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(4), one Si(6), and one Si(8) atom. In the second Mg site, Mg(2) is bonded in a 3-coordinate geometry to one Si(2), one Si(6), and one Si(9) atom. In the third Mg site, Mg(3) is bonded in a 4-coordinate geometry to 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(10), one Si(2), one Si(3), and one Si(9) atom. In the fifth Mg site, Mg(5) is bonded in a 3-coordinate geometry to one Si(3), one Si(8), and one Si(9) atom. In the sixth Mg site, Mg(6) is bonded in a 4-coordinate geometry to one Si(10), one Si(3), one Si(6), 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), one Si(5), and one Si(7) atom. In the eighth Mg site, Mg(8) is bonded to one Si(1), one Si(5), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the ninth Mg site, Mg(9) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(5), and one Si(7) atom. In the tenth Mg site, Mg(10) is bonded to one Si(1), one Si(5), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the eleventh Mg site, Mg(11) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(5), and one Si(7) atom. In the twelfth Mg site, Mg(12) is bonded to one Si(1), one Si(5), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the thirteenth Mg site, Mg(13) is bonded in a 4-coordinate geometry to one Si(2), one Si(3), one Si(5), and one Si(9) atom. In the fourteenth Mg site, Mg(14) is bonded to one Si(4), one Si(6), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the fifteenth Mg site, Mg(15) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), one Si(3), one Si(5), and one Si(9) atom. In the sixteenth Mg site, Mg(16) is bonded to one Si(4), one Si(6), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. In the seventeenth Mg site, Mg(17) is bonded to one Si(10), one Si(2), one Si(3), and one Si(5) atom to form distorted corner-sharing MgSi4 tetrahedra. In the eighteenth Mg site, Mg(18) is bonded in a distorted trigonal non-coplanar geometry to one Si(4), one Si(7), and one Si(8) atom. 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(12), one Mg(7), one Mg(8), one Mg(9), and one Si(4) atom. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(13), one Mg(15), one Mg(17), one Mg(2), one Mg(4), one Mg(7), and one Mg(9) atom. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(13), one Mg(15), one Mg(17), one Mg(4), one Mg(5), one Mg(6), and one Si(6) atom. In the fourth Si site, Si(4) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(18), one Mg(3), and one Si(1) atom. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(11), one Mg(12), one Mg(13), one Mg(15), one Mg(17), one Mg(7), one Mg(8), and one Mg(9) atom. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(2), one Mg(3), one Mg(6), and one Si(3) 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(7), one Mg(8), and one Mg(9) atom. 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(16), one Mg(18), one Mg(3), one Mg(5), and one Mg(8) atom. In the ninth Si site, Si(9) is bonded in a 8-coordinate geometry to one Mg(13), one Mg(15), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), and one Si(10) atom. In the tenth Si site, Si(10) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(15), one Mg(17), one Mg(4), one Mg(6), one Mg(7), one Mg(9), and one Si(9) atom.
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(4), one Si(6), and one Si(8) atom. The Mg(1)-Si(3) bond length is 2.78 Å. The Mg(1)-Si(4) bond length is 2.70 Å. The Mg(1)-Si(6) bond length is 2.78 Å. The Mg(1)-Si(8) bond length is 2.91 Å. In the second Mg site, Mg(2) is bonded in a 3-coordinate geometry to one Si(2), one Si(6), and one Si(9) atom. The Mg(2)-Si(2) bond length is 2.74 Å. The Mg(2)-Si(6) bond length is 2.72 Å. The Mg(2)-Si(9) bond length is 2.71 Å. In the third Mg site, Mg(3) is bonded in a 4-coordinate geometry to one Si(4), one Si(6), one Si(8), and one Si(9) atom. The Mg(3)-Si(4) bond length is 2.72 Å. The Mg(3)-Si(6) bond length is 2.98 Å. The Mg(3)-Si(8) bond length is 2.81 Å. The Mg(3)-Si(9) bond length is 2.71 Å. In the fourth Mg site, Mg(4) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), one Si(3), and one Si(9) atom. The Mg(4)-Si(10) bond length is 2.68 Å. The Mg(4)-Si(2) bond length is 2.91 Å. The Mg(4)-Si(3) bond length is 2.70 Å. The Mg(4)-Si(9) bond length is 2.73 Å. In the fifth Mg site, Mg(5) is bonded in a 3-coordinate geometry to one Si(3), one Si(8), and one Si(9) atom. The Mg(5)-Si(3) bond length is 2.73 Å. The Mg(5)-Si(8) bond length is 2.74 Å. The Mg(5)-Si(9) bond length is 2.94 Å. In the sixth Mg site, Mg(6) is bonded in a 4-coordinate geometry to one Si(10), one Si(3), one Si(6), and one Si(9) atom. The Mg(6)-Si(10) bond length is 2.84 Å. The Mg(6)-Si(3) bond length is 2.89 Å. The Mg(6)-Si(6) bond length is 2.82 Å. The Mg(6)-Si(9) bond length is 2.78 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), one Si(5), and one Si(7) atom. The Mg(7)-Si(1) bond length is 2.84 Å. The