Mg5Bi crystallizes in the orthorhombic Amm2 space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(5), and four equivalent Mg(4) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(1)Mg12 cuboctahedra, corners with six equivalent Mg(2)Mg4Bi4 cuboctahedra, edges with four equivalent Mg(4)Mg10Bi2 cuboctahedra, edges with eight equivalent Bi(1)Mg10 cuboctahedra, faces with two equivalent Mg(2)Mg4Bi4 cuboctahedra, faces with two equivalent Bi(1)Mg10 cuboctahedra, faces with four equivalent Mg(4)Mg10Bi2 cuboctahedra, and faces with four equivalent Mg(1)Mg12 cuboctahedra. In the second Mg site, Mg(2) is bonded to two equivalent Mg(1), two equivalent Mg(4), and four equivalent Bi(1) atoms to form distorted MgMg4Bi4 cuboctahedra that share corners with four equivalent Mg(2)Mg4Bi4 cuboctahedra, corners with four equivalent Bi(1)Mg10 cuboctahedra, corners with six equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with four equivalent Mg(2)Mg4Bi4 cuboctahedra, and faces with six equivalent Mg(4)Mg10Bi2 cuboctahedra. In the third Mg site, Mg(3) is bonded in a distorted water-like geometry to two equivalent Mg(1) and two equivalent Bi(1) atoms. In the fourth Mg site, Mg(4) is bonded to two equivalent Mg(2), two equivalent Mg(4), two equivalent Mg(5), four equivalent Mg(1), and two equivalent Bi(1) atoms to form distorted MgMg10Bi2 cuboctahedra that share corners with six equivalent Mg(4)Mg10Bi2 cuboctahedra, corners with eight equivalent Bi(1)Mg10 cuboctahedra,  an edgeedge with one Bi(1)Mg10 cuboctahedra, edges with four equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Bi(1)Mg10 cuboctahedra, faces with four equivalent Mg(4)Mg10Bi2 cuboctahedra, faces with four equivalent Mg(1)Mg12 cuboctahedra, and faces with six equivalent Mg(2)Mg4Bi4 cuboctahedra. In the fifth Mg site, Mg(5) is bonded in a 2-coordinate geometry to two equivalent Mg(1), two equivalent Mg(4), and two equivalent Bi(1) atoms. Bi(1) is bonded to two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(5), and four equivalent Mg(2) atoms to form distorted BiMg10 cuboctahedra that share corners with four equivalent Mg(2)Mg4Bi4 cuboctahedra, corners with four equivalent Bi(1)Mg10 cuboctahedra, corners with eight equivalent Mg(4)Mg10Bi2 cuboctahedra,  an edgeedge with one Mg(4)Mg10Bi2 cuboctahedra, edges with eight equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Mg(4)Mg10Bi2 cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, and faces with four equivalent Bi(1)Mg10 cuboctahedra.
Mg5Bi crystallizes in the orthorhombic Amm2 space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(5), and four equivalent Mg(4) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(1)Mg12 cuboctahedra, corners with six equivalent Mg(2)Mg4Bi4 cuboctahedra, edges with four equivalent Mg(4)Mg10Bi2 cuboctahedra, edges with eight equivalent Bi(1)Mg10 cuboctahedra, faces with two equivalent Mg(2)Mg4Bi4 cuboctahedra, faces with two equivalent Bi(1)Mg10 cuboctahedra, faces with four equivalent Mg(4)Mg10Bi2 cuboctahedra, and faces with four equivalent Mg(1)Mg12 cuboctahedra. Both Mg(1)-Mg(1) bond lengths are 3.36 Å. Both Mg(1)-Mg(2) bond lengths are 3.19 Å. Both Mg(1)-Mg(3) bond lengths are 3.14 Å. Both Mg(1)-Mg(5) bond lengths are 3.16 Å. All Mg(1)-Mg(4) bond lengths are 3.20 Å. In the second Mg site, Mg(2) is bonded to two equivalent Mg(1), two equivalent Mg(4), and four equivalent Bi(1) atoms to form distorted MgMg4Bi4 cuboctahedra that share corners with four equivalent Mg(2)Mg4Bi4 cuboctahedra, corners with four equivalent Bi(1)Mg10 cuboctahedra, corners with six equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with four equivalent Mg(2)Mg4Bi4 cuboctahedra, and faces with six equivalent Mg(4)Mg10Bi2 cuboctahedra. Both Mg(2)-Mg(4) bond lengths are 3.22 Å. All Mg(2)-Bi(1) bond lengths are 3.24 Å. In the third Mg site, Mg(3) is bonded in a distorted water-like geometry to two equivalent Mg(1) and two equivalent Bi(1) atoms. Both Mg(3)-Bi(1) bond lengths are 3.22 Å. In the fourth Mg site, Mg(4) is bonded to two equivalent Mg(2), two equivalent Mg(4), two equivalent Mg(5), four equivalent Mg(1), and two equivalent Bi(1) atoms to form distorted MgMg10Bi2 cuboctahedra that share corners with six equivalent Mg(4)Mg10Bi2 cuboctahedra, corners with eight equivalent Bi(1)Mg10 cuboctahedra,  an edgeedge with one Bi(1)Mg10 cuboctahedra, edges with four equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Bi(1)Mg10 cuboctahedra, faces with four equivalent Mg(4)Mg10Bi2 cuboctahedra, faces with four equivalent Mg(1)Mg12 cuboctahedra, and faces with six equivalent Mg(2)Mg4Bi4 cuboctahedra. Both Mg(4)-Mg(4) bond lengths are 3.36 Å. Both Mg(4)-Mg(5) bond lengths are 3.09 Å. Both Mg(4)-Bi(1) bond lengths are 3.30 Å. In the fifth Mg site, Mg(5) is bonded in a 2-coordinate geometry to two equivalent Mg(1), two equivalent Mg(4), and two equivalent Bi(1) atoms. Both Mg(5)-Bi(1) bond lengths are 3.24 Å. Bi(1) is bonded to two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(5), and four equivalent Mg(2) atoms to form distorted BiMg10 cuboctahedra that share corners with four equivalent Mg(2)Mg4Bi4 cuboctahedra, corners with four equivalent Bi(1)Mg10 cuboctahedra, corners with eight equivalent Mg(4)Mg10Bi2 cuboctahedra,  an edgeedge with one Mg(4)Mg10Bi2 cuboctahedra, edges with eight equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Mg(4)Mg10Bi2 cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, and faces with four equivalent Bi(1)Mg10 cuboctahedra.