MgLa2I8 crystallizes in the monoclinic C2/c space group. Mg(1) is bonded to two equivalent I(2), two equivalent I(3), and two equivalent I(4) atoms to form MgI6 octahedra that share corners with two equivalent La(1)I7 pentagonal bipyramids and edges with four equivalent La(1)I7 pentagonal bipyramids. La(1) is bonded to one I(3), two equivalent I(1), two equivalent I(2), and two equivalent I(4) atoms to form distorted LaI7 pentagonal bipyramids that share  a cornercorner with one Mg(1)I6 octahedra, edges with two equivalent Mg(1)I6 octahedra, and edges with three equivalent La(1)I7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 52°. There are four inequivalent I sites. In the first I site, I(1) is bonded in a water-like geometry to two equivalent La(1) atoms. In the second I site, I(2) is bonded in a distorted T-shaped geometry to one Mg(1) and two equivalent La(1) atoms. In the third I site, I(3) is bonded in a water-like geometry to one Mg(1) and one La(1) atom. In the fourth I site, I(4) is bonded in a trigonal non-coplanar geometry to one Mg(1) and two equivalent La(1) atoms.
MgLa2I8 crystallizes in the monoclinic C2/c space group. Mg(1) is bonded to two equivalent I(2), two equivalent I(3), and two equivalent I(4) atoms to form MgI6 octahedra that share corners with two equivalent La(1)I7 pentagonal bipyramids and edges with four equivalent La(1)I7 pentagonal bipyramids. Both Mg(1)-I(2) bond lengths are 3.12 Å. Both Mg(1)-I(3) bond lengths are 2.87 Å. Both Mg(1)-I(4) bond lengths are 3.03 Å. La(1) is bonded to one I(3), two equivalent I(1), two equivalent I(2), and two equivalent I(4) atoms to form distorted LaI7 pentagonal bipyramids that share  a cornercorner with one Mg(1)I6 octahedra, edges with two equivalent Mg(1)I6 octahedra, and edges with three equivalent La(1)I7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 52°. The La(1)-I(3) bond length is 3.17 Å. There is one shorter (3.19 Å) and one longer (3.21 Å) La(1)-I(1) bond length. There is one shorter (3.24 Å) and one longer (3.39 Å) La(1)-I(2) bond length. There is one shorter (3.30 Å) and one longer (3.50 Å) La(1)-I(4) bond length. There are four inequivalent I sites. In the first I site, I(1) is bonded in a water-like geometry to two equivalent La(1) atoms. In the second I site, I(2) is bonded in a distorted T-shaped geometry to one Mg(1) and two equivalent La(1) atoms. In the third I site, I(3) is bonded in a water-like geometry to one Mg(1) and one La(1) atom. In the fourth I site, I(4) is bonded in a trigonal non-coplanar geometry to one Mg(1) and two equivalent La(1) atoms.