KMg14Nb crystallizes in the orthorhombic Amm2 space group. K(1) is bonded to two equivalent Mg(6), four equivalent Mg(3), four equivalent Mg(5), and two equivalent Nb(1) atoms to form KMg10Nb2 cuboctahedra that share corners with four equivalent Mg(2)Mg12 cuboctahedra, corners with six equivalent K(1)Mg10Nb2 cuboctahedra, corners with eight equivalent Mg(4)Mg12 cuboctahedra, edges with two equivalent Nb(1)K2Mg10 cuboctahedra, edges with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with four equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Nb(1)K2Mg10 cuboctahedra, faces with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, and faces with six equivalent Mg(7)Mg11Nb cuboctahedra. There are seven inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(2), two equivalent Mg(6), four equivalent Mg(4), and four equivalent Mg(5) atoms to form MgMg12 cuboctahedra that share corners with four equivalent Nb(1)K2Mg10 cuboctahedra, corners with six equivalent Mg(1)Mg12 cuboctahedra, corners with eight equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with two equivalent Mg(2)Mg12 cuboctahedra, edges with four equivalent Mg(6)KMg11 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra, faces with two equivalent K(1)Mg10Nb2 cuboctahedra, faces with two equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(2)Mg12 cuboctahedra, faces with four equivalent Mg(4)Mg12 cuboctahedra, and faces with six equivalent Mg(7)Mg11Nb cuboctahedra. In the second Mg site, Mg(2) is bonded to two equivalent Mg(1), two equivalent Mg(7), four equivalent Mg(4), and four equivalent Mg(5) atoms to form MgMg12 cuboctahedra that share corners with four equivalent K(1)Mg10Nb2 cuboctahedra, corners with six equivalent Mg(2)Mg12 cuboctahedra, corners with eight equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with four equivalent Mg(7)Mg11Nb cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra, faces with two equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Nb(1)K2Mg10 cuboctahedra, faces with four equivalent Mg(4)Mg12 cuboctahedra, and faces with six equivalent Mg(6)KMg11 cuboctahedra. In the third Mg site, Mg(3) is bonded to two equivalent K(1), two equivalent Mg(3), two equivalent Mg(5), two equivalent Mg(6), two equivalent Mg(7), and two equivalent Nb(1) atoms to form distorted MgK2Mg8Nb2 cuboctahedra that share corners with four equivalent Mg(1)Mg12 cuboctahedra, corners with four equivalent Mg(2)Mg12 cuboctahedra, corners with four equivalent Mg(4)Mg12 cuboctahedra, corners with six equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with two equivalent K(1)Mg10Nb2 cuboctahedra, edges with two equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with two equivalent Nb(1)K2Mg10 cuboctahedra, edges with four equivalent Mg(6)KMg11 cuboctahedra, edges with four equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent K(1)Mg10Nb2 cuboctahedra, faces with two equivalent Mg(3)K2Mg8Nb2 cuboctahedra, faces with two equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, and faces with two equivalent Nb(1)K2Mg10 cuboctahedra. In the fourth Mg site, Mg(4) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), two equivalent Mg(5), two equivalent Mg(6), and two equivalent Mg(7) atoms to form MgMg12 cuboctahedra that share corners with four equivalent K(1)Mg10Nb2 cuboctahedra, corners with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, corners with four equivalent Nb(1)K2Mg10 cuboctahedra, corners with six equivalent Mg(4)Mg12 cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with two equivalent Mg(2)Mg12 cuboctahedra, edges with two equivalent Mg(4)Mg12 cuboctahedra, edges