Mg(7)-Si(10) bond length is 2.87 Å. The Mg(7)-Si(2) bond length is 2.95 Å. The Mg(7)-Si(5) bond length is 2.84 Å. The Mg(7)-Si(7) bond length is 2.97 Å. In the eighth Mg site, Mg(8) is bonded to one Si(1), one Si(5), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. The Mg(8)-Si(1) bond length is 2.68 Å. The Mg(8)-Si(5) bond length is 2.83 Å. The Mg(8)-Si(7) bond length is 2.84 Å. The Mg(8)-Si(8) bond length is 2.75 Å. In the ninth Mg site, Mg(9) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(5), and one Si(7) atom. The Mg(9)-Si(1) bond length is 2.88 Å. The Mg(9)-Si(10) bond length is 2.82 Å. The Mg(9)-Si(2) bond length is 2.88 Å. The Mg(9)-Si(5) bond length is 2.88 Å. The Mg(9)-Si(7) bond length is 2.92 Å. In the tenth Mg site, Mg(10) is bonded to one Si(1), one Si(5), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. The Mg(10)-Si(1) bond length is 2.68 Å. The Mg(10)-Si(5) bond length is 2.83 Å. The Mg(10)-Si(7) bond length is 2.80 Å. The Mg(10)-Si(8) bond length is 2.77 Å. In the eleventh Mg site, Mg(11) is bonded in a 5-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(5), and one Si(7) atom. The Mg(11)-Si(1) bond length is 2.78 Å. The Mg(11)-Si(10) bond length is 2.85 Å. The Mg(11)-Si(2) bond length is 2.82 Å. The Mg(11)-Si(5) bond length is 2.91 Å. The Mg(11)-Si(7) bond length is 2.98 Å. In the twelfth Mg site, Mg(12) is bonded to one Si(1), one Si(5), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. The Mg(12)-Si(1) bond length is 2.69 Å. The Mg(12)-Si(5) bond length is 2.82 Å. The Mg(12)-Si(7) bond length is 2.82 Å. The Mg(12)-Si(8) bond length is 2.85 Å. In the thirteenth Mg site, Mg(13) is bonded in a 4-coordinate geometry to one Si(2), one Si(3), one Si(5), and one Si(9) atom. The Mg(13)-Si(2) bond length is 2.65 Å. The Mg(13)-Si(3) bond length is 2.96 Å. The Mg(13)-Si(5) bond length is 2.73 Å. The Mg(13)-Si(9) bond length is 2.68 Å. In the fourteenth Mg site, Mg(14) is bonded to one Si(4), one Si(6), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. The Mg(14)-Si(4) bond length is 2.71 Å. The Mg(14)-Si(6) bond length is 2.93 Å. The Mg(14)-Si(7) bond length is 2.80 Å. The Mg(14)-Si(8) bond length is 2.87 Å. In the fifteenth Mg site, Mg(15) is bonded in a 4-coordinate geometry to one Si(10), one Si(2), one Si(3), one Si(5), and one Si(9) atom. The Mg(15)-Si(10) bond length is 2.89 Å. The Mg(15)-Si(2) bond length is 2.76 Å. The Mg(15)-Si(3) bond length is 2.95 Å. The Mg(15)-Si(5) bond length is 2.88 Å. The Mg(15)-Si(9) bond length is 3.17 Å. In the sixteenth Mg site, Mg(16) is bonded to one Si(4), one Si(6), one Si(7), and one Si(8) atom to form a mixture of distorted edge and corner-sharing MgSi4 tetrahedra. The Mg(16)-Si(4) bond length is 2.73 Å. The Mg(16)-Si(6) bond length is 2.83 Å. The Mg(16)-Si(7) bond length is 2.82 Å. The Mg(16)-Si(8) bond length is 2.75 Å. In the seventeenth Mg site, Mg(17) is bonded to one Si(10), one Si(2), one Si(3), and one Si(5) atom to form distorted corner-sharing MgSi4 tetrahedra. The Mg(17)-Si(10) bond length is 2.69 Å. The Mg(17)-Si(2) bond length is 2.66 Å. The Mg(17)-Si(3) bond length is 2.77 Å. The Mg(17)-Si(5) bond length is 2.81 Å. In the eighteenth Mg site, Mg(18) is bonded in a distorted trigonal non-coplanar geometry to one Si(4), one Si(7), and one Si(8) atom. The Mg(18)-Si(4) bond length is 2.82 Å. The Mg(18)-Si(7) bond length is 2.78 Å. The Mg(18)-Si(8) bond length is 2.79 Å. 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(12), one Mg(7), one Mg(8), one Mg(9), and one Si(4) atom. The Si(1)-Si(4) bond length is 2.46 Å. In the second Si site, Si(2) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(13), one Mg(15), one Mg(17), one Mg(2), one Mg(4), one Mg(7), and one Mg(9) atom. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(13), one Mg(15), one Mg(17), one Mg(4), one Mg(5), one Mg(6), and one Si(6) atom. The Si(3)-Si(6) bond length is 2.56 Å. In the fourth Si site, Si(4) is bonded in a 6-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(18), one Mg(3), and one Si(1) atom. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to one Mg(10), one Mg(11), one Mg(12), one Mg(13), one Mg(15), one Mg(17), one Mg(7), one Mg(8), and one Mg(9) atom. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to one Mg(1), one Mg(14), one Mg(16), one Mg(2), one Mg(3), one Mg(6), and one Si(3) 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(7), one Mg(8), and one Mg(9) atom. 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(16), one Mg(18), one Mg(3), one Mg(5), and one Mg(8) atom. In the ninth Si site, Si(9) is bonded in a 8-coordinate geometry to one Mg(13), one Mg(15), one Mg(2), one Mg(3), one Mg(4), one Mg(5), one Mg(6), and one Si(10) atom. The Si(9)-Si(10) bond length is 2.50 Å. In the tenth Si site, Si(10) is bonded in a 8-coordinate geometry to one Mg(11), one Mg(15), one Mg(17), one Mg(4), one Mg(6), one Mg(7), one Mg(9), and one Si(9) atom.