Ba2MgTmNbO6 crystallizes in the monoclinic Cm space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a distorted q6 geometry to one O(1), two equivalent O(3), two equivalent O(4), and four equivalent O(2) atoms. In the second Ba site, Ba(2) is bonded in a 10-coordinate geometry to one Mg(1), one O(4), two equivalent O(1), two equivalent O(2), and four equivalent O(3) atoms. Mg(1) is bonded in a 3-coordinate geometry to one Ba(2), one O(4), and two equivalent O(2) atoms. Tm(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form TmO6 octahedra that share corners with six equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-8°. Nb(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form distorted NbO6 octahedra that share corners with six equivalent Tm(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-8°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Ba(1), two equivalent Ba(2), one Tm(1), and one Nb(1) atom. In the second O site, O(2) is bonded to one Ba(2), two equivalent Ba(1), one Mg(1), one Tm(1), and one Nb(1) atom to form a mixture of distorted corner and face-sharing OBa3TmMgNb octahedra. The corner-sharing octahedral tilt angles range from 8-61°. In the third O site, O(3) is bonded in a distorted linear geometry to one Ba(1), two equivalent Ba(2), one Tm(1), and one Nb(1) atom. In the fourth O site, O(4) is bonded to one Ba(2), two equivalent Ba(1), one Mg(1), one Tm(1), and one Nb(1) atom to form a mixture of distorted corner and face-sharing OBa3TmMgNb octahedra. The corner-sharing octahedral tilt angles range from 8-61°.
Ba2MgTmNbO6 crystallizes in the monoclinic Cm space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a distorted q6 geometry to one O(1), two equivalent O(3), two equivalent O(4), and four equivalent O(2) atoms. The Ba(1)-O(1) bond length is 3.00 Å. Both Ba(1)-O(3) bond lengths are 3.00 Å. Both Ba(1)-O(4) bond lengths are 2.98 Å. All Ba(1)-O(2) bond lengths are 2.98 Å. In the second Ba site, Ba(2) is bonded in a 10-coordinate geometry to one Mg(1), one O(4), two equivalent O(1), two equivalent O(2), and four equivalent O(3) atoms. The Ba(2)-Mg(1) bond length is 2.95 Å. The Ba(2)-O(4) bond length is 2.53 Å. Both Ba(2)-O(1) bond lengths are 3.09 Å. Both Ba(2)-O(2) bond lengths are 2.53 Å. All Ba(2)-O(3) bond lengths are 3.09 Å. Mg(1) is bonded in a 3-coordinate geometry to one Ba(2), one O(4), and two equivalent O(2) atoms. The Mg(1)-O(4) bond length is 1.96 Å. Both Mg(1)-O(2) bond lengths are 1.96 Å. Tm(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form TmO6 octahedra that share corners with six equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-8°. The Tm(1)-O(1) bond length is 2.24 Å. The Tm(1)-O(4) bond length is 2.52 Å. Both Tm(1)-O(2) bond lengths are 2.53 Å. Both Tm(1)-O(3) bond lengths are 2.24 Å. Nb(1) is bonded to one O(1), one O(4), two equivalent O(2), and two equivalent O(3) atoms to form distorted NbO6 octahedra that share corners with six equivalent Tm(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 0-8°. The Nb(1)-O(1) bond length is 1.99 Å. The Nb(1)-O(4) bond length is 2.29 Å. Both Nb(1)-O(2) bond lengths are 2.28 Å. Both Nb(1)-O(3) bond lengths are 1.99 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Ba(1), two equivalent Ba(2), one Tm(1), and one Nb(1) atom. In the second O site, O(2) is bonded to one Ba(2), two equivalent Ba(1), one Mg(1), one Tm(1), and one Nb(1) atom to form a mixture of distorted corner and face-sharing OBa3TmMgNb octahedra. The corner-sharing octahedral tilt angles range from 8-61°. In the third O site, O(3) is bonded in a distorted linear geometry to one Ba(1), two equivalent Ba(2), one Tm(1), and one Nb(1) atom. In the fourth O site, O(4) is bonded to one Ba(2), two equivalent Ba(1), one Mg(1), one Tm(1), and one Nb(1) atom to form a mixture of distorted corner and face-sharing OBa3TmMgNb octahedra. The corner-sharing octahedral tilt angles range from 8-61°.