Mg3Si4 crystallizes in the monoclinic Pm space group. There are six inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(2), two equivalent Si(3), and two equivalent Si(6) atoms. In the second Mg site, Mg(2) is bonded in a 12-coordinate geometry to one Mg(3), two equivalent Mg(4), one Si(3), one Si(6), one Si(7), two equivalent Si(4), two equivalent Si(5), and two equivalent Si(8) atoms. In the third Mg site, Mg(3) is bonded in a 9-coordinate geometry to one Mg(2), one Si(7), two equivalent Si(1), two equivalent Si(2), two equivalent Si(4), and two equivalent Si(5) atoms. In the fourth Mg site, Mg(4) is bonded in a 1-coordinate geometry to two equivalent Mg(2), one Si(4), one Si(5), one Si(8), two equivalent Si(3), two equivalent Si(6), and two equivalent Si(7) atoms. In the fifth Mg site, Mg(5) is bonded in a distorted rectangular see-saw-like geometry to one Si(6), one Si(7), two equivalent Si(1), and two equivalent Si(5) atoms. In the sixth Mg site, Mg(6) is bonded in a 8-coordinate geometry to one Si(3), one Si(6), two equivalent Si(1), two equivalent Si(2), and two equivalent Si(8) atoms. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to two equivalent Mg(3), two equivalent Mg(5), two equivalent Mg(6), one Si(2), and one Si(5) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Mg(3), two equivalent Mg(6), one Si(1), and two equivalent Si(7) atoms. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(6), two equivalent Mg(1), two equivalent Mg(4), one Si(6), and two equivalent Si(4) atoms. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(4), two equivalent Mg(2), two equivalent Mg(3), one Si(5), one Si(8), and two equivalent Si(3) atoms. In the fifth Si site, Si(5) is bonded in a 11-coordinate geometry to one Mg(4), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(5), one Si(1), one Si(4), and two equivalent Si(7) atoms. In the sixth Si site, Si(6) is bonded in a 10-coordinate geometry to one Mg(2), one Mg(5), one Mg(6), two equivalent Mg(1), two equivalent Mg(4), one Si(3), and two equivalent Si(8) atoms. In the seventh Si site, Si(7) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(3), one Mg(5), two equivalent Mg(4), two equivalent Si(2), and two equivalent Si(5) atoms. In the eighth Si site, Si(8) is bonded in a 8-coordinate geometry to one Mg(4), two equivalent Mg(2), two equivalent Mg(6), one Si(4), and two equivalent Si(6) atoms.
Mg3Si4 crystallizes in the monoclinic Pm space group. There are six inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(2), two equivalent Si(3), and two equivalent Si(6) atoms. The Mg(1)-Si(2) bond length is 2.87 Å. Both Mg(1)-Si(3) bond lengths are 2.73 Å. Both Mg(1)-Si(6) bond lengths are 2.93 Å. In the second Mg site, Mg(2) is bonded in a 12-coordinate geometry to one Mg(3), two equivalent Mg(4), one Si(3), one Si(6), one Si(7), two equivalent Si(4), two equivalent Si(5), and two equivalent Si(8) atoms. The Mg(2)-Mg(3) bond length is 3.06 Å. Both Mg(2)-Mg(4) bond lengths are 3.01 Å. The Mg(2)-Si(3) bond length is 3.07 Å. The Mg(2)-Si(6) bond length is 2.70 Å. The Mg(2)-Si(7) bond length is 2.76 Å. Both Mg(2)-Si(4) bond lengths are 2.71 Å. Both Mg(2)-Si(5) bond lengths are 2.75 Å. Both Mg(2)-Si(8) bond lengths are 2.85 Å. In the third Mg site, Mg(3) is bonded in a 9-coordinate geometry to one Mg(2), one Si(7), two equivalent Si(1), two equivalent Si(2), two equivalent Si(4), and two equivalent Si(5) atoms. The Mg(3)-Si(7) bond length is 2.71 Å. Both Mg(3)-Si(1) bond lengths are 2.79 Å. Both Mg(3)-Si(2) bond lengths are 3.05 Å. Both Mg(3)-Si(4) bond lengths are 2.97 Å. Both Mg(3)-Si(5) bond lengths are 2.90 Å. In the fourth Mg site, Mg(4) is bonded in a 1-coordinate geometry to two equivalent Mg(2), one Si(4), one Si(5), one Si(8), two equivalent Si(3), two equivalent Si(6), and two equivalent Si(7) atoms. The Mg(4)-Si(4) bond length is 2.68 Å. The Mg(4)-Si(5) bond length is 3.15 Å. The Mg(4)-Si(8) bond length is 3.10 Å. Both Mg(4)-Si(3) bond lengths are 3.04 Å. Both Mg(4)-Si(6) bond lengths are 3.01 Å. Both Mg(4)-Si(7) bond lengths are 3.04 Å. In the fifth Mg site, Mg(5) is bonded in a distorted rectangular see-saw-like geometry to one Si(6), one Si(7), two equivalent Si(1), and two equivalent Si(5) atoms. The Mg(5)-Si(6) bond length is 2.88 Å. The Mg(5)-Si(7) bond length is 2.68 Å. Both Mg(5)-Si(1) bond lengths are 2.71 Å. Both Mg(5)-Si(5) bond lengths are 3.16 Å. In the sixth Mg site, Mg(6) is bonded in a 8-coordinate geometry to one Si(3), one Si(6), two equivalent Si(1), two equivalent Si(2), and two equivalent Si(8) atoms. The Mg(6)-Si(3) bond length is 2.98 Å. The Mg(6)-Si(6) bond length is 3.08 Å. Both Mg(6)-Si(1) bond lengths are 2.84 Å. Both Mg(6)-Si(2) bond lengths are 3.08 Å. Both Mg(6)-Si(8) bond lengths are 2.88 Å. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to two equivalent Mg(3), two equivalent Mg(5), two equivalent Mg(6), one Si(2), and one Si(5) atom. The Si(1)-Si(2) bond length is 2.49 Å. The Si(1)-Si(5) bond length is 2.41 Å. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(1), two equivalent Mg(3), two equivalent Mg(6), one Si(1), and two equivalent Si(7) atoms. Both Si(2)-Si(7) bond lengths are 2.55 Å. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(6), two equivalent Mg(1), two equivalent Mg(4), one Si(6), and two equivalent Si(4) atoms. The Si(3)-Si(6) bond length is 2.60 Å. Both Si(3)-Si(4) bond lengths are 2.54 Å. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(4), two equivalent Mg(2), two equivalent Mg(3), one Si(5), one Si(8), and two equivalent Si(3) atoms. The Si(4)-Si(5) bond length is 2.59 Å. The Si(4)-Si(8) bond length is 2.51 Å. In the fifth Si site, Si(5) is bonded in a 11-coordinate geometry to one Mg(4), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(5), one Si(1), one Si(4), and two equivalent Si(7) atoms. Both Si(5)-Si(7) bond lengths are 2.80 Å. In the sixth Si site, Si(6) is bonded in a 10-coordinate geometry to one Mg(2), one Mg(5), one Mg(6), two equivalent Mg(1), two equivalent Mg(4), one Si(3), and two equivalent Si(8) atoms. Both Si(6)-Si(8) bond lengths are 2.64 Å. In the seventh Si site, Si(7) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(3), one Mg(5), two equivalent Mg(4), two equivalent Si(2), and two equivalent Si(5) atoms. In the eighth Si site, Si(8) is bonded in a 8-coordinate geometry to one Mg(4), two equivalent Mg(2), two equivalent Mg(6), one Si(4), and two equivalent Si(6) atoms.