 3-coordinate geometry to one Si(1) and two equivalent Si(2) atoms. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to two equivalent Si(1) and two equivalent Si(2) atoms. In the third Mg site, Mg(3) is bonded in a 4-coordinate geometry to one Si(2) and three equivalent Si(1) atoms. In the fourth Mg site, Mg(4) is bonded in a 3-coordinate geometry to one Si(2) and two equivalent Si(1) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Mg(2), two equivalent Mg(4), and three equivalent Mg(3) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to one Mg(3), one Mg(4), two equivalent Mg(1), two equivalent Mg(2), and one Si(2) atom.
Mg2Si crystallizes in the triclinic P-1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 3-coordinate geometry to one Si(1) and two equivalent Si(2) atoms. The Mg(1)-Si(1) bond length is 2.71 Å. There is one shorter (2.78 Å) and one longer (3.02 Å) Mg(1)-Si(2) bond length. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to two equivalent Si(1) and two equivalent Si(2) atoms. There is one shorter (2.82 Å) and one longer (2.85 Å) Mg(2)-Si(1) bond length. There is one shorter (2.85 Å) and one longer (3.01 Å) Mg(2)-Si(2) bond length. In the third Mg site, Mg(3) is bonded in a 4-coordinate geometry to one Si(2) and three equivalent Si(1) atoms. The Mg(3)-Si(2) bond length is 2.90 Å. There are a spread of Mg(3)-Si(1) bond distances ranging from 2.77-2.93 Å. In the fourth Mg site, Mg(4) is bonded in a 3-coordinate geometry to one Si(2) and two equivalent Si(1) atoms. The Mg(4)-Si(2) bond length is 2.65 Å. There is one shorter (2.75 Å) and one longer (2.81 Å) Mg(4)-Si(1) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Mg(2), two equivalent Mg(4), and three equivalent Mg(3) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to one Mg(3), one Mg(4), two equivalent Mg(1), two equivalent Mg(2), and one Si(2) atom. The Si(2)-Si(2) bond length is 2.41 Å.