Mg14CuCO16 crystallizes in the tetragonal P4/mmm space group. There are seven 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 Cu(1)O6 octahedra; corners with two equivalent C(1)O6 octahedra; edges with four Mg(2,2)O6 octahedra; edges with four Mg(3,3)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 Mg(2,2)O6 octahedra; edges with two equivalent Mg(1)O6 octahedra; edges with two Mg(2,2)O6 octahedra; edges with two Mg(3,3)O6 octahedra; edges with two equivalent Cu(1)O6 octahedra; and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. In the third 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 Mg(2,2)O6 octahedra; edges with two equivalent Mg(1)O6 octahedra; edges with two Mg(2,2)O6 octahedra; edges with two Mg(3,3)O6 octahedra; edges with two equivalent Cu(1)O6 octahedra; and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. In the fourth 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 MgO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra; corners with four Mg(3,3)O6 octahedra; edges with two equivalent Mg(1)O6 octahedra; edges with two Mg(2,2)O6 octahedra; edges with two Mg(3,3)O6 octahedra; edges with two equivalent C(1)O6 octahedra; and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. In the fifth 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 MgO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra; corners with four Mg(3,3)O6 octahedra; edges with two equivalent Mg(1)O6 octahedra; edges with two Mg(2,2)O6 octahedra; edges with two Mg(3,3)O6 octahedra; edges with two equivalent C(1)O6 octahedra; and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. In the sixth 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 MgO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra; corners with four Mg(3,3)O6 octahedra; edges with two equivalent Mg(1)O6 octahedra; edges with two Mg(2,2)O6 octahedra; edges with two Mg(3,3)O6 octahedra; edges with two equivalent C(1)O6 octahedra; and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. In the seventh 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 Cu(1)O6 octahedra,  an edgeedge with one C(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 are 1°. Cu(1) is bonded to two equivalent O(4) and four equivalent O(1) atoms to form CuO6 octahedra that share corners with two equivalent Cu(1)O6 octahedra; corners with four equivalent Mg(1)O6 octahedra; edges with four equivalent Mg(4)O6 octahedra; and edges with eight Mg(2,2)O6 octahedra. The corner-sharing octahedra are not tilted. C(1) is bonded to two equivalent O(6) and four equivalent O(2) atoms to form distorted CO6 octahedra that share corners with two equivalent C(1)O6 octahedra; corners with four equivalent Mg(1)O6 octahedra; edges with four equivalent Mg(4)O6 octahedra; and edges with eight Mg(3,3,3)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 Cu(1) atom to form OMg5Cu octahedra that share corners with four equivalent O(1)Mg5Cu octahedra, corners with two equivalent O(2)Mg5C square pyramids, edges with two equivalent O(4)Mg4Cu2 octahedra, edges with two equivalent O(1)Mg5Cu octahedra, edges with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with two equivalent O(2)Mg5C square pyramids. The corner-sharing octahedral tilt angles range from 0-2°. In the second O site, O(2) is bonded to one Mg(1), two equivalent Mg(3), two equivalent Mg(4), and one C(1) atom to form distorted OMg5C square pyramids that share corners with two equivalent O(1)Mg5Cu octahedra, corners with four equivalent O(2)Mg5C square pyramids, edges with two equivalent O(6)Mg4C2 octahedra, edges with two equivalent O(1)Mg5Cu octahedra, edges with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with two equivalent O(2)Mg5C square pyramids. The corner-sharing octahedra are not tilted. 