MgSi2 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Si(1), two equivalent Si(4), and three 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(4) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one Mg(1), two equivalent Mg(2), one Si(3), and two equivalent Si(2) atoms to form distorted edge-sharing SiMg3Si3 pentagonal pyramids. In the second Si site, Si(2) is bonded in a 6-coordinate geometry to three equivalent Mg(1), one Si(4), and two equivalent Si(1) atoms. In the third Si site, Si(3) is bonded in a 6-coordinate geometry to one Mg(2), one Si(1), two equivalent Si(3), and two equivalent Si(4) atoms. In the fourth Si site, Si(4) is bonded in a 8-coordinate geometry to two equivalent Mg(1), three equivalent Mg(2), one Si(2), and two equivalent Si(3) atoms.
MgSi2 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Si(1), two equivalent Si(4), and three equivalent Si(2) atoms. The Mg(1)-Si(1) bond length is 2.90 Å. Both Mg(1)-Si(4) bond lengths are 2.79 Å. There is one shorter (2.66 Å) and two longer (3.18 Å) Mg(1)-Si(2) bond lengths. 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(4) atoms. The Mg(2)-Si(3) bond length is 2.65 Å. Both Mg(2)-Si(1) bond lengths are 2.88 Å. There is one shorter (2.65 Å) and two longer (2.97 Å) Mg(2)-Si(4) bond lengths. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one Mg(1), two equivalent Mg(2), one Si(3), and two equivalent Si(2) atoms to form distorted edge-sharing SiMg3Si3 pentagonal pyramids. The Si(1)-Si(3) bond length is 2.39 Å. Both Si(1)-Si(2) bond lengths are 2.39 Å. In the second Si site, Si(2) is bonded in a 6-coordinate geometry to three equivalent Mg(1), one Si(4), and two equivalent Si(1) atoms. The Si(2)-Si(4) bond length is 2.50 Å. In the third Si site, Si(3) is bonded in a 6-coordinate geometry to one Mg(2), one Si(1), two equivalent Si(3), and two equivalent Si(4) atoms. Both Si(3)-Si(3) bond lengths are 2.52 Å. Both Si(3)-Si(4) bond lengths are 2.52 Å. In the fourth Si site, Si(4) is bonded in a 8-coordinate geometry to two equivalent Mg(1), three equivalent Mg(2), one Si(2), and two equivalent Si(3) atoms.