Mg9Si5 crystallizes in the triclinic P1 space group. There are eighteen inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Si(3), one Si(8), one Si(9), and two equivalent Si(6) atoms. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Si(10), one Si(2), one Si(6), and two equivalent Si(3) atoms. In the third Mg site, Mg(3) is bonded in a 5-coordinate geometry to one Si(3), one Si(4), one Si(6), one Si(8), and one Si(9) atom. In the fourth Mg site, Mg(4) is bonded in a 4-coordinate geometry to one Si(2), one Si(3), one Si(6), and one Si(9) atom. In the fifth Mg site, Mg(5) is bonded in a 5-coordinate geometry to one Si(3), one Si(4), one Si(6), and two equivalent Si(9) atoms. In the sixth Mg site, Mg(6) is bonded in a distorted T-shaped geometry to one Si(10), one Si(3), and one Si(9) atom. In the seventh Mg site, Mg(7) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), and two equivalent Si(5) atoms. In the eighth Mg site, Mg(8) is bonded in a 4-coordinate geometry to one Si(4), one Si(5), and two equivalent Si(7) atoms. In the ninth Mg site, Mg(9) is bonded in a 4-coordinate geometry to one Si(5), one Si(7), and two equivalent Si(1) atoms. In the tenth Mg site, Mg(10) is bonded in a 3-coordinate geometry to one Si(1), one Si(5), one Si(7), and one Si(8) atom. In the eleventh Mg site, Mg(11) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), one Si(5), and one Si(7) atom. In the twelfth Mg site, Mg(12) is bonded in a 4-coordinate geometry to one Si(4), one Si(5), one Si(7), and one Si(8) atom. In the thirteenth Mg site, Mg(13) is bonded in a 5-coordinate geometry to one Si(1), one Si(2), one Si(3), and two equivalent Si(10) atoms. In the fourteenth Mg site, Mg(14) is bonded in a 5-coordinate geometry to one Si(4), one Si(6), one Si(7), one Si(8), and one Si(9) atom. In the fifteenth Mg site, Mg(15) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), and two equivalent Si(2) atoms. In the sixteenth Mg site, Mg(16) is bonded in a 5-coordinate geometry to one Si(4), one Si(6), one Si(7), and two equivalent Si(8) atoms. In the seventeenth Mg site, Mg(17) is bonded in a 5-coordinate geometry to one Si(2), one Si(3), one Si(5), and two equivalent Si(10) atoms. In the eighteenth Mg site, Mg(18) is bonded in a 4-coordinate geometry to one Si(7), one Si(8), one Si(9), and two equivalent Si(4) atoms. There are ten inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to one Mg(10), one Mg(11), one Mg(13), one Mg(15), one Mg(7), two equivalent Mg(9), and one Si(2) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(13), one Mg(17), one Mg(2), one Mg(4), one Mg(7), two equivalent Mg(15), and one Si(1) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(13), one Mg(17), one Mg(3), one Mg(4), one Mg(5), one Mg(6), and two equivalent Mg(2) atoms. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(12), one Mg(14), one Mg(16), one Mg(3), one Mg(5), one Mg(8), two equivalent Mg(18), and one Si(8) atom. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to one Mg(10), one Mg(11), one Mg(12), one Mg(17), one Mg(8), one Mg(9), and two equivalent Mg(7) atoms. In the sixth Si site, Si(6) is bonded in a 9-coordinate geometry to one Mg(14), one Mg(16), one Mg(2), one Mg(3), one Mg(4), one Mg(5), two equivalent Mg(1), and one Si(9) atom. In the seventh Si site, Si(7) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(11), one Mg(12), one Mg(14), one Mg(16), one Mg(18), one Mg(9), and two equivalent Mg(8) atoms. In the eighth Si site, Si(8) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(10), one Mg(12), one Mg(14), one Mg(18), one Mg(3), two equivalent Mg(16), and one Si(4) atom. In the ninth Si site, Si(9) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(14), one Mg(18), one Mg(3), one Mg(4), one Mg(6), two equivalent Mg(5), and one Si(6) atom. In the tenth Si site, Si(10) is bonded in a 9-coordinate geometry to one Mg(11), one Mg(15), one Mg(2), one Mg(6), one Mg(7), two equivalent Mg(13), and two equivalent Mg(17) atoms.
