SrMg5 crystallizes in the hexagonal P-6m2 space group. Sr(1) is bonded to six equivalent Sr(1) and six equivalent Mg(1) atoms to form SrSr6Mg6 cuboctahedra that share corners with six equivalent Sr(1)Sr6Mg6 cuboctahedra, corners with twelve equivalent Mg(2)Mg6 cuboctahedra, edges with six equivalent Sr(1)Sr6Mg6 cuboctahedra, faces with two equivalent Mg(2)Mg6 cuboctahedra, and faces with six equivalent Sr(1)Sr6Mg6 cuboctahedra. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to three equivalent Sr(1) and three equivalent Mg(2) atoms. In the second Mg site, Mg(2) is bonded to three equivalent Mg(1) and three equivalent Mg(3) atoms to form distorted MgMg6 cuboctahedra that share corners with six equivalent Sr(1)Sr6Mg6 cuboctahedra, corners with six equivalent Mg(2)Mg6 cuboctahedra, edges with six equivalent Mg(2)Mg6 cuboctahedra,  a faceface with one Sr(1)Sr6Mg6 cuboctahedra, and  a faceface with one Mg(2)Mg6 cuboctahedra. In the third Mg site, Mg(3) is bonded to six equivalent Mg(2) atoms to form distorted edge-sharing MgMg6 cuboctahedra.
SrMg5 crystallizes in the hexagonal P-6m2 space group. Sr(1) is bonded to six equivalent Sr(1) and six equivalent Mg(1) atoms to form SrSr6Mg6 cuboctahedra that share corners with six equivalent Sr(1)Sr6Mg6 cuboctahedra, corners with twelve equivalent Mg(2)Mg6 cuboctahedra, edges with six equivalent Sr(1)Sr6Mg6 cuboctahedra, faces with two equivalent Mg(2)Mg6 cuboctahedra, and faces with six equivalent Sr(1)Sr6Mg6 cuboctahedra. All Sr(1)-Sr(1) bond lengths are 3.52 Å. All Sr(1)-Mg(1) bond lengths are 3.60 Å. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to three equivalent Sr(1) and three equivalent Mg(2) atoms. All Mg(1)-Mg(2) bond lengths are 3.11 Å. In the second Mg site, Mg(2) is bonded to three equivalent Mg(1) and three equivalent Mg(3) atoms to form distorted MgMg6 cuboctahedra that share corners with six equivalent Sr(1)Sr6Mg6 cuboctahedra, corners with six equivalent Mg(2)Mg6 cuboctahedra, edges with six equivalent Mg(2)Mg6 cuboctahedra,  a faceface with one Sr(1)Sr6Mg6 cuboctahedra, and  a faceface with one Mg(2)Mg6 cuboctahedra. All Mg(2)-Mg(3) bond lengths are 3.12 Å. In the third Mg site, Mg(3) is bonded to six equivalent Mg(2) atoms to form distorted edge-sharing MgMg6 cuboctahedra.