NdNb3O9 crystallizes in the monoclinic P2_1/c space group. Nd(1) is bonded in a 8-coordinate geometry to one O(3), one O(7), one O(8), one O(9), two equivalent O(2), and two equivalent O(6) atoms. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(3), one O(4), one O(8), one O(9), 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 28-52°. In the second Nb site, Nb(2) is bonded to one O(3), one O(5), one O(7), one O(8), and two equivalent O(2) atoms to form a mixture of distorted corner and edge-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 28-46°. In the third Nb site, Nb(3) is bonded to one O(4), one O(5), one O(7), one O(9), and two equivalent O(1) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 31-52°. There are nine inequivalent O sites. In the first O site, O(5) is bonded in a bent 150 degrees geometry to one Nb(2) and one Nb(3) atom. In the second O site, O(6) is bonded to two equivalent Nd(1) and two equivalent Nb(1) atoms to form a mixture of distorted corner and edge-sharing ONd2Nb2 tetrahedra. In the third O site, O(7) is bonded in a distorted trigonal planar geometry to one Nd(1), one Nb(2), and one Nb(3) atom. In the fourth O site, O(8) is bonded in a 3-coordinate geometry to one Nd(1), one Nb(1), and one Nb(2) atom. In the fifth O site, O(1) is bonded in a bent 150 degrees geometry to two equivalent Nb(3) atoms. In the sixth O site, O(9) is bonded in a distorted trigonal planar geometry to one Nd(1), one Nb(1), and one Nb(3) atom. In the seventh O site, O(2) is bonded to two equivalent Nd(1) and two equivalent Nb(2) atoms to form a mixture of distorted corner and edge-sharing ONd2Nb2 tetrahedra. In the eighth O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Nd(1), one Nb(1), and one Nb(2) atom. In the ninth O site, O(4) is bonded in a bent 150 degrees geometry to one Nb(1) and one Nb(3) atom.
NdNb3O9 crystallizes in the monoclinic P2_1/c space group. Nd(1) is bonded in a 8-coordinate geometry to one O(3), one O(7), one O(8), one O(9), two equivalent O(2), and two equivalent O(6) atoms. The Nd(1)-O(3) bond length is 2.49 Å. The Nd(1)-O(7) bond length is 2.54 Å. The Nd(1)-O(8) bond length is 2.45 Å. The Nd(1)-O(9) bond length is 2.57 Å. There is one shorter (2.46 Å) and one longer (2.54 Å) Nd(1)-O(2) bond length. There is one shorter (2.45 Å) and one longer (2.55 Å) Nd(1)-O(6) bond length. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(3), one O(4), one O(8), one O(9), 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 28-52°. The Nb(1)-O(3) bond length is 2.07 Å. The Nb(1)-O(4) bond length is 1.87 Å. The Nb(1)-O(8) bond length is 1.97 Å. The Nb(1)-O(9) bond length is 1.99 Å. There is one shorter (2.03 Å) and one longer (2.25 Å) Nb(1)-O(6) bond length. In the second Nb site, Nb(2) is bonded to one O(3), one O(5), one O(7), one O(8), and two equivalent O(2) atoms to form a mixture of distorted corner and edge-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 28-46°. The Nb(2)-O(3) bond length is 1.95 Å. The Nb(2)-O(5) bond length is 1.86 Å. The Nb(2)-O(7) bond length is 1.99 Å. The Nb(2)-O(8) bond length is 2.13 Å. There is one shorter (2.03 Å) and one longer (2.25 Å) Nb(2)-O(2) bond length. In the third Nb site, Nb(3) is bonded to one O(4), one O(5), one O(7), one O(9), and two equivalent O(1) atoms to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 31-52°. The Nb(3)-O(4) bond length is 2.02 Å. The Nb(3)-O(5) bond length is 2.03 Å. The Nb(3)-O(7) bond length is 2.05 Å. The Nb(3)-O(9) bond length is 2.05 Å. There is one shorter (1.82 Å) and one longer (2.20 Å) Nb(3)-O(1) bond length. There are nine inequivalent O sites. In the first O site, O(5) is bonded in a bent 150 degrees geometry to one Nb(2) and one Nb(3) atom. In the second O site, O(6) is bonded to two equivalent Nd(1) and two equivalent Nb(1) atoms to form a mixture of distorted corner and edge-sharing ONd2Nb2 tetrahedra. In the third O site, O(7) is bonded in a distorted trigonal planar geometry to one Nd(1), one Nb(2), and one Nb(3) atom. In the fourth O site, O(8) is bonded in a 3-coordinate geometry to one Nd(1), one Nb(1), and one Nb(2) atom. In the fifth O site, O(1) is bonded in a bent 150 degrees geometry to two equivalent Nb(3) atoms. In the sixth O site, O(9) is bonded in a distorted trigonal planar geometry to one Nd(1), one Nb(1), and one Nb(3) atom. In the seventh O site, O(2) is bonded to two equivalent Nd(1) and two equivalent Nb(2) atoms to form a mixture of distorted corner and edge-sharing ONd2Nb2 tetrahedra. In the eighth O site, O(3) is bonded in a distorted trigonal non-coplanar geometry to one Nd(1), one Nb(1), and one Nb(2) atom. In the ninth O site, O(4) is bonded in a bent 150 degrees geometry to one Nb(1) and one Nb(3) atom.