with four equivalent Mg(6)KMg11 cuboctahedra, edges with four equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(3)K2Mg8Nb2 cuboctahedra, faces with two equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Mg(2)Mg12 cuboctahedra, and faces with two equivalent Mg(4)Mg12 cuboctahedra. In the fifth Mg site, Mg(5) is bonded in a 2-coordinate geometry to one K(1), one Mg(1), one Mg(2), one Mg(3), one Mg(4), two equivalent Mg(6), two equivalent Mg(7), and one Nb(1) atom. In the sixth Mg site, Mg(6) is bonded to one K(1), one Mg(1), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(7), and four equivalent Mg(5) atoms to form distorted MgKMg11 cuboctahedra that share corners with four equivalent Mg(7)Mg11Nb cuboctahedra, corners with six equivalent Mg(6)KMg11 cuboctahedra, edges with two equivalent K(1)Mg10Nb2 cuboctahedra, edges with two equivalent Mg(7)Mg11Nb cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra,  a faceface with one K(1)Mg10Nb2 cuboctahedra,  a faceface with one Mg(1)Mg12 cuboctahedra, faces with two equivalent Mg(3)K2Mg8Nb2 cuboctahedra, faces with two equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with three equivalent Mg(2)Mg12 cuboctahedra, and faces with three equivalent Nb(1)K2Mg10 cuboctahedra. In the seventh Mg site, Mg(7) is bonded to one Mg(2), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(6), four equivalent Mg(5), and one Nb(1) atom to form distorted MgMg11Nb cuboctahedra that share corners with four equivalent Mg(6)KMg11 cuboctahedra, corners with six equivalent Mg(7)Mg11Nb cuboctahedra, edges with two equivalent Mg(6)KMg11 cuboctahedra, edges with two equivalent Mg(2)Mg12 cuboctahedra, edges with two equivalent Nb(1)K2Mg10 cuboctahedra, edges with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra,  a faceface with one Mg(2)Mg12 cuboctahedra,  a faceface with one Nb(1)K2Mg10 cuboctahedra, faces with two equivalent Mg(3)K2Mg8Nb2 cuboctahedra, faces with two equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with three equivalent K(1)Mg10Nb2 cuboctahedra, and faces with three equivalent Mg(1)Mg12 cuboctahedra. Nb(1) is bonded to two equivalent K(1), two equivalent Mg(7), four equivalent Mg(3), and four equivalent Mg(5) atoms to form NbK2Mg10 cuboctahedra that share corners with four equivalent Mg(1)Mg12 cuboctahedra, corners with six equivalent Nb(1)K2Mg10 cuboctahedra, corners with eight equivalent Mg(4)Mg12 cuboctahedra, edges with two equivalent K(1)Mg10Nb2 cuboctahedra, edges with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with four equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent K(1)Mg10Nb2 cuboctahedra, faces with two equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(2)Mg12 cuboctahedra, faces with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, and faces with six equivalent Mg(6)KMg11 cuboctahedra.
KMg14Nb crystallizes in the orthorhombic Amm2 space group. K(1) is bonded to two equivalent Mg(6), four equivalent Mg(3), four equivalent Mg(5), and two equivalent Nb(1) atoms to form KMg10Nb2 cuboctahedra that share corners with four equivalent Mg(2)Mg12 cuboctahedra, corners with six equivalent K(1)Mg10Nb2 cuboctahedra, corners with eight equivalent Mg(4)Mg12 cuboctahedra, edges with two equivalent Nb(1)K2Mg10 cuboctahedra, edges with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with four equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Nb(1)K2Mg10 cuboctahedra, faces with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, and faces with six equivalent Mg(7)Mg11Nb cuboctahedra. Both K(1)-Mg(6) bond lengths are 3.30 Å. All K(1)-Mg(3) bond lengths are 3.24 Å. All