Mg4Si3 crystallizes in the monoclinic C2 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(4), two equivalent Si(1), and two equivalent Si(2) atoms. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Si(3), one Si(4), two equivalent Si(1), and two equivalent Si(2) atoms. In the third Mg site, Mg(3) is bonded in a 6-coordinate geometry to one Si(3), one Si(4), two equivalent Si(1), and two equivalent Si(2) atoms. In the fourth Mg site, Mg(4) is bonded in a 5-coordinate geometry to one Si(3), two equivalent Si(1), and two equivalent Si(2) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), and two equivalent Mg(4) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), and one Si(3) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), one Si(4), and two equivalent Si(2) atoms. In the fourth Si site, Si(4) is bonded in a 7-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), and one Si(3) atom.
Mg4Si3 crystallizes in the monoclinic C2 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(4), two equivalent Si(1), and two equivalent Si(2) atoms. The Mg(1)-Si(4) bond length is 2.69 Å. There is one shorter (2.77 Å) and one longer (2.83 Å) Mg(1)-Si(1) bond length. There is one shorter (2.96 Å) and one longer (3.00 Å) Mg(1)-Si(2) bond length. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Si(3), one Si(4), two equivalent Si(1), and two equivalent Si(2) atoms. The Mg(2)-Si(3) bond length is 2.87 Å. The Mg(2)-Si(4) bond length is 2.87 Å. There is one shorter (2.75 Å) and one longer (2.87 Å) Mg(2)-Si(1) bond length. There is one shorter (2.75 Å) and one longer (2.80 Å) Mg(2)-Si(2) bond length. In the third Mg site, Mg(3) is bonded in a 6-coordinate geometry to one Si(3), one Si(4), two equivalent Si(1), and two equivalent Si(2) atoms. The Mg(3)-Si(3) bond length is 2.96 Å. The Mg(3)-Si(4) bond length is 2.95 Å. There is one shorter (2.75 Å) and one longer (2.91 Å) Mg(3)-Si(1) bond length. There is one shorter (2.72 Å) and one longer (2.84 Å) Mg(3)-Si(2) bond length. In the fourth Mg site, Mg(4) is bonded in a 5-coordinate geometry to one Si(3), two equivalent Si(1), and two equivalent Si(2) atoms. The Mg(4)-Si(3) bond length is 2.76 Å. There is one shorter (2.96 Å) and one longer (2.98 Å) Mg(4)-Si(1) bond length. There is one shorter (2.73 Å) and one longer (2.81 Å) Mg(4)-Si(2) bond length. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), and two equivalent Mg(4) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), and one Si(3) atom. The Si(2)-Si(3) bond length is 2.69 Å. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), one Si(4), and two equivalent Si(2) atoms. The Si(3)-Si(4) bond length is 2.59 Å. In the fourth Si site, Si(4) is bonded in a 7-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), and one Si(3) atom.