Mg4Si7 crystallizes in the monoclinic Cm space group. There are eight inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 14-coordinate geometry to two equivalent Mg(5), one Si(13), one Si(3), one Si(4), one Si(9), two equivalent Si(1), two equivalent Si(12), two equivalent Si(2), and two equivalent Si(8) atoms. In the second Mg site, Mg(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(7), two equivalent Mg(8), one Si(10), one Si(9), and two equivalent Si(5) atoms. In the third Mg site, Mg(3) is bonded in a 13-coordinate geometry to one Mg(8), two equivalent Mg(2), two equivalent Mg(7), one Si(11), one Si(7), two equivalent Si(10), two equivalent Si(5), and two equivalent Si(6) atoms. In the fourth Mg site, Mg(4) is bonded in a 13-coordinate geometry to one Mg(7), two equivalent Mg(2), two equivalent Mg(8), one Si(12), one Si(8), two equivalent Si(13), two equivalent Si(5), and two equivalent Si(9) atoms. In the fifth Mg site, Mg(5) is bonded in a 14-coordinate geometry to two equivalent Mg(1), one Si(13), one Si(3), one Si(4), one Si(9), two equivalent Si(1), two equivalent Si(12), two equivalent Si(2), and two equivalent Si(8) atoms. In the sixth Mg site, Mg(6) is bonded in a 14-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(6), two equivalent Si(11), two equivalent Si(14), two equivalent Si(3), two equivalent Si(4), and two equivalent Si(7) atoms. In the seventh Mg site, Mg(7) is bonded in a 13-coordinate geometry to one Mg(4), two equivalent Mg(2), two equivalent Mg(3), one Si(11), one Si(7), two equivalent Si(10), two equivalent Si(5), and two equivalent Si(6) atoms. In the eighth Mg site, Mg(8) is bonded in a 13-coordinate geometry to one Mg(3), two equivalent Mg(2), two equivalent Mg(4), one Si(12), one Si(8), two equivalent Si(13), two equivalent Si(5), and two equivalent Si(9) atoms. There are fourteen inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(6), two equivalent Mg(1), two equivalent Mg(5), one Si(12), one Si(2), and two equivalent Si(3) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(6), two equivalent Mg(1), two equivalent Mg(5), one Si(1), one Si(8), and two equivalent Si(4) atoms. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(5), two equivalent Mg(6), one Si(11), one Si(4), and two equivalent Si(1) atoms. In the fourth Si site, Si(4) is bonded in a 10-coordinate geometry to one Mg(1), one Mg(5), two equivalent Mg(6), one Si(3), one Si(7), two equivalent Si(14), and two equivalent Si(2) atoms. In the fifth Si site, Si(5) is bonded to two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(7), two equivalent Mg(8), one Si(13), and one Si(6) atom to form a mixture of distorted corner and face-sharing SiMg10Si2 cuboctahedra. In the sixth Si site, Si(6) is bonded in a 11-coordinate geometry to one Mg(6), two equivalent Mg(3), two equivalent Mg(7), one Si(14), one Si(5), two equivalent Si(10), and two equivalent Si(7) atoms. In the seventh Si site, Si(7) is bonded in a 10-coordinate geometry to one Mg(3), one Mg(7), two equivalent Mg(6), one Si(11), one Si(4), two equivalent Si(14), and two equivalent Si(6) atoms. In the eighth Si site, Si(8) is bonded in a 10-coordinate geometry to one Mg(4), one Mg(8), two equivalent Mg(1), two equivalent Mg(5), one Si(12), one Si(2), and two equivalent Si(13) atoms. In the ninth Si site, Si(9) is bonded in a 10-coordinate geometry to one Mg(1), one Mg(2), one Mg(5), two equivalent Mg(4), two equivalent Mg(8), one Si(13), and two equivalent Si(12) atoms. In the tenth Si site, Si(10) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(6), two equivalent Mg(3), two equivalent Mg(7), two equivalent Si(11), and two equivalent Si(6) atoms. In the eleventh Si site, Si(11) is bonded in a 8-coordinate geometry to one Mg(3), one Mg(7), two equivalent Mg(6), one Si(3), one Si(7), and two equivalent Si(10) atoms. In the twelfth Si site, Si(12) is bonded in a 10-coordinate geometry to one Mg(4), one Mg(8), two equivalent Mg(1), two equivalent Mg(5), one Si(1), one Si(8), and two equivalent Si(9) atoms. In the thirteenth Si site, Si(13) is bonded in a 10-coordinate geometry to one Mg(1), one Mg(5), two equivalent Mg(4), two equivalent Mg(8), one Si(5), one Si(9), and two equivalent Si(8) atoms. In the fourteenth Si site, Si(14) is bonded in a distorted linear geometry to two equivalent Mg(6), one Si(6), two equivalent Si(4), and two equivalent Si(7) atoms.