Mg9Si5 crystallizes in the triclinic P1 space group. There are eighteen inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 4-coordinate geometry to one Si(3), one Si(8), one Si(9), and two equivalent Si(6) atoms. The Mg(1)-Si(3) bond length is 2.66 Å. The Mg(1)-Si(8) bond length is 2.71 Å. The Mg(1)-Si(9) bond length is 3.09 Å. There is one shorter (2.69 Å) and one longer (2.94 Å) Mg(1)-Si(6) bond length. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Si(10), one Si(2), one Si(6), and two equivalent Si(3) atoms. The Mg(2)-Si(10) bond length is 2.91 Å. The Mg(2)-Si(2) bond length is 2.78 Å. The Mg(2)-Si(6) bond length is 3.09 Å. There is one shorter (2.78 Å) and one longer (2.87 Å) Mg(2)-Si(3) bond length. In the third Mg site, Mg(3) is bonded in a 5-coordinate geometry to one Si(3), one Si(4), one Si(6), one Si(8), and one Si(9) atom. The Mg(3)-Si(3) bond length is 2.96 Å. The Mg(3)-Si(4) bond length is 2.83 Å. The Mg(3)-Si(6) bond length is 2.95 Å. The Mg(3)-Si(8) bond length is 2.91 Å. The Mg(3)-Si(9) bond length is 3.11 Å. In the fourth Mg site, Mg(4) is bonded in a 4-coordinate geometry to one Si(2), one Si(3), one Si(6), and one Si(9) atom. The Mg(4)-Si(2) bond length is 2.79 Å. The Mg(4)-Si(3) bond length is 3.03 Å. The Mg(4)-Si(6) bond length is 3.05 Å. The Mg(4)-Si(9) bond length is 2.83 Å. In the fifth Mg site, Mg(5) is bonded in a 5-coordinate geometry to one Si(3), one Si(4), one Si(6), and two equivalent Si(9) atoms. The Mg(5)-Si(3) bond length is 2.79 Å. The Mg(5)-Si(4) bond length is 2.93 Å. The Mg(5)-Si(6) bond length is 3.05 Å. There is one shorter (2.77 Å) and one longer (2.79 Å) Mg(5)-Si(9) bond length. In the sixth Mg site, Mg(6) is bonded in a distorted T-shaped geometry to one Si(10), one Si(3), and one Si(9) atom. The Mg(6)-Si(10) bond length is 2.76 Å. The Mg(6)-Si(3) bond length is 2.82 Å. The Mg(6)-Si(9) bond length is 2.75 Å. In the seventh Mg site, Mg(7) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), and two equivalent Si(5) atoms. The Mg(7)-Si(1) bond length is 2.75 Å. The Mg(7)-Si(10) bond length is 2.74 Å. The Mg(7)-Si(2) bond length is 3.02 Å. There is one shorter (2.74 Å) and one longer (3.07 Å) Mg(7)-Si(5) bond length. In the eighth Mg site, Mg(8) is bonded in a 4-coordinate geometry to one Si(4), one Si(5), and two equivalent Si(7) atoms. The Mg(8)-Si(4) bond length is 3.10 Å. The Mg(8)-Si(5) bond length is 2.78 Å. There is one shorter (2.74 Å) and one longer (2.84 Å) Mg(8)-Si(7) bond length. In the ninth Mg site, Mg(9) is bonded in a 4-coordinate geometry to one Si(5), one Si(7), and two equivalent Si(1) atoms. The Mg(9)-Si(5) bond length is 2.67 Å. The Mg(9)-Si(7) bond length is 2.71 Å. There is one shorter (2.77 Å) and one longer (2.98 Å) Mg(9)-Si(1) bond length. In the tenth Mg site, Mg(10) is bonded in a 3-coordinate geometry to one Si(1), one Si(5), one Si(7), and one Si(8) atom. The Mg(10)-Si(1) bond length is 2.93 Å. The Mg(10)-Si(5) bond length is 3.21 Å. The Mg(10)-Si(7) bond length is 2.82 Å. The Mg(10)-Si(8) bond length is 2.74 Å. In the eleventh Mg site, Mg(11) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), one Si(5), and one Si(7) atom. The Mg(11)-Si(1) bond length is 2.92 Å. The Mg(11)-Si(10) bond length is 2.70 Å. The Mg(11)-Si(5) bond length is 2.89 Å. The Mg(11)-Si(7) bond length is 2.91 Å. In the twelfth Mg site, Mg(12) is bonded in a 4-coordinate geometry to one Si(4), one Si(5), one Si(7), and one Si(8) atom. The Mg(12)-Si(4) bond length is 3.01 Å. The Mg(12)-Si(5) bond length is 2.70 Å. The Mg(12)-Si(7) bond length is 3.03 Å. The