Mg14CeNb crystallizes in the hexagonal P-6m2 space group. There are six inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(4); four Mg(1,1); four Mg(3,3); and two equivalent Ce(1) atoms to form distorted MgCe2Mg10 cuboctahedra that share corners with four equivalent Nb(1)Mg12 cuboctahedra; corners with six equivalent Mg(1)Ce2Mg10 cuboctahedra; corners with eight equivalent Mg(2)Mg10Nb2 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with four Mg(1,1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight Mg(3,3)CeMg10Nb cuboctahedra; faces with two equivalent Mg(2)Mg10Nb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Ce(1)Mg12 cuboctahedra; faces with four Mg(1,1)Ce2Mg10 cuboctahedra; and faces with ten Mg(3,3)CeMg10Nb cuboctahedra. In the second Mg site, Mg(2) is bonded to two equivalent Mg(4); four equivalent Mg(2); four Mg(3,3); and two equivalent Nb(1) atoms to form MgMg10Nb2 cuboctahedra that share corners with four equivalent Ce(1)Mg12 cuboctahedra; corners with six equivalent Mg(2)Mg10Nb2 cuboctahedra; corners with eight Mg(1,1)Ce2Mg10 cuboctahedra; edges with two equivalent Nb(1)Mg12 cuboctahedra; edges with four equivalent Mg(2)Mg10Nb2 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight Mg(3,3)CeMg10Nb cuboctahedra; faces with two equivalent Mg(1)Ce2Mg10 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Nb(1)Mg12 cuboctahedra; faces with four equivalent Mg(2)Mg10Nb2 cuboctahedra; and faces with ten Mg(3,3)CeMg10Nb cuboctahedra. In the third Mg site, Mg(1) is bonded to two equivalent Mg(4); four equivalent Mg(1); four Mg(3,3); and two equivalent Ce(1) atoms to form distorted MgCe2Mg10 cuboctahedra that share corners with four equivalent Nb(1)Mg12 cuboctahedra; corners with six equivalent Mg(1)Ce2Mg10 cuboctahedra; corners with eight equivalent Mg(2)Mg10Nb2 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight Mg(3,3)CeMg10Nb cuboctahedra; faces with two equivalent Mg(2)Mg10Nb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Ce(1)Mg12 cuboctahedra; faces with four equivalent Mg(1)Ce2Mg10 cuboctahedra; and faces with ten Mg(3,3)CeMg10Nb cuboctahedra. In the fourth Mg site, Mg(3) is bonded to two Mg(1,1); two equivalent Mg(2); two equivalent Mg(4); four equivalent Mg(3); one Ce(1); and one Nb(1) atom to form distorted MgCeMg10Nb cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)CeMg10Nb cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with two equivalent Nb(1)Mg12 cuboctahedra; edges with four Mg(1,1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(3)CeMg10Nb cuboctahedra; edges with four equivalent Mg(2)Mg10Nb2 cuboctahedra;  a faceface with one Ce(1)Mg12 cuboctahedra;  a faceface with one Nb(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five Mg(1,1)Ce2Mg10 cuboctahedra; faces with five equivalent Mg(2)Mg10Nb2 cuboctahedra; and faces with six Mg(3,3)CeMg10Nb cuboctahedra. In the fifth Mg site, Mg(3) is bonded to two equivalent Mg(1); two equivalent Mg(2); two equivalent Mg(4); four Mg(3,3); one Ce(1); and one Nb(1) atom to form distorted MgCeMg10Nb cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)CeMg10Nb cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with two equivalent Nb(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Ce2Mg10 cuboctahedra; edges with four Mg(3,3)CeMg10Nb cuboctahedra; edges with four equivalent Mg(2)Mg10Nb2 cuboctahedra;  a faceface with one Ce(1)Mg12 cuboctahedra;  a faceface with one Nb(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five Mg(1,1)Ce2Mg10 cuboctahedra; faces with five equivalent Mg(2)Mg10Nb2 cuboctahedra; and faces with six Mg(3,3)CeMg10Nb cuboctahedra. In the sixth Mg site, Mg(4) is bonded to three Mg(1,1); three equivalent Mg(2); and six Mg(3,3) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(4)Mg12 cuboctahedra; corners with twelve Mg(3,3)CeMg10Nb