Mg7Cu crystallizes in the hexagonal P-6m2 space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(3); four Mg(1,1); four Mg(2,2); and two equivalent Cu(1) atoms to form distorted MgMg10Cu2 cuboctahedra that share corners with four equivalent Cu(1)Mg12 cuboctahedra; corners with fourteen Mg(1,1)Mg10Cu2 cuboctahedra; edges with two equivalent Cu(1)Mg12 cuboctahedra; edges with four Mg(1,1)Mg10Cu2 cuboctahedra; edges with four equivalent Mg(3)Mg12 cuboctahedra; edges with eight Mg(2,2)Mg10Cu2 cuboctahedra; faces with two equivalent Mg(3)Mg12 cuboctahedra; faces with two equivalent Cu(1)Mg12 cuboctahedra; faces with six Mg(1,1)Mg10Cu2 cuboctahedra; and faces with ten Mg(2,2)Mg10Cu2 cuboctahedra. In the second Mg site, Mg(1) is bonded to two equivalent Mg(3), four equivalent Mg(1), four equivalent Mg(2), and two equivalent Cu(1) atoms to form distorted MgMg10Cu2 cuboctahedra that share corners with four equivalent Cu(1)Mg12 cuboctahedra; corners with fourteen Mg(1,1)Mg10Cu2 cuboctahedra; edges with two equivalent Cu(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Mg10Cu2 cuboctahedra; edges with four equivalent Mg(3)Mg12 cuboctahedra; edges with eight equivalent Mg(2)Mg10Cu2 cuboctahedra; faces with two equivalent Mg(3)Mg12 cuboctahedra; faces with two equivalent Cu(1)Mg12 cuboctahedra; faces with six Mg(1,1)Mg10Cu2 cuboctahedra; and faces with ten Mg(2,2)Mg10Cu2 cuboctahedra. In the third Mg site, Mg(2) is bonded to two equivalent Mg(3), four equivalent Mg(1), four equivalent Mg(2), and two equivalent Cu(1) atoms to form distorted MgMg10Cu2 cuboctahedra that share corners with four equivalent Mg(3)Mg12 cuboctahedra; corners with fourteen Mg(2,2)Mg10Cu2 cuboctahedra; edges with two equivalent Mg(3)Mg12 cuboctahedra; edges with four equivalent Mg(2)Mg10Cu2 cuboctahedra; edges with four equivalent Cu(1)Mg12 cuboctahedra; edges with eight equivalent Mg(1)Mg10Cu2 cuboctahedra; faces with two equivalent Mg(3)Mg12 cuboctahedra; faces with two equivalent Cu(1)Mg12 cuboctahedra; faces with six Mg(2,2)Mg10Cu2 cuboctahedra; and faces with ten Mg(1,1)Mg10Cu2 cuboctahedra. In the fourth Mg site, Mg(2) is bonded to two equivalent Mg(3); four Mg(1,1); four Mg(2,2); and two equivalent Cu(1) atoms to form distorted MgMg10Cu2 cuboctahedra that share corners with four equivalent Mg(3)Mg12 cuboctahedra; corners with fourteen Mg(2,2)Mg10Cu2 cuboctahedra; edges with two equivalent Mg(3)Mg12 cuboctahedra; edges with four Mg(2,2)Mg10Cu2 cuboctahedra; edges with four equivalent Cu(1)Mg12 cuboctahedra; edges with eight Mg(1,1)Mg10Cu2 cuboctahedra; faces with two equivalent Mg(3)Mg12 cuboctahedra; faces with two equivalent Cu(1)Mg12 cuboctahedra; faces with six Mg(2,2)Mg10Cu2 cuboctahedra; and faces with ten Mg(1,1)Mg10Cu2 cuboctahedra. In the fifth Mg site, Mg(3) is bonded to six Mg(1,1) and six Mg(2,2) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(3)Mg12 cuboctahedra; corners with twelve Mg(2,2)Mg10Cu2 cuboctahedra; edges with six Mg(2,2)Mg10Cu2 cuboctahedra; edges with twelve Mg(1,1)Mg10Cu2 cuboctahedra; faces with two equivalent Mg(3)Mg12 cuboctahedra; faces with six Mg(1,1)Mg10Cu2 cuboctahedra; faces with six Mg(2,2)Mg10Cu2 cuboctahedra; and faces with six equivalent Cu(1)Mg12 cuboctahedra. Cu(1) is bonded to six Mg(1,1) and six Mg(2,2) atoms to form CuMg12 cuboctahedra that share corners with six equivalent Cu(1)Mg12 cuboctahedra; corners with twelve Mg(1,1)Mg10Cu2 cuboctahedra; edges with six Mg(1,1)Mg10Cu2 cuboctahedra; edges with twelve Mg(2,2)Mg10Cu2 cuboctahedra; faces with two equivalent Cu(1)Mg12 cuboctahedra; faces with six Mg(1,1)Mg10Cu2 cuboctahedra; faces with six Mg(2,2)Mg10Cu2 cuboctahedra; and faces with six equivalent Mg(3)Mg12 cuboctahedra.
