Mg14NbSb 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 equivalent Mg(1), four equivalent Mg(3), and two equivalent Nb(1) atoms to form MgMg10Nb2 cuboctahedra that share corners with four equivalent Sb(1)Mg12 cuboctahedra; corners with six equivalent Mg(1)Mg10Nb2 cuboctahedra; corners with eight Mg(2,2)Mg10Sb2 cuboctahedra; edges with two equivalent Nb(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight equivalent Mg(3)Mg10NbSb cuboctahedra; faces with two equivalent Mg(2)Mg10Sb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Nb(1)Mg12 cuboctahedra; faces with four equivalent Mg(1)Mg10Nb2 cuboctahedra; and faces with ten Mg(3,3)Mg10NbSb cuboctahedra. In the second Mg site, Mg(2) is bonded to two equivalent Mg(4); four Mg(2,2); four equivalent Mg(3); and two equivalent Sb(1) atoms to form distorted MgMg10Sb2 cuboctahedra that share corners with four equivalent Nb(1)Mg12 cuboctahedra; corners with six equivalent Mg(2)Mg10Sb2 cuboctahedra; corners with eight equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with two equivalent Sb(1)Mg12 cuboctahedra; edges with four Mg(2,2)Mg10Sb2 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight equivalent Mg(3)Mg10NbSb cuboctahedra; faces with two equivalent Mg(1)Mg10Nb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Sb(1)Mg12 cuboctahedra; faces with four Mg(2,2)Mg10Sb2 cuboctahedra; and faces with ten Mg(3,3)Mg10NbSb cuboctahedra. In the third Mg site, Mg(2) is bonded to two equivalent Mg(4); four equivalent Mg(2); four Mg(3,3); and two equivalent Sb(1) atoms to form distorted MgMg10Sb2 cuboctahedra that share corners with four equivalent Nb(1)Mg12 cuboctahedra; corners with six equivalent Mg(2)Mg10Sb2 cuboctahedra; corners with eight equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with two equivalent Sb(1)Mg12 cuboctahedra; edges with four equivalent Mg(2)Mg10Sb2 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight Mg(3,3)Mg10NbSb cuboctahedra; faces with two equivalent Mg(1)Mg10Nb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Sb(1)Mg12 cuboctahedra; faces with four equivalent Mg(2)Mg10Sb2 cuboctahedra; and faces with ten Mg(3,3)Mg10NbSb cuboctahedra. In the fourth Mg site, Mg(3) is bonded to two equivalent Mg(1); two Mg(2,2); two equivalent Mg(4); four Mg(3,3); one Nb(1); and one Sb(1) atom to form distorted MgMg10NbSb cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)Mg10NbSb cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Nb(1)Mg12 cuboctahedra; edges with two equivalent Sb(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with four Mg(3,3)Mg10NbSb cuboctahedra; edges with four Mg(2,2)Mg10Sb2 cuboctahedra;  a faceface with one Nb(1)Mg12 cuboctahedra;  a faceface with one Sb(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five equivalent Mg(1)Mg10Nb2 cuboctahedra; faces with five Mg(2,2)Mg10Sb2 cuboctahedra; and faces with six Mg(3,3)Mg10NbSb cuboctahedra. In the fifth Mg site, Mg(3) is bonded to two equivalent Mg(1); two Mg(2,2); two equivalent Mg(4); four equivalent Mg(3); one Nb(1); and one Sb(1) atom to form distorted MgMg10NbSb cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)Mg10NbSb cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Nb(1)Mg12 cuboctahedra; edges with two equivalent Sb(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with four equivalent Mg(3)Mg10NbSb cuboctahedra; edges with four Mg(2,2)Mg10Sb2 cuboctahedra;  a faceface with one Nb(1)Mg12 cuboctahedra;  a faceface with one Sb(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five equivalent Mg(1)Mg10Nb2 cuboctahedra; faces with five Mg(2,2)Mg10Sb2 cuboctahedra; and faces with six Mg(3,3)Mg10NbSb cuboctahedra. In the sixth Mg site, Mg(4) is bonded to three equivalent Mg(1); three Mg(2,2); 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)Mg10NbSb cuboctahedra; edges with six equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with