Mg2Cd crystallizes in the trigonal P-3m1 space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent Mg(2), six equivalent Mg(1), and three equivalent Cd(1) atoms to form distorted MgMg9Cd3 cuboctahedra that share corners with six equivalent Mg(2)Mg12 cuboctahedra; corners with six equivalent Mg(1)Mg9Cd3 cuboctahedra; corners with six equivalent Cd(1)Mg3Cd9 cuboctahedra; edges with six equivalent Mg(2)Mg12 cuboctahedra; edges with six equivalent Mg(1)Mg9Cd3 cuboctahedra; edges with six equivalent Cd(1)Mg3Cd9 cuboctahedra; faces with six equivalent Mg(1)Mg9Cd3 cuboctahedra; faces with seven Mg(2,2)Mg12 cuboctahedra; and faces with seven equivalent Cd(1)Mg3Cd9 cuboctahedra. In the second Mg site, Mg(2) is bonded to three equivalent Mg(1) and nine Mg(2,2) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(2)Mg12 cuboctahedra; corners with six equivalent Mg(1)Mg9Cd3 cuboctahedra; corners with six equivalent Cd(1)Mg3Cd9 cuboctahedra; edges with six equivalent Mg(1)Mg9Cd3 cuboctahedra; edges with twelve Mg(2,2)Mg12 cuboctahedra;  a faceface with one Cd(1)Mg3Cd9 cuboctahedra; faces with seven equivalent Mg(1)Mg9Cd3 cuboctahedra; and faces with twelve Mg(2,2)Mg12 cuboctahedra. In the third Mg site, Mg(2) is bonded to three equivalent Mg(1) and nine Mg(2,2) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(2)Mg12 cuboctahedra; corners with six equivalent Mg(1)Mg9Cd3 cuboctahedra; corners with six equivalent Cd(1)Mg3Cd9 cuboctahedra; edges with six equivalent Mg(1)Mg9Cd3 cuboctahedra; edges with twelve Mg(2,2)Mg12 cuboctahedra;  a faceface with one Cd(1)Mg3Cd9 cuboctahedra; faces with seven equivalent Mg(1)Mg9Cd3 cuboctahedra; and faces with twelve Mg(2,2)Mg12 cuboctahedra. Cd(1) is bonded to three equivalent Mg(1) and nine equivalent Cd(1) atoms to form distorted CdMg3Cd9 cuboctahedra that share corners with six equivalent Mg(2)Mg12 cuboctahedra, corners with six equivalent Mg(1)Mg9Cd3 cuboctahedra, corners with six equivalent Cd(1)Mg3Cd9 cuboctahedra, edges with six equivalent Mg(1)Mg9Cd3 cuboctahedra, edges with twelve equivalent Cd(1)Mg3Cd9 cuboctahedra,  a faceface with one Mg(2)Mg12 cuboctahedra, faces with seven equivalent Mg(1)Mg9Cd3 cuboctahedra, and faces with twelve equivalent Cd(1)Mg3Cd9 cuboctahedra.
Mg2Cd crystallizes in the trigonal P-3m1 space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent Mg(2), six equivalent Mg(1), and three equivalent Cd(1) atoms to form distorted MgMg9Cd3 cuboctahedra that share corners with six equivalent Mg(2)Mg12 cuboctahedra; corners with six equivalent Mg(1)Mg9Cd3 cuboctahedra; corners with six equivalent Cd(1)Mg3Cd9 cuboctahedra; edges with six equivalent Mg(2)Mg12 cuboctahedra; edges with six equivalent Mg(1)Mg9Cd3 cuboctahedra; edges with six equivalent Cd(1)Mg3Cd9 cuboctahedra; faces with six equivalent Mg(1)Mg9Cd3 cuboctahedra; faces with seven Mg(2,2)Mg12 cuboctahedra; and faces with seven equivalent Cd(1)Mg3Cd9 cuboctahedra. All Mg(1)-Mg(2) bond lengths are 3.23 Å. All Mg(1)-Mg(1) bond lengths are 3.13 Å. All Mg(1)-Cd(1) bond lengths are 3.18 Å. In the second Mg site, Mg(2) is bonded to three equivalent Mg(1) and nine Mg(2,2) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(2)Mg12 cuboctahedra; corners with six equivalent Mg(1)Mg9Cd3 cuboctahedra; corners with six equivalent Cd(1)Mg3Cd9 cuboctahedra; edges with six equivalent Mg(1)Mg9Cd3 cuboctahedra; edges with twelve Mg(2,2)Mg12 cuboctahedra;  a faceface with one Cd(1)Mg3Cd9 cuboctahedra; faces with seven equivalent Mg(1)Mg9Cd3 cuboctahedra; and faces with twelve Mg(2,2)Mg12 cuboctahedra. There are six shorter (3.13 Å) and three longer (3.22 Å) Mg(2)-Mg(2,2) bond lengths. In the third Mg site, Mg(2) is bonded to three equivalent Mg(1) and nine Mg(2,2) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(2)Mg12 cuboctahedra; corners with six equivalent Mg(1)Mg9Cd3 cuboctahedra; corners with six equivalent Cd(1)Mg3Cd9 cuboctahedra; edges with six equivalent Mg(1)Mg9Cd3 cuboctahedra; edges with twelve Mg(2,2)Mg12 cuboctahedra;  a faceface with one Cd(1)Mg3Cd9 cuboctahedra; faces with seven equivalent Mg(1)Mg9Cd3 cuboctahedra; and faces with twelve Mg(2,2)Mg12 cuboctahedra. All Mg(2)-Mg(1) bond lengths are 3.23 Å. All Mg(2)-Mg(2) bond lengths are 3.13 Å. Cd(1) is bonded to three equivalent Mg(1) and nine equivalent Cd(1) atoms to form distorted CdMg3Cd9 cuboctahedra that share corners with six equivalent Mg(2)Mg12 cuboctahedra, corners with six equivalent Mg(1)Mg9Cd3 cuboctahedra, corners with six equivalent Cd(1)Mg3Cd9 cuboctahedra, edges with six equivalent Mg(1)Mg9Cd3 cuboctahedra, edges with twelve equivalent Cd(1)Mg3Cd9 cuboctahedra,  a faceface with one Mg(2)Mg12 cuboctahedra, faces with seven equivalent Mg(1)Mg9Cd3 cuboctahedra, and faces with twelve equivalent Cd(1)Mg3Cd9 cuboctahedra. There are six shorter (3.13 Å) and three longer (3.25 Å) Cd(1)-Cd(1) bond lengths.