MgSi2 crystallizes in the monoclinic C2/m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 7-coordinate geometry to one Si(1), two equivalent Si(2), two equivalent Si(3), and two equivalent Si(4) atoms. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to two equivalent Si(2) and four equivalent Si(4) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 5-coordinate geometry to one Mg(1), one Si(1), one Si(2), and two equivalent Si(3) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), one Si(1), and two equivalent Si(4) atoms. In the third Si site, Si(3) is bonded in a 5-coordinate geometry to two equivalent Mg(1), one Si(3), and two equivalent Si(1) atoms. In the fourth Si site, Si(4) is bonded in a 8-coordinate geometry to two equivalent Mg(1), four equivalent Mg(2), and two equivalent Si(2) atoms.
MgSi2 crystallizes in the monoclinic C2/m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 7-coordinate geometry to one Si(1), two equivalent Si(2), two equivalent Si(3), and two equivalent Si(4) atoms. The Mg(1)-Si(1) bond length is 3.11 Å. There is one shorter (2.72 Å) and one longer (2.89 Å) Mg(1)-Si(2) bond length. Both Mg(1)-Si(3) bond lengths are 2.75 Å. Both Mg(1)-Si(4) bond lengths are 2.89 Å. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to two equivalent Si(2) and four equivalent Si(4) atoms. Both Mg(2)-Si(2) bond lengths are 2.89 Å. There are a spread of Mg(2)-Si(4) bond distances ranging from 2.75-2.89 Å. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 5-coordinate geometry to one Mg(1), one Si(1), one Si(2), and two equivalent Si(3) atoms. The Si(1)-Si(1) bond length is 2.42 Å. The Si(1)-Si(2) bond length is 2.52 Å. Both Si(1)-Si(3) bond lengths are 2.35 Å. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), one Si(1), and two equivalent Si(4) atoms. Both Si(2)-Si(4) bond lengths are 2.40 Å. In the third Si site, Si(3) is bonded in a 5-coordinate geometry to two equivalent Mg(1), one Si(3), and two equivalent Si(1) atoms. The Si(3)-Si(3) bond length is 2.34 Å. In the fourth Si site, Si(4) is bonded in a 8-coordinate geometry to two equivalent Mg(1), four equivalent Mg(2), and two equivalent Si(2) atoms.