Mg5Zn crystallizes in the monoclinic Cm space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(2), two equivalent Mg(4), three equivalent Mg(5), and two equivalent Zn(1) atoms to form distorted MgMg7Zn2 cuboctahedra that share corners with two equivalent Mg(5)Mg10Zn2 cuboctahedra, corners with four equivalent Mg(1)Mg7Zn2 cuboctahedra, corners with six equivalent Mg(2)Mg9Zn3 cuboctahedra, corners with eight equivalent Mg(4)Mg11Zn cuboctahedra,  an edgeedge with one Mg(2)Mg9Zn3 cuboctahedra, edges with two equivalent Mg(5)Mg10Zn2 cuboctahedra, edges with four equivalent Mg(4)Mg11Zn cuboctahedra, edges with six equivalent Mg(3)Mg7Zn2 cuboctahedra, faces with two equivalent Mg(1)Mg7Zn2 cuboctahedra, faces with two equivalent Mg(3)Mg7Zn2 cuboctahedra, faces with three equivalent Mg(5)Mg10Zn2 cuboctahedra, and faces with three equivalent Mg(2)Mg9Zn3 cuboctahedra. In the second Mg site, Mg(2) is bonded to one Mg(5), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), and three equivalent Zn(1) atoms to form distorted MgMg9Zn3 cuboctahedra that share corners with four equivalent Mg(3)Mg7Zn2 cuboctahedra, corners with six equivalent Mg(4)Mg11Zn cuboctahedra, corners with six equivalent Mg(1)Mg7Zn2 cuboctahedra, corners with six equivalent Mg(2)Mg9Zn3 cuboctahedra,  an edgeedge with one Mg(1)Mg7Zn2 cuboctahedra, edges with two equivalent Mg(3)Mg7Zn2 cuboctahedra, edges with three equivalent Mg(4)Mg11Zn cuboctahedra, edges with four equivalent Mg(5)Mg10Zn2 cuboctahedra, faces with two equivalent Mg(2)Mg9Zn3 cuboctahedra, faces with three equivalent Mg(4)Mg11Zn cuboctahedra, faces with three equivalent Mg(1)Mg7Zn2 cuboctahedra, faces with three equivalent Mg(3)Mg7Zn2 cuboctahedra, and faces with four equivalent Mg(5)Mg10Zn2 cuboctahedra. In the third Mg site, Mg(3) is bonded to two equivalent Mg(2), two equivalent Mg(5), three equivalent Mg(4), and two equivalent Zn(1) atoms to form distorted MgMg7Zn2 cuboctahedra that share corners with two equivalent Mg(4)Mg11Zn cuboctahedra, corners with four equivalent Mg(3)Mg7Zn2 cuboctahedra, corners with four equivalent Mg(2)Mg9Zn3 cuboctahedra, corners with eight equivalent Mg(5)Mg10Zn2 cuboctahedra, edges with two equivalent Mg(4)Mg11Zn cuboctahedra, edges with two equivalent Mg(2)Mg9Zn3 cuboctahedra, edges with four equivalent Mg(5)Mg10Zn2 cuboctahedra, edges with six equivalent Mg(1)Mg7Zn2 cuboctahedra, faces with two equivalent Mg(1)Mg7Zn2 cuboctahedra, faces with two equivalent Mg(3)Mg7Zn2 cuboctahedra, faces with three equivalent Mg(4)Mg11Zn cuboctahedra, and faces with three equivalent Mg(2)Mg9Zn3 cuboctahedra. In the fourth Mg site, Mg(4) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), two equivalent Mg(5), three equivalent Mg(3), and one Zn(1) atom to form distorted MgMg11Zn cuboctahedra that share corners with two equivalent Mg(3)Mg7Zn2 cuboctahedra, corners with six equivalent Mg(4)Mg11Zn cuboctahedra, corners with six equivalent Mg(2)Mg9Zn3 cuboctahedra, corners with eight equivalent Mg(1)Mg7Zn2 cuboctahedra, edges with two equivalent Mg(3)Mg7Zn2 cuboctahedra, edges with three equivalent Mg(2)Mg9Zn3 cuboctahedra, edges with four equivalent Mg(1)Mg7Zn2 cuboctahedra, edges with six equivalent Mg(5)Mg10Zn2 cuboctahedra, faces with two