Mg17Ba2 crystallizes in the trigonal R-3m space group. Ba(1) is bonded in a 19-coordinate geometry to one Mg(2), three equivalent Mg(3), six equivalent Mg(4), and nine equivalent Mg(1) atoms. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent Ba(1), one Mg(2), two equivalent Mg(1), two equivalent Mg(3), and four equivalent Mg(4) atoms to form MgBa3Mg9 cuboctahedra that share corners with five equivalent Mg(3)Ba2Mg10 cuboctahedra, corners with ten equivalent Mg(1)Ba3Mg9 cuboctahedra, edges with three equivalent Mg(3)Ba2Mg10 cuboctahedra, edges with five equivalent Mg(1)Ba3Mg9 cuboctahedra, faces with three equivalent Mg(3)Ba2Mg10 cuboctahedra, and faces with seven equivalent Mg(1)Ba3Mg9 cuboctahedra. In the second Mg site, Mg(2) is bonded in a 14-coordinate geometry to one Ba(1), one Mg(2), three equivalent Mg(1), three equivalent Mg(3), and six equivalent Mg(4) atoms. In the third Mg site, Mg(3) is bonded to two equivalent Ba(1), two equivalent Mg(2), four equivalent Mg(1), and four equivalent Mg(4) atoms to form distorted MgBa2Mg10 cuboctahedra that share corners with four equivalent Mg(3)Ba2Mg10 cuboctahedra, corners with ten equivalent Mg(1)Ba3Mg9 cuboctahedra, edges with six equivalent Mg(1)Ba3Mg9 cuboctahedra, faces with four equivalent Mg(3)Ba2Mg10 cuboctahedra, and faces with six equivalent Mg(1)Ba3Mg9 cuboctahedra. In the fourth Mg site, Mg(4) is bonded in a 12-coordinate geometry to two equivalent Ba(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), and four equivalent Mg(1) atoms.
Mg17Ba2 crystallizes in the trigonal R-3m space group. Ba(1) is bonded in a 19-coordinate geometry to one Mg(2), three equivalent Mg(3), six equivalent Mg(4), and nine equivalent Mg(1) atoms. The Ba(1)-Mg(2) bond length is 3.73 Å. All Ba(1)-Mg(3) bond lengths are 4.06 Å. All Ba(1)-Mg(4) bond lengths are 3.77 Å. There are a spread of Ba(1)-Mg(1) bond distances ranging from 3.83-4.09 Å. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent Ba(1), one Mg(2), two equivalent Mg(1), two equivalent Mg(3), and four equivalent Mg(4) atoms to form MgBa3Mg9 cuboctahedra that share corners with five equivalent Mg(3)Ba2Mg10 cuboctahedra, corners with ten equivalent Mg(1)Ba3Mg9 cuboctahedra, edges with three equivalent Mg(3)Ba2Mg10 cuboctahedra, edges with five equivalent Mg(1)Ba3Mg9 cuboctahedra, faces with three equivalent Mg(3)Ba2Mg10 cuboctahedra, and faces with seven equivalent Mg(1)Ba3Mg9 cuboctahedra. The Mg(1)-Mg(2) bond length is 3.32 Å. Both Mg(1)-Mg(1) bond lengths are 3.09 Å. Both Mg(1)-Mg(3) bond lengths are 3.07 Å. There are two shorter (3.21 Å) and two longer (3.24 Å) Mg(1)-Mg(4) bond lengths. In the second Mg site, Mg(2) is bonded in a 14-coordinate geometry to one Ba(1), one Mg(2), three equivalent Mg(1), three equivalent Mg(3), and six equivalent Mg(4) atoms. The Mg(2)-Mg(2) bond length is 3.01 Å. All Mg(2)-Mg(3) bond lengths are 3.25 Å. All Mg(2)-Mg(4) bond lengths are 3.45 Å. In the third Mg site, Mg(3) is bonded to two equivalent Ba(1), two equivalent Mg(2), four equivalent Mg(1), and four equivalent Mg(4) atoms to form distorted MgBa2Mg10 cuboctahedra that share corners with four equivalent Mg(3)Ba2Mg10 cuboctahedra, corners with ten equivalent Mg(1)Ba3Mg9 cuboctahedra, edges with six equivalent Mg(1)Ba3Mg9 cuboctahedra, faces with four equivalent Mg(3)Ba2Mg10 cuboctahedra, and faces with six equivalent Mg(1)Ba3Mg9 cuboctahedra. All Mg(3)-Mg(4) bond lengths are 3.03 Å. In the fourth Mg site, Mg(4) is bonded in a 12-coordinate geometry to two equivalent Ba(1), two equivalent Mg(2), two equivalent Mg(3), two equivalent Mg(4), and four equivalent Mg(1) atoms. Both Mg(4)-Mg(4) bond lengths are 3.11 Å.