Mg14SnSi crystallizes in the hexagonal P-6m2 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(4), four equivalent Mg(1), four equivalent Mg(3), and two equivalent Sn(1) atoms to form distorted MgMg10Sn2 cuboctahedra that share corners with four equivalent Si(1)Mg12 cuboctahedra, corners with six equivalent Mg(1)Mg10Sn2 cuboctahedra, corners with eight equivalent Mg(2)Mg10Si2 cuboctahedra, edges with two equivalent Sn(1)Mg12 cuboctahedra, edges with four equivalent Mg(1)Mg10Sn2 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra, edges with eight equivalent Mg(3)Mg10SiSn cuboctahedra, faces with two equivalent Mg(2)Mg10Si2 cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with two equivalent Sn(1)Mg12 cuboctahedra, faces with four equivalent Mg(1)Mg10Sn2 cuboctahedra, and faces with ten equivalent Mg(3)Mg10SiSn cuboctahedra. In the second Mg site, Mg(2) is bonded to two equivalent Mg(4), four equivalent Mg(2), four equivalent Mg(3), and two equivalent Si(1) atoms to form distorted MgMg10Si2 cuboctahedra that share corners with four equivalent Sn(1)Mg12 cuboctahedra, corners with six equivalent Mg(2)Mg10Si2 cuboctahedra, corners with eight equivalent Mg(1)Mg10Sn2 cuboctahedra, edges with two equivalent Si(1)Mg12 cuboctahedra, edges with four equivalent Mg(2)Mg10Si2 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra, edges with eight equivalent Mg(3)Mg10SiSn cuboctahedra, faces with two equivalent Mg(1)Mg10Sn2 cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with two equivalent Si(1)Mg12 cuboctahedra, faces with four equivalent Mg(2)Mg10Si2 cuboctahedra, and faces with ten equivalent Mg(3)Mg10SiSn cuboctahedra. In the third Mg site, Mg(3) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), four equivalent Mg(3), one Sn(1), and one Si(1) atom to form distorted MgMg10SiSn cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra, corners with fourteen equivalent Mg(3)Mg10SiSn cuboctahedra, edges with two equivalent Mg(4)Mg12 cuboctahedra, edges with two equivalent Sn(1)Mg12 cuboctahedra, edges with two equivalent Si(1)Mg12 cuboctahedra, edges with four equivalent Mg(2)Mg10Si2 cuboctahedra, edges with four equivalent Mg(3)Mg10SiSn cuboctahedra, edges with four equivalent Mg(1)Mg10Sn2 cuboctahedra,  a faceface with one Sn(1)Mg12 cuboctahedra,  a faceface with one Si(1)Mg12 cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with five equivalent Mg(2)Mg10Si2 cuboctahedra, faces with five equivalent Mg(1)Mg10Sn2 cuboctahedra, and faces with six equivalent Mg(3)Mg10SiSn cuboctahedra. In the fourth Mg site, Mg(4) is bonded to three equivalent Mg(1), three equivalent Mg(2), and six equivalent Mg(3) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(4)Mg12 cuboctahedra, corners with twelve equivalent Mg(3)Mg10SiSn cuboctahedra, edges with six equivalent Mg(2)Mg10Si2 cuboctahedra, edges with six equivalent Mg(3)Mg10SiSn cuboctahedra, edges with six equivalent Mg(1)Mg10Sn2 cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with three equivalent Mg(2)Mg10Si2 cuboctahedra, faces with three equivalent Mg(1)Mg10Sn2 cuboctahedra, faces with three equivalent Sn(1)Mg12 cuboctahedra, faces with three equivalent Si(1)Mg12 cuboctahedra, and faces with six equivalent Mg(3)Mg10SiSn cuboctahedra. Sn(1) is bonded to six equivalent Mg(1) and six equivalent Mg(3) atoms to form SnMg12 cuboctahedra that share corners with six equivalent Sn(1)Mg12 cuboctahedra, corners with twelve equivalent Mg(2)Mg10Si2 cuboctahedra, edges with six equivalent Mg(1)Mg10Sn2 cuboctahedra, edges with twelve equivalent Mg(3)Mg10SiSn cuboctahedra, faces with two equivalent Si(1)Mg12 cuboctahedra, faces with six equivalent Mg(3)Mg10SiSn cuboctahedra, faces with six equivalent Mg(1)Mg10Sn2 cuboctahedra, and faces with six equivalent Mg(4)Mg12 cuboctahedra. Si(1) is bonded to six equivalent Mg(2) and six equivalent Mg(3) atoms to form SiMg12 cuboctahedra that share corners with six equivalent Si(1)Mg12 cuboctahedra, corners with twelve equivalent Mg(1)Mg10Sn2 cuboctahedra, edges with six equivalent Mg(2)Mg10Si2 cuboctahedra, edges with twelve equivalent Mg(3)Mg10SiSn cuboctahedra, faces with two equivalent Sn(1)Mg12 cuboctahedra, faces with six equivalent Mg(2)Mg10Si2 cuboctahedra, faces with six equivalent Mg(3)Mg10SiSn cuboctahedra, and faces with six equivalent Mg(4)Mg12 cuboctahedra.
