RbMg6AlO8 is Caswellsilverite-derived structured and crystallizes in the tetragonal P4/mmm space group. Rb(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form RbO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with four equivalent Rb(1)O6 octahedra, edges with four equivalent Al(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 Al(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 Rb(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 Rb(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Al(1)O6 octahedra, and edges with four equivalent Mg(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-13°. Al(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form AlO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with four equivalent Al(1)O6 octahedra, edges 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 four inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), four equivalent Mg(3), and one Al(1) atom to form OMg5Al octahedra that share corners with six equivalent O(1)Mg5Al octahedra, edges with four equivalent O(4)Mg6 octahedra, edges with four equivalent O(3)Rb2Mg2Al2 octahedra, and edges with four equivalent O(2)RbMg5 octahedra. The corner-sharing octahedral tilt angles range from 0-13°. In the second O site, O(2) is bonded to one Rb(1), one Mg(2), and four equivalent Mg(3) atoms to form distorted ORbMg5 octahedra that share corners with six equivalent O(2)RbMg5 octahedra, edges with four equivalent O(1)Mg5Al octahedra, edges with four equivalent O(4)Mg6 octahedra, and edges with four equivalent O(3)Rb2Mg2Al2 octahedra. The corner-sharing octahedral tilt angles range from 0-13°. In the third O site, O(3) is bonded to two equivalent Rb(1), two equivalent Mg(3), and two equivalent Al(1) atoms to form ORb2Mg2Al2 octahedra that share corners with two equivalent O(4)Mg6 octahedra, corners with four equivalent O(3)Rb2Mg2Al2 octahedra, edges with four equivalent O(1)Mg5Al octahedra, edges with four equivalent O(3)Rb2Mg2Al2 octahedra, and edges with four equivalent O(2)RbMg5 octahedra. 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)Rb2Mg2Al2 octahedra, corners with four equivalent O(4)Mg6 octahedra, edges with four equivalent O(1)Mg5Al octahedra, edges with four equivalent O(4)Mg6 octahedra, and edges with four equivalent O(2)RbMg5 octahedra. The corner-sharing octahedra are not tilted.
RbMg6AlO8 is Caswellsilverite-derived structured and crystallizes in the tetragonal P4/mmm space group. Rb(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form RbO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with four equivalent Rb(1)O6 octahedra, edges with four equivalent Al(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. Both Rb(1)-O(2) bond lengths are 2.44 Å. All Rb(1)-O(3) bond lengths are 2.27 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 Al(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 2.41 Å. All Mg(1)-O(4) bond lengths are 2.27 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 Rb(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 1.90 Å. All Mg(2)-O(4) bond lengths are 2.27 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 Rb(1)O6 octahedra, edges with two equivalent Mg(1)O6 octahedra, edges with two equivalent Mg(2)O6 octahedra, edges with two equivalent Al(1)O6 octahedra, and edges with four equivalent Mg(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-13°. The Mg(3)-O(3) bond length is 2.18 Å. The Mg(3)-O(4) bond length is 2.16 Å. Both Mg(3)-O(1) bond lengths are 2.28 Å. Both Mg(3)-O(2) bond lengths are 2.29 Å. Al(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form AlO6 octahedra that share corners with two equivalent Mg(1)O6 octahedra, corners with four equivalent Al(1)O6 octahedra, edges with four equivalent Rb(1)O6 octahedra, and edges with eight equivalent Mg(3)O6 octahedra. The corner-sharing octahedra are not tilted. Both Al(1)-O(1) bond lengths are 1.93 Å. All Al(1)-O(3) bond lengths are 2.27 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 Al(1) atom to form OMg5Al octahedra that share corners with six equivalent O(1)Mg5Al octahedra, edges with four equivalent O(4)Mg6 octahedra, edges with four equivalent O(3)Rb2Mg2Al2 octahedra, and edges with four equivalent O(2)RbMg5 octahedra. The corner-sharing octahedral tilt angles range from 0-13°. In the second O site, O(2) is bonded to one Rb(1), one Mg(2), and four equivalent Mg(3) atoms to form distorted ORbMg5 octahedra that share corners with six equivalent O(2)RbMg5 octahedra, edges with four equivalent O(1)Mg5Al octahedra, edges with four equivalent O(4)Mg6 octahedra, and edges with four equivalent O(3)Rb2Mg2Al2 octahedra. The corner-sharing octahedral tilt angles range from 0-13°. In the third O site, O(3) is bonded to two equivalent Rb(1), two equivalent Mg(3), and two equivalent Al(1) atoms to form ORb2Mg2Al2 octahedra that share corners with two equivalent O(4)Mg6 octahedra, corners with four equivalent O(3)Rb2Mg2Al2 octahedra, edges with four equivalent O(1)Mg5Al octahedra, edges with four equivalent O(3)Rb2Mg2Al2 octahedra, and edges with four equivalent O(2)RbMg5 octahedra. 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)Rb2Mg2Al2 octahedra, corners with four equivalent O(4)Mg6 octahedra, edges with four equivalent O(1)Mg5Al octahedra, edges with four equivalent O(4)Mg6 octahedra, and edges with four equivalent O(2)RbMg5 octahedra. The corner-sharing octahedra are not tilted.