K(1)-Mg(5) bond lengths are 3.28 Å. Both K(1)-Nb(1) bond lengths are 3.33 Å. There are seven inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent Mg(2), two equivalent Mg(6), four equivalent Mg(4), and four equivalent Mg(5) atoms to form MgMg12 cuboctahedra that share corners with four equivalent Nb(1)K2Mg10 cuboctahedra, corners with six equivalent Mg(1)Mg12 cuboctahedra, corners with eight equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with two equivalent Mg(2)Mg12 cuboctahedra, edges with four equivalent Mg(6)KMg11 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra, faces with two equivalent K(1)Mg10Nb2 cuboctahedra, faces with two equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(2)Mg12 cuboctahedra, faces with four equivalent Mg(4)Mg12 cuboctahedra, and faces with six equivalent Mg(7)Mg11Nb cuboctahedra. Both Mg(1)-Mg(2) bond lengths are 3.33 Å. Both Mg(1)-Mg(6) bond lengths are 3.12 Å. There are two shorter (3.22 Å) and two longer (3.27 Å) Mg(1)-Mg(4) bond lengths. All Mg(1)-Mg(5) bond lengths are 3.20 Å. In the second Mg site, Mg(2) is bonded to two equivalent Mg(1), two equivalent Mg(7), four equivalent Mg(4), and four equivalent Mg(5) atoms to form MgMg12 cuboctahedra that share corners with four equivalent K(1)Mg10Nb2 cuboctahedra, corners with six equivalent Mg(2)Mg12 cuboctahedra, corners with eight equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with four equivalent Mg(7)Mg11Nb cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra, faces with two equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Nb(1)K2Mg10 cuboctahedra, faces with four equivalent Mg(4)Mg12 cuboctahedra, and faces with six equivalent Mg(6)KMg11 cuboctahedra. Both Mg(2)-Mg(7) bond lengths are 3.21 Å. There are two shorter (3.22 Å) and two longer (3.27 Å) Mg(2)-Mg(4) bond lengths. All Mg(2)-Mg(5) bond lengths are 3.11 Å. In the third Mg site, Mg(3) is bonded to two equivalent K(1), two equivalent Mg(3), two equivalent Mg(5), two equivalent Mg(6), two equivalent Mg(7), and two equivalent Nb(1) atoms to form distorted MgK2Mg8Nb2 cuboctahedra that share corners with four equivalent Mg(1)Mg12 cuboctahedra, corners with four equivalent Mg(2)Mg12 cuboctahedra, corners with four equivalent Mg(4)Mg12 cuboctahedra, corners with six equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with two equivalent K(1)Mg10Nb2 cuboctahedra, edges with two equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with two equivalent Nb(1)K2Mg10 cuboctahedra, edges with four equivalent Mg(6)KMg11 cuboctahedra, edges with four equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent K(1)Mg10Nb2 cuboctahedra, faces with two equivalent Mg(3)K2Mg8Nb2 cuboctahedra, faces with two equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, and faces with two equivalent Nb(1)K2Mg10 cuboctahedra. There is one shorter (3.32 Å) and one longer (3.33 Å) Mg(3)-Mg(3) bond length. Both Mg(3)-Mg(5) bond lengths are 3.20 Å. Both Mg(3)-Mg(6) bond lengths are 3.28 Å. Both Mg(3)-Mg(7) bond lengths are 3.14 Å. There is one shorter (3.14 Å) and one longer (3.35 Å) Mg(3)-Nb(1) bond length. In the fourth Mg site, Mg(4) is bonded to two equivalent Mg(1), two equivalent Mg(2), two equivalent Mg(4), two equivalent Mg(5), two equivalent Mg(6), and two equivalent Mg(7) atoms to form MgMg12 cuboctahedra that share corners with four equivalent K(1)Mg10Nb2 cuboctahedra, corners with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, corners with four equivalent Nb(1)K2Mg10 cuboctahedra, corners with six equivalent Mg(4)Mg12 cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with two equivalent Mg(2)Mg12 