Mg5Hg crystallizes in the hexagonal P-62m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to four equivalent Mg(2), six equivalent Mg(1), and two equivalent Hg(1) atoms to form distorted MgMg10Hg2 cuboctahedra that share corners with eighteen equivalent Mg(1)Mg10Hg2 cuboctahedra, edges with four equivalent Hg(1)Mg12 cuboctahedra, edges with six equivalent Mg(1)Mg10Hg2 cuboctahedra, edges with eight equivalent Mg(2)Mg9Hg3 cuboctahedra, faces with four equivalent Hg(1)Mg12 cuboctahedra, faces with eight equivalent Mg(1)Mg10Hg2 cuboctahedra, and faces with eight equivalent Mg(2)Mg9Hg3 cuboctahedra. In the second Mg site, Mg(2) is bonded to three equivalent Mg(2), six equivalent Mg(1), and three equivalent Hg(1) atoms to form distorted MgMg9Hg3 cuboctahedra that share corners with nine equivalent Mg(2)Mg9Hg3 cuboctahedra, corners with nine equivalent Hg(1)Mg12 cuboctahedra, edges with six equivalent Mg(2)Mg9Hg3 cuboctahedra, edges with twelve equivalent Mg(1)Mg10Hg2 cuboctahedra, faces with three equivalent Hg(1)Mg12 cuboctahedra, faces with five equivalent Mg(2)Mg9Hg3 cuboctahedra, and faces with twelve equivalent Mg(1)Mg10Hg2 cuboctahedra. Hg(1) is bonded to six equivalent Mg(1) and six equivalent Mg(2) atoms to form HgMg12 cuboctahedra that share corners with eighteen equivalent Mg(2)Mg9Hg3 cuboctahedra, edges with six equivalent Hg(1)Mg12 cuboctahedra, edges with twelve equivalent Mg(1)Mg10Hg2 cuboctahedra, faces with two equivalent Hg(1)Mg12 cuboctahedra, faces with six equivalent Mg(2)Mg9Hg3 cuboctahedra, and faces with twelve equivalent Mg(1)Mg10Hg2 cuboctahedra.
Mg5Hg crystallizes in the hexagonal P-62m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to four equivalent Mg(2), six equivalent Mg(1), and two equivalent Hg(1) atoms to form distorted MgMg10Hg2 cuboctahedra that share corners with eighteen equivalent Mg(1)Mg10Hg2 cuboctahedra, edges with four equivalent Hg(1)Mg12 cuboctahedra, edges with six equivalent Mg(1)Mg10Hg2 cuboctahedra, edges with eight equivalent Mg(2)Mg9Hg3 cuboctahedra, faces with four equivalent Hg(1)Mg12 cuboctahedra, faces with eight equivalent Mg(1)Mg10Hg2 cuboctahedra, and faces with eight equivalent Mg(2)Mg9Hg3 cuboctahedra. All Mg(1)-Mg(2) bond lengths are 3.12 Å. There are two shorter (3.05 Å) and four longer (3.14 Å) Mg(1)-Mg(1) bond lengths. Both Mg(1)-Hg(1) bond lengths are 3.09 Å. In the second Mg site, Mg(2) is bonded to three equivalent Mg(2), six equivalent Mg(1), and three equivalent Hg(1) atoms to form distorted MgMg9Hg3 cuboctahedra that share corners with nine equivalent Mg(2)Mg9Hg3 cuboctahedra, corners with nine equivalent Hg(1)Mg12 cuboctahedra, edges with six equivalent Mg(2)Mg9Hg3 cuboctahedra, edges with twelve equivalent Mg(1)Mg10Hg2 cuboctahedra, faces with three equivalent Hg(1)Mg12 cuboctahedra, faces with five equivalent Mg(2)Mg9Hg3 cuboctahedra, and faces with twelve equivalent Mg(1)Mg10Hg2 cuboctahedra. All Mg(2)-Mg(2) bond lengths are 3.11 Å. All Mg(2)-Hg(1) bond lengths are 3.11 Å. Hg(1) is bonded to six equivalent Mg(1) and six equivalent Mg(2) atoms to form HgMg12 cuboctahedra that share corners with eighteen equivalent Mg(2)Mg9Hg3 cuboctahedra, edges with six equivalent Hg(1)Mg12 cuboctahedra, edges with twelve equivalent Mg(1)Mg10Hg2 cuboctahedra, faces with two equivalent Hg(1)Mg12 cuboctahedra, faces with six equivalent Mg(2)Mg9Hg3 cuboctahedra, and faces with twelve equivalent Mg(1)Mg10Hg2 cuboctahedra.