Mg7Cu crystallizes in the hexagonal P-6m2 space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(3); four Mg(1,1); four Mg(2,2); and two equivalent Cu(1) atoms to form distorted MgMg10Cu2 cuboctahedra that share corners with four equivalent Cu(1)Mg12 cuboctahedra; corners with fourteen Mg(1,1)Mg10Cu2 cuboctahedra; edges with two equivalent Cu(1)Mg12 cuboctahedra; edges with four Mg(1,1)Mg10Cu2 cuboctahedra; edges with four equivalent Mg(3)Mg12 cuboctahedra; edges with eight Mg(2,2)Mg10Cu2 cuboctahedra; faces with two equivalent Mg(3)Mg12 cuboctahedra; faces with two equivalent Cu(1)Mg12 cuboctahedra; faces with six Mg(1,1)Mg10Cu2 cuboctahedra; and faces with ten Mg(2,2)Mg10Cu2 cuboctahedra. Both Mg(1)-Mg(3) bond lengths are 3.07 Å. There are two shorter (3.08 Å) and two longer (3.11 Å) Mg(1)-Mg(1,1) bond lengths. All Mg(1)-Mg(2,2) bond lengths are 3.10 Å. Both Mg(1)-Cu(1) bond lengths are 3.10 Å. In the second Mg site, Mg(1) is bonded to two equivalent Mg(3), four equivalent Mg(1), four equivalent Mg(2), and two equivalent Cu(1) atoms to form distorted MgMg10Cu2 cuboctahedra that share corners with four equivalent Cu(1)Mg12 cuboctahedra; corners with fourteen Mg(1,1)Mg10Cu2 cuboctahedra; edges with two equivalent Cu(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Mg10Cu2 cuboctahedra; edges with four equivalent Mg(3)Mg12 cuboctahedra; edges with eight equivalent Mg(2)Mg10Cu2 cuboctahedra; faces with two equivalent Mg(3)Mg12 cuboctahedra; faces with two equivalent Cu(1)Mg12 cuboctahedra; faces with six Mg(1,1)Mg10Cu2 cuboctahedra; and faces with ten Mg(2,2)Mg10Cu2 cuboctahedra. Both Mg(1)-Mg(3) bond lengths are 3.07 Å. All Mg(1)-Mg(2) bond lengths are 3.10 Å. Both Mg(1)-Cu(1) bond lengths are 3.10 Å. In the third Mg site, Mg(2) is bonded to two equivalent Mg(3), four equivalent Mg(1), four equivalent Mg(2), and two equivalent Cu(1) atoms to form distorted MgMg10Cu2 cuboctahedra that share corners with four equivalent Mg(3)Mg12 cuboctahedra; corners with fourteen Mg(2,2)Mg10Cu2 cuboctahedra; edges with two equivalent Mg(3)Mg12 cuboctahedra; edges with four equivalent Mg(2)Mg10Cu2 cuboctahedra; edges with four equivalent Cu(1)Mg12 cuboctahedra; edges with eight equivalent Mg(1)Mg10Cu2 cuboctahedra; faces with two equivalent Mg(3)Mg12 cuboctahedra; faces with two equivalent Cu(1)Mg12 cuboctahedra; faces with six Mg(2,2)Mg10Cu2 cuboctahedra; and faces with ten Mg(1,1)Mg10Cu2 cuboctahedra. Both Mg(2)-Mg(3) bond lengths are 3.10 Å. There are two shorter (3.00 Å) and two longer (3.19 Å) Mg(2)-Mg(2) bond lengths. Both Mg(2)-Cu(1) bond lengths are 3.05 Å. In the fourth Mg site, Mg(2) is bonded to two equivalent Mg(3); four Mg(1,1); four Mg(2,2); and two equivalent Cu(1) atoms to form distorted MgMg10Cu2 cuboctahedra that share corners with four equivalent Mg(3)Mg12 cuboctahedra; corners with fourteen Mg(2,2)Mg10Cu2 cuboctahedra; edges with two equivalent Mg(3)Mg12 cuboctahedra; edges with four Mg(2,2)Mg10Cu2 cuboctahedra; edges with four equivalent Cu(1)Mg12 cuboctahedra; edges with eight Mg(1,1)Mg10Cu2 cuboctahedra; faces with two equivalent Mg(3)Mg12 cuboctahedra; faces with two equivalent Cu(1)Mg12 cuboctahedra; faces with six Mg(2,2)Mg10Cu2 cuboctahedra; and faces with ten Mg(1,1)Mg10Cu2 cuboctahedra. Both Mg(2)-Mg(3) bond lengths are 3.10 Å. There is one shorter (3.00 Å) and one longer (3.19 Å) Mg(2)-Mg(2) bond length. Both Mg(2)-Cu(1) bond lengths are 3.05 Å. In the fifth Mg site, Mg(3) is bonded to six Mg(1,1) and six Mg(2,2) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(3)Mg12 cuboctahedra; corners with twelve Mg(2,2)Mg10Cu2 cuboctahedra; edges with six Mg(2,2)Mg10Cu2 cuboctahedra; edges with twelve Mg(1,1)Mg10Cu2 cuboctahedra; faces with two equivalent Mg(3)Mg12 cuboctahedra; faces with six Mg(1,1)Mg10Cu2 cuboctahedra; faces with six Mg(2,2)Mg10Cu2 cuboctahedra; and faces with six equivalent Cu(1)Mg12 cuboctahedra. Cu(1) is bonded to six Mg(1,1) and six Mg(2,2) atoms to form CuMg12 cuboctahedra that share corners with six equivalent Cu(1)Mg12 cuboctahedra; corners with twelve Mg(1,1)Mg10Cu2 cuboctahedra; edges with six Mg(1,1)Mg10Cu2 cuboctahedra; edges with twelve Mg(2,2)Mg10Cu2 cuboctahedra; faces with two equivalent Cu(1)Mg12 cuboctahedra; faces with six Mg(1,1)Mg10Cu2 cuboctahedra; faces with six Mg(2,2)Mg10Cu2 cuboctahedra; and faces with six equivalent Mg(3)Mg12 cuboctahedra.