equivalent Mg(4)Mg11Zn cuboctahedra, faces with three equivalent Mg(5)Mg10Zn2 cuboctahedra, faces with three equivalent Mg(3)Mg7Zn2 cuboctahedra, and faces with three equivalent Mg(2)Mg9Zn3 cuboctahedra. In the fifth Mg site, Mg(5) is bonded to one Mg(2), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(5), three equivalent Mg(1), and two equivalent Zn(1) atoms to form distorted MgMg10Zn2 cuboctahedra that share corners with two equivalent Mg(1)Mg7Zn2 cuboctahedra, corners with six equivalent Mg(5)Mg10Zn2 cuboctahedra, corners with eight equivalent Mg(3)Mg7Zn2 cuboctahedra, edges with two equivalent Mg(1)Mg7Zn2 cuboctahedra, edges with four equivalent Mg(3)Mg7Zn2 cuboctahedra, edges with four equivalent Mg(2)Mg9Zn3 cuboctahedra, edges with six equivalent Mg(4)Mg11Zn cuboctahedra, faces with two equivalent Mg(5)Mg10Zn2 cuboctahedra, faces with three equivalent Mg(4)Mg11Zn cuboctahedra, faces with three equivalent Mg(1)Mg7Zn2 cuboctahedra, and faces with four equivalent Mg(2)Mg9Zn3 cuboctahedra. Zn(1) is bonded in a 12-coordinate geometry to one Mg(4), two equivalent Mg(1), two equivalent Mg(3), two equivalent Mg(5), three equivalent Mg(2), and two equivalent Zn(1) atoms.
Mg5Zn crystallizes in the monoclinic Cm space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(2), two equivalent Mg(4), three equivalent Mg(5), and two equivalent Zn(1) atoms to form distorted MgMg7Zn2 cuboctahedra that share corners with two equivalent Mg(5)Mg10Zn2 cuboctahedra, corners with four equivalent Mg(1)Mg7Zn2 cuboctahedra, corners with six equivalent Mg(2)Mg9Zn3 cuboctahedra, corners with eight equivalent Mg(4)Mg11Zn cuboctahedra,  an edgeedge with one Mg(2)Mg9Zn3 cuboctahedra, edges with two equivalent Mg(5)Mg10Zn2 cuboctahedra, edges with four equivalent Mg(4)Mg11Zn cuboctahedra, edges with six equivalent Mg(3)Mg7Zn2 cuboctahedra, faces with two equivalent Mg(1)Mg7Zn2 cuboctahedra, faces with two equivalent Mg(3)Mg7Zn2 cuboctahedra, faces with three equivalent Mg(5)Mg10Zn2 cuboctahedra, and faces with three equivalent Mg(2)Mg9Zn3 cuboctahedra. Both Mg(1)-Mg(2) bond lengths are 3.08 Å. Both Mg(1)-Mg(4) bond lengths are 3.12 Å. There is one shorter (3.03 Å) and two longer (3.19 Å) Mg(1)-Mg(5) bond lengths. Both Mg(1)-Zn(1) bond lengths are 2.97 Å. In the second Mg site, Mg(2) is bonded to one Mg(5), two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), and three equivalent Zn(1) atoms to form distorted MgMg9Zn3 cuboctahedra that share corners with four equivalent Mg(3)Mg7Zn2 cuboctahedra, corners with six equivalent Mg(4)Mg11Zn cuboctahedra, corners with six equivalent Mg(1)Mg7Zn2 cuboctahedra, corners with six equivalent Mg(2)Mg9Zn3 cuboctahedra,  an edgeedge with one Mg(1)Mg7Zn2 cuboctahedra, edges with two equivalent Mg(3)Mg7Zn2 cuboctahedra, edges with three equivalent Mg(4)Mg11Zn cuboctahedra, edges with four equivalent Mg(5)Mg10Zn2 cuboctahedra, faces with two equivalent Mg(2)Mg9Zn3 cuboctahedra, faces with three equivalent Mg(4)Mg11Zn cuboctahedra, faces with three equivalent Mg(1)Mg7Zn2 cuboctahedra, faces with three equivalent Mg(3)Mg7Zn2 cuboctahedra, and faces with four equivalent Mg(5)Mg10Zn2 cuboctahedra. The Mg(2)-Mg(5) bond length is 2.96 Å. Both Mg(2)-Mg(2) bond lengths are 3.09 Å. Both