Mg(12)-Si(8) bond length is 2.79 Å. In the thirteenth Mg site, Mg(13) is bonded in a 5-coordinate geometry to one Si(1), one Si(2), one Si(3), and two equivalent Si(10) atoms. The Mg(13)-Si(1) bond length is 2.95 Å. The Mg(13)-Si(2) bond length is 2.76 Å. The Mg(13)-Si(3) bond length is 2.91 Å. There is one shorter (2.75 Å) and one longer (2.81 Å) Mg(13)-Si(10) bond length. In the fourteenth Mg site, Mg(14) is bonded in a 5-coordinate geometry to one Si(4), one Si(6), one Si(7), one Si(8), and one Si(9) atom. The Mg(14)-Si(4) bond length is 2.96 Å. The Mg(14)-Si(6) bond length is 2.82 Å. The Mg(14)-Si(7) bond length is 3.01 Å. The Mg(14)-Si(8) bond length is 3.03 Å. The Mg(14)-Si(9) bond length is 2.93 Å. In the fifteenth Mg site, Mg(15) is bonded in a 4-coordinate geometry to one Si(1), one Si(10), and two equivalent Si(2) atoms. The Mg(15)-Si(1) bond length is 2.88 Å. The Mg(15)-Si(10) bond length is 2.83 Å. There is one shorter (2.76 Å) and one longer (2.89 Å) Mg(15)-Si(2) bond length. In the sixteenth Mg site, Mg(16) is bonded in a 5-coordinate geometry to one Si(4), one Si(6), one Si(7), and two equivalent Si(8) atoms. The Mg(16)-Si(4) bond length is 3.08 Å. The Mg(16)-Si(6) bond length is 2.95 Å. The Mg(16)-Si(7) bond length is 2.83 Å. There is one shorter (2.76 Å) and one longer (2.77 Å) Mg(16)-Si(8) bond length. In the seventeenth Mg site, Mg(17) is bonded in a 5-coordinate geometry to one Si(2), one Si(3), one Si(5), and two equivalent Si(10) atoms. The Mg(17)-Si(2) bond length is 2.99 Å. The Mg(17)-Si(3) bond length is 3.10 Å. The Mg(17)-Si(5) bond length is 3.06 Å. There is one shorter (3.03 Å) and one longer (3.07 Å) Mg(17)-Si(10) bond length. In the eighteenth Mg site, Mg(18) is bonded in a 4-coordinate geometry to one Si(7), one Si(8), one Si(9), and two equivalent Si(4) atoms. The Mg(18)-Si(7) bond length is 2.68 Å. The Mg(18)-Si(8) bond length is 3.16 Å. The Mg(18)-Si(9) bond length is 2.72 Å. There is one shorter (2.68 Å) and one longer (2.96 Å) Mg(18)-Si(4) bond length. There are ten inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to one Mg(10), one Mg(11), one Mg(13), one Mg(15), one Mg(7), two equivalent Mg(9), and one Si(2) atom. The Si(1)-Si(2) bond length is 2.65 Å. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(13), one Mg(17), one Mg(2), one Mg(4), one Mg(7), two equivalent Mg(15), and one Si(1) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(13), one Mg(17), one Mg(3), one Mg(4), one Mg(5), one Mg(6), and two equivalent Mg(2) atoms. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(12), one Mg(14), one Mg(16), one Mg(3), one Mg(5), one Mg(8), two equivalent Mg(18), and one Si(8) atom. The Si(4)-Si(8) bond length is 2.46 Å. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to one Mg(10), one Mg(11), one Mg(12), one Mg(17), one Mg(8), one Mg(9), and two equivalent Mg(7) atoms. In the sixth Si site, Si(6) is bonded in a 9-coordinate geometry to one Mg(14), one Mg(16), one Mg(2), one Mg(3), one Mg(4), one Mg(5), two equivalent Mg(1), and one Si(9) atom. The Si(6)-Si(9) bond length is 2.46 Å. In the seventh Si site, Si(7) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(11), one Mg(12), one Mg(14), one Mg(16), one Mg(18), one Mg(9), and two equivalent Mg(8) atoms. In the eighth Si site, Si(8) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(10), one Mg(12), one Mg(14), one Mg(18), one Mg(3), two equivalent Mg(16), and one Si(4) atom. In the ninth Si site, Si(9) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(14), one Mg(18), one Mg(3), one Mg(4), one Mg(6), two equivalent Mg(5), and one Si(6) atom. In the tenth Si site, Si(10) is bonded in a 9-coordinate geometry to one Mg(11), one Mg(15), one Mg(2), one Mg(6), one Mg(7), two equivalent Mg(13), and two equivalent Mg(17) atoms.