CsMgI3 crystallizes in the hexagonal P6_3/mmc space group. Cs(1) is bonded to twelve equivalent I(1) atoms to form CsI12 cuboctahedra that share corners with six equivalent Cs(1)I12 cuboctahedra, corners with six equivalent Mg(1)I6 octahedra, faces with eight equivalent Cs(1)I12 cuboctahedra, and faces with six equivalent Mg(1)I6 octahedra. The corner-sharing octahedral tilt angles are 18°. Mg(1) is bonded to six equivalent I(1) atoms to form MgI6 octahedra that share corners with six equivalent Cs(1)I12 cuboctahedra, faces with six equivalent Cs(1)I12 cuboctahedra, and faces with two equivalent Mg(1)I6 octahedra. I(1) is bonded in a 2-coordinate geometry to four equivalent Cs(1) and two equivalent Mg(1) atoms.
CsMgI3 crystallizes in the hexagonal P6_3/mmc space group. Cs(1) is bonded to twelve equivalent I(1) atoms to form CsI12 cuboctahedra that share corners with six equivalent Cs(1)I12 cuboctahedra, corners with six equivalent Mg(1)I6 octahedra, faces with eight equivalent Cs(1)I12 cuboctahedra, and faces with six equivalent Mg(1)I6 octahedra. The corner-sharing octahedral tilt angles are 18°. There are six shorter (4.15 Å) and six longer (4.29 Å) Cs(1)-I(1) bond lengths. Mg(1) is bonded to six equivalent I(1) atoms to form MgI6 octahedra that share corners with six equivalent Cs(1)I12 cuboctahedra, faces with six equivalent Cs(1)I12 cuboctahedra, and faces with two equivalent Mg(1)I6 octahedra. All Mg(1)-I(1) bond lengths are 2.93 Å. I(1) is bonded in a 2-coordinate geometry to four equivalent Cs(1) and two equivalent Mg(1) atoms.