Mg6BCO8 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(2) and four equivalent O(3) atoms to form a mixture of corner and edge-sharing MgO6 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 a mixture of corner and edge-sharing MgO6 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 a mixture of corner and edge-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles range from 0-32°. B(1) is bonded in a distorted linear geometry to two equivalent O(1) and four equivalent O(3) atoms. C(1) is bonded in a square co-planar geometry to four equivalent O(4) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to four equivalent Mg(3) and one B(1) atom. In the second O site, O(2) is bonded to one Mg(1), one Mg(2), and four equivalent Mg(3) atoms to form OMg6 octahedra that share corners with six equivalent O(2)Mg6 octahedra, edges with four equivalent O(3)Mg4B2 octahedra, and edges with four equivalent O(4)Mg4C2 octahedra. The corner-sharing octahedral tilt angles range from 0-4°. In the third O site, O(3) is bonded to two equivalent Mg(1), two equivalent Mg(3), and two equivalent B(1) atoms to form OMg4B2 octahedra that share corners with two equivalent O(4)Mg4C2 octahedra, corners with four equivalent O(3)Mg4B2 octahedra, edges with four equivalent O(3)Mg4B2 octahedra, and edges with four equivalent O(2)Mg6 octahedra. The corner-sharing octahedra are not tilted. In the fourth O site, O(4) is bonded to two equivalent Mg(2), two equivalent Mg(3), and two equivalent C(1) atoms to form distorted OMg4C2 octahedra that share corners with two equivalent O(3)Mg4B2 octahedra, corners with four equivalent O(4)Mg4C2 octahedra, edges with four equivalent O(4)Mg4C2 octahedra, and edges with four equivalent O(2)Mg6 octahedra. The corner-sharing octahedra are not tilted.
Mg6BCO8 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(2) and four equivalent O(3) atoms to form a mixture of corner and edge-sharing MgO6 octahedra. The corner-sharing octahedra are not tilted. Both Mg(1)-O(2) bond lengths are 2.10 Å. All Mg(1)-O(3) bond lengths are 2.12 Å. In the second Mg site, Mg(2) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form a mixture of corner and edge-sharing MgO6 octahedra. The corner-sharing octahedra are not tilted. Both Mg(2)-O(2) bond lengths are 2.05 Å. All Mg(2)-O(4) bond lengths are 2.12 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 a mixture of corner and edge-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles range from 0-32°. The Mg(3)-O(3) bond length is 2.02 Å. The Mg(3)-O(4) bond length is 2.13 Å. Both Mg(3)-O(1) bond lengths are 2.20 Å. Both Mg(3)-O(2) bond lengths are 2.12 Å. B(1) is bonded in a distorted linear geometry to two equivalent O(1) and four equivalent O(3) atoms. Both B(1)-O(1) bond lengths are 1.43 Å. All B(1)-O(3) bond lengths are 2.12 Å. C(1) is bonded in a square co-planar geometry to four equivalent O(4) atoms. All C(1)-O(4) bond lengths are 2.12 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to four equivalent Mg(3) and one B(1) atom. In the second O site, O(2) is bonded to one Mg(1), one Mg(2), and four equivalent Mg(3) atoms to form OMg6 octahedra that share corners with six equivalent O(2)Mg6 octahedra, edges with four equivalent O(3)Mg4B2 octahedra, and edges with four equivalent O(4)Mg4C2 octahedra. The corner-sharing octahedral tilt angles range from 0-4°. In the third O site, O(3) is bonded to two equivalent Mg(1), two equivalent Mg(3), and two equivalent B(1) atoms to form OMg4B2 octahedra that share corners with two equivalent O(4)Mg4C2 octahedra, corners with four equivalent O(3)Mg4B2 octahedra, edges with four equivalent O(3)Mg4B2 octahedra, and edges with four equivalent O(2)Mg6 octahedra. The corner-sharing octahedra are not tilted. In the fourth O site, O(4) is bonded to two equivalent Mg(2), two equivalent Mg(3), and two equivalent C(1) atoms to form distorted OMg4C2 octahedra that share corners with two equivalent O(3)Mg4B2 octahedra, corners with four equivalent O(4)Mg4C2 octahedra, edges with four equivalent O(4)Mg4C2 octahedra, and edges with four equivalent O(2)Mg6 octahedra. The corner-sharing octahedra are not tilted.