NdTa3O9 crystallizes in the triclinic P-1 space group. There are two inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 12-coordinate geometry to one O(1), one O(10), one O(12), one O(14), one O(17), two equivalent O(11), two equivalent O(2), and three equivalent O(8) atoms. In the second Nd site, Nd(2) is bonded in a 12-coordinate geometry to one O(10), one O(13), one O(16), one O(3), one O(4), two equivalent O(15), two equivalent O(18), and three equivalent O(9) atoms. There are six inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), one O(10), one O(12), one O(13), one O(4), and one O(5) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 8-24°. In the second Ta site, Ta(2) is bonded to one O(1), one O(11), one O(12), one O(2), one O(5), and one O(8) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 2-24°. In the third Ta site, Ta(3) is bonded to one O(13), one O(15), one O(18), one O(4), one O(6), and one O(9) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 8-28°. In the fourth Ta site, Ta(4) is bonded to one O(11), one O(14), one O(17), one O(2), one O(6), and one O(8) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 2-25°. In the fifth Ta site, Ta(5) is bonded to one O(15), one O(16), one O(18), one O(3), one O(7), and one O(9) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 6-28°. In the sixth Ta site, Ta(6) is bonded to one O(10), one O(14), one O(16), one O(17), one O(3), and one O(7) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 6-25°. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Nd(1), one Ta(1), and one Ta(2) atom. In the second O site, O(2) is bonded to two equivalent Nd(1), one Ta(2), and one Ta(4) atom to form distorted ONd2Ta2 trigonal pyramids that share corners with two equivalent O(8)Nd3Ta2 trigonal pyramids,  an edgeedge with one O(2)Nd2Ta2 trigonal pyramid, and faces with two equivalent O(8)Nd3Ta2 trigonal pyramids. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Nd(2), one Ta(5), and one Ta(6) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Nd(2), one Ta(1), and one Ta(3) atom. In the fifth O site, O(5) is bonded in a linear geometry to one Ta(1) and one Ta(2) atom. In the sixth O site, O(6) is bonded in a linear geometry to one Ta(3) and one Ta(4) atom. In the seventh O site, O(7) is bonded in a linear geometry to one Ta(5) and one Ta(6) atom. In the eighth O site, O(8) is bonded to three equivalent Nd(1), one Ta(2), and one Ta(4) atom to form distorted ONd3Ta2 trigonal pyramids that share corners with two equivalent O(2)Nd2Ta2 trigonal pyramids, corners with two equivalent O(8)Nd3Ta2 trigonal pyramids, edges with two equivalent O(8)Nd3Ta2 trigonal pyramids, and faces with two equivalent O(2)Nd2Ta2 trigonal pyramids. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to three equivalent Nd(2), one Ta(3), and one Ta(5) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Nd(1), one Nd(2), one Ta(1), and one Ta(6) atom. In the eleventh O site, O(11) is bonded in a distorted linear geometry to two equivalent Nd(1), one Ta(2), and one Ta(4) atom. In the twelfth O site, O(12) is bonded in a distorted T-shaped geometry to one Nd(1), one Ta(1), and one Ta(2) atom. In the thirteenth O site, O(13) is bonded in a distorted linear geometry to one Nd(2), one Ta(1), and one Ta(3) atom. In the fourteenth O site, O(14) is bonded in a distorted T-shaped geometry to one Nd(1), one Ta(4), and one Ta(6) atom. In the fifteenth O site, O(15) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Nd(2), one Ta(3), and one Ta(5) atom. In the sixteenth O site, O(16) is bonded in a distorted linear geometry to one Nd(2), one Ta(5), and one Ta(6) atom. In the seventeenth O site, O(17) is bonded in a distorted T-shaped geometry to one Nd(1), one Ta(4), and one Ta(6) atom. In the eighteenth O site, O(18) is bonded to two equivalent Nd(2), one Ta(3), and one Ta(5) atom to form distorted edge-sharing ONd2Ta2 tetrahedra.
NdTa3O9 crystallizes in the triclinic P-1 space group. There are two inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 12-coordinate geometry to one O(1), one O(10), one O(12), one O(14), one O(17), two equivalent O(11), two equivalent O(2), and three equivalent O(8) atoms. The Nd(1)-O(1) bond length is 2.57 Å. The Nd(1)-O(10) bond length is 3.08 Å. The Nd(1)-O(12) bond length is 2.64 Å. The Nd(1)-O(14) bond length is 2.63 Å. The Nd(1)-O(17) bond length is 2.57 Å. Both Nd(1)-O(11) bond lengths are 2.78 Å. Both Nd(1)-O(2) bond lengths are 2.61 Å. There are a spread of Nd(1)-O(8) bond distances ranging from 2.44-3.12 Å. In the second Nd site, Nd(2) is bonded in a 12-coordinate geometry to one O(10), one O(13), one O(16), one O(3), one O(4), two equivalent O(15), two equivalent O(18), and three equivalent O(9) atoms. The Nd(2)-O(10) bond length is 2.56 Å. The Nd(2)-O(13) bond length is 2.82 Å. The Nd(2)-O(16) bond length is 2.80 Å. The Nd(2)-O(3) bond length is 2.63 Å. The Nd(2)-O(4) bond length is 2.65 Å. There is one shorter (2.63 Å) and one longer (2.64 Å) Nd(2)-O(15) bond length. There