cuboctahedra, edges with two equivalent Mg(4)Mg12 cuboctahedra, edges with four equivalent Mg(6)KMg11 cuboctahedra, edges with four equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(3)K2Mg8Nb2 cuboctahedra, faces with two equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(1)Mg12 cuboctahedra, faces with two equivalent Mg(2)Mg12 cuboctahedra, and faces with two equivalent Mg(4)Mg12 cuboctahedra. There is one shorter (3.27 Å) and one longer (3.38 Å) Mg(4)-Mg(4) bond length. Both Mg(4)-Mg(5) bond lengths are 3.15 Å. Both Mg(4)-Mg(6) bond lengths are 3.08 Å. Both Mg(4)-Mg(7) bond lengths are 3.27 Å. In the fifth Mg site, Mg(5) is bonded in a 2-coordinate geometry to one K(1), one Mg(1), one Mg(2), one Mg(3), one Mg(4), two equivalent Mg(6), two equivalent Mg(7), and one Nb(1) atom. There is one shorter (3.15 Å) and one longer (3.35 Å) Mg(5)-Mg(6) bond length. There is one shorter (3.14 Å) and one longer (3.36 Å) Mg(5)-Mg(7) bond length. The Mg(5)-Nb(1) bond length is 3.14 Å. In the sixth Mg site, Mg(6) is bonded to one K(1), one Mg(1), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(7), and four equivalent Mg(5) atoms to form distorted MgKMg11 cuboctahedra that share corners with four equivalent Mg(7)Mg11Nb cuboctahedra, corners with six equivalent Mg(6)KMg11 cuboctahedra, edges with two equivalent K(1)Mg10Nb2 cuboctahedra, edges with two equivalent Mg(7)Mg11Nb cuboctahedra, edges with two equivalent Mg(1)Mg12 cuboctahedra, edges with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra,  a faceface with one K(1)Mg10Nb2 cuboctahedra,  a faceface with one Mg(1)Mg12 cuboctahedra, faces with two equivalent Mg(3)K2Mg8Nb2 cuboctahedra, faces with two equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with three equivalent Mg(2)Mg12 cuboctahedra, and faces with three equivalent Nb(1)K2Mg10 cuboctahedra. Both Mg(6)-Mg(7) bond lengths are 3.34 Å. In the seventh Mg site, Mg(7) is bonded to one Mg(2), two equivalent Mg(3), two equivalent Mg(4), two equivalent Mg(6), four equivalent Mg(5), and one Nb(1) atom to form distorted MgMg11Nb cuboctahedra that share corners with four equivalent Mg(6)KMg11 cuboctahedra, corners with six equivalent Mg(7)Mg11Nb cuboctahedra, edges with two equivalent Mg(6)KMg11 cuboctahedra, edges with two equivalent Mg(2)Mg12 cuboctahedra, edges with two equivalent Nb(1)K2Mg10 cuboctahedra, edges with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with four equivalent Mg(4)Mg12 cuboctahedra,  a faceface with one Mg(2)Mg12 cuboctahedra,  a faceface with one Nb(1)K2Mg10 cuboctahedra, faces with two equivalent Mg(3)K2Mg8Nb2 cuboctahedra, faces with two equivalent Mg(6)KMg11 cuboctahedra, faces with two equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(4)Mg12 cuboctahedra, faces with three equivalent K(1)Mg10Nb2 cuboctahedra, and faces with three equivalent Mg(1)Mg12 cuboctahedra. The Mg(7)-Nb(1) bond length is 3.13 Å. Nb(1) is bonded to two equivalent K(1), two equivalent Mg(7), four equivalent Mg(3), and four equivalent Mg(5) atoms to form NbK2Mg10 cuboctahedra that share corners with four equivalent Mg(1)Mg12 cuboctahedra, corners with six equivalent Nb(1)K2Mg10 cuboctahedra, corners with eight equivalent Mg(4)Mg12 cuboctahedra, edges with two equivalent K(1)Mg10Nb2 cuboctahedra, edges with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, edges with four equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent K(1)Mg10Nb2 cuboctahedra, faces with two equivalent Mg(7)Mg11Nb cuboctahedra, faces with two equivalent Mg(2)Mg12 cuboctahedra, faces with four equivalent Mg(3)K2Mg8Nb2 cuboctahedra, and faces with six equivalent Mg(6)KMg11 cuboctahedra.