RbK2MgTbV2O8 crystallizes in the trigonal P3m1 space group. Rb(1) is bonded in a 7-coordinate geometry to one Mg(1), three equivalent O(2), and three equivalent O(3) atoms. There are two inequivalent K sites. In the first K site, K(1) is bonded in a distorted single-bond geometry to one O(4) atom. In the second K site, K(2) is bonded in a distorted hexagonal planar geometry to six equivalent O(1) atoms. Mg(1) is bonded in a 3-coordinate geometry to one Rb(1) and three equivalent O(1) atoms. Tb(1) is bonded to three equivalent O(1) and three equivalent O(2) 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(4) and three equivalent O(1) atoms to form VO4 tetrahedra that share corners with three equivalent Tb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 22°. In the second V site, V(2) is bonded to one O(3) and three equivalent O(2) atoms to form VO4 tetrahedra that share corners with three equivalent Tb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 20°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent K(2), one Mg(1), one Tb(1), and one V(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Rb(1), one Tb(1), and one V(2) atom. In the third O site, O(3) is bonded in a single-bond geometry to three equivalent Rb(1) and one V(2) atom. In the fourth O site, O(4) is bonded in a linear geometry to one K(1) and one V(1) atom.
RbK2MgTbV2O8 crystallizes in the trigonal P3m1 space group. Rb(1) is bonded in a 7-coordinate geometry to one Mg(1), three equivalent O(2), and three equivalent O(3) atoms. The Rb(1)-Mg(1) bond length is 3.16 Å. All Rb(1)-O(2) bond lengths are 2.87 Å. All Rb(1)-O(3) bond lengths are 3.44 Å. There are two inequivalent K sites. In the first K site, K(1) is bonded in a distorted single-bond geometry to one O(4) atom. The K(1)-O(4) bond length is 2.64 Å. In the second K site, K(2) is bonded in a distorted hexagonal planar geometry to six equivalent O(1) atoms. All K(2)-O(1) bond lengths are 2.98 Å. Mg(1) is bonded in a 3-coordinate geometry to one Rb(1) and three equivalent O(1) atoms. All Mg(1)-O(1) bond lengths are 1.95 Å. Tb(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form TbO6 octahedra that share corners with three equivalent V(1)O4 tetrahedra and corners with three equivalent V(2)O4 tetrahedra. All Tb(1)-O(1) bond lengths are 2.33 Å. All Tb(1)-O(2) bond lengths are 2.28 Å. There are two inequivalent V sites. In the first V site, V(1) is bonded to one O(4) and three equivalent O(1) atoms to form VO4 tetrahedra that share corners with three equivalent Tb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 22°. The V(1)-O(4) bond length is 1.82 Å. All V(1)-O(1) bond lengths are 1.96 Å. In the second V site, V(2) is bonded to one O(3) and three equivalent O(2) atoms to form VO4 tetrahedra that share corners with three equivalent Tb(1)O6 octahedra. The corner-sharing octahedral tilt angles are 20°. The V(2)-O(3) bond length is 1.68 Å. All V(2)-O(2) bond lengths are 1.76 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent K(2), one Mg(1), one Tb(1), and one V(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Rb(1), one Tb(1), and one V(2) atom. In the third O site, O(3) is bonded in a single-bond geometry to three equivalent Rb(1) and one V(2) atom. In the fourth O site, O(4) is bonded in a linear geometry to one K(1) and one V(1) atom.