is one shorter (2.54 Å) and one longer (2.55 Å) Nd(2)-O(18) bond length. There are a spread of Nd(2)-O(9) bond distances ranging from 2.51-3.06 Å. There are six inequivalent Ta sites. In the first Ta site, Ta(1) is bonded to one O(1), one O(10), one O(12), one O(13), one O(4), and one O(5) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 8-24°. The Ta(1)-O(1) bond length is 1.99 Å. The Ta(1)-O(10) bond length is 2.00 Å. The Ta(1)-O(12) bond length is 1.99 Å. The Ta(1)-O(13) bond length is 1.99 Å. The Ta(1)-O(4) bond length is 2.00 Å. The Ta(1)-O(5) bond length is 1.97 Å. In the second Ta site, Ta(2) is bonded to one O(1), one O(11), one O(12), one O(2), one O(5), and one O(8) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 2-24°. The Ta(2)-O(1) bond length is 1.97 Å. The Ta(2)-O(11) bond length is 2.00 Å. The Ta(2)-O(12) bond length is 1.96 Å. The Ta(2)-O(2) bond length is 2.05 Å. The Ta(2)-O(5) bond length is 1.90 Å. The Ta(2)-O(8) bond length is 2.14 Å. In the third Ta site, Ta(3) is bonded to one O(13), one O(15), one O(18), one O(4), one O(6), and one O(9) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 8-28°. The Ta(3)-O(13) bond length is 1.92 Å. The Ta(3)-O(15) bond length is 2.04 Å. The Ta(3)-O(18) bond length is 2.08 Å. The Ta(3)-O(4) bond length is 1.94 Å. The Ta(3)-O(6) bond length is 1.95 Å. The Ta(3)-O(9) bond length is 2.04 Å. In the fourth Ta site, Ta(4) is bonded to one O(11), one O(14), one O(17), one O(2), one O(6), and one O(8) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 2-25°. The Ta(4)-O(11) bond length is 2.01 Å. The Ta(4)-O(14) bond length is 1.95 Å. The Ta(4)-O(17) bond length is 1.97 Å. The Ta(4)-O(2) bond length is 2.05 Å. The Ta(4)-O(6) bond length is 1.91 Å. The Ta(4)-O(8) bond length is 2.12 Å. In the fifth Ta site, Ta(5) is bonded to one O(15), one O(16), one O(18), one O(3), one O(7), and one O(9) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 6-28°. The Ta(5)-O(15) bond length is 2.03 Å. The Ta(5)-O(16) bond length is 1.93 Å. The Ta(5)-O(18) bond length is 2.07 Å. The Ta(5)-O(3) bond length is 1.95 Å. The Ta(5)-O(7) bond length is 1.92 Å. The Ta(5)-O(9) bond length is 2.10 Å. In the sixth Ta site, Ta(6) is bonded to one O(10), one O(14), one O(16), one O(17), one O(3), and one O(7) atom to form corner-sharing TaO6 octahedra. The corner-sharing octahedral tilt angles range from 6-25°. The Ta(6)-O(10) bond length is 2.03 Å. The Ta(6)-O(14) bond length is 1.99 Å. The Ta(6)-O(16) bond length is 1.98 Å. The Ta(6)-O(17) bond length is 2.00 Å. The Ta(6)-O(3) bond length is 1.99 Å. The Ta(6)-O(7) bond length is 1.94 Å. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Nd(1), one Ta(1), and one Ta(2) atom. In the second O site, O(2) is bonded to two equivalent Nd(1), one Ta(2), and one Ta(4) atom to form distorted ONd2Ta2 trigonal pyramids that share corners with two equivalent O(8)Nd3Ta2 trigonal pyramids,  an edgeedge with one O(2)Nd2Ta2 trigonal pyramid, and faces with two equivalent O(8)Nd3Ta2 trigonal pyramids. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Nd(2), one Ta(5), and one Ta(6) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Nd(2), one Ta(1), and one Ta(3) atom. In the fifth O site, O(5) is bonded in a linear geometry to one Ta(1) and one Ta(2) atom. In the sixth O site, O(6) is bonded in a linear geometry to one Ta(3) and one Ta(4) atom. In the seventh O site, O(7) is bonded in a linear geometry to one Ta(5) and one Ta(6) atom. In the eighth O site, O(8) is bonded to three equivalent Nd(1), one Ta(2), and one Ta(4) atom to form distorted ONd3Ta2 trigonal pyramids that share corners with two equivalent O(2)Nd2Ta2 trigonal pyramids, corners with two equivalent O(8)Nd3Ta2 trigonal pyramids, edges with two equivalent O(8)Nd3Ta2 trigonal pyramids, and faces with two equivalent O(2)Nd2Ta2 trigonal pyramids. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to three equivalent Nd(2), one Ta(3), and one Ta(5) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Nd(1), one Nd(2), one Ta(1), and one Ta(6) atom. In the eleventh O site, O(11) is bonded in a distorted linear geometry to two equivalent Nd(1), one Ta(2), and one Ta(4) atom. In the twelfth O site, O(12) is bonded in a distorted T-shaped geometry to one Nd(1), one Ta(1), and one Ta(2) atom. In the thirteenth O site, O(13) is bonded in a distorted linear geometry to one Nd(2), one Ta(1), and one Ta(3) atom. In the fourteenth O site, O(14) is bonded in a distorted T-shaped geometry to one Nd(1), one Ta(4), and one Ta(6) atom. In the fifteenth O site, O(15) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Nd(2), one Ta(3), and one Ta(5) atom. In the sixteenth O site, O(16) is bonded in a distorted linear geometry to one Nd(2), one Ta(5), and one Ta(6) atom. In the seventeenth O site, O(17) is bonded in a distorted T-shaped geometry to one Nd(1), one Ta(4), and one Ta(6) atom. In the eighteenth O site, O(18) is bonded to two equivalent Nd(2), one Ta(3), and one Ta(5) atom to form distorted edge-sharing ONd2Ta2 tetrahedra.