Mg6FeCO8 crystallizes in the tetragonal P4/mmm space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1) and four equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with four equivalent Mg(1)O6 octahedra, edges with four equivalent Mg(2)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. In the second Mg site, Mg(2) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent C(1)O6 octahedra, corners with four equivalent Mg(2)O6 octahedra, edges with four equivalent Mg(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. In the third Mg site, Mg(3) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Mg(3)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, edges with two equivalent C(1)O6 octahedra, and edges with four equivalent Mg(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. Fe(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form FeO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with four equivalent Fe(1)O6 octahedra, edges with four equivalent C(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. C(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form CO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with four equivalent C(1)O6 octahedra, edges with four equivalent Fe(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), four equivalent Mg(3), and one Fe(1) atom to form OMg5Fe octahedra that share corners with six equivalent O(1)Mg5Fe octahedra, edges with four equivalent O(3)Mg2Fe2C2 octahedra, edges with four equivalent O(4)Mg6 octahedra, and edges with four 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(2), four equivalent Mg(3), and one C(1) atom to form distorted OMg5C square pyramids that share corners with six equivalent O(2)Mg5C square pyramids, edges with four equivalent O(3)Mg2Fe2C2 octahedra, edges with four equivalent O(1)Mg5Fe octahedra, and edges with four equivalent O(4)Mg6 octahedra. In the third O site, O(3) is bonded to two equivalent Mg(3), two equivalent Fe(1), and two equivalent C(1) atoms to form distorted OMg2Fe2C2 octahedra that share corners with two equivalent O(4)Mg6 octahedra, corners with four equivalent O(3)Mg2Fe2C2 octahedra, edges with four equivalent O(3)Mg2Fe2C2 octahedra, edges with four equivalent O(1)Mg5Fe octahedra, and edges with four equivalent O(2)Mg5C square pyramids. The corner-sharing octahedra are not tilted. In the fourth O site, O(4) 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(3)Mg2Fe2C2 octahedra, corners with four equivalent O(4)Mg6 octahedra, edges with four equivalent O(1)Mg5Fe octahedra, edges with four equivalent O(4)Mg6 octahedra, and edges with four equivalent O(2)Mg5C square pyramids. The corner-sharing octahedra are not tilted.
Mg6FeCO8 crystallizes in the tetragonal P4/mmm space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1) and four equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent Fe(1)O6 octahedra, corners with four equivalent Mg(1)O6 octahedra, edges with four equivalent Mg(2)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. Both Mg(1)-O(1) bond lengths are 2.12 Å. All Mg(1)-O(4) bond lengths are 2.13 Å. In the second Mg site, Mg(2) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form MgO6 octahedra that share corners with two equivalent C(1)O6 octahedra, corners with four equivalent Mg(2)O6 octahedra, edges with four equivalent Mg(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. Both Mg(2)-O(2) bond lengths are 2.12 Å. All Mg(2)-O(4) bond lengths are 2.13 Å. In the third Mg site, Mg(3) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form MgO6 octahedra that share corners with six equivalent Mg(3)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, edges with two equivalent C(1)O6 octahedra, and edges with four equivalent Mg(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-2°. The Mg(3)-O(3) bond length is 2.09 Å. The Mg(3)-O(4) bond length is 2.16 Å. Both Mg(3)-O(1) bond lengths are 2.13 Å. Both Mg(3)-O(2) bond lengths are 2.13 Å. Fe(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form FeO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with four equivalent Fe(1)O6 octahedra, edges with four equivalent C(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. Both Fe(1)-O(1) bond lengths are 2.13 Å. All Fe(1)-O(3) bond lengths are 2.13 Å. C(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form CO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with four equivalent C(1)O6 octahedra, edges with four equivalent Fe(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. Both C(1)-O(2) bond lengths are 2.13 Å. All C(1)-O(3) bond lengths are 2.13 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), four equivalent Mg(3), and one Fe(1) atom to form OMg5Fe octahedra that share corners with six equivalent O(1)Mg5Fe octahedra, edges with four equivalent O(3)Mg2Fe2C2 octahedra, edges with four equivalent O(4)Mg6 octahedra, and edges with four 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(2), four equivalent Mg(3), and one C(1) atom to form distorted OMg5C square pyramids that share corners with six equivalent O(2)Mg5C square pyramids, edges with four equivalent O(3)Mg2Fe2C2 octahedra, edges with four equivalent O(1)Mg5Fe octahedra, and edges with four equivalent O(4)Mg6 octahedra. In the third O site, O(3) is bonded to two equivalent Mg(3), two equivalent Fe(1), and two equivalent C(1) atoms to form distorted OMg2Fe2C2 octahedra that share corners with two equivalent O(4)Mg6 octahedra, corners with four equivalent O(3)Mg2Fe2C2 octahedra, edges with four equivalent O(3)Mg2Fe2C2 octahedra, edges with four equivalent O(1)Mg5Fe octahedra, and edges with four equivalent O(2)Mg5C square pyramids. The corner-sharing octahedra are not tilted. In the fourth O site, O(4) 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(3)Mg2Fe2C2 octahedra, corners with four equivalent O(4)Mg6 octahedra, edges with four equivalent O(1)Mg5Fe octahedra, edges with four equivalent O(4)Mg6 octahedra, and edges with four equivalent O(2)Mg5C square pyramids. The corner-sharing octahedra are not tilted.