Ba2Nb6Te2O21 crystallizes in the monoclinic C2/m space group. Ba(1) is bonded in a 11-coordinate geometry to one O(2), two equivalent O(4), two equivalent O(6), two equivalent O(7), and four equivalent O(8) atoms. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), two equivalent O(5), and two equivalent O(8) atoms to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 8-14°. In the second Nb site, Nb(2) is bonded to one O(1), one O(7), two equivalent O(4), and two equivalent O(6) atoms to form a mixture of distorted corner and edge-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 9-14°. In the third Nb site, Nb(3) is bonded to one O(2), one O(3), two equivalent O(4), and two equivalent O(5) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 0-13°. Te(1) is bonded in a distorted T-shaped geometry to one O(7) and two equivalent O(8) atoms. There are eight inequivalent O sites. In the first O site, O(7) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Nb(2), and one Te(1) atom. In the second O site, O(8) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Nb(1), and one Te(1) atom. In the third O site, O(1) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the fourth O site, O(2) is bonded in a distorted linear geometry to one Ba(1), one Nb(1), and one Nb(3) atom. In the fifth O site, O(3) is bonded in a linear geometry to two equivalent Nb(3) atoms. In the sixth O site, O(4) is bonded in a linear geometry to one Ba(1), one Nb(2), and one Nb(3) atom. In the seventh O site, O(5) is bonded in a linear geometry to one Nb(1) and one Nb(3) atom. In the eighth O site, O(6) is bonded to two equivalent Ba(1) and two equivalent Nb(2) atoms to form distorted edge-sharing OBa2Nb2 tetrahedra.
Ba2Nb6Te2O21 crystallizes in the monoclinic C2/m space group. Ba(1) is bonded in a 11-coordinate geometry to one O(2), two equivalent O(4), two equivalent O(6), two equivalent O(7), and four equivalent O(8) atoms. The Ba(1)-O(2) bond length is 3.23 Å. Both Ba(1)-O(4) bond lengths are 3.22 Å. Both Ba(1)-O(6) bond lengths are 2.86 Å. Both Ba(1)-O(7) bond lengths are 2.98 Å. There are two shorter (2.84 Å) and two longer (3.02 Å) Ba(1)-O(8) bond lengths. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), two equivalent O(5), and two equivalent O(8) atoms to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 8-14°. The Nb(1)-O(1) bond length is 2.05 Å. The Nb(1)-O(2) bond length is 1.97 Å. Both Nb(1)-O(5) bond lengths are 1.88 Å. Both Nb(1)-O(8) bond lengths are 2.25 Å. In the second Nb site, Nb(2) is bonded to one O(1), one O(7), two equivalent O(4), and two equivalent O(6) atoms to form a mixture of distorted corner and edge-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 9-14°. The Nb(2)-O(1) bond length is 1.86 Å. The Nb(2)-O(7) bond length is 2.23 Å. Both Nb(2)-O(4) bond lengths are 1.99 Å. Both Nb(2)-O(6) bond lengths are 2.04 Å. In the third Nb site, Nb(3) is bonded to one O(2), one O(3), two equivalent O(4), and two equivalent O(5) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 0-13°. The Nb(3)-O(2) bond length is 2.07 Å. The Nb(3)-O(3) bond length is 1.95 Å. Both Nb(3)-O(4) bond lengths are 1.96 Å. Both Nb(3)-O(5) bond lengths are 2.08 Å. Te(1) is bonded in a distorted T-shaped geometry to one O(7) and two equivalent O(8) atoms. The Te(1)-O(7) bond length is 1.90 Å. Both Te(1)-O(8) bond lengths are 1.91 Å. There are eight inequivalent O sites. In the first O site, O(7) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Nb(2), and one Te(1) atom. In the second O site, O(8) is bonded in a 4-coordinate geometry to two equivalent Ba(1), one Nb(1), and one Te(1) atom. In the third O site, O(1) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the fourth O site, O(2) is bonded in a distorted linear geometry to one Ba(1), one Nb(1), and one Nb(3) atom. In the fifth O site, O(3) is bonded in a linear geometry to two equivalent Nb(3) atoms. In the sixth O site, O(4) is bonded in a linear geometry to one Ba(1), one Nb(2), and one Nb(3) atom. In the seventh O site, O(5) is bonded in a linear geometry to one Nb(1) and one Nb(3) atom. In the eighth O site, O(6) is bonded to two equivalent Ba(1) and two equivalent Nb(2) atoms to form distorted edge-sharing OBa2Nb2 tetrahedra.