Mg4Si3 crystallizes in the triclinic P1 space group. There are eight inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(2), one Si(3), one Si(4), one Si(5), and one Si(6) atom. In the second Mg site, Mg(2) is bonded to one Si(1), one Si(3), one Si(4), and one Si(5) atom to form distorted MgSi4 trigonal pyramids that share  a cornercorner with one Mg(3)Si5 tetrahedra, corners with three equivalent Mg(6)Si4 tetrahedra,  an edgeedge with one Mg(7)Si4 tetrahedra, and  an edgeedge with one Mg(3)Si5 tetrahedra. In the third Mg site, Mg(3) is bonded to one Si(1), one Si(2), one Si(3), one Si(5), and one Si(6) atom to form a mixture of distorted edge and corner-sharing MgSi5 tetrahedra. In the fourth Mg site, Mg(4) is bonded in a 5-coordinate geometry to one Si(1), one Si(2), one Si(3), one Si(4), one Si(5), and one Si(6) atom. In the fifth Mg site, Mg(5) is bonded in a 5-coordinate geometry to one Si(1), one Si(3), one Si(4), one Si(5), and one Si(6) atom. In the sixth Mg site, Mg(6) is bonded to one Si(1), one Si(4), one Si(5), and one Si(6) atom to form distorted MgSi4 tetrahedra that share  a cornercorner with one Mg(3)Si5 tetrahedra, corners with two equivalent Mg(7)Si4 tetrahedra, corners with three equivalent Mg(2)Si4 trigonal pyramids, and  an edgeedge with one Mg(3)Si5 tetrahedra. In the seventh Mg site, Mg(7) is bonded to one Si(1), one Si(2), one Si(3), and one Si(6) atom to form distorted MgSi4 tetrahedra that share corners with two equivalent Mg(6)Si4 tetrahedra, corners with two equivalent Mg(3)Si5 tetrahedra,  an edgeedge with one Mg(3)Si5 tetrahedra, and  an edgeedge with one Mg(2)Si4 trigonal pyramid. In the eighth Mg site, Mg(8) is bonded in a 5-coordinate geometry to one Si(1), one Si(2), one Si(3), one Si(4), and one Si(6) atom. There are six inequivalent Si sites. In the first Si site, Si(1) is bonded in a distorted pentagonal bipyramidal geometry to one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), one Mg(7), and one Mg(8) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(3), one Mg(4), one Mg(7), one Mg(8), one Si(3), one Si(4), and one Si(5) atom. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(7), one Mg(8), and one Si(2) atom. In the fourth Si site, Si(4) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(2), one Mg(4), one Mg(5), one Mg(6), one Mg(8), and one Si(2) atom. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), one Si(2), and one Si(6) atom. In the sixth Si site, Si(6) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(3), one Mg(4), one Mg(5), one Mg(6), one Mg(7), one Mg(8), and one Si(5) atom.
Mg4Si3 crystallizes in the triclinic P1 space group. There are eight inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 5-coordinate geometry to one Si(2), one Si(3), one Si(4), one Si(5), and one Si(6) atom. The Mg(1)-Si(2) bond length is 2.90 Å. The Mg(1)-Si(3) bond length is 2.67 Å. The Mg(1)-Si(4) bond length is 2.65 Å. The Mg(1)-Si(5) bond length is 2.76 Å. The Mg(1)-Si(6) bond length is 2.70 Å. In the second Mg site, Mg(2) is bonded to one Si(1), one Si(3), one Si(4), and one Si(5) atom to form distorted MgSi4 trigonal pyramids that share  a cornercorner with one Mg(3)Si5 tetrahedra, corners with three equivalent Mg(6)Si4 tetrahedra,  an edgeedge with one Mg(7)Si4 tetrahedra, and  an edgeedge with one Mg(3)Si5 tetrahedra. The Mg(2)-Si(1) bond length is 2.83 Å. The Mg(2)-Si(3) bond length is 2.81 Å. The Mg(2)-Si(4) bond