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(6)Mg4C2 octahedra,  an edgeedge with one O(4)Mg4Cu2 octahedra, edges with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(1)Mg5Cu octahedra, and edges with four equivalent O(2)Mg5C square pyramids. The corner-sharing octahedral tilt angles range from 0-1°. In the fourth O site, O(4) is bonded to four Mg(2,2) and two equivalent Cu(1) atoms to form OMg4Cu2 octahedra that share corners with two equivalent O(4)Mg4Cu2 octahedra, corners with four equivalent O(5)Mg6 octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with eight equivalent O(1)Mg5Cu octahedra. The corner-sharing octahedra are not tilted. In the fifth O site, O(5) is bonded to two equivalent Mg(1); two Mg(2,2); and two Mg(3,3) atoms to form OMg6 octahedra that share corners with two equivalent O(6)Mg4C2 octahedra, corners with two equivalent O(4)Mg4Cu2 octahedra, corners with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(1)Mg5Cu octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with four equivalent O(2)Mg5C square pyramids. The corner-sharing octahedra are not tilted. In the sixth O site, O(6) is bonded to four Mg(3,3,3) and two equivalent C(1) atoms to form distorted OMg4C2 octahedra that share corners with two equivalent O(6)Mg4C2 octahedra, corners with four equivalent O(5)Mg6 octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with eight equivalent O(2)Mg5C square pyramids. The corner-sharing octahedra are not tilted.
Mg14CuCO16 crystallizes in the tetragonal P4/mmm space group. There are seven 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 Cu(1)O6 octahedra; corners with two equivalent C(1)O6 octahedra; edges with four Mg(2,2)O6 octahedra; edges with four Mg(3,3)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 2.09 Å. Both Mg(1)-O(2) bond lengths are 2.12 Å. Both Mg(1)-O(5) bond lengths are 2.11 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 Mg(2,2)O6 octahedra; edges with two equivalent Mg(1)O6 octahedra; edges with two Mg(2,2)O6 octahedra; edges with two Mg(3,3)O6 octahedra; edges with two equivalent Cu(1)O6 octahedra; and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. The Mg(2)-O(4) bond length is 2.13 Å. The Mg(2)-O(5) bond length is 2.13 Å. Both Mg(2)-O(1) bond lengths are 2.11 Å. Both Mg(2)-O(3) bond lengths are 2.13 Å. In the third 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 Mg(2,2)O6 octahedra; edges with two equivalent Mg(1)O6 octahedra; edges with two Mg(2,2)O6 octahedra; edges with two Mg(3,3)O6 octahedra; edges with two equivalent Cu(1)O6 octahedra; and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. The Mg(2)-O(4) bond length is 2.13 Å. The Mg(2)-O(5) bond length is 2.13 Å. Both Mg(2)-O(1) bond lengths are 2.11 Å. Both Mg(2)-O(3) bond lengths are 2.13 Å. In the fourth 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 MgO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra; corners with four Mg(3,3)O6 octahedra; edges with two equivalent Mg(1)O6 octahedra; edges with two Mg(2,2)O6 octahedra; edges with two Mg(3,3)O6 octahedra; edges with two equivalent C(1)O6 octahedra; and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. The Mg(3)-O(5) bond length is 2.16 Å. The Mg(3)-O(6) bond length is 2.10 Å. Both Mg(3)-O(2) bond lengths are 2.11 Å. Both Mg(3)-O(3) bond lengths are 2.13 Å. In the fifth 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 MgO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra; corners with four Mg(3,3)O6 octahedra; edges with two equivalent Mg(1)O6 octahedra; edges with two Mg(2,2)O6 octahedra; edges with two Mg(3,3)O6 octahedra; edges with two equivalent C(1)O6 octahedra; and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. The Mg(3)-O(5) bond length is 2.16 Å. The Mg(3)-O(6) bond length is 2.10 Å. Both Mg(3)-O(2) bond lengths are 2.11 Å. Both Mg(3)-O(3) bond lengths are 2.13 Å. In the sixth 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 MgO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra; corners with four Mg(3,3)O6 octahedra; edges with two equivalent Mg(1)O6 octahedra; edges with two Mg(2,2)O6 