Sr4Mg3Al5 is Hexagonal Laves-derived structured and crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 16-coordinate geometry to one Sr(1), three equivalent Sr(2), three equivalent Mg(1), three equivalent Al(1), and six equivalent Al(2) atoms. In the second Sr site, Sr(2) is bonded in a 12-coordinate geometry to three equivalent Sr(1), six equivalent Mg(1), three equivalent Al(1), and three equivalent Al(2) atoms. Mg(1) is bonded to two equivalent Sr(1), four equivalent Sr(2), four equivalent Mg(1), and two equivalent Al(1) atoms to form MgSr6Mg4Al2 cuboctahedra that share corners with four equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, corners with four equivalent Al(1)Sr6Mg3Al3 cuboctahedra, corners with ten equivalent Al(2)Sr6Al6 cuboctahedra, edges with two equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, edges with four equivalent Al(2)Sr6Al6 cuboctahedra, faces with four equivalent Al(2)Sr6Al6 cuboctahedra, faces with six equivalent Al(1)Sr6Mg3Al3 cuboctahedra, and faces with eight equivalent Mg(1)Sr6Mg4Al2 cuboctahedra. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to three equivalent Sr(1), three equivalent Sr(2), three equivalent Mg(1), and three equivalent Al(2) atoms to form AlSr6Mg3Al3 cuboctahedra that share corners with three equivalent Al(1)Sr6Mg3Al3 cuboctahedra, corners with six equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, corners with six equivalent Al(2)Sr6Al6 cuboctahedra, edges with six equivalent Al(1)Sr6Mg3Al3 cuboctahedra,  a faceface with one Al(1)Sr6Mg3Al3 cuboctahedra, faces with nine equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, and faces with nine equivalent Al(2)Sr6Al6 cuboctahedra. In the second Al site, Al(2) is bonded to two equivalent Sr(2), four equivalent Sr(1), two equivalent Al(1), and four equivalent Al(2) atoms to form distorted AlSr6Al6 cuboctahedra that share corners with four equivalent Al(2)Sr6Al6 cuboctahedra, corners with four equivalent Al(1)Sr6Mg3Al3 cuboctahedra, corners with ten equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, edges with two equivalent Al(2)Sr6Al6 cuboctahedra, edges with four equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, faces with four equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, faces with six equivalent Al(1)Sr6Mg3Al3 cuboctahedra, and faces with eight equivalent Al(2)Sr6Al6 cuboctahedra.
Sr4Mg3Al5 is Hexagonal Laves-derived structured and crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 16-coordinate geometry to one Sr(1), three equivalent Sr(2), three equivalent Mg(1), three equivalent Al(1), and six equivalent Al(2) atoms. The Sr(1)-Sr(1) bond length is 3.55 Å. All Sr(1)-Sr(2) bond lengths are 3.68 Å. All Sr(1)-Mg(1) bond lengths are 3.66 Å. All Sr(1)-Al(1) bond lengths are 3.52 Å. All Sr(1)-Al(2) bond lengths are 3.51 Å. In the second Sr site, Sr(2) is bonded in a 12-coordinate geometry to three equivalent Sr(1), six equivalent Mg(1), three equivalent Al(1), and three equivalent Al(2) atoms. All Sr(2)-Mg(1) bond lengths are 3.65 Å. All Sr(2)-Al(1) bond lengths are 3.57 Å. All Sr(2)-Al(2) bond lengths are 3.41 Å. Mg(1) is bonded to two equivalent Sr(1), four equivalent Sr(2), four equivalent Mg(1), and two equivalent Al(1) atoms to form MgSr6Mg4Al2 cuboctahedra that share corners with four equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, corners with four equivalent Al(1)Sr6Mg3Al3 cuboctahedra, corners with ten equivalent Al(2)Sr6Al6 cuboctahedra, edges with two equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, edges with four equivalent Al(2)Sr6Al6 cuboctahedra, faces with four equivalent Al(2)Sr6Al6 cuboctahedra, faces with six equivalent Al(1)Sr6Mg3Al3 cuboctahedra, and faces with eight equivalent Mg(1)Sr6Mg4Al2 cuboctahedra. All Mg(1)-Mg(1) bond lengths are 3.02 Å. Both Mg(1)-Al(1) bond lengths are 3.29 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to three equivalent Sr(1), three equivalent Sr(2), three equivalent Mg(1), and three equivalent Al(2) atoms to form AlSr6Mg3Al3 cuboctahedra that share corners with three equivalent Al(1)Sr6Mg3Al3 cuboctahedra, corners with six equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, corners with six equivalent Al(2)Sr6Al6 cuboctahedra, edges with six equivalent Al(1)Sr6Mg3Al3 cuboctahedra,  a faceface with one Al(1)Sr6Mg3Al3 cuboctahedra, faces with nine equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, and faces with nine equivalent Al(2)Sr6Al6 cuboctahedra. All Al(1)-Al(2) bond lengths are 2.82 Å. In the second Al site, Al(2) is bonded to two equivalent Sr(2), four equivalent Sr(1), two equivalent Al(1), and four equivalent Al(2) atoms to form distorted AlSr6Al6 cuboctahedra that share corners with four equivalent Al(2)Sr6Al6 cuboctahedra, corners with four equivalent Al(1)Sr6Mg3Al3 cuboctahedra, corners with ten equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, edges with two equivalent Al(2)Sr6Al6 cuboctahedra, edges with four equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, faces with four equivalent Mg(1)Sr6Mg4Al2 cuboctahedra, faces with six equivalent Al(1)Sr6Mg3Al3 cuboctahedra, and faces with eight equivalent Al(2)Sr6Al6 cuboctahedra. There are two shorter (3.00 Å) and two longer (3.05 Å) Al(2)-Al(2) bond lengths.