RbMgCr3O8 crystallizes in the monoclinic Cm space group. Rb(1) is bonded in a 5-coordinate geometry to one O(6), two equivalent O(2), and two equivalent O(5) atoms. Mg(1) is bonded in a rectangular see-saw-like geometry to one O(4), one O(5), and two equivalent O(1) atoms. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(3), one O(6), and two equivalent O(2) atoms to form corner-sharing CrO4 tetrahedra. The corner-sharing octahedral tilt angles range from 17-37°. In the second Cr site, Cr(2) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form corner-sharing CrO4 tetrahedra. The corner-sharing octahedral tilt angles range from 13-47°. In the third Cr site, Cr(3) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form corner-sharing CrO6 octahedra. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1), one Cr(2), and one Cr(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Rb(1), one Cr(1), and one Cr(3) atom. In the third O site, O(3) is bonded in a linear geometry to one Cr(1) and one Cr(3) atom. In the fourth O site, O(4) is bonded in a T-shaped geometry to one Mg(1), one Cr(2), and one Cr(3) atom. In the fifth O site, O(5) is bonded in a distorted L-shaped geometry to two equivalent Rb(1), one Mg(1), and one Cr(2) atom. In the sixth O site, O(6) is bonded in a distorted single-bond geometry to one Rb(1) and one Cr(1) atom.
RbMgCr3O8 crystallizes in the monoclinic Cm space group. Rb(1) is bonded in a 5-coordinate geometry to one O(6), two equivalent O(2), and two equivalent O(5) atoms. The Rb(1)-O(6) bond length is 2.79 Å. Both Rb(1)-O(2) bond lengths are 2.92 Å. Both Rb(1)-O(5) bond lengths are 3.16 Å. Mg(1) is bonded in a rectangular see-saw-like geometry to one O(4), one O(5), and two equivalent O(1) atoms. The Mg(1)-O(4) bond length is 2.05 Å. The Mg(1)-O(5) bond length is 1.92 Å. Both Mg(1)-O(1) bond lengths are 1.96 Å. There are three inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(3), one O(6), and two equivalent O(2) atoms to form corner-sharing CrO4 tetrahedra. The corner-sharing octahedral tilt angles range from 17-37°. The Cr(1)-O(3) bond length is 1.66 Å. The Cr(1)-O(6) bond length is 1.64 Å. Both Cr(1)-O(2) bond lengths are 1.69 Å. In the second Cr site, Cr(2) is bonded to one O(4), one O(5), and two equivalent O(1) atoms to form corner-sharing CrO4 tetrahedra. The corner-sharing octahedral tilt angles range from 13-47°. The Cr(2)-O(4) bond length is 1.81 Å. The Cr(2)-O(5) bond length is 1.82 Å. Both Cr(2)-O(1) bond lengths are 1.79 Å. In the third Cr site, Cr(3) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form corner-sharing CrO6 octahedra. The Cr(3)-O(3) bond length is 2.04 Å. The Cr(3)-O(4) bond length is 1.99 Å. Both Cr(3)-O(1) bond lengths are 2.04 Å. Both Cr(3)-O(2) bond lengths are 2.01 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1), one Cr(2), and one Cr(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Rb(1), one Cr(1), and one Cr(3) atom. In the third O site, O(3) is bonded in a linear geometry to one Cr(1) and one Cr(3) atom. In the fourth O site, O(4) is bonded in a T-shaped geometry to one Mg(1), one Cr(2), and one Cr(3) atom. In the fifth O site, O(5) is bonded in a distorted L-shaped geometry to two equivalent Rb(1), one Mg(1), and one Cr(2) atom. In the sixth O site, O(6) is bonded in a distorted single-bond geometry to one Rb(1) and one Cr(1) atom.