six Mg(3,3)Mg10NbSb cuboctahedra; edges with six Mg(2,2)Mg10Sb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with three equivalent Mg(1)Mg10Nb2 cuboctahedra; faces with three Mg(2,2)Mg10Sb2 cuboctahedra; faces with three equivalent Nb(1)Mg12 cuboctahedra; faces with three equivalent Sb(1)Mg12 cuboctahedra; and faces with six Mg(3,3)Mg10NbSb cuboctahedra. Nb(1) is bonded to six equivalent Mg(1) and six Mg(3,3) atoms to form NbMg12 cuboctahedra that share corners with six equivalent Nb(1)Mg12 cuboctahedra; corners with twelve Mg(2,2)Mg10Sb2 cuboctahedra; edges with six equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with twelve Mg(3,3)Mg10NbSb cuboctahedra; faces with two equivalent Sb(1)Mg12 cuboctahedra; faces with six equivalent Mg(1)Mg10Nb2 cuboctahedra; faces with six Mg(3,3)Mg10NbSb cuboctahedra; and faces with six equivalent Mg(4)Mg12 cuboctahedra. Sb(1) is bonded to six Mg(2,2) and six Mg(3,3) atoms to form SbMg12 cuboctahedra that share corners with six equivalent Sb(1)Mg12 cuboctahedra; corners with twelve equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with six Mg(2,2)Mg10Sb2 cuboctahedra; edges with twelve Mg(3,3)Mg10NbSb cuboctahedra; faces with two equivalent Nb(1)Mg12 cuboctahedra; faces with six Mg(3,3)Mg10NbSb cuboctahedra; faces with six Mg(2,2)Mg10Sb2 cuboctahedra; and faces with six equivalent Mg(4)Mg12 cuboctahedra.
Mg14NbSb 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 equivalent Mg(1), four equivalent Mg(3), and two equivalent Nb(1) atoms to form MgMg10Nb2 cuboctahedra that share corners with four equivalent Sb(1)Mg12 cuboctahedra; corners with six equivalent Mg(1)Mg10Nb2 cuboctahedra; corners with eight Mg(2,2)Mg10Sb2 cuboctahedra; edges with two equivalent Nb(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight equivalent Mg(3)Mg10NbSb cuboctahedra; faces with two equivalent Mg(2)Mg10Sb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Nb(1)Mg12 cuboctahedra; faces with four equivalent Mg(1)Mg10Nb2 cuboctahedra; and faces with ten Mg(3,3)Mg10NbSb cuboctahedra. Both Mg(1)-Mg(4) bond lengths are 3.12 Å. There are two shorter (3.15 Å) and two longer (3.18 Å) Mg(1)-Mg(1) bond lengths. All Mg(1)-Mg(3) bond lengths are 3.10 Å. Both Mg(1)-Nb(1) bond lengths are 3.17 Å. In the second Mg site, Mg(2) is bonded to two equivalent Mg(4); four Mg(2,2); four equivalent Mg(3); and two equivalent Sb(1) atoms to form distorted MgMg10Sb2 cuboctahedra that share corners with four equivalent Nb(1)Mg12 cuboctahedra; corners with six equivalent Mg(2)Mg10Sb2 cuboctahedra; corners with eight equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with two equivalent Sb(1)Mg12 cuboctahedra; edges with four Mg(2,2)Mg10Sb2 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight equivalent Mg(3)Mg10NbSb cuboctahedra; faces with two equivalent Mg(1)Mg10Nb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Sb(1)Mg12 cuboctahedra; faces with four Mg(2,2)Mg10Sb2 cuboctahedra; and faces with ten Mg(3,3)Mg10NbSb cuboctahedra. Both Mg(2)-Mg(4) bond lengths are 3.16 Å. There are two shorter (3.16 Å) and two longer (3.18 Å) Mg(2)-Mg(2,2) bond lengths. All Mg(2)-Mg(3) bond lengths are 3.20 Å. Both Mg(2)-Sb(1) bond lengths are 3.17 Å. In the third Mg site, Mg(2) is bonded to two equivalent Mg(4); four equivalent Mg(2); four Mg(3,3); and two equivalent Sb(1) atoms to form distorted MgMg10Sb2 cuboctahedra that share corners with four equivalent Nb(1)Mg12 cuboctahedra; corners with six equivalent Mg(2)Mg10Sb2 cuboctahedra; corners with eight equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with two equivalent Sb(1)Mg12 cuboctahedra; edges with four equivalent Mg(2)Mg10Sb2 cuboctahedra; edges with four equivalent Mg(4)Mg12 cuboctahedra; edges with eight Mg(3,3)Mg10NbSb cuboctahedra; faces with two equivalent Mg(1)Mg10Nb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with two equivalent Sb(1)Mg12 