Mg14NbO16C crystallizes in the tetragonal P4/mmm space group. The structure consists of one 02329_fluka atom inside a Mg14NbO16 framework. In the Mg14NbO16 framework, there are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(5) atoms to form MgO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Nb(1)O6 octahedra, edges with four equivalent Mg(2)O6 octahedra, edges with four equivalent Mg(3)O6 octahedra, and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedra are not tilted. In the second Mg site, Mg(2) is bonded to one O(4), one O(5), two equivalent O(1), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with two equivalent Mg(3)O6 octahedra, corners with four equivalent Mg(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, edges with two equivalent Nb(1)O6 octahedra, and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-5°. In the third Mg site, Mg(3) is bonded to one O(5), one O(6), two equivalent O(2), and two equivalent O(3) atoms to form a mixture of corner and edge-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles range from 0-7°. In the fourth Mg site, Mg(4) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with six equivalent Mg(4)O6 octahedra,  an edgeedge with one Nb(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with four equivalent Mg(2)O6 octahedra, and edges with four equivalent Mg(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-7°. Nb(1) is bonded to two equivalent O(4) and four equivalent O(1) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Mg(1)O6 octahedra, edges with four equivalent Mg(4)O6 octahedra, and edges with eight equivalent Mg(2)O6 octahedra. The corner-sharing octahedra are not tilted. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), two equivalent Mg(2), two equivalent Mg(4), and one Nb(1) atom to form OMg5Nb octahedra that share corners with four equivalent O(1)Mg5Nb octahedra, corners with two equivalent O(2)Mg5 square pyramids, edges with two equivalent O(4)Mg4Nb2 octahedra, edges with two equivalent O(1)Mg5Nb octahedra, edges with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with two equivalent O(2)Mg5 square pyramids. The corner-sharing octahedral tilt angles range from 0-1°. In the second O site, O(2) is bonded to one Mg(1), two equivalent Mg(3), and two equivalent Mg(4) atoms to form OMg5 square pyramids that share corners with two equivalent O(1)Mg5Nb octahedra, corners with five equivalent O(2)Mg5 square pyramids, edges with two equivalent O(1)Mg5Nb octahedra, edges with two equivalent O(5)Mg6 octahedra, and edges with four equivalent O(3)Mg6 octahedra. The corner-sharing octahedral tilt angles are 4°. In the third O site, O(3) is bonded to two equivalent Mg(2), two equivalent Mg(3), and two equivalent Mg(4) atoms to form OMg6 octahedra that share corners with six equivalent O(3)Mg6 octahedra,  an edgeedge with one O(4)Mg4Nb2 octahedra, edges with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(1)Mg5Nb octahedra, and edges with four equivalent O(2)Mg5 square pyramids. The corner-sharing octahedral tilt angles range from 4-6°. In the fourth O site, O(4) is bonded to four equivalent Mg(2) and two equivalent Nb(1) atoms to form OMg4Nb2 octahedra that share corners with two equivalent O(4)Mg4Nb2 octahedra, corners with four equivalent O(5)Mg6 octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with eight equivalent O(1)Mg5Nb octahedra. The corner-sharing octahedra are not tilted. In the fifth O site, O(5) is bonded to two equivalent Mg(1), two equivalent Mg(2), and two equivalent Mg(3) atoms to form OMg6 octahedra that share corners with two equivalent O(4)Mg4Nb2 octahedra, corners with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(1)Mg5Nb octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with four equivalent O(2)Mg5 square pyramids. The corner-sharing octahedra are not tilted. In the sixth O site, O(6) is bonded in a square co-planar geometry to four equivalent Mg(3) atoms.
