RbMg6BO8 crystallizes in the tetragonal P4/mmm space group. Rb(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form RbO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with four equivalent Rb(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. 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 Rb(1)O6 octahedra, corners 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 second Mg site, Mg(2) is bonded in a square co-planar geometry to four equivalent O(4) atoms. 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 distorted MgO6 octahedra that share corners with six equivalent Mg(3)O6 octahedra, edges with two equivalent Rb(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with four equivalent Mg(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-28°. B(1) is bonded in a linear geometry to two equivalent O(2) atoms. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Rb(1), one Mg(1), and four equivalent Mg(3) atoms to form distorted ORbMg5 octahedra that share corners with six equivalent O(1)RbMg5 octahedra and edges with four equivalent O(4)Mg6 octahedra. The corner-sharing octahedral tilt angles range from 0-20°. In the second O site, O(2) is bonded in a distorted single-bond geometry to four equivalent Mg(3) and one B(1) atom. In the third O site, O(3) is bonded in a square co-planar geometry to two equivalent Rb(1) and two equivalent Mg(3) atoms. 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 four equivalent O(4)Mg6 octahedra, edges with four equivalent O(4)Mg6 octahedra, and edges with four equivalent O(1)RbMg5 octahedra. The corner-sharing octahedra are not tilted.
RbMg6BO8 crystallizes in the tetragonal P4/mmm space group. Rb(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form RbO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with four equivalent Rb(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. Both Rb(1)-O(1) bond lengths are 2.42 Å. All Rb(1)-O(3) bond lengths are 2.31 Å. 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 Rb(1)O6 octahedra, corners 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(1)-O(1) bond lengths are 1.89 Å. All Mg(1)-O(4) bond lengths are 2.31 Å. In the second Mg site, Mg(2) is bonded in a square co-planar geometry to four equivalent O(4) atoms. All Mg(2)-O(4) bond lengths are 2.31 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 distorted MgO6 octahedra that share corners with six equivalent Mg(3)O6 octahedra, edges with two equivalent Rb(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, and edges with four equivalent Mg(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-28°. The Mg(3)-O(3) bond length is 2.01 Å. The Mg(3)-O(4) bond length is 2.30 Å. Both Mg(3)-O(1) bond lengths are 2.35 Å. Both Mg(3)-O(2) bond lengths are 2.38 Å. B(1) is bonded in a linear geometry to two equivalent O(2) atoms. Both B(1)-O(2) bond lengths are 1.42 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to one Rb(1), one Mg(1), and four equivalent Mg(3) atoms to form distorted ORbMg5 octahedra that share corners with six equivalent O(1)RbMg5 octahedra and edges with four equivalent O(4)Mg6 octahedra. The corner-sharing octahedral tilt angles range from 0-20°. In the second O site, O(2) is bonded in a distorted single-bond geometry to four equivalent Mg(3) and one B(1) atom. In the third O site, O(3) is bonded in a square co-planar geometry to two equivalent Rb(1) and two equivalent Mg(3) atoms. 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 four equivalent O(4)Mg6 octahedra, edges with four equivalent O(4)Mg6 octahedra, and edges with four equivalent O(1)RbMg5 octahedra. The corner-sharing octahedra are not tilted.