K3MgNbO8 crystallizes in the monoclinic Cm space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 9-coordinate geometry to one Mg(1), one O(1), one O(3), one O(4), one O(6), two equivalent O(2), and two equivalent O(5) atoms. In the second K site, K(2) is bonded in a 8-coordinate geometry to one O(1), one O(3), one O(4), one O(6), two equivalent O(2), and two equivalent O(5) atoms. Mg(1) is bonded in a 5-coordinate geometry to two equivalent K(1), one O(1), one O(3), one O(6), and two equivalent O(5) atoms. Nb(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), one O(4), one O(6), two equivalent O(2), and two equivalent O(5) atoms. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal bipyramidal geometry to one K(2), two equivalent K(1), one Mg(1), and one Nb(1) atom. In the second O site, O(2) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), one Nb(1), and one O(5) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one K(2), two equivalent K(1), one Mg(1), one Nb(1), and one O(4) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one K(2), two equivalent K(1), one Nb(1), and one O(3) atom. In the fifth O site, O(5) is bonded in a 6-coordinate geometry to one K(2), two equivalent K(1), one Mg(1), one Nb(1), and one O(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one K(2), two equivalent K(1), one Mg(1), and one Nb(1) atom.
K3MgNbO8 crystallizes in the monoclinic Cm space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 9-coordinate geometry to one Mg(1), one O(1), one O(3), one O(4), one O(6), two equivalent O(2), and two equivalent O(5) atoms. The K(1)-Mg(1) bond length is 3.18 Å. The K(1)-O(1) bond length is 2.71 Å. The K(1)-O(3) bond length is 3.34 Å. The K(1)-O(4) bond length is 2.97 Å. The K(1)-O(6) bond length is 3.29 Å. There is one shorter (2.76 Å) and one longer (2.93 Å) K(1)-O(2) bond length. There is one shorter (2.66 Å) and one longer (2.82 Å) K(1)-O(5) bond length. In the second K site, K(2) is bonded in a 8-coordinate geometry to one O(1), one O(3), one O(4), one O(6), two equivalent O(2), and two equivalent O(5) atoms. The K(2)-O(1) bond length is 2.82 Å. The K(2)-O(3) bond length is 2.60 Å. The K(2)-O(4) bond length is 3.19 Å. The K(2)-O(6) bond length is 2.50 Å. Both K(2)-O(2) bond lengths are 3.12 Å. Both K(2)-O(5) bond lengths are 3.22 Å. Mg(1) is bonded in a 5-coordinate geometry to two equivalent K(1), one O(1), one O(3), one O(6), and two equivalent O(5) atoms. The Mg(1)-O(1) bond length is 2.06 Å. The Mg(1)-O(3) bond length is 2.14 Å. The Mg(1)-O(6) bond length is 1.93 Å. Both Mg(1)-O(5) bond lengths are 2.09 Å. Nb(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), one O(4), one O(6), two equivalent O(2), and two equivalent O(5) atoms. The Nb(1)-O(1) bond length is 2.00 Å. The Nb(1)-O(3) bond length is 2.29 Å. The Nb(1)-O(4) bond length is 2.05 Å. The Nb(1)-O(6) bond length is 1.92 Å. Both Nb(1)-O(2) bond lengths are 2.10 Å. Both Nb(1)-O(5) bond lengths are 2.33 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal bipyramidal geometry to one K(2), two equivalent K(1), one Mg(1), and one Nb(1) atom. In the second O site, O(2) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), one Nb(1), and one O(5) atom. The O(2)-O(5) bond length is 1.51 Å. In the third O site, O(3) is bonded in a 4-coordinate geometry to one K(2), two equivalent K(1), one Mg(1), one Nb(1), and one O(4) atom. The O(3)-O(4) bond length is 1.47 Å. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one K(2), two equivalent K(1), one Nb(1), and one O(3) atom. In the fifth O site, O(5) is bonded in a 6-coordinate geometry to one K(2), two equivalent K(1), one Mg(1), one Nb(1), and one O(2) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one K(2), two equivalent K(1), one Mg(1), and one Nb(1) atom.