Mg5Si6 is Magnesium tetraboride-like structured and crystallizes in the monoclinic C2 space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted rectangular see-saw-like geometry to one Si(1), one Si(2), one Si(3), and one Si(4) atom. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Si(5), two equivalent Si(1), and three equivalent Si(3) atoms. In the third Mg site, Mg(3) is bonded in a 5-coordinate geometry to one Si(6), two equivalent Si(1), and two equivalent Si(2) atoms. In the fourth Mg site, Mg(4) is bonded in a 8-coordinate geometry to two equivalent Si(2), three equivalent Si(4), and three equivalent Si(6) atoms. In the fifth Mg site, Mg(5) is bonded in a 9-coordinate geometry to two equivalent Si(1), two equivalent Si(2), two equivalent Si(3), and three equivalent Si(5) atoms. There are six inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(5), one Si(2), and one Si(5) atom. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(5), one Si(1), and one Si(6) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(5), three equivalent Mg(2), one Si(5), and two equivalent Si(3) atoms. In the fourth Si site, Si(4) is bonded in a 7-coordinate geometry to one Mg(1), three equivalent Mg(4), and three equivalent Si(6) atoms. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to one Mg(2), three equivalent Mg(5), one Si(1), one Si(3), and two equivalent Si(5) atoms. In the sixth Si site, Si(6) is bonded in a 8-coordinate geometry to one Mg(3), three equivalent Mg(4), one Si(2), and three equivalent Si(4) atoms.
Mg5Si6 is Magnesium tetraboride-like structured and crystallizes in the monoclinic C2 space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a distorted rectangular see-saw-like geometry to one Si(1), one Si(2), one Si(3), and one Si(4) atom. The Mg(1)-Si(1) bond length is 2.62 Å. The Mg(1)-Si(2) bond length is 2.66 Å. The Mg(1)-Si(3) bond length is 2.79 Å. The Mg(1)-Si(4) bond length is 2.92 Å. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one Si(5), two equivalent Si(1), and three equivalent Si(3) atoms. The Mg(2)-Si(5) bond length is 3.01 Å. Both Mg(2)-Si(1) bond lengths are 2.84 Å. There are a spread of Mg(2)-Si(3) bond distances ranging from 2.83-3.01 Å. In the third Mg site, Mg(3) is bonded in a 5-coordinate geometry to one Si(6), two equivalent Si(1), and two equivalent Si(2) atoms. The Mg(3)-Si(6) bond length is 2.82 Å. There is one shorter (2.92 Å) and one longer (2.96 Å) Mg(3)-Si(1) bond length. There is one shorter (2.93 Å) and one longer (3.07 Å) Mg(3)-Si(2) bond length. In the fourth Mg site, Mg(4) is bonded in a 8-coordinate geometry to two equivalent Si(2), three equivalent Si(4), and three equivalent Si(6) atoms. There is one shorter (2.78 Å) and one longer (2.79 Å) Mg(4)-Si(2) bond length. There are a spread of Mg(4)-Si(4) bond distances ranging from 2.83-2.99 Å. There are two shorter (2.83 Å) and one longer (2.98 Å) Mg(4)-Si(6) bond length. In the fifth Mg site, Mg(5) is bonded in a 9-coordinate geometry to two equivalent Si(1), two equivalent Si(2), two equivalent Si(3), and three equivalent Si(5) atoms. There is one shorter (3.06 Å) and one longer (3.13 Å) Mg(5)-Si(1) bond length. There is one shorter (2.91 Å) and one longer (3.03 Å) Mg(5)-Si(2) bond length. There is one shorter (3.01 Å) and one longer (3.06 Å) Mg(5)-Si(3) bond length. There are a spread of Mg(5)-Si(5) bond distances ranging from 3.00-3.07 Å. There are six inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(5), one Si(2), and one Si(5) atom. The Si(1)-Si(2) bond length is 2.38 Å. The Si(1)-Si(5) bond length is 2.33 Å. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(5), one Si(1), and one Si(6) atom. The Si(2)-Si(6) bond length is 2.48 Å. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(1), two equivalent Mg(5), three equivalent Mg(2), one Si(5), and two equivalent Si(3) atoms. The Si(3)-Si(5) bond length is 2.48 Å. There is one shorter (2.59 Å) and one longer (2.60 Å) Si(3)-Si(3) bond length. In the fourth Si site, Si(4) is bonded in a 7-coordinate geometry to one Mg(1), three equivalent Mg(4), and three equivalent Si(6) atoms. There are a spread of Si(4)-Si(6) bond distances ranging from 2.49-2.62 Å. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to one Mg(2), three equivalent Mg(5), one Si(1), one Si(3), and two equivalent Si(5) atoms. There is one shorter (2.44 Å) and one longer (2.46 Å) Si(5)-Si(5) bond length. In the sixth Si site, Si(6) is bonded in a 8-coordinate geometry to one Mg(3), three equivalent Mg(4), one Si(2), and three equivalent Si(4) atoms.