Mg14NbO16C crystallizes in the tetragonal P4/mmm space group. The structure consists of one 02329_fluka atom inside a Mg14NbO16 framework. In the Mg14NbO16 framework, there are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(5) atoms to form MgO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with two equivalent Nb(1)O6 octahedra, edges with four equivalent Mg(2)O6 octahedra, edges with four equivalent Mg(3)O6 octahedra, and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedra are not tilted. Both Mg(1)-O(1) bond lengths are 2.08 Å. Both Mg(1)-O(2) bond lengths are 2.08 Å. Both Mg(1)-O(5) bond lengths are 2.15 Å. In the second Mg site, Mg(2) is bonded to one O(4), one O(5), two equivalent O(1), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with two equivalent Mg(3)O6 octahedra, corners with four equivalent Mg(2)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Mg(3)O6 octahedra, edges with two equivalent Nb(1)O6 octahedra, and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-5°. The Mg(2)-O(4) bond length is 2.23 Å. The Mg(2)-O(5) bond length is 2.06 Å. Both Mg(2)-O(1) bond lengths are 2.15 Å. Both Mg(2)-O(3) bond lengths are 2.14 Å. In the third Mg site, Mg(3) is bonded to one O(5), one O(6), two equivalent O(2), and two equivalent O(3) atoms to form a mixture of corner and edge-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles range from 0-7°. The Mg(3)-O(5) bond length is 2.22 Å. The Mg(3)-O(6) bond length is 2.07 Å. Both Mg(3)-O(2) bond lengths are 2.16 Å. Both Mg(3)-O(3) bond lengths are 2.15 Å. In the fourth Mg site, Mg(4) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MgO6 octahedra that share corners with six equivalent Mg(4)O6 octahedra,  an edgeedge with one Nb(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with four equivalent Mg(2)O6 octahedra, and edges with four equivalent Mg(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-7°. Both Mg(4)-O(1) bond lengths are 2.21 Å. Both Mg(4)-O(2) bond lengths are 2.08 Å. Both Mg(4)-O(3) bond lengths are 2.15 Å. Nb(1) is bonded to two equivalent O(4) and four equivalent O(1) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Mg(1)O6 octahedra, edges with four equivalent Mg(4)O6 octahedra, and edges with eight equivalent Mg(2)O6 octahedra. The corner-sharing octahedra are not tilted. Both Nb(1)-O(4) bond lengths are 2.15 Å. All Nb(1)-O(1) bond lengths are 2.20 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), two equivalent Mg(2), two equivalent Mg(4), and one Nb(1) atom to form OMg5Nb octahedra that share corners with four equivalent O(1)Mg5Nb octahedra, corners with two equivalent O(2)Mg5 square pyramids, edges with two equivalent O(4)Mg4Nb2 octahedra, edges with two equivalent O(1)Mg5Nb octahedra, edges with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with two equivalent O(2)Mg5 square pyramids. The corner-sharing octahedral tilt angles range from 0-1°. In the second O site, O(2) is bonded to one Mg(1), two equivalent Mg(3), and two equivalent Mg(4) atoms to form OMg5 square pyramids that share corners with two equivalent O(1)Mg5Nb octahedra, corners with five equivalent O(2)Mg5 square pyramids, edges with two equivalent O(1)Mg5Nb octahedra, edges with two equivalent O(5)Mg6 octahedra, and edges with four equivalent O(3)Mg6 octahedra. The corner-sharing octahedral tilt angles are 4°. In the third O site, O(3) is bonded to two equivalent Mg(2), two equivalent Mg(3), and two equivalent Mg(4) atoms to form OMg6 octahedra that share corners with six equivalent O(3)Mg6 octahedra,  an edgeedge with one O(4)Mg4Nb2 octahedra, edges with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(1)Mg5Nb octahedra, and edges with four equivalent O(2)Mg5 square pyramids. The corner-sharing octahedral tilt angles range from 4-6°. In the fourth O site, O(4) is bonded to four equivalent Mg(2) and two equivalent Nb(1) atoms to form OMg4Nb2 octahedra that share corners with two equivalent O(4)Mg4Nb2 octahedra, corners with four equivalent O(5)Mg6 octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with eight equivalent O(1)Mg5Nb octahedra. The corner-sharing octahedra are not tilted. In the fifth O site, O(5) is bonded to two equivalent Mg(1), two equivalent Mg(2), and two equivalent Mg(3) atoms to form OMg6 octahedra that share corners with two equivalent O(4)Mg4Nb2 octahedra, corners with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(1)Mg5Nb octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with four equivalent O(2)Mg5 square pyramids. The corner-sharing octahedra are not tilted. In the sixth O site, O(6) is bonded in a square co-planar geometry to four equivalent Mg(3) atoms.