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 12-coordinate geometry to two equivalent Mg(2), one Si(4), three equivalent Si(1), three equivalent Si(2), and three equivalent Si(3) atoms. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to two equivalent Mg(1), three equivalent Si(2), and five equivalent Si(4) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to three equivalent Mg(1), one Si(1), one Si(2), and four equivalent Si(3) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to three equivalent Mg(1), three equivalent Mg(2), one Si(1), and two equivalent Si(4) atoms. In the third Si site, Si(3) is bonded in a 10-coordinate geometry to three equivalent Mg(1), three equivalent Si(3), and four equivalent Si(1) atoms. In the fourth Si site, Si(4) is bonded in a 10-coordinate geometry to one Mg(1), five equivalent Mg(2), two equivalent Si(2), and two equivalent Si(4) 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 12-coordinate geometry to two equivalent Mg(2), one Si(4), three equivalent Si(1), three equivalent Si(2), and three equivalent Si(3) atoms. Both Mg(1)-Mg(2) bond lengths are 3.10 Å. The Mg(1)-Si(4) bond length is 3.10 Å. There is one shorter (2.81 Å) and two longer (3.02 Å) Mg(1)-Si(1) bond lengths. There are two shorter (2.91 Å) and one longer (3.16 Å) Mg(1)-Si(2) bond length. There is one shorter (2.82 Å) and two longer (2.93 Å) Mg(1)-Si(3) bond lengths. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to two equivalent Mg(1), three equivalent Si(2), and five equivalent Si(4) atoms. There are two shorter (2.85 Å) and one longer (2.98 Å) Mg(2)-Si(2) bond length. There are a spread of Mg(2)-Si(4) bond distances ranging from 2.70-3.28 Å. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to three equivalent Mg(1), one Si(1), one Si(2), and four equivalent Si(3) atoms. The Si(1)-Si(1) bond length is 2.62 Å. The Si(1)-Si(2) bond length is 2.43 Å. There are two shorter (2.57 Å) and two longer (2.69 Å) Si(1)-Si(3) bond lengths. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to three equivalent Mg(1), three equivalent Mg(2), one Si(1), and two equivalent Si(4) atoms. Both Si(2)-Si(4) bond lengths are 2.47 Å. In the third Si site, Si(3) is bonded in a 10-coordinate geometry to three equivalent Mg(1), three equivalent Si(3), and four equivalent Si(1) atoms. There are two shorter (2.70 Å) and one longer (2.82 Å) Si(3)-Si(3) bond length. In the fourth Si site, Si(4) is bonded in a 10-coordinate geometry to one Mg(1), five equivalent Mg(2), two equivalent Si(2), and two equivalent Si(4) atoms. Both Si(4)-Si(4) bond lengths are 2.86 Å.