MgMg2Si crystallizes in the orthorhombic Pmm2 space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(1), two equivalent Mg(2), four equivalent Mg(3), and four equivalent Si(1) atoms to form distorted MgMg8Si4 cuboctahedra that share corners with ten equivalent Mg(1)Mg8Si4 cuboctahedra, edges with two equivalent Mg(1)Mg8Si4 cuboctahedra, edges with four equivalent Mg(2)Mg8Si4 cuboctahedra, edges with eight equivalent Mg(3)Mg10Si2 cuboctahedra, faces with four equivalent Mg(3)Mg10Si2 cuboctahedra, faces with four equivalent Mg(1)Mg8Si4 cuboctahedra, and faces with eight equivalent Mg(2)Mg8Si4 cuboctahedra. In the second Mg site, Mg(2) is bonded to two equivalent Mg(1), two equivalent Mg(2), four equivalent Mg(3), and four equivalent Si(1) atoms to form distorted MgMg8Si4 cuboctahedra that share corners with eight equivalent Mg(3)Mg10Si2 cuboctahedra, corners with ten equivalent Mg(2)Mg8Si4 cuboctahedra, edges with two equivalent Mg(2)Mg8Si4 cuboctahedra, edges with four equivalent Mg(3)Mg10Si2 cuboctahedra, edges with four equivalent Mg(1)Mg8Si4 cuboctahedra, faces with four equivalent Mg(3)Mg10Si2 cuboctahedra, faces with four equivalent Mg(2)Mg8Si4 cuboctahedra, and faces with eight equivalent Mg(1)Mg8Si4 cuboctahedra. In the third Mg site, Mg(3) is bonded to two equivalent Mg(3), four equivalent Mg(1), four equivalent Mg(2), and two equivalent Si(1) atoms to form distorted MgMg10Si2 cuboctahedra that share corners with eight equivalent Mg(2)Mg8Si4 cuboctahedra, corners with ten equivalent Mg(3)Mg10Si2 cuboctahedra, edges with two equivalent Mg(3)Mg10Si2 cuboctahedra, edges with four equivalent Mg(2)Mg8Si4 cuboctahedra, edges with eight equivalent Mg(1)Mg8Si4 cuboctahedra, faces with four equivalent Mg(3)Mg10Si2 cuboctahedra, faces with four equivalent Mg(1)Mg8Si4 cuboctahedra, and faces with four equivalent Mg(2)Mg8Si4 cuboctahedra. Si(1) is bonded in a distorted q6 geometry to two equivalent Mg(3), four equivalent Mg(1), and four equivalent Mg(2) atoms.
MgMg2Si crystallizes in the orthorhombic Pmm2 space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(1), two equivalent Mg(2), four equivalent Mg(3), and four equivalent Si(1) atoms to form distorted MgMg8Si4 cuboctahedra that share corners with ten equivalent Mg(1)Mg8Si4 cuboctahedra, edges with two equivalent Mg(1)Mg8Si4 cuboctahedra, edges with four equivalent Mg(2)Mg8Si4 cuboctahedra, edges with eight equivalent Mg(3)Mg10Si2 cuboctahedra, faces with four equivalent Mg(3)Mg10Si2 cuboctahedra, faces with four equivalent Mg(1)Mg8Si4 cuboctahedra, and faces with eight equivalent Mg(2)Mg8Si4 cuboctahedra. Both Mg(1)-Mg(1) bond lengths are 3.13 Å. Both Mg(1)-Mg(2) bond lengths are 3.04 Å. All Mg(1)-Mg(3) bond lengths are 3.06 Å. There are two shorter (3.02 Å) and two longer (3.05 Å) Mg(1)-Si(1) bond lengths. In the second Mg site, Mg(2) is bonded to two equivalent Mg(1), two equivalent Mg(2), four equivalent Mg(3), and four equivalent Si(1) atoms to form distorted MgMg8Si4 cuboctahedra that share corners with eight equivalent Mg(3)Mg10Si2 cuboctahedra, corners with ten equivalent Mg(2)Mg8Si4 cuboctahedra, edges with two equivalent Mg(2)Mg8Si4 cuboctahedra, edges with four equivalent Mg(3)Mg10Si2 cuboctahedra, edges with four equivalent Mg(1)Mg8Si4 cuboctahedra, faces with four equivalent Mg(3)Mg10Si2 cuboctahedra, faces with four equivalent Mg(2)Mg8Si4 cuboctahedra, and faces with eight equivalent Mg(1)Mg8Si4 cuboctahedra. Both Mg(2)-Mg(2) bond lengths are 3.13 Å. There are two shorter (2.97 Å) and two longer (3.10 Å) Mg(2)-Mg(3) bond lengths. All Mg(2)-Si(1) bond lengths are 3.04 Å. In the third Mg site, Mg(3) is bonded to two equivalent Mg(3), four equivalent Mg(1), four equivalent Mg(2), and two equivalent Si(1) atoms to form distorted MgMg10Si2 cuboctahedra that share corners with eight equivalent Mg(2)Mg8Si4 cuboctahedra, corners with ten equivalent Mg(3)Mg10Si2 cuboctahedra, edges with two equivalent Mg(3)Mg10Si2 cuboctahedra, edges with four equivalent Mg(2)Mg8Si4 cuboctahedra, edges with eight equivalent Mg(1)Mg8Si4 cuboctahedra, faces with four equivalent Mg(3)Mg10Si2 cuboctahedra, faces with four equivalent Mg(1)Mg8Si4 cuboctahedra, and faces with four equivalent Mg(2)Mg8Si4 cuboctahedra. Both Mg(3)-Mg(3) bond lengths are 3.13 Å. Both Mg(3)-Si(1) bond lengths are 2.98 Å. Si(1) is bonded in a distorted q6 geometry to two equivalent Mg(3), four equivalent Mg(1), and four equivalent Mg(2) atoms.