Mg3Bi2 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to four equivalent Bi(1) atoms to form MgBi4 tetrahedra that share corners with six equivalent Mg(2)Bi6 octahedra, corners with six equivalent Mg(1)Bi4 tetrahedra, edges with three equivalent Mg(2)Bi6 octahedra, and edges with three equivalent Mg(1)Bi4 tetrahedra. The corner-sharing octahedral tilt angles range from 10-59°. In the second Mg site, Mg(2) is bonded to six equivalent Bi(1) atoms to form MgBi6 octahedra that share corners with twelve equivalent Mg(1)Bi4 tetrahedra, edges with six equivalent Mg(2)Bi6 octahedra, and edges with six equivalent Mg(1)Bi4 tetrahedra. Bi(1) is bonded to three equivalent Mg(2) and four equivalent Mg(1) atoms to form a mixture of distorted edge and corner-sharing BiMg7 pentagonal bipyramids.
Mg3Bi2 crystallizes in the trigonal P-3m1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to four equivalent Bi(1) atoms to form MgBi4 tetrahedra that share corners with six equivalent Mg(2)Bi6 octahedra, corners with six equivalent Mg(1)Bi4 tetrahedra, edges with three equivalent Mg(2)Bi6 octahedra, and edges with three equivalent Mg(1)Bi4 tetrahedra. The corner-sharing octahedral tilt angles range from 10-59°. There are three shorter (2.91 Å) and one longer (3.01 Å) Mg(1)-Bi(1) bond length. In the second Mg site, Mg(2) is bonded to six equivalent Bi(1) atoms to form MgBi6 octahedra that share corners with twelve equivalent Mg(1)Bi4 tetrahedra, edges with six equivalent Mg(2)Bi6 octahedra, and edges with six equivalent Mg(1)Bi4 tetrahedra. All Mg(2)-Bi(1) bond lengths are 3.17 Å. Bi(1) is bonded to three equivalent Mg(2) and four equivalent Mg(1) atoms to form a mixture of distorted edge and corner-sharing BiMg7 pentagonal bipyramids.