MgSi2 crystallizes in the monoclinic Cm space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to two equivalent Si(2), two equivalent Si(5), and two equivalent Si(8) atoms. In the second Mg site, Mg(2) is bonded to one Si(1), two equivalent Si(2), two equivalent Si(5), and two equivalent Si(6) atoms to form a mixture of distorted corner and edge-sharing MgSi7 pentagonal bipyramids. In the third Mg site, Mg(3) is bonded in a 10-coordinate geometry to two equivalent Si(1), two equivalent Si(3), two equivalent Si(4), two equivalent Si(6), and two equivalent Si(7) atoms. In the fourth Mg site, Mg(4) is bonded in a 8-coordinate geometry to two equivalent Si(3), two equivalent Si(4), two equivalent Si(5), and two equivalent Si(8) atoms. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 6-coordinate geometry to one Mg(2), two equivalent Mg(3), one Si(2), and two equivalent Si(6) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), one Si(1), and two equivalent Si(5) atoms. In the third Si site, Si(3) is bonded in a distorted q6 geometry to two equivalent Mg(3), two equivalent Mg(4), two equivalent Si(4), two equivalent Si(7), and two equivalent Si(8) atoms. In the fourth Si site, Si(4) is bonded in a distorted q6 geometry to two equivalent Mg(3), two equivalent Mg(4), two equivalent Si(3), two equivalent Si(7), and two equivalent Si(8) atoms. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), and two equivalent Si(2) atoms. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to two equivalent Mg(2), two equivalent Mg(3), one Si(7), and two equivalent Si(1) atoms. In the seventh Si site, Si(7) is bonded in a 7-coordinate geometry to two equivalent Mg(3), one Si(6), two equivalent Si(3), and two equivalent Si(4) atoms. In the eighth Si site, Si(8) is bonded in a 8-coordinate geometry to two equivalent Mg(1), two equivalent Mg(4), two equivalent Si(3), and two equivalent Si(4) atoms.
MgSi2 crystallizes in the monoclinic Cm space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to two equivalent Si(2), two equivalent Si(5), and two equivalent Si(8) atoms. Both Mg(1)-Si(2) bond lengths are 2.86 Å. There is one shorter (2.73 Å) and one longer (2.83 Å) Mg(1)-Si(5) bond length. Both Mg(1)-Si(8) bond lengths are 2.85 Å. In the second Mg site, Mg(2) is bonded to one Si(1), two equivalent Si(2), two equivalent Si(5), and two equivalent Si(6) atoms to form a mixture of distorted corner and edge-sharing MgSi7 pentagonal bipyramids. The Mg(2)-Si(1) bond length is 2.92 Å. There is one shorter (2.81 Å) and one longer (2.86 Å) Mg(2)-Si(2) bond length. Both Mg(2)-Si(5) bond lengths are 2.94 Å. Both Mg(2)-Si(6) bond lengths are 2.86 Å. In the third Mg site, Mg(3) is bonded in a 10-coordinate geometry to two equivalent Si(1), two equivalent Si(3), two equivalent Si(4), two equivalent Si(6), and two equivalent Si(7) atoms. Both Mg(3)-Si(1) bond lengths are 2.82 Å. Both Mg(3)-Si(3) bond lengths are 3.12 Å. Both Mg(3)-Si(4) bond lengths are 3.06 Å. There is one shorter (3.01 Å) and one longer (3.04 Å) Mg(3)-Si(6) bond length. There is one shorter (2.76 Å) and one longer (2.90 Å) Mg(3)-Si(7) bond length. In the fourth Mg site, Mg(4) is bonded in a 8-coordinate geometry to two equivalent Si(3), two equivalent Si(4), two equivalent Si(5), and two equivalent Si(8) atoms. Both Mg(4)-Si(3) bond lengths are 3.06 Å. Both Mg(4)-Si(4) bond lengths are 3.03 Å. Both Mg(4)-Si(5) bond lengths are 2.84 Å. There is one shorter (2.77 Å) and one longer (2.80 Å) Mg(4)-Si(8) bond length. There are eight inequivalent Si sites. In the first Si site, Si(1) is bonded in a 6-coordinate geometry to one Mg(2), two equivalent Mg(3), one Si(2), and two equivalent Si(6) atoms. The Si(1)-Si(2) bond length is 2.40 Å. Both Si(1)-Si(6) bond lengths are 2.37 Å. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), one Si(1), and two equivalent Si(5) atoms. Both Si(2)-Si(5) bond lengths are 2.38 Å. In the third Si site, Si(3) is bonded in a distorted q6 geometry to two equivalent Mg(3), two equivalent Mg(4), two equivalent Si(4), two equivalent Si(7), and two equivalent Si(8) atoms. There is one shorter (2.66 Å) and one longer (2.67 Å) Si(3)-Si(4) bond length. Both Si(3)-Si(7) bond lengths are 2.55 Å. Both Si(3)-Si(8) bond lengths are 2.54 Å. In the fourth Si site, Si(4) is bonded in a distorted q6 geometry to two equivalent Mg(3), two equivalent Mg(4), two equivalent Si(3), two equivalent Si(7), and two equivalent Si(8) atoms. Both Si(4)-Si(7) bond lengths are 2.51 Å. Both Si(4)-Si(8) bond lengths are 2.59 Å. In the fifth Si site, Si(5) is bonded in a 8-coordinate geometry to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), and two equivalent Si(2) atoms. In the sixth Si site, Si(6) is bonded in a 7-coordinate geometry to two equivalent Mg(2), two equivalent Mg(3), one Si(7), and two equivalent Si(1) atoms. The Si(6)-Si(7) bond length is 2.39 Å. In the seventh Si site, Si(7) is bonded in a 7-coordinate geometry to two equivalent Mg(3), one Si(6), two equivalent Si(3), and two equivalent Si(4) atoms. In the eighth Si site, Si(8) is bonded in a 8-coordinate geometry to two equivalent Mg(1), two equivalent Mg(4), two equivalent Si(3), and two equivalent Si(4) atoms.