Li12Mg3Si4 crystallizes in the cubic I-43d space group. Li(1) is bonded in a 5-coordinate geometry to two equivalent Mg(1) and three equivalent Si(1) atoms. Mg(1) is bonded to eight equivalent Li(1) and four equivalent Si(1) atoms to form MgLi8Si4 cuboctahedra that share corners with eight equivalent Si(1)Li9Mg3 cuboctahedra, edges with eight equivalent Mg(1)Li8Si4 cuboctahedra, and faces with four equivalent Si(1)Li9Mg3 cuboctahedra. Si(1) is bonded to nine equivalent Li(1) and three equivalent Mg(1) atoms to form distorted SiLi9Mg3 cuboctahedra that share corners with six equivalent Mg(1)Li8Si4 cuboctahedra, edges with six equivalent Si(1)Li9Mg3 cuboctahedra, faces with three equivalent Mg(1)Li8Si4 cuboctahedra, and faces with five equivalent Si(1)Li9Mg3 cuboctahedra.
Li12Mg3Si4 crystallizes in the cubic I-43d space group. Li(1) is bonded in a 5-coordinate geometry to two equivalent Mg(1) and three equivalent Si(1) atoms. There is one shorter (2.79 Å) and one longer (2.80 Å) Li(1)-Mg(1) bond length. There are a spread of Li(1)-Si(1) bond distances ranging from 2.66-2.78 Å. Mg(1) is bonded to eight equivalent Li(1) and four equivalent Si(1) atoms to form MgLi8Si4 cuboctahedra that share corners with eight equivalent Si(1)Li9Mg3 cuboctahedra, edges with eight equivalent Mg(1)Li8Si4 cuboctahedra, and faces with four equivalent Si(1)Li9Mg3 cuboctahedra. All Mg(1)-Si(1) bond lengths are 2.89 Å. Si(1) is bonded to nine equivalent Li(1) and three equivalent Mg(1) atoms to form distorted SiLi9Mg3 cuboctahedra that share corners with six equivalent Mg(1)Li8Si4 cuboctahedra, edges with six equivalent Si(1)Li9Mg3 cuboctahedra, faces with three equivalent Mg(1)Li8Si4 cuboctahedra, and faces with five equivalent Si(1)Li9Mg3 cuboctahedra.