Mg3Si4 crystallizes in the monoclinic P2/m 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(2), two equivalent Si(1), two equivalent Si(4), and four equivalent Si(3) atoms. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to two equivalent Si(1), two equivalent Si(2), and two equivalent Si(4) atoms. In the third Mg site, Mg(3) is bonded in a distorted square co-planar geometry to two equivalent Si(4) and four equivalent Si(2) atoms. In the fourth Mg site, Mg(4) is bonded in a 8-coordinate geometry to four equivalent Si(3) and four equivalent Si(4) atoms. There are four 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(1), and two equivalent Si(2) atoms. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Mg(2), two equivalent Mg(3), one Si(2), and two equivalent Si(1) atoms. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to two equivalent Mg(4), four equivalent Mg(1), one Si(3), and two equivalent Si(4) atoms. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(3), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), and two equivalent Si(3) atoms.
Mg3Si4 crystallizes in the monoclinic P2/m 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(2), two equivalent Si(1), two equivalent Si(4), and four equivalent Si(3) atoms. The Mg(1)-Si(2) bond length is 2.80 Å. Both Mg(1)-Si(1) bond lengths are 3.06 Å. Both Mg(1)-Si(4) bond lengths are 2.89 Å. There are two shorter (2.85 Å) and two longer (3.13 Å) Mg(1)-Si(3) bond lengths. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to two equivalent Si(1), two equivalent Si(2), and two equivalent Si(4) atoms. Both Mg(2)-Si(1) bond lengths are 2.98 Å. There is one shorter (2.75 Å) and one longer (3.22 Å) Mg(2)-Si(2) bond length. Both Mg(2)-Si(4) bond lengths are 2.73 Å. In the third Mg site, Mg(3) is bonded in a distorted square co-planar geometry to two equivalent Si(4) and four equivalent Si(2) atoms. Both Mg(3)-Si(4) bond lengths are 3.21 Å. All Mg(3)-Si(2) bond lengths are 2.93 Å. In the fourth Mg site, Mg(4) is bonded in a 8-coordinate geometry to four equivalent Si(3) and four equivalent Si(4) atoms. All Mg(4)-Si(3) bond lengths are 2.78 Å. All Mg(4)-Si(4) bond lengths are 2.82 Å. There are four 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(1), and two equivalent Si(2) atoms. The Si(1)-Si(1) bond length is 2.67 Å. Both Si(1)-Si(2) bond lengths are 2.47 Å. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Mg(2), two equivalent Mg(3), one Si(2), and two equivalent Si(1) atoms. The Si(2)-Si(2) bond length is 2.41 Å. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to two equivalent Mg(4), four equivalent Mg(1), one Si(3), and two equivalent Si(4) atoms. The Si(3)-Si(3) bond length is 2.79 Å. There is one shorter (2.54 Å) and one longer (2.61 Å) Si(3)-Si(4) bond length. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(3), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), and two equivalent Si(3) atoms.