Mg4Si7 crystallizes in the monoclinic Cm space group. There are eight inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 14-coordinate geometry to two equivalent Mg(5), one Si(13), one Si(3), one Si(4), one Si(9), two equivalent Si(1), two equivalent Si(12), two equivalent Si(2), and two equivalent Si(8) atoms. There is one shorter (2.84 Å) and one longer (2.86 Å) Mg(1)-Mg(5) bond length. The Mg(1)-Si(13) bond length is 2.94 Å. The Mg(1)-Si(3) bond length is 2.99 Å. The Mg(1)-Si(4) bond length is 2.95 Å. The Mg(1)-Si(9) bond length is 2.90 Å. Both Mg(1)-Si(1) bond lengths are 2.92 Å. Both Mg(1)-Si(12) bond lengths are 2.94 Å. Both Mg(1)-Si(2) bond lengths are 2.94 Å. Both Mg(1)-Si(8) bond lengths are 2.93 Å. In the second Mg site, Mg(2) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(7), two equivalent Mg(8), one Si(10), one Si(9), and two equivalent Si(5) atoms. Both Mg(2)-Mg(3) bond lengths are 3.08 Å. Both Mg(2)-Mg(4) bond lengths are 3.08 Å. Both Mg(2)-Mg(7) bond lengths are 3.04 Å. Both Mg(2)-Mg(8) bond lengths are 3.04 Å. The Mg(2)-Si(10) bond length is 2.86 Å. The Mg(2)-Si(9) bond length is 2.87 Å. There is one shorter (2.84 Å) and one longer (2.85 Å) Mg(2)-Si(5) bond length. In the third Mg site, Mg(3) is bonded in a 13-coordinate geometry to one Mg(8), two equivalent Mg(2), two equivalent Mg(7), one Si(11), one Si(7), two equivalent Si(10), two equivalent Si(5), and two equivalent Si(6) atoms. The Mg(3)-Mg(8) bond length is 3.11 Å. There is one shorter (2.82 Å) and one longer (2.88 Å) Mg(3)-Mg(7) bond length. The Mg(3)-Si(11) bond length is 2.94 Å. The Mg(3)-Si(7) bond length is 2.89 Å. Both Mg(3)-Si(10) bond lengths are 2.94 Å. Both Mg(3)-Si(5) bond lengths are 3.12 Å. Both Mg(3)-Si(6) bond lengths are 2.91 Å. In the fourth Mg site, Mg(4) is bonded in a 13-coordinate geometry to one Mg(7), two equivalent Mg(2), two equivalent Mg(8), one Si(12), one Si(8), two equivalent Si(13), two equivalent Si(5), and two equivalent Si(9) atoms. The Mg(4)-Mg(7) bond length is 3.08 Å. There is one shorter (2.82 Å) and one longer (2.88 Å) Mg(4)-Mg(8) bond length. The Mg(4)-Si(12) bond length is 2.89 Å. The Mg(4)-Si(8) bond length is 2.87 Å. Both Mg(4)-Si(13) bond lengths are 2.95 Å. Both Mg(4)-Si(5) bond lengths are 3.08 Å. Both Mg(4)-Si(9) bond lengths are 2.99 Å. In the fifth Mg site, Mg(5) is bonded in a 14-coordinate geometry to two equivalent Mg(1), one Si(13), one Si(3), one Si(4), one Si(9), two equivalent Si(1), two equivalent Si(12), two equivalent Si(2), and two equivalent Si(8) atoms. The Mg(5)-Si(13) bond length is 2.95 Å. The Mg(5)-Si(3) bond length is 2.94 Å. The Mg(5)-Si(4) bond length is 2.95 Å. The Mg(5)-Si(9) bond length is 2.89 Å. Both Mg(5)-Si(1) bond lengths are 2.95 Å. Both Mg(5)-Si(12) bond lengths are 2.92 Å. Both Mg(5)-Si(2) bond lengths are 2.96 Å. Both Mg(5)-Si(8) bond lengths are 2.91 Å. In the sixth Mg site, Mg(6) is bonded in a 14-coordinate geometry to one Si(1), one Si(10), one Si(2), one Si(6), two equivalent Si(11), two equivalent Si(14), two equivalent Si(3), two equivalent Si(4), and two equivalent Si(7) atoms. The Mg(6)-Si(1) bond length is 2.95 Å. The Mg(6)-Si(10) bond length is 2.87 Å. The Mg(6)-Si(2) bond length is 2.95 Å. The Mg(6)-Si(6) bond length is 3.00 Å. Both Mg(6)-Si(11) bond lengths are 2.98 Å. There is one shorter (2.82 Å) and one longer (2.87 Å) Mg(6)-Si(14) bond length. Both Mg(6)-Si(3) bond lengths are 3.01 Å. Both Mg(6)-Si(4) bond lengths are 3.04 Å. Both Mg(6)-Si(7) bond lengths are 3.04 Å. In the seventh Mg site, Mg(7) is bonded in a 13-coordinate geometry to one Mg(4), two equivalent Mg(2), two equivalent Mg(3), one Si(11), one Si(7), two equivalent Si(10), two equivalent Si(5), and two equivalent Si(6) atoms. The Mg(7)-Si(11) bond length is 2.90 Å. The