Mg2Si crystallizes in the triclinic P1 space group. There are eight inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 2-coordinate geometry to one Si(1), one Si(2), and one Si(3) atom. In the second Mg site, Mg(2) is bonded in a 2-coordinate geometry to one Si(1), one Si(3), and one Si(4) atom. In the third Mg site, Mg(3) is bonded in a 2-coordinate geometry to one Si(1), one Si(3), and one Si(4) atom. In the fourth Mg site, Mg(4) is bonded in a 5-coordinate geometry to one Si(1), one Si(3), one Si(4), and two equivalent Si(2) atoms. In the fifth Mg site, Mg(5) is bonded in a 3-coordinate geometry to one Si(1), one Si(2), one Si(3), and two equivalent Si(4) atoms. In the sixth Mg site, Mg(6) is bonded in a distorted water-like geometry to one Si(3) and one Si(4) atom. In the seventh Mg site, Mg(7) is bonded in a 3-coordinate geometry to one Si(1), one Si(2), and one Si(4) atom. In the eighth Mg site, Mg(8) is bonded in a 4-coordinate geometry to one Si(1), one Si(2), one Si(4), and two equivalent Si(3) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(7), one Mg(8), one Si(2), and one Si(3) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(5), one Mg(7), one Mg(8), two equivalent Mg(4), one Si(1), and one Si(4) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), two equivalent Mg(8), and one Si(1) atom. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(3), one Mg(4), one Mg(6), one Mg(7), one Mg(8), two equivalent Mg(5), and one Si(2) atom.
Mg2Si crystallizes in the triclinic P1 space group. There are eight inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 2-coordinate geometry to one Si(1), one Si(2), and one Si(3) atom. The Mg(1)-Si(1) bond length is 3.20 Å. The Mg(1)-Si(2) bond length is 2.77 Å. The Mg(1)-Si(3) bond length is 2.89 Å. In the second Mg site, Mg(2) is bonded in a 2-coordinate geometry to one Si(1), one Si(3), and one Si(4) atom. The Mg(2)-Si(1) bond length is 3.08 Å. The Mg(2)-Si(3) bond length is 2.84 Å. The Mg(2)-Si(4) bond length is 2.74 Å. In the third Mg site, Mg(3) is bonded in a 2-coordinate geometry to one Si(1), one Si(3), and one Si(4) atom. The Mg(3)-Si(1) bond length is 2.73 Å. The Mg(3)-Si(3) bond length is 3.26 Å. The Mg(3)-Si(4) bond length is 3.00 Å. In the fourth Mg site, Mg(4) is bonded in a 5-coordinate geometry to one Si(1), one Si(3), one Si(4), and two equivalent Si(2) atoms. The Mg(4)-Si(1) bond length is 2.81 Å. The Mg(4)-Si(3) bond length is 2.79 Å. The Mg(4)-Si(4) bond length is 2.89 Å. There is one shorter (2.91 Å) and one longer (3.05 Å) Mg(4)-Si(2) bond length. In the fifth Mg site, Mg(5) is bonded in a 3-coordinate geometry to one Si(1), one Si(2), one Si(3), and two equivalent Si(4) atoms. The Mg(5)-Si(1) bond length is 2.96 Å. The Mg(5)-Si(2) bond length is 2.77 Å. The Mg(5)-Si(3) bond length is 2.83 Å. There is one shorter (2.74 Å) and one longer (3.14 Å) Mg(5)-Si(4) bond length. In the sixth Mg site, Mg(6) is bonded in a distorted water-like geometry to one Si(3) and one Si(4) atom. The Mg(6)-Si(3) bond length is 2.82 Å. The Mg(6)-Si(4) bond length is 2.79 Å. In the seventh Mg site, Mg(7) is bonded in a 3-coordinate geometry to one Si(1), one Si(2), and one Si(4) atom. The Mg(7)-Si(1) bond length is 2.74 Å. The Mg(7)-Si(2) bond length is 2.94 Å. The Mg(7)-Si(4) bond length is 2.71 Å. In the eighth Mg site, Mg(8) is bonded in a 4-coordinate geometry to one Si(1), one Si(2), one Si(4), and two equivalent Si(3) atoms. The Mg(8)-Si(1) bond length is 2.91 Å. The Mg(8)-Si(2) bond length is 2.82 Å. The Mg(8)-Si(4) bond length is 2.81 Å. There is one shorter (2.74 Å) and one longer (3.16 Å) Mg(8)-Si(3) bond length. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(7), one Mg(8), one Si(2), and one Si(3) atom. The Si(1)-Si(2) bond length is 2.50 Å. The Si(1)-Si(3) bond length is 2.43 Å. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(5), one Mg(7), one Mg(8), two equivalent Mg(4), one Si(1), and one Si(4) atom. The Si(2)-Si(4) bond length is 2.42 Å. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), two equivalent Mg(8), and one Si(1) atom. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(3), one Mg(4), one Mg(6), one Mg(7), one Mg(8), two equivalent Mg(5), and one Si(2) atom.