cuboctahedra; faces with four equivalent Mg(2)Mg10Sb2 cuboctahedra; and faces with ten Mg(3,3)Mg10NbSb cuboctahedra. Both Mg(2)-Mg(4) bond lengths are 3.16 Å. All Mg(2)-Mg(3,3) bond lengths are 3.20 Å. Both Mg(2)-Sb(1) bond lengths are 3.17 Å. In the fourth Mg site, Mg(3) is bonded to two equivalent Mg(1); two Mg(2,2); two equivalent Mg(4); four Mg(3,3); one Nb(1); and one Sb(1) atom to form distorted MgMg10NbSb cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)Mg10NbSb cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Nb(1)Mg12 cuboctahedra; edges with two equivalent Sb(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with four Mg(3,3)Mg10NbSb cuboctahedra; edges with four Mg(2,2)Mg10Sb2 cuboctahedra;  a faceface with one Nb(1)Mg12 cuboctahedra;  a faceface with one Sb(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five equivalent Mg(1)Mg10Nb2 cuboctahedra; faces with five Mg(2,2)Mg10Sb2 cuboctahedra; and faces with six Mg(3,3)Mg10NbSb cuboctahedra. Both Mg(3)-Mg(4) bond lengths are 3.17 Å. There are two shorter (3.10 Å) and two longer (3.24 Å) Mg(3)-Mg(3,3) bond lengths. The Mg(3)-Nb(1) bond length is 3.06 Å. The Mg(3)-Sb(1) bond length is 3.16 Å. In the fifth Mg site, Mg(3) is bonded to two equivalent Mg(1); two Mg(2,2); two equivalent Mg(4); four equivalent Mg(3); one Nb(1); and one Sb(1) atom to form distorted MgMg10NbSb cuboctahedra that share corners with four equivalent Mg(4)Mg12 cuboctahedra; corners with fourteen Mg(3,3)Mg10NbSb cuboctahedra; edges with two equivalent Mg(4)Mg12 cuboctahedra; edges with two equivalent Nb(1)Mg12 cuboctahedra; edges with two equivalent Sb(1)Mg12 cuboctahedra; edges with four equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with four equivalent Mg(3)Mg10NbSb cuboctahedra; edges with four Mg(2,2)Mg10Sb2 cuboctahedra;  a faceface with one Nb(1)Mg12 cuboctahedra;  a faceface with one Sb(1)Mg12 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with five equivalent Mg(1)Mg10Nb2 cuboctahedra; faces with five Mg(2,2)Mg10Sb2 cuboctahedra; and faces with six Mg(3,3)Mg10NbSb cuboctahedra. Both Mg(3)-Mg(1) bond lengths are 3.10 Å. The Mg(3)-Mg(2) bond length is 3.20 Å. Both Mg(3)-Mg(4) bond lengths are 3.17 Å. The Mg(3)-Nb(1) bond length is 3.06 Å. The Mg(3)-Sb(1) bond length is 3.16 Å. In the sixth Mg site, Mg(4) is bonded to three equivalent Mg(1); three Mg(2,2); 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)Mg10NbSb cuboctahedra; edges with six equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with six Mg(3,3)Mg10NbSb cuboctahedra; edges with six Mg(2,2)Mg10Sb2 cuboctahedra; faces with two equivalent Mg(4)Mg12 cuboctahedra; faces with three equivalent Mg(1)Mg10Nb2 cuboctahedra; faces with three Mg(2,2)Mg10Sb2 cuboctahedra; faces with three equivalent Nb(1)Mg12 cuboctahedra; faces with three equivalent Sb(1)Mg12 cuboctahedra; and faces with six Mg(3,3)Mg10NbSb cuboctahedra. Nb(1) is bonded to six equivalent Mg(1) and six Mg(3,3) atoms to form NbMg12 cuboctahedra that share corners with six equivalent Nb(1)Mg12 cuboctahedra; corners with twelve Mg(2,2)Mg10Sb2 cuboctahedra; edges with six equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with twelve Mg(3,3)Mg10NbSb cuboctahedra; faces with two equivalent Sb(1)Mg12 cuboctahedra; faces with six equivalent Mg(1)Mg10Nb2 cuboctahedra; faces with six Mg(3,3)Mg10NbSb cuboctahedra; and faces with six equivalent Mg(4)Mg12 cuboctahedra. Sb(1) is bonded to six Mg(2,2) and six Mg(3,3) atoms to form SbMg12 cuboctahedra that share corners with six equivalent Sb(1)Mg12 cuboctahedra; corners with twelve equivalent Mg(1)Mg10Nb2 cuboctahedra; edges with six Mg(2,2)Mg10Sb2 cuboctahedra; edges with twelve Mg(3,3)Mg10NbSb cuboctahedra; faces with two equivalent Nb(1)Mg12 cuboctahedra; faces with six Mg(3,3)Mg10NbSb cuboctahedra; faces with six Mg(2,2)Mg10Sb2 cuboctahedra; and faces with six equivalent Mg(4)Mg12 cuboctahedra.