Mg(7)-Si(7) bond length is 2.89 Å. Both Mg(7)-Si(10) bond lengths are 2.96 Å. Both Mg(7)-Si(5) bond lengths are 3.00 Å. Both Mg(7)-Si(6) bond lengths are 2.91 Å. In the eighth Mg site, Mg(8) is bonded in a 13-coordinate geometry to one Mg(3), two equivalent Mg(2), two equivalent Mg(4), one Si(12), one Si(8), two equivalent Si(13), two equivalent Si(5), and two equivalent Si(9) atoms. The Mg(8)-Si(12) bond length is 2.95 Å. The Mg(8)-Si(8) bond length is 2.94 Å. Both Mg(8)-Si(13) bond lengths are 2.86 Å. Both Mg(8)-Si(5) bond lengths are 2.98 Å. Both Mg(8)-Si(9) bond lengths are 2.91 Å. There are fourteen inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(6), two equivalent Mg(1), two equivalent Mg(5), one Si(12), one Si(2), and two equivalent Si(3) atoms. The Si(1)-Si(12) bond length is 2.57 Å. The Si(1)-Si(2) bond length is 2.73 Å. Both Si(1)-Si(3) bond lengths are 2.57 Å. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Mg(6), two equivalent Mg(1), two equivalent Mg(5), one Si(1), one Si(8), and two equivalent Si(4) atoms. The Si(2)-Si(8) bond length is 2.63 Å. Both Si(2)-Si(4) bond lengths are 2.53 Å. In the third Si site, Si(3) is bonded in a 8-coordinate geometry to one Mg(1), one Mg(5), two equivalent Mg(6), one Si(11), one Si(4), and two equivalent Si(1) atoms. The Si(3)-Si(11) bond length is 2.57 Å. The Si(3)-Si(4) bond length is 2.47 Å. In the fourth Si site, Si(4) is bonded in a 10-coordinate geometry to one Mg(1), one Mg(5), two equivalent Mg(6), one Si(3), one Si(7), two equivalent Si(14), and two equivalent Si(2) atoms. The Si(4)-Si(7) bond length is 2.59 Å. Both Si(4)-Si(14) bond lengths are 2.86 Å. In the fifth Si site, Si(5) is bonded to two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(7), two equivalent Mg(8), one Si(13), and one Si(6) atom to form a mixture of distorted corner and face-sharing SiMg10Si2 cuboctahedra. The Si(5)-Si(13) bond length is 2.77 Å. The Si(5)-Si(6) bond length is 2.83 Å. In the sixth Si site, Si(6) is bonded in a 11-coordinate geometry to one Mg(6), two equivalent Mg(3), two equivalent Mg(7), one Si(14), one Si(5), two equivalent Si(10), and two equivalent Si(7) atoms. The Si(6)-Si(14) bond length is 2.79 Å. There is one shorter (2.72 Å) and one longer (2.96 Å) Si(6)-Si(10) bond length. Both Si(6)-Si(7) bond lengths are 2.55 Å. In the seventh Si site, Si(7) is bonded in a 10-coordinate geometry to one Mg(3), one Mg(7), two equivalent Mg(6), one Si(11), one Si(4), two equivalent Si(14), and two equivalent Si(6) atoms. The Si(7)-Si(11) bond length is 2.52 Å. Both Si(7)-Si(14) bond lengths are 2.79 Å. In the eighth Si site, Si(8) is bonded in a 10-coordinate geometry to one Mg(4), one Mg(8), two equivalent Mg(1), two equivalent Mg(5), one Si(12), one Si(2), and two equivalent Si(13) atoms. The Si(8)-Si(12) bond length is 2.73 Å. Both Si(8)-Si(13) bond lengths are 2.57 Å. In the ninth Si site, Si(9) is bonded in a 10-coordinate geometry to one Mg(1), one Mg(2), one Mg(5), two equivalent Mg(4), two equivalent Mg(8), one Si(13), and two equivalent Si(12) atoms. The Si(9)-Si(13) bond length is 2.54 Å. Both Si(9)-Si(12) bond lengths are 2.53 Å. In the tenth Si site, Si(10) is bonded in a 9-coordinate geometry to one Mg(2), one Mg(6), two equivalent Mg(3), two equivalent Mg(7), two equivalent Si(11), and two equivalent Si(6) atoms. Both Si(10)-Si(11) bond lengths are 2.53 Å. In the eleventh Si site, Si(11) is bonded in a 8-coordinate geometry to one Mg(3), one Mg(7), two equivalent Mg(6), one Si(3), one Si(7), and two equivalent Si(10) atoms. In the twelfth Si site, Si(12) is bonded in a 10-coordinate geometry to one Mg(4), one Mg(8), two equivalent Mg(1), two equivalent Mg(5), one Si(1), one Si(8), and two equivalent Si(9) atoms. In the thirteenth Si site, Si(13) is bonded in a 10-coordinate geometry to one Mg(1), one Mg(5), two equivalent Mg(4), two equivalent Mg(8), one Si(5), one Si(9), and two equivalent Si(8) atoms. In the fourteenth Si site, Si(14) is bonded in a distorted linear geometry to two equivalent Mg(6), one Si(6), two equivalent Si(4), and two equivalent Si(7) atoms.