MgCd2 crystallizes in the orthorhombic Cmcm space group. Mg(1) is bonded to four equivalent Cd(2) and six equivalent Cd(1) atoms to form distorted MgCd10 cuboctahedra that share corners with four equivalent Mg(1)Cd10 cuboctahedra, corners with eight equivalent Cd(2)Mg4Cd8 cuboctahedra, corners with twelve equivalent Cd(1)Mg6Cd6 cuboctahedra,  an edgeedge with one Cd(2)Mg4Cd8 cuboctahedra,  an edgeedge with one Cd(1)Mg6Cd6 cuboctahedra, edges with eight equivalent Mg(1)Cd10 cuboctahedra, faces with six equivalent Mg(1)Cd10 cuboctahedra, faces with six equivalent Cd(1)Mg6Cd6 cuboctahedra, and faces with eight equivalent Cd(2)Mg4Cd8 cuboctahedra. There are two inequivalent Cd sites. In the first Cd site, Cd(1) is bonded to six equivalent Mg(1), two equivalent Cd(2), and four equivalent Cd(1) atoms to form distorted CdMg6Cd6 cuboctahedra that share corners with six equivalent Cd(2)Mg4Cd8 cuboctahedra, corners with six equivalent Cd(1)Mg6Cd6 cuboctahedra, corners with twelve equivalent Mg(1)Cd10 cuboctahedra,  an edgeedge with one Mg(1)Cd10 cuboctahedra, edges with eleven equivalent Cd(2)Mg4Cd8 cuboctahedra, faces with four equivalent Cd(2)Mg4Cd8 cuboctahedra, faces with six equivalent Mg(1)Cd10 cuboctahedra, and faces with ten equivalent Cd(1)Mg6Cd6 cuboctahedra. In the second Cd site, Cd(2) is bonded to four equivalent Mg(1), two equivalent Cd(1), and six equivalent Cd(2) atoms to form distorted CdMg4Cd8 cuboctahedra that share corners with six equivalent Cd(2)Mg4Cd8 cuboctahedra, corners with six equivalent Cd(1)Mg6Cd6 cuboctahedra, corners with eight equivalent Mg(1)Cd10 cuboctahedra,  an edgeedge with one Mg(1)Cd10 cuboctahedra, edges with four equivalent Cd(2)Mg4Cd8 cuboctahedra, edges with eleven equivalent Cd(1)Mg6Cd6 cuboctahedra, faces with four equivalent Cd(1)Mg6Cd6 cuboctahedra, faces with eight equivalent Mg(1)Cd10 cuboctahedra, and faces with eight equivalent Cd(2)Mg4Cd8 cuboctahedra.
MgCd2 crystallizes in the orthorhombic Cmcm space group. Mg(1) is bonded to four equivalent Cd(2) and six equivalent Cd(1) atoms to form distorted MgCd10 cuboctahedra that share corners with four equivalent Mg(1)Cd10 cuboctahedra, corners with eight equivalent Cd(2)Mg4Cd8 cuboctahedra, corners with twelve equivalent Cd(1)Mg6Cd6 cuboctahedra,  an edgeedge with one Cd(2)Mg4Cd8 cuboctahedra,  an edgeedge with one Cd(1)Mg6Cd6 cuboctahedra, edges with eight equivalent Mg(1)Cd10 cuboctahedra, faces with six equivalent Mg(1)Cd10 cuboctahedra, faces with six equivalent Cd(1)Mg6Cd6 cuboctahedra, and faces with eight equivalent Cd(2)Mg4Cd8 cuboctahedra. There are two shorter (3.06 Å) and two longer (3.09 Å) Mg(1)-Cd(2) bond lengths. There are two shorter (3.04 Å) and four longer (3.10 Å) Mg(1)-Cd(1) bond lengths. There are two inequivalent Cd sites. In the first Cd site, Cd(1) is bonded to six equivalent Mg(1), two equivalent Cd(2), and four equivalent Cd(1) atoms to form distorted CdMg6Cd6 cuboctahedra that share corners with six equivalent Cd(2)Mg4Cd8 cuboctahedra, corners with six equivalent Cd(1)Mg6Cd6 cuboctahedra, corners with twelve equivalent Mg(1)Cd10 cuboctahedra,  an edgeedge with one Mg(1)Cd10 cuboctahedra, edges with eleven equivalent Cd(2)Mg4Cd8 cuboctahedra, faces with four equivalent Cd(2)Mg4Cd8 cuboctahedra, faces with six equivalent Mg(1)Cd10 cuboctahedra, and faces with ten equivalent Cd(1)Mg6Cd6 cuboctahedra. Both Cd(1)-Cd(2) bond lengths are 3.08 Å. There are two shorter (3.04 Å) and two longer (3.20 Å) Cd(1)-Cd(1) bond lengths. In the second Cd site, Cd(2) is bonded to four equivalent Mg(1), two equivalent Cd(1), and six equivalent Cd(2) atoms to form distorted CdMg4Cd8 cuboctahedra that share corners with six equivalent Cd(2)Mg4Cd8 cuboctahedra, corners with six equivalent Cd(1)Mg6Cd6 cuboctahedra, corners with eight equivalent Mg(1)Cd10 cuboctahedra,  an edgeedge with one Mg(1)Cd10 cuboctahedra, edges with four equivalent Cd(2)Mg4Cd8 cuboctahedra, edges with eleven equivalent Cd(1)Mg6Cd6 cuboctahedra, faces with four equivalent Cd(1)Mg6Cd6 cuboctahedra, faces with eight equivalent Mg(1)Cd10 cuboctahedra, and faces with eight equivalent Cd(2)Mg4Cd8 cuboctahedra. There are four shorter (3.10 Å) and two longer (3.20 Å) Cd(2)-Cd(2) bond lengths.