SrMg7 crystallizes in the hexagonal P-6m2 space group. Sr(1) is bonded to six equivalent Mg(1) and six equivalent Mg(2) atoms to form SrMg12 cuboctahedra that share corners with six equivalent Sr(1)Mg12 cuboctahedra, corners with twelve equivalent Mg(1)Sr2Mg10 cuboctahedra, edges with six equivalent Mg(1)Sr2Mg10 cuboctahedra, faces with two equivalent Sr(1)Mg12 cuboctahedra, faces with six equivalent Mg(3)Mg12 cuboctahedra, and faces with six equivalent Mg(1)Sr2Mg10 cuboctahedra. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Sr(1), two equivalent Mg(3), four equivalent Mg(1), and four equivalent Mg(2) atoms to form distorted MgSr2Mg10 cuboctahedra that share corners with four equivalent Sr(1)Mg12 cuboctahedra, corners with fourteen equivalent Mg(1)Sr2Mg10 cuboctahedra, edges with two equivalent Sr(1)Mg12 cuboctahedra, edges with four equivalent Mg(3)Mg12 cuboctahedra, edges with four equivalent Mg(1)Sr2Mg10 cuboctahedra, faces with two equivalent Sr(1)Mg12 cuboctahedra, faces with two equivalent Mg(3)Mg12 cuboctahedra, and faces with six equivalent Mg(1)Sr2Mg10 cuboctahedra. In the second Mg site, Mg(2) is bonded in a 2-coordinate geometry to two equivalent Sr(1), two equivalent Mg(3), and four equivalent Mg(1) atoms. In the third Mg site, Mg(3) is bonded to six equivalent Mg(1) and six equivalent Mg(2) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(3)Mg12 cuboctahedra, edges with twelve equivalent Mg(1)Sr2Mg10 cuboctahedra, faces with two equivalent Mg(3)Mg12 cuboctahedra, faces with six equivalent Sr(1)Mg12 cuboctahedra, and faces with six equivalent Mg(1)Sr2Mg10 cuboctahedra.
SrMg7 crystallizes in the hexagonal P-6m2 space group. Sr(1) is bonded to six equivalent Mg(1) and six equivalent Mg(2) atoms to form SrMg12 cuboctahedra that share corners with six equivalent Sr(1)Mg12 cuboctahedra, corners with twelve equivalent Mg(1)Sr2Mg10 cuboctahedra, edges with six equivalent Mg(1)Sr2Mg10 cuboctahedra, faces with two equivalent Sr(1)Mg12 cuboctahedra, faces with six equivalent Mg(3)Mg12 cuboctahedra, and faces with six equivalent Mg(1)Sr2Mg10 cuboctahedra. All Sr(1)-Mg(1) bond lengths are 3.40 Å. All Sr(1)-Mg(2) bond lengths are 3.35 Å. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Sr(1), two equivalent Mg(3), four equivalent Mg(1), and four equivalent Mg(2) atoms to form distorted MgSr2Mg10 cuboctahedra that share corners with four equivalent Sr(1)Mg12 cuboctahedra, corners with fourteen equivalent Mg(1)Sr2Mg10 cuboctahedra, edges with two equivalent Sr(1)Mg12 cuboctahedra, edges with four equivalent Mg(3)Mg12 cuboctahedra, edges with four equivalent Mg(1)Sr2Mg10 cuboctahedra, faces with two equivalent Sr(1)Mg12 cuboctahedra, faces with two equivalent Mg(3)Mg12 cuboctahedra, and faces with six equivalent Mg(1)Sr2Mg10 cuboctahedra. Both Mg(1)-Mg(3) bond lengths are 3.32 Å. There are two shorter (3.32 Å) and two longer (3.47 Å) Mg(1)-Mg(1) bond lengths. All Mg(1)-Mg(2) bond lengths are 3.26 Å. In the second Mg site, Mg(2) is bonded in a 2-coordinate geometry to two equivalent Sr(1), two equivalent Mg(3), and four equivalent Mg(1) atoms. Both Mg(2)-Mg(3) bond lengths are 3.40 Å. In the third Mg site, Mg(3) is bonded to six equivalent Mg(1) and six equivalent Mg(2) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(3)Mg12 cuboctahedra, edges with twelve equivalent Mg(1)Sr2Mg10 cuboctahedra, faces with two equivalent Mg(3)Mg12 cuboctahedra, faces with six equivalent Sr(1)Mg12 cuboctahedra, and faces with six equivalent Mg(1)Sr2Mg10 cuboctahedra.