MgSi2 crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(3), two equivalent Si(1), two equivalent Si(2), two equivalent Si(5), and two equivalent Si(6) atoms. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to two equivalent Si(1), two equivalent Si(4), and two equivalent Si(6) atoms. In the third Mg site, Mg(3) is bonded in a 5-coordinate geometry to one Si(6), one Si(7), one Si(8), and two equivalent Si(4) atoms. In the fourth Mg site, Mg(4) is bonded in a 9-coordinate geometry to one Si(2), one Si(4), one Si(5), two equivalent Si(3), two equivalent Si(7), and two equivalent Si(8) atoms. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), one Si(2), and two equivalent Si(6) atoms. In the second Si site, Si(2) is bonded to one Mg(4), two equivalent Mg(1), one Si(1), one Si(3), and two equivalent Si(5) atoms to form distorted corner-sharing SiMg3Si4 pentagonal bipyramids. In the third Si site, Si(3) is bonded in a 7-coordinate geometry to one Mg(1), two equivalent Mg(4), one Si(2), one Si(5), and two equivalent Si(8) atoms. In the fourth Si site, Si(4) is bonded in a 7-coordinate geometry to one Mg(4), two equivalent Mg(2), two equivalent Mg(3), and two equivalent Si(7) atoms. In the fifth Si site, Si(5) is bonded in a 6-coordinate geometry to one Mg(4), two equivalent Mg(1), one Si(3), and two equivalent Si(2) atoms. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to one Mg(3), two equivalent Mg(1), two equivalent Mg(2), and two equivalent Si(1) atoms. In the seventh Si site, Si(7) is bonded in a 6-coordinate geometry to one Mg(3), two equivalent Mg(4), one Si(8), and two equivalent Si(4) atoms. In the eighth Si site, Si(8) is bonded in a 6-coordinate geometry to one Mg(3), two equivalent Mg(4), one Si(7), and two equivalent Si(3) atoms.
MgSi2 crystallizes in the triclinic P1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(3), two equivalent Si(1), two equivalent Si(2), two equivalent Si(5), and two equivalent Si(6) atoms. The Mg(1)-Si(3) bond length is 3.23 Å. There is one shorter (2.79 Å) and one longer (2.87 Å) Mg(1)-Si(1) bond length. There is one shorter (2.98 Å) and one longer (3.15 Å) Mg(1)-Si(2) bond length. There is one shorter (2.83 Å) and one longer (2.84 Å) Mg(1)-Si(5) bond length. There is one shorter (2.84 Å) and one longer (3.10 Å) Mg(1)-Si(6) bond length. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to two equivalent Si(1), two equivalent Si(4), and two equivalent Si(6) atoms. There is one shorter (2.83 Å) and one longer (2.95 Å) Mg(2)-Si(1) bond length. There is one shorter (2.79 Å) and one longer (2.82 Å) Mg(2)-Si(4) bond length. There is one shorter (2.70 Å) and one longer (2.83 Å) Mg(2)-Si(6) bond length. In the third Mg site, Mg(3) is bonded in a 5-coordinate geometry to one Si(6), one Si(7), one Si(8), and two equivalent Si(4) atoms. The Mg(3)-Si(6) bond length is 2.78 Å. The Mg(3)-Si(7) bond length is 2.72 Å. The Mg(3)-Si(8) bond length is 2.97 Å. There is one shorter (2.76 Å) and one longer (2.85 Å) Mg(3)-Si(4) bond length. In the fourth Mg site, Mg(4) is bonded in a 9-coordinate geometry to one Si(2), one Si(4), one Si(5), two equivalent Si(3), two equivalent Si(7), and two equivalent Si(8) atoms. The Mg(4)-Si(2) bond length is 3.10 Å. The Mg(4)-Si(4) bond length is 2.90 Å. The Mg(4)-Si(5) bond length is 2.90 Å. There is one shorter (2.99 Å) and one longer (3.14 Å) Mg(4)-Si(3) bond length. There is one shorter (2.83 Å) and one longer (2.92 Å) Mg(4)-Si(7) bond length. There is one shorter (2.83 Å) and one longer (2.92 Å) Mg(4)-Si(8) bond length. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), one Si(2), and two equivalent Si(6) atoms. The Si(1)-Si(2) bond length is 2.42 Å. There is one shorter (2.37 Å) and one longer (2.39 Å) Si(1)-Si(6) bond length. In the second Si site, Si(2) is bonded to one Mg(4), two equivalent Mg(1), one Si(1), one Si(3), and two equivalent Si(5) atoms to form distorted corner-sharing SiMg3Si4 pentagonal bipyramids. The Si(2)-Si(3) bond length is 2.44 Å. There is one shorter (2.35 Å) and one longer (2.41 Å) Si(2)-Si(5) bond length. In the third Si site, Si(3) is bonded in a 7-coordinate geometry to one Mg(1), two equivalent Mg(4), one Si(2), one Si(5), and two equivalent Si(8) atoms. The Si(3)-Si(5) bond length is 2.44 Å. There is one shorter (2.37 Å) and one longer (2.39 Å) Si(3)-Si(8) bond length. In the fourth Si site, Si(4) is bonded in a 7-coordinate geometry to one Mg(4), two equivalent Mg(2), two equivalent Mg(3), and two equivalent Si(7) atoms. Both Si(4)-Si(7) bond lengths are 2.35 Å. In the fifth Si site, Si(5) is bonded in a 6-coordinate geometry to one Mg(4), two equivalent Mg(1), one Si(3), and two equivalent Si(2) atoms. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to one Mg(3), two equivalent Mg(1), two equivalent Mg(2), and two equivalent Si(1) atoms. In the seventh Si site, Si(7) is bonded in a 6-coordinate geometry to one Mg(3), two equivalent Mg(4), one Si(8), and two equivalent Si(4) atoms. The Si(7)-Si(8) bond length is 2.38 Å. In the eighth Si site, Si(8) is bonded in a 6-coordinate geometry to one Mg(3), two equivalent Mg(4), one Si(7), and two equivalent Si(3) atoms.