RbK2MgTbV2O8 crystallizes in the monoclinic Cm space group. Rb(1) is bonded in a 8-coordinate geometry to one Mg(1), one O(1), one O(4), one O(5), two equivalent O(2), and two equivalent O(6) atoms. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 7-coordinate geometry to one O(6), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. In the second K site, K(2) is bonded in a 7-coordinate geometry to one O(5), two equivalent O(1), and four equivalent O(2) atoms. Mg(1) is bonded in a distorted trigonal planar geometry to one Rb(1), one O(6), and two equivalent O(3) atoms. Tb(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form TbO6 octahedra that share corners with three equivalent V(1)O4 tetrahedra and corners with three equivalent V(2)O4 tetrahedra. There are two inequivalent V sites. In the first V site, V(1) is bonded to one O(1), one O(6), and two equivalent O(2) atoms to form VO4 tetrahedra that share corners with three equivalent Tb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 9-15°. In the second V site, V(2) is bonded to one O(4), one O(5), and two equivalent O(3) atoms to form VO4 tetrahedra that share corners with three equivalent Tb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 17-24°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Rb(1), two equivalent K(2), one Tb(1), and one V(1) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to one Rb(1), one K(1), two equivalent K(2), one Tb(1), and one V(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one K(1), one Mg(1), one Tb(1), and one V(2) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Rb(1), two equivalent K(1), one Tb(1), and one V(2) atom. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Rb(1), one K(2), and one V(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to two equivalent Rb(1), one K(1), one Mg(1), and one V(1) atom.
RbK2MgTbV2O8 crystallizes in the monoclinic Cm space group. Rb(1) is bonded in a 8-coordinate geometry to one Mg(1), one O(1), one O(4), one O(5), two equivalent O(2), and two equivalent O(6) atoms. The Rb(1)-Mg(1) bond length is 3.11 Å. The Rb(1)-O(1) bond length is 3.00 Å. The Rb(1)-O(4) bond length is 3.00 Å. The Rb(1)-O(5) bond length is 2.74 Å. Both Rb(1)-O(2) bond lengths are 2.85 Å. Both Rb(1)-O(6) bond lengths are 3.33 Å. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 7-coordinate geometry to one O(6), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. The K(1)-O(6) bond length is 3.01 Å. Both K(1)-O(2) bond lengths are 2.88 Å. Both K(1)-O(3) bond lengths are 2.81 Å. Both K(1)-O(4) bond lengths are 3.10 Å. In the second K site, K(2) is bonded in a 7-coordinate geometry to one O(5), two equivalent O(1), and four equivalent O(2) atoms. The K(2)-O(5) bond length is 2.65 Å. Both K(2)-O(1) bond lengths are 3.04 Å. There are two shorter (3.10 Å) and two longer (3.11 Å) K(2)-O(2) bond lengths. Mg(1) is bonded in a distorted trigonal planar geometry to one Rb(1), one O(6), and two equivalent O(3) atoms. The Mg(1)-O(6) bond length is 1.90 Å. Both Mg(1)-O(3) bond lengths are 1.95 Å. Tb(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form TbO6 octahedra that share corners with three equivalent V(1)O4 tetrahedra and corners with three equivalent V(2)O4 tetrahedra. The Tb(1)-O(1) bond length is 2.34 Å. The Tb(1)-O(4) bond length is 2.33 Å. Both Tb(1)-O(2) bond lengths are 2.22 Å. Both Tb(1)-O(3) bond lengths are 2.36 Å. There are two inequivalent V sites. In the first V site, V(1) is bonded to one O(1), one O(6), and two equivalent O(2) atoms to form VO4 tetrahedra that share corners with three equivalent Tb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 9-15°. The V(1)-O(1) bond length is 1.80 Å. The V(1)-O(6) bond length is 1.83 Å. Both V(1)-O(2) bond lengths are 1.85 Å. In the second V site, V(2) is bonded to one O(4), one O(5), and two equivalent O(3) atoms to form VO4 tetrahedra that share corners with three equivalent Tb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 17-24°. The V(2)-O(4) bond length is 1.81 Å. The V(2)-O(5) bond length is 1.73 Å. Both V(2)-O(3) bond lengths are 1.91 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Rb(1), two equivalent K(2), one Tb(1), and one V(1) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to one Rb(1), one K(1), two equivalent K(2), one Tb(1), and one V(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one K(1), one Mg(1), one Tb(1), and one V(2) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Rb(1), two equivalent K(1), one Tb(1), and one V(2) atom. In the fifth O site, O(5) is bonded in a distorted T-shaped geometry to one Rb(1), one K(2), and one V(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to two equivalent Rb(1), one K(1), one Mg(1), and one V(1) atom.