Rb3MgNbO8 crystallizes in the monoclinic Cm space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(5), one O(6), two equivalent O(1), and two equivalent O(4) atoms. In the second Rb site, Rb(2) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(6), and two equivalent O(1) atoms. Mg(1) is bonded in a 5-coordinate geometry to one O(2), one O(5), one O(6), and two equivalent O(1) atoms. Nb(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(5), one O(6), two equivalent O(1), and two equivalent O(4) atoms. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to one Rb(1), two equivalent Rb(2), one Mg(1), one Nb(1), and one O(4) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Rb(1), one Mg(1), and one Nb(1) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Rb(1), two equivalent Rb(2), one Nb(1), and one O(5) atom. In the fourth O site, O(4) is bonded in a 1-coordinate geometry to one Rb(1), one Rb(2), one Nb(1), and one O(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Rb(1), one Mg(1), one Nb(1), and one O(3) atom. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Rb(1), two equivalent Rb(2), one Mg(1), and one Nb(1) atom.
Rb3MgNbO8 crystallizes in the monoclinic Cm space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(5), one O(6), two equivalent O(1), and two equivalent O(4) atoms. The Rb(1)-O(2) bond length is 2.58 Å. The Rb(1)-O(3) bond length is 3.07 Å. The Rb(1)-O(5) bond length is 2.79 Å. The Rb(1)-O(6) bond length is 2.95 Å. Both Rb(1)-O(1) bond lengths are 3.20 Å. Both Rb(1)-O(4) bond lengths are 3.36 Å. In the second Rb site, Rb(2) is bonded in a 5-coordinate geometry to one O(3), one O(4), one O(6), and two equivalent O(1) atoms. The Rb(2)-O(3) bond length is 3.07 Å. The Rb(2)-O(4) bond length is 2.94 Å. The Rb(2)-O(6) bond length is 2.90 Å. There is one shorter (2.82 Å) and one longer (2.98 Å) Rb(2)-O(1) bond length. Mg(1) is bonded in a 5-coordinate geometry to one O(2), one O(5), one O(6), and two equivalent O(1) atoms. The Mg(1)-O(2) bond length is 1.92 Å. The Mg(1)-O(5) bond length is 2.13 Å. The Mg(1)-O(6) bond length is 2.08 Å. Both Mg(1)-O(1) bond lengths are 2.12 Å. Nb(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(5), one O(6), two equivalent O(1), and two equivalent O(4) atoms. The Nb(1)-O(2) bond length is 1.93 Å. The Nb(1)-O(3) bond length is 2.05 Å. The Nb(1)-O(5) bond length is 2.36 Å. The Nb(1)-O(6) bond length is 2.00 Å. Both Nb(1)-O(1) bond lengths are 2.26 Å. Both Nb(1)-O(4) bond lengths are 2.11 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to one Rb(1), two equivalent Rb(2), one Mg(1), one Nb(1), and one O(4) atom. The O(1)-O(4) bond length is 1.51 Å. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Rb(1), one Mg(1), and one Nb(1) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Rb(1), two equivalent Rb(2), one Nb(1), and one O(5) atom. The O(3)-O(5) bond length is 1.47 Å. In the fourth O site, O(4) is bonded in a 1-coordinate geometry to one Rb(1), one Rb(2), one Nb(1), and one O(1) atom. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to one Rb(1), one Mg(1), one Nb(1), and one O(3) atom. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Rb(1), two equivalent Rb(2), one Mg(1), and one Nb(1) atom.