length is 2.85 Å. The Mg(2)-Si(5) bond length is 2.75 Å. In the third Mg site, Mg(3) is bonded to one Si(1), one Si(2), one Si(3), one Si(5), and one Si(6) atom to form a mixture of distorted edge and corner-sharing MgSi5 tetrahedra. The Mg(3)-Si(1) bond length is 2.66 Å. The Mg(3)-Si(2) bond length is 2.94 Å. The Mg(3)-Si(3) bond length is 2.69 Å. The Mg(3)-Si(5) bond length is 3.20 Å. The Mg(3)-Si(6) bond length is 2.74 Å. In the fourth Mg site, Mg(4) is bonded in a 5-coordinate geometry to one Si(1), one Si(2), one Si(3), one Si(4), one Si(5), and one Si(6) atom. The Mg(4)-Si(1) bond length is 2.68 Å. The Mg(4)-Si(2) bond length is 2.82 Å. The Mg(4)-Si(3) bond length is 2.97 Å. The Mg(4)-Si(4) bond length is 3.04 Å. The Mg(4)-Si(5) bond length is 3.18 Å. The Mg(4)-Si(6) bond length is 2.83 Å. In the fifth Mg site, Mg(5) is bonded in a 5-coordinate geometry to one Si(1), one Si(3), one Si(4), one Si(5), and one Si(6) atom. The Mg(5)-Si(1) bond length is 2.78 Å. The Mg(5)-Si(3) bond length is 3.07 Å. The Mg(5)-Si(4) bond length is 2.88 Å. The Mg(5)-Si(5) bond length is 2.89 Å. The Mg(5)-Si(6) bond length is 2.81 Å. In the sixth Mg site, Mg(6) is bonded to one Si(1), one Si(4), one Si(5), and one Si(6) atom to form distorted MgSi4 tetrahedra that share  a cornercorner with one Mg(3)Si5 tetrahedra, corners with two equivalent Mg(7)Si4 tetrahedra, corners with three equivalent Mg(2)Si4 trigonal pyramids, and  an edgeedge with one Mg(3)Si5 tetrahedra. The Mg(6)-Si(1) bond length is 2.67 Å. The Mg(6)-Si(4) bond length is 2.60 Å. The Mg(6)-Si(5) bond length is 2.84 Å. The Mg(6)-Si(6) bond length is 2.78 Å. In the seventh Mg site, Mg(7) is bonded to one Si(1), one Si(2), one Si(3), and one Si(6) atom to form distorted MgSi4 tetrahedra that share corners with two equivalent Mg(6)Si4 tetrahedra, corners with two equivalent Mg(3)Si5 tetrahedra,  an edgeedge with one Mg(3)Si5 tetrahedra, and  an edgeedge with one Mg(2)Si4 trigonal pyramid. The Mg(7)-Si(1) bond length is 2.67 Å. The Mg(7)-Si(2) bond length is 2.82 Å. The Mg(7)-Si(3) bond length is 2.79 Å. The Mg(7)-Si(6) bond length is 2.72 Å. In the eighth Mg site, Mg(8) is bonded in a 5-coordinate geometry to one Si(1), one Si(2), one Si(3), one Si(4), and one Si(6) atom. The Mg(8)-Si(1) bond length is 2.69 Å. The Mg(8)-Si(2) bond length is 2.97 Å. The Mg(8)-Si(3) bond length is 3.09 Å. The Mg(8)-Si(4) bond length is 2.83 Å. The Mg(8)-Si(6) bond length is 2.87 Å. There are six inequivalent Si sites. In the first Si site, Si(1) is bonded in a distorted pentagonal bipyramidal geometry to one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), one Mg(7), and one Mg(8) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(3), one Mg(4), one Mg(7), one Mg(8), one Si(3), one Si(4), and one Si(5) atom. The Si(2)-Si(3) bond length is 2.40 Å. The Si(2)-Si(4) bond length is 2.44 Å. The Si(2)-Si(5) bond length is 2.46 Å. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(7), one Mg(8), and one Si(2) atom. In the fourth Si site, Si(4) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(2), one Mg(4), one Mg(5), one Mg(6), one Mg(8), and one Si(2) atom. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), one Si(2), and one Si(6) atom. The Si(5)-Si(6) bond length is 2.44 Å. In the sixth Si site, Si(6) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(3), one Mg(4), one Mg(5), one Mg(6), one Mg(7), one Mg(8), and one Si(5) atom.