Mg(2)-Mg(3) bond lengths are 3.11 Å. Both Mg(2)-Mg(4) bond lengths are 3.02 Å. There are two shorter (3.00 Å) and one longer (3.22 Å) Mg(2)-Zn(1) bond length. In the third Mg site, Mg(3) is bonded to two equivalent Mg(2), two equivalent Mg(5), three equivalent Mg(4), and two equivalent Zn(1) atoms to form distorted MgMg7Zn2 cuboctahedra that share corners with two equivalent Mg(4)Mg11Zn cuboctahedra, corners with four equivalent Mg(3)Mg7Zn2 cuboctahedra, corners with four equivalent Mg(2)Mg9Zn3 cuboctahedra, corners with eight equivalent Mg(5)Mg10Zn2 cuboctahedra, edges with two equivalent Mg(4)Mg11Zn cuboctahedra, edges with two equivalent Mg(2)Mg9Zn3 cuboctahedra, edges with four equivalent Mg(5)Mg10Zn2 cuboctahedra, edges with six equivalent Mg(1)Mg7Zn2 cuboctahedra, faces with two equivalent Mg(1)Mg7Zn2 cuboctahedra, faces with two equivalent Mg(3)Mg7Zn2 cuboctahedra, faces with three equivalent Mg(4)Mg11Zn cuboctahedra, and faces with three equivalent Mg(2)Mg9Zn3 cuboctahedra. Both Mg(3)-Mg(5) bond lengths are 3.23 Å. There are two shorter (3.08 Å) and one longer (3.18 Å) Mg(3)-Mg(4) bond length. Both Mg(3)-Zn(1) bond lengths are 2.94 Å. In the fourth Mg site, Mg(4) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), two equivalent Mg(5), three equivalent Mg(3), and one Zn(1) atom to form distorted MgMg11Zn cuboctahedra that share corners with two equivalent Mg(3)Mg7Zn2 cuboctahedra, corners with six equivalent Mg(4)Mg11Zn cuboctahedra, corners with six equivalent Mg(2)Mg9Zn3 cuboctahedra, corners with eight equivalent Mg(1)Mg7Zn2 cuboctahedra, edges with two equivalent Mg(3)Mg7Zn2 cuboctahedra, edges with three equivalent Mg(2)Mg9Zn3 cuboctahedra, edges with four equivalent Mg(1)Mg7Zn2 cuboctahedra, edges with six equivalent Mg(5)Mg10Zn2 cuboctahedra, faces with two equivalent Mg(4)Mg11Zn cuboctahedra, faces with three equivalent Mg(5)Mg10Zn2 cuboctahedra, faces with three equivalent Mg(3)Mg7Zn2 cuboctahedra, and faces with three equivalent Mg(2)Mg9Zn3 cuboctahedra. Both Mg(4)-Mg(4) bond lengths are 3.09 Å. Both Mg(4)-Mg(5) bond lengths are 3.12 Å. The Mg(4)-Zn(1) bond length is 3.05 Å. In the fifth Mg site, Mg(5) is bonded to one Mg(2), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(5), three equivalent Mg(1), and two equivalent Zn(1) atoms to form distorted MgMg10Zn2 cuboctahedra that share corners with two equivalent Mg(1)Mg7Zn2 cuboctahedra, corners with six equivalent Mg(5)Mg10Zn2 cuboctahedra, corners with eight equivalent Mg(3)Mg7Zn2 cuboctahedra, edges with two equivalent Mg(1)Mg7Zn2 cuboctahedra, edges with four equivalent Mg(3)Mg7Zn2 cuboctahedra, edges with four equivalent Mg(2)Mg9Zn3 cuboctahedra, edges with six equivalent Mg(4)Mg11Zn cuboctahedra, faces with two equivalent Mg(5)Mg10Zn2 cuboctahedra, faces with three equivalent Mg(4)Mg11Zn cuboctahedra, faces with three equivalent Mg(1)Mg7Zn2 cuboctahedra, and faces with four equivalent Mg(2)Mg9Zn3 cuboctahedra. Both Mg(5)-Mg(5) bond lengths are 3.09 Å. Both Mg(5)-Zn(1) bond lengths are 3.05 Å. Zn(1) is bonded in a 12-coordinate geometry to one Mg(4), two equivalent Mg(1), two equivalent Mg(3), two equivalent Mg(5), three equivalent Mg(2), and two equivalent Zn(1) atoms. Both Zn(1)-Zn(1) bond lengths are 3.09 Å.