Mg14SnSi crystallizes in the hexagonal P-6m2 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(4), four equivalent Mg(1), four equivalent Mg(3), and two equivalent Sn(1) atoms to form distorted MgMg10Sn2 cuboctahedra that share corners with four equivalent Si(1)Mg12 cuboctahedra, corners with six equivalent Mg(1)Mg10Sn2 cuboctahedra, corners with eight equivalent Mg(2)Mg10Si2 cuboctahedra, edges with two equivalent Sn(1)Mg12 cuboctahedra, edges with four equivalent Mg(1)Mg10Sn2 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra, edges with eight equivalent Mg(3)Mg10SiSn cuboctahedra, faces with two equivalent Mg(2)Mg10Si2 cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with two equivalent Sn(1)Mg12 cuboctahedra, faces with four equivalent Mg(1)Mg10Sn2 cuboctahedra, and faces with ten equivalent Mg(3)Mg10SiSn cuboctahedra. Both Mg(1)-Mg(4) bond lengths are 3.14 Å. There are two shorter (3.15 Å) and two longer (3.16 Å) Mg(1)-Mg(1) bond lengths. All Mg(1)-Mg(3) bond lengths are 3.19 Å. Both Mg(1)-Sn(1) bond lengths are 3.15 Å. In the second Mg site, Mg(2) is bonded to two equivalent Mg(4), four equivalent Mg(2), four equivalent Mg(3), and two equivalent Si(1) atoms to form distorted MgMg10Si2 cuboctahedra that share corners with four equivalent Sn(1)Mg12 cuboctahedra, corners with six equivalent Mg(2)Mg10Si2 cuboctahedra, corners with eight equivalent Mg(1)Mg10Sn2 cuboctahedra, edges with two equivalent Si(1)Mg12 cuboctahedra, edges with four equivalent Mg(2)Mg10Si2 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra, edges with eight equivalent Mg(3)Mg10SiSn cuboctahedra, faces with two equivalent Mg(1)Mg10Sn2 cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with two equivalent Si(1)Mg12 cuboctahedra, faces with four equivalent Mg(2)Mg10Si2 cuboctahedra, and faces with ten equivalent Mg(3)Mg10SiSn cuboctahedra. Both Mg(2)-Mg(4) bond lengths are 3.13 Å. There are two shorter (3.14 Å) and two longer (3.17 Å) Mg(2)-Mg(2) bond lengths. All Mg(2)-Mg(3) bond lengths are 3.09 Å. Both Mg(2)-Si(1) bond lengths are 3.15 Å. In the third Mg site, Mg(3) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), four equivalent Mg(3), one Sn(1), and one Si(1) atom to form distorted MgMg10SiSn cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra, corners with fourteen equivalent Mg(3)Mg10SiSn cuboctahedra, edges with two equivalent Mg(4)Mg12 cuboctahedra, edges with two equivalent Sn(1)Mg12 cuboctahedra, edges with two equivalent Si(1)Mg12 cuboctahedra, edges with four equivalent Mg(2)Mg10Si2 cuboctahedra, edges with four equivalent Mg(3)Mg10SiSn cuboctahedra, edges with four equivalent Mg(1)Mg10Sn2 cuboctahedra,  a faceface with one Sn(1)Mg12 cuboctahedra,  a faceface with one Si(1)Mg12 cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with five equivalent Mg(2)Mg10Si2 cuboctahedra, faces with five equivalent Mg(1)Mg10Sn2 cuboctahedra, and faces with six equivalent Mg(3)Mg10SiSn cuboctahedra. Both Mg(3)-Mg(4) bond lengths are 3.15 Å. There are two shorter (3.15 Å) and two longer (3.16 Å) Mg(3)-Mg(3) bond lengths. The Mg(3)-Sn(1) bond length is 3.20 Å. The Mg(3)-Si(1) bond length is 3.09 Å. In the fourth Mg site, Mg(4) is bonded to three equivalent Mg(1), three equivalent Mg(2), and six equivalent Mg(3) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(4)Mg12 cuboctahedra, corners with twelve equivalent Mg(3)Mg10SiSn cuboctahedra, edges with six equivalent Mg(2)Mg10Si2 cuboctahedra, edges with six equivalent Mg(3)Mg10SiSn cuboctahedra, edges with six equivalent Mg(1)Mg10Sn2 cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with three equivalent Mg(2)Mg10Si2 cuboctahedra, faces with three equivalent Mg(1)Mg10Sn2 cuboctahedra, faces with three equivalent Sn(1)Mg12 cuboctahedra, faces with three equivalent Si(1)Mg12 cuboctahedra, and faces with six equivalent Mg(3)Mg10SiSn cuboctahedra. Sn(1) is bonded to six equivalent Mg(1) and six equivalent Mg(3) atoms to form SnMg12 cuboctahedra that share corners with six equivalent Sn(1)Mg12 cuboctahedra, corners with twelve equivalent Mg(2)Mg10Si2 cuboctahedra, edges with six equivalent Mg(1)Mg10Sn2 cuboctahedra, edges with twelve equivalent Mg(3)Mg10SiSn cuboctahedra, faces with two equivalent Si(1)Mg12 cuboctahedra, faces with six equivalent Mg(3)Mg10SiSn cuboctahedra, faces with six equivalent Mg(1)Mg10Sn2 cuboctahedra, and faces with six equivalent Mg(4)Mg12 cuboctahedra. Si(1) is bonded to six equivalent Mg(2) and six equivalent Mg(3) atoms to form SiMg12 cuboctahedra that share corners with six equivalent Si(1)Mg12 cuboctahedra, corners with twelve equivalent Mg(1)Mg10Sn2 cuboctahedra, edges with six equivalent Mg(2)Mg10Si2 cuboctahedra, edges with twelve equivalent Mg(3)Mg10SiSn cuboctahedra, faces with two equivalent Sn(1)Mg12 cuboctahedra, faces with six equivalent Mg(2)Mg10Si2 cuboctahedra, faces with six equivalent Mg(3)Mg10SiSn cuboctahedra, and faces with six equivalent Mg(4)Mg12 cuboctahedra.