cuboctahedra; edges with six Mg(1,1)Ce2Mg10 cuboctahedra; edges with six Mg(3,3)CeMg10Nb cuboctahedra; edges with six equivalent Mg(2)Mg10Nb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with three Mg(1,1)Ce2Mg10 cuboctahedra; faces with three equivalent Mg(2)Mg10Nb2 cuboctahedra; faces with three equivalent Ce(1)Mg12 cuboctahedra; faces with three equivalent Nb(1)Mg12 cuboctahedra; and faces with six Mg(3,3)CeMg10Nb cuboctahedra. Ce(1) is bonded to six Mg(1,1) and six Mg(3,3) atoms to form CeMg12 cuboctahedra that share corners with six equivalent Ce(1)Mg12 cuboctahedra; corners with twelve equivalent Mg(2)Mg10Nb2 cuboctahedra; edges with six Mg(1,1)Ce2Mg10 cuboctahedra; edges with twelve Mg(3,3)CeMg10Nb cuboctahedra; faces with two equivalent Nb(1)Mg12 cuboctahedra; faces with six Mg(1,1)Ce2Mg10 cuboctahedra; faces with six Mg(3,3)CeMg10Nb cuboctahedra; and faces with six equivalent Mg(4)Mg12 cuboctahedra. Nb(1) is bonded to six equivalent Mg(2) and six Mg(3,3) atoms to form NbMg12 cuboctahedra that share corners with six equivalent Nb(1)Mg12 cuboctahedra; corners with twelve Mg(1,1)Ce2Mg10 cuboctahedra; edges with six equivalent Mg(2)Mg10Nb2 cuboctahedra; edges with twelve Mg(3,3)CeMg10Nb cuboctahedra; faces with two equivalent Ce(1)Mg12 cuboctahedra; faces with six Mg(3,3)CeMg10Nb cuboctahedra; faces with six equivalent Mg(2)Mg10Nb2 cuboctahedra; and faces with six equivalent Mg(4)Mg12 cuboctahedra.
Mg14CeNb crystallizes in the hexagonal P-6m2 space group. There are six inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(4); four Mg(1,1); four Mg(3,3); and two equivalent Ce(1) atoms to form distorted MgCe2Mg10 cuboctahedra that share corners with four equivalent Nb(1)Mg12 cuboctahedra; corners with six equivalent Mg(1)Ce2Mg10 cuboctahedra; corners with eight equivalent Mg(2)Mg10Nb2 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with four Mg(1,1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight Mg(3,3)CeMg10Nb cuboctahedra; faces with two equivalent Mg(2)Mg10Nb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Ce(1)Mg12 cuboctahedra; faces with four Mg(1,1)Ce2Mg10 cuboctahedra; and faces with ten Mg(3,3)CeMg10Nb cuboctahedra. Both Mg(1)-Mg(4) bond lengths are 3.11 Å. There are two shorter (3.10 Å) and two longer (3.40 Å) Mg(1)-Mg(1,1) bond lengths. All Mg(1)-Mg(3,3) bond lengths are 3.24 Å. Both Mg(1)-Ce(1) bond lengths are 3.25 Å. In the second Mg site, Mg(2) is bonded to two equivalent Mg(4); four equivalent Mg(2); four Mg(3,3); and two equivalent Nb(1) atoms to form MgMg10Nb2 cuboctahedra that share corners with four equivalent Ce(1)Mg12 cuboctahedra; corners with six equivalent Mg(2)Mg10Nb2 cuboctahedra; corners with eight Mg(1,1)Ce2Mg10 cuboctahedra; edges with two equivalent Nb(1)Mg12 cuboctahedra; edges with four equivalent Mg(2)Mg10Nb2 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight Mg(3,3)CeMg10Nb cuboctahedra; faces with two equivalent Mg(1)Ce2Mg10 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Nb(1)Mg12 cuboctahedra; faces with four equivalent Mg(2)Mg10Nb2 cuboctahedra; and faces with ten Mg(3,3)CeMg10Nb cuboctahedra. Both Mg(2)-Mg(4) bond lengths are 3.23 Å. There are two shorter (3.21 Å) and two longer (3.29 Å) Mg(2)-Mg(2) bond lengths. All Mg(2)-Mg(3,3) bond lengths are 3.06 Å. Both Mg(2)-Nb(1) bond lengths are 3.25 Å. In the third Mg site, Mg(1) is bonded to two equivalent Mg(4); four equivalent Mg(1); four Mg(3,3); and two equivalent Ce(1) atoms to form distorted MgCe2Mg10 cuboctahedra that share corners with four equivalent Nb(1)Mg12 cuboctahedra; corners with six equivalent Mg(1)Ce2Mg10 cuboctahedra; corners with eight equivalent Mg(2)Mg10Nb2 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight Mg(3,3)CeMg10Nb cuboctahedra; faces with two equivalent Mg(2)Mg10Nb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Ce(1)Mg12 