La3MgBi5 crystallizes in the hexagonal P6_3/mcm space group. Mg(1) is bonded to six equivalent Bi(1) atoms to form face-sharing MgBi6 octahedra. La(1) is bonded in a 9-coordinate geometry to four equivalent Bi(2) and five equivalent Bi(1) atoms. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to two equivalent Mg(1) and five equivalent La(1) atoms to form a mixture of distorted face, corner, and edge-sharing BiLa5Mg2 pentagonal bipyramids. In the second Bi site, Bi(2) is bonded in a 8-coordinate geometry to six equivalent La(1) and two equivalent Bi(2) atoms.
La3MgBi5 crystallizes in the hexagonal P6_3/mcm space group. Mg(1) is bonded to six equivalent Bi(1) atoms to form face-sharing MgBi6 octahedra. All Mg(1)-Bi(1) bond lengths are 3.10 Å. La(1) is bonded in a 9-coordinate geometry to four equivalent Bi(2) and five equivalent Bi(1) atoms. All La(1)-Bi(2) bond lengths are 3.50 Å. There are two shorter (3.34 Å) and three longer (3.49 Å) La(1)-Bi(1) bond lengths. There are two inequivalent Bi sites. In the first Bi site, Bi(1) is bonded to two equivalent Mg(1) and five equivalent La(1) atoms to form a mixture of distorted face, corner, and edge-sharing BiLa5Mg2 pentagonal bipyramids. In the second Bi site, Bi(2) is bonded in a 8-coordinate geometry to six equivalent La(1) and two equivalent Bi(2) atoms. Both Bi(2)-Bi(2) bond lengths are 3.31 Å.