Ba2Mg3Si4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 14-coordinate geometry to one Mg(1), four equivalent Mg(2), two equivalent Si(1), two equivalent Si(4), and five equivalent Si(2) atoms. In the second Ba site, Ba(2) is bonded in a 16-coordinate geometry to one Mg(2), three equivalent Mg(1), four equivalent Mg(3), two equivalent Si(1), two equivalent Si(4), and four equivalent Si(3) atoms. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Ba(1), three equivalent Ba(2), one Si(3), one Si(4), and two equivalent Si(1) atoms to form a mixture of edge, corner, and face-sharing MgBa4Si4 tetrahedra. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Ba(2), four equivalent Ba(1), one Si(1), two equivalent Si(2), and two equivalent Si(4) atoms. In the third Mg site, Mg(3) is bonded to four equivalent Ba(2), one Si(1), and three equivalent Si(3) atoms to form a mixture of distorted edge, corner, and face-sharing MgBa4Si4 tetrahedra. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), one Mg(2), one Mg(3), two equivalent Mg(1), and one Si(4) atom. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to five equivalent Ba(1), two equivalent Mg(2), one Si(2), and one Si(4) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to four equivalent Ba(2), one Mg(1), three equivalent Mg(3), and one Si(3) atom. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), one Mg(1), two equivalent Mg(2), one Si(1), and one Si(2) atom.
Ba2Mg3Si4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 14-coordinate geometry to one Mg(1), four equivalent Mg(2), two equivalent Si(1), two equivalent Si(4), and five equivalent Si(2) atoms. The Ba(1)-Mg(1) bond length is 3.73 Å. There are a spread of Ba(1)-Mg(2) bond distances ranging from 3.44-3.84 Å. Both Ba(1)-Si(1) bond lengths are 3.50 Å. Both Ba(1)-Si(4) bond lengths are 3.43 Å. There are a spread of Ba(1)-Si(2) bond distances ranging from 3.42-3.51 Å. In the second Ba site, Ba(2) is bonded in a 16-coordinate geometry to one Mg(2), three equivalent Mg(1), four equivalent Mg(3), two equivalent Si(1), two equivalent Si(4), and four equivalent Si(3) atoms. The Ba(2)-Mg(2) bond length is 3.71 Å. There are two shorter (3.63 Å) and one longer (3.64 Å) Ba(2)-Mg(1) bond length. There are two shorter (3.60 Å) and two longer (3.62 Å) Ba(2)-Mg(3) bond lengths. Both Ba(2)-Si(1) bond lengths are 3.58 Å. Both Ba(2)-Si(4) bond lengths are 3.43 Å. There are two shorter (3.47 Å) and two longer (3.51 Å) Ba(2)-Si(3) bond lengths. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Ba(1), three equivalent Ba(2), one Si(3), one Si(4), and two equivalent Si(1) atoms to form a mixture of edge, corner, and face-sharing MgBa4Si4 tetrahedra. The Mg(1)-Si(3) bond length is 2.79 Å. The Mg(1)-Si(4) bond length is 2.75 Å. Both Mg(1)-Si(1) bond lengths are 2.77 Å. In the second Mg site, Mg(2) is bonded in a 5-coordinate geometry to one Ba(2), four equivalent Ba(1), one Si(1), two equivalent Si(2), and two equivalent Si(4) atoms. The Mg(2)-Si(1) bond length is 2.72 Å. Both Mg(2)-Si(2) bond lengths are 2.86 Å. Both Mg(2)-Si(4) bond lengths are 2.87 Å. In the third Mg site, Mg(3) is bonded to four equivalent Ba(2), one Si(1), and three equivalent Si(3) atoms to form a mixture of distorted edge, corner, and face-sharing MgBa4Si4 tetrahedra. The Mg(3)-Si(1) bond length is 2.80 Å. There are two shorter (2.78 Å) and one longer (2.79 Å) Mg(3)-Si(3) bond length. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), one Mg(2), one Mg(3), two equivalent Mg(1), and one Si(4) atom. The Si(1)-Si(4) bond length is 2.44 Å. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to five equivalent Ba(1), two equivalent Mg(2), one Si(2), and one Si(4) atom. The Si(2)-Si(2) bond length is 2.40 Å. The Si(2)-Si(4) bond length is 2.43 Å. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to four equivalent Ba(2), one Mg(1), three equivalent Mg(3), and one Si(3) atom. The Si(3)-Si(3) bond length is 2.50 Å. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), one Mg(1), two equivalent Mg(2), one Si(1), and one Si(2) atom.