Ce2Mg17 crystallizes in the hexagonal P6_3/mmc space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(4), four equivalent Mg(2), four equivalent Mg(3), and two equivalent Ce(2) atoms to form distorted MgCe2Mg10 cuboctahedra that share corners with four equivalent Mg(1)Ce2Mg10 cuboctahedra, corners with ten equivalent Mg(2)Ce3Mg9 cuboctahedra, edges with six equivalent Mg(2)Ce3Mg9 cuboctahedra, faces with four equivalent Mg(2)Ce3Mg9 cuboctahedra, faces with six equivalent Mg(1)Ce2Mg10 cuboctahedra, and faces with two equivalent Ce(2)Mg20 hexagonal bipyramids. In the second Mg site, Mg(2) is bonded to one Mg(4), two equivalent Mg(1), two equivalent Mg(2), four equivalent Mg(3), one Ce(2), and two equivalent Ce(1) atoms to form distorted MgCe3Mg9 cuboctahedra that share corners with five equivalent Mg(1)Ce2Mg10 cuboctahedra, corners with ten equivalent Mg(2)Ce3Mg9 cuboctahedra, edges with three equivalent Mg(1)Ce2Mg10 cuboctahedra, edges with five equivalent Mg(2)Ce3Mg9 cuboctahedra, faces with two equivalent Mg(1)Ce2Mg10 cuboctahedra, faces with eight equivalent Mg(2)Ce3Mg9 cuboctahedra, and faces with three equivalent Ce(2)Mg20 hexagonal bipyramids. In the third Mg site, Mg(3) is bonded in a 10-coordinate geometry to two equivalent Mg(1), two equivalent Mg(3), four equivalent Mg(2), one Ce(1), and one Ce(2) atom. In the fourth Mg site, Mg(4) is bonded in a 8-coordinate geometry to one Mg(4), three equivalent Mg(1), three equivalent Mg(2), and one Ce(2) atom. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded in a distorted hexagonal planar geometry to six equivalent Mg(3) and twelve equivalent Mg(2) atoms. In the second Ce site, Ce(2) is bonded to two equivalent Mg(4), six equivalent Mg(1), six equivalent Mg(2), and six equivalent Mg(3) atoms to form distorted CeMg20 hexagonal bipyramids that share corners with six equivalent Ce(2)Mg20 hexagonal bipyramids, faces with six equivalent Mg(1)Ce2Mg10 cuboctahedra, and faces with eighteen equivalent Mg(2)Ce3Mg9 cuboctahedra.
Ce2Mg17 crystallizes in the hexagonal P6_3/mmc space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(4), four equivalent Mg(2), four equivalent Mg(3), and two equivalent Ce(2) atoms to form distorted MgCe2Mg10 cuboctahedra that share corners with four equivalent Mg(1)Ce2Mg10 cuboctahedra, corners with ten equivalent Mg(2)Ce3Mg9 cuboctahedra, edges with six equivalent Mg(2)Ce3Mg9 cuboctahedra, faces with four equivalent Mg(2)Ce3Mg9 cuboctahedra, faces with six equivalent Mg(1)Ce2Mg10 cuboctahedra, and faces with two equivalent Ce(2)Mg20 hexagonal bipyramids. Both Mg(1)-Mg(4) bond lengths are 3.16 Å. All Mg(1)-Mg(2) bond lengths are 2.99 Å. All Mg(1)-Mg(3) bond lengths are 3.06 Å. Both Mg(1)-Ce(2) bond lengths are 3.91 Å. In the second Mg site, Mg(2) is bonded to one Mg(4), two equivalent Mg(1), two equivalent Mg(2), four equivalent Mg(3), one Ce(2), and two equivalent Ce(1) atoms to form distorted MgCe3Mg9 cuboctahedra that share corners with five equivalent Mg(1)Ce2Mg10 cuboctahedra, corners with ten equivalent Mg(2)Ce3Mg9 cuboctahedra, edges with three equivalent Mg(1)Ce2Mg10 cuboctahedra, edges with five equivalent Mg(2)Ce3Mg9 cuboctahedra, faces with two equivalent Mg(1)Ce2Mg10 cuboctahedra, faces with eight equivalent Mg(2)Ce3Mg9 cuboctahedra, and faces with three equivalent Ce(2)Mg20 hexagonal bipyramids. The Mg(2)-Mg(4) bond length is 3.20 Å. Both Mg(2)-Mg(2) bond lengths are 2.95 Å. There are two shorter (3.07 Å) and two longer (3.08 Å) Mg(2)-Mg(3) bond lengths. The Mg(2)-Ce(2) bond length is 3.92 Å. There is one shorter (3.88 Å) and one longer (3.91 Å) Mg(2)-Ce(1) bond length. In the third Mg site, Mg(3) is bonded in a 10-coordinate geometry to two equivalent Mg(1), two equivalent Mg(3), four equivalent Mg(2), one Ce(1), and one Ce(2) atom. There is one shorter (3.39 Å) and one longer (3.40 Å) Mg(3)-Mg(3) bond length. The Mg(3)-Ce(1) bond length is 3.46 Å. The Mg(3)-Ce(2) bond length is 3.47 Å. In the fourth Mg site, Mg(4) is bonded in a 8-coordinate geometry to one Mg(4), three equivalent Mg(1), three equivalent Mg(2), and one Ce(2) atom. The Mg(4)-Mg(4) bond length is 2.94 Å. The Mg(4)-Ce(2) bond length is 3.61 Å. There are two inequivalent Ce sites. In the first Ce site, Ce(1) is bonded in a distorted hexagonal planar geometry to six equivalent Mg(3) and twelve equivalent Mg(2) atoms. In the second Ce site, Ce(2) is bonded to two equivalent Mg(4), six equivalent Mg(1), six equivalent Mg(2), and six equivalent Mg(3) atoms to form distorted CeMg20 hexagonal bipyramids that share corners with six equivalent Ce(2)Mg20 hexagonal bipyramids, faces with six equivalent Mg(1)Ce2Mg10 cuboctahedra, and faces with eighteen equivalent Mg(2)Ce3Mg9 cuboctahedra.