cuboctahedra; faces with four equivalent Mg(1)Ce2Mg10 cuboctahedra; and faces with ten Mg(3,3)CeMg10Nb cuboctahedra. Both Mg(1)-Mg(4) bond lengths are 3.11 Å. All Mg(1)-Mg(3,3) bond lengths are 3.24 Å. Both Mg(1)-Ce(1) bond lengths are 3.25 Å. In the fourth Mg site, Mg(3) is bonded to two Mg(1,1); two equivalent Mg(2); two equivalent Mg(4); four equivalent Mg(3); one Ce(1); and one Nb(1) atom to form distorted MgCeMg10Nb cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)CeMg10Nb cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with two equivalent Nb(1)Mg12 cuboctahedra; edges with four Mg(1,1)Ce2Mg10 cuboctahedra; edges with four equivalent Mg(3)CeMg10Nb cuboctahedra; edges with four equivalent Mg(2)Mg10Nb2 cuboctahedra;  a faceface with one Ce(1)Mg12 cuboctahedra;  a faceface with one Nb(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five Mg(1,1)Ce2Mg10 cuboctahedra; faces with five equivalent Mg(2)Mg10Nb2 cuboctahedra; and faces with six Mg(3,3)CeMg10Nb cuboctahedra. Both Mg(3)-Mg(4) bond lengths are 3.26 Å. There are two shorter (3.22 Å) and two longer (3.28 Å) Mg(3)-Mg(3) bond lengths. The Mg(3)-Ce(1) bond length is 3.25 Å. The Mg(3)-Nb(1) bond length is 3.03 Å. In the fifth Mg site, Mg(3) is bonded to two equivalent Mg(1); two equivalent Mg(2); two equivalent Mg(4); four Mg(3,3); one Ce(1); and one Nb(1) atom to form distorted MgCeMg10Nb cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)CeMg10Nb cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Ce(1)Mg12 cuboctahedra; edges with two equivalent Nb(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Ce2Mg10 cuboctahedra; edges with four Mg(3,3)CeMg10Nb cuboctahedra; edges with four equivalent Mg(2)Mg10Nb2 cuboctahedra;  a faceface with one Ce(1)Mg12 cuboctahedra;  a faceface with one Nb(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five Mg(1,1)Ce2Mg10 cuboctahedra; faces with five equivalent Mg(2)Mg10Nb2 cuboctahedra; and faces with six Mg(3,3)CeMg10Nb cuboctahedra. Both Mg(3)-Mg(4) bond lengths are 3.26 Å. There is one shorter (3.22 Å) and one longer (3.28 Å) Mg(3)-Mg(3) bond length. The Mg(3)-Ce(1) bond length is 3.25 Å. The Mg(3)-Nb(1) bond length is 3.03 Å. In the sixth Mg site, Mg(4) is bonded to three Mg(1,1); three equivalent Mg(2); and six Mg(3,3) atoms to form MgMg12 cuboctahedra that share corners with six equivalent Mg(4)Mg12 cuboctahedra; corners with twelve Mg(3,3)CeMg10Nb cuboctahedra; edges with six Mg(1,1)Ce2Mg10 cuboctahedra; edges with six Mg(3,3)CeMg10Nb cuboctahedra; edges with six equivalent Mg(2)Mg10Nb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with three Mg(1,1)Ce2Mg10 cuboctahedra; faces with three equivalent Mg(2)Mg10Nb2 cuboctahedra; faces with three equivalent Ce(1)Mg12 cuboctahedra; faces with three equivalent Nb(1)Mg12 cuboctahedra; and faces with six Mg(3,3)CeMg10Nb cuboctahedra. Ce(1) is bonded to six Mg(1,1) and six Mg(3,3) atoms to form CeMg12 cuboctahedra that share corners with six equivalent Ce(1)Mg12 cuboctahedra; corners with twelve equivalent Mg(2)Mg10Nb2 cuboctahedra; edges with six Mg(1,1)Ce2Mg10 cuboctahedra; edges with twelve Mg(3,3)CeMg10Nb cuboctahedra; faces with two equivalent Nb(1)Mg12 cuboctahedra; faces with six Mg(1,1)Ce2Mg10 cuboctahedra; faces with six Mg(3,3)CeMg10Nb cuboctahedra; and faces with six equivalent Mg(4)Mg12 cuboctahedra. Nb(1) is bonded to six equivalent Mg(2) and six Mg(3,3) atoms to form NbMg12 cuboctahedra that share corners with six equivalent Nb(1)Mg12 cuboctahedra; corners with twelve Mg(1,1)Ce2Mg10 cuboctahedra; edges with six equivalent Mg(2)Mg10Nb2 cuboctahedra; edges with twelve Mg(3,3)CeMg10Nb cuboctahedra; faces with two equivalent Ce(1)Mg12 cuboctahedra; faces with six Mg(3,3)CeMg10Nb cuboctahedra; faces with six equivalent Mg(2)Mg10Nb2 cuboctahedra; and faces with six equivalent Mg(4)Mg12 cuboctahedra.