octahedra; edges with two Mg(3,3)O6 octahedra; edges with two equivalent C(1)O6 octahedra; and edges with four equivalent Mg(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. The Mg(3)-O(5) bond length is 2.16 Å. The Mg(3)-O(6) bond length is 2.10 Å. Both Mg(3)-O(2) bond lengths are 2.11 Å. Both Mg(3)-O(3) bond lengths are 2.13 Å. In the seventh 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 Cu(1)O6 octahedra,  an edgeedge with one C(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 are 1°. Both Mg(4)-O(1) bond lengths are 2.14 Å. Both Mg(4)-O(2) bond lengths are 2.12 Å. Both Mg(4)-O(3) bond lengths are 2.11 Å. Cu(1) is bonded to two equivalent O(4) and four equivalent O(1) atoms to form CuO6 octahedra that share corners with two equivalent Cu(1)O6 octahedra; corners with four equivalent Mg(1)O6 octahedra; edges with four equivalent Mg(4)O6 octahedra; and edges with eight Mg(2,2)O6 octahedra. The corner-sharing octahedra are not tilted. Both Cu(1)-O(4) bond lengths are 2.11 Å. All Cu(1)-O(1) bond lengths are 2.17 Å. C(1) is bonded to two equivalent O(6) and four equivalent O(2) atoms to form distorted CO6 octahedra that share corners with two equivalent C(1)O6 octahedra; corners with four equivalent Mg(1)O6 octahedra; edges with four equivalent Mg(4)O6 octahedra; and edges with eight Mg(3,3,3)O6 octahedra. The corner-sharing octahedra are not tilted. Both C(1)-O(6) bond lengths are 2.11 Å. All C(1)-O(2) bond lengths are 2.14 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 Cu(1) atom to form OMg5Cu octahedra that share corners with four equivalent O(1)Mg5Cu octahedra, corners with two equivalent O(2)Mg5C square pyramids, edges with two equivalent O(4)Mg4Cu2 octahedra, edges with two equivalent O(1)Mg5Cu octahedra, edges with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with two equivalent O(2)Mg5C square pyramids. The corner-sharing octahedral tilt angles range from 0-2°. In the second O site, O(2) is bonded to one Mg(1), two equivalent Mg(3), two equivalent Mg(4), and one C(1) atom to form distorted OMg5C square pyramids that share corners with two equivalent O(1)Mg5Cu octahedra, corners with four equivalent O(2)Mg5C square pyramids, edges with two equivalent O(6)Mg4C2 octahedra, edges with two equivalent O(1)Mg5Cu octahedra, edges with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with two equivalent O(2)Mg5C square pyramids. The corner-sharing octahedra are not tilted. 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(6)Mg4C2 octahedra,  an edgeedge with one O(4)Mg4Cu2 octahedra, edges with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(1)Mg5Cu octahedra, and edges with four equivalent O(2)Mg5C square pyramids. The corner-sharing octahedral tilt angles range from 0-1°. In the fourth O site, O(4) is bonded to four Mg(2,2) and two equivalent Cu(1) atoms to form OMg4Cu2 octahedra that share corners with two equivalent O(4)Mg4Cu2 octahedra, corners with four equivalent O(5)Mg6 octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with eight equivalent O(1)Mg5Cu octahedra. The corner-sharing octahedra are not tilted. In the fifth O site, O(5) is bonded to two equivalent Mg(1); two Mg(2,2); and two Mg(3,3) atoms to form OMg6 octahedra that share corners with two equivalent O(6)Mg4C2 octahedra, corners with two equivalent O(4)Mg4Cu2 octahedra, corners with two equivalent O(5)Mg6 octahedra, edges with four equivalent O(1)Mg5Cu octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with four equivalent O(2)Mg5C square pyramids. The corner-sharing octahedra are not tilted. In the sixth O site, O(6) is bonded to four Mg(3,3,3) and two equivalent C(1) atoms to form distorted OMg4C2 octahedra that share corners with two equivalent O(6)Mg4C2 octahedra, corners with four equivalent O(5)Mg6 octahedra, edges with four equivalent O(3)Mg6 octahedra, and edges with eight equivalent O(2)Mg5C square pyramids. The corner-sharing octahedra are not tilted.