Mg15B crystallizes in the hexagonal P-6m2 space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to six equivalent Mg(3) and six equivalent Mg(4) atoms to form a mixture of edge, corner, and face-sharing MgMg12 cuboctahedra. In the second Mg site, Mg(2) is bonded in a 10-coordinate geometry to two equivalent Mg(5) and four equivalent Mg(4) atoms. In the third Mg site, Mg(3) is bonded to two equivalent Mg(1), two equivalent Mg(5), four equivalent Mg(3), and four equivalent Mg(4) atoms to form a mixture of edge, corner, and face-sharing MgMg12 cuboctahedra. In the fourth Mg site, Mg(4) is bonded in a 12-coordinate geometry to one Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(5), four equivalent Mg(4), and one B(1) atom. In the fifth Mg site, Mg(5) is bonded to three equivalent Mg(2), three equivalent Mg(3), and six equivalent Mg(4) atoms to form a mixture of edge, corner, and face-sharing MgMg12 cuboctahedra. B(1) is bonded in a 6-coordinate geometry to six equivalent Mg(4) atoms.
Mg15B crystallizes in the hexagonal P-6m2 space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to six equivalent Mg(3) and six equivalent Mg(4) atoms to form a mixture of edge, corner, and face-sharing MgMg12 cuboctahedra. All Mg(1)-Mg(3) bond lengths are 3.14 Å. All Mg(1)-Mg(4) bond lengths are 3.17 Å. In the second Mg site, Mg(2) is bonded in a 10-coordinate geometry to two equivalent Mg(5) and four equivalent Mg(4) atoms. Both Mg(2)-Mg(5) bond lengths are 3.09 Å. All Mg(2)-Mg(4) bond lengths are 3.03 Å. In the third Mg site, Mg(3) is bonded to two equivalent Mg(1), two equivalent Mg(5), four equivalent Mg(3), and four equivalent Mg(4) atoms to form a mixture of edge, corner, and face-sharing MgMg12 cuboctahedra. Both Mg(3)-Mg(5) bond lengths are 3.10 Å. There are two shorter (3.12 Å) and two longer (3.17 Å) Mg(3)-Mg(3) bond lengths. All Mg(3)-Mg(4) bond lengths are 3.21 Å. In the fourth Mg site, Mg(4) is bonded in a 12-coordinate geometry to one Mg(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(5), four equivalent Mg(4), and one B(1) atom. Both Mg(4)-Mg(5) bond lengths are 3.15 Å. There are two shorter (3.05 Å) and two longer (3.24 Å) Mg(4)-Mg(4) bond lengths. The Mg(4)-B(1) bond length is 2.97 Å. In the fifth Mg site, Mg(5) is bonded to three equivalent Mg(2), three equivalent Mg(3), and six equivalent Mg(4) atoms to form a mixture of edge, corner, and face-sharing MgMg12 cuboctahedra. B(1) is bonded in a 6-coordinate geometry to six equivalent Mg(4) atoms.