Tb3NbO7 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to one O(3), two equivalent O(1), and four equivalent O(2) atoms to form distorted TbO7 pentagonal bipyramids that share corners with two equivalent Nb(1)O6 octahedra, corners with three equivalent Tb(1)O7 pentagonal bipyramids, edges with two equivalent Nb(1)O6 octahedra, and edges with two equivalent Tb(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 42°. In the second Tb site, Tb(2) is bonded in a body-centered cubic geometry to four equivalent O(1) and four equivalent O(2) atoms. Nb(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Tb(1)O7 pentagonal bipyramids, and edges with four equivalent Tb(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 33°. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Tb(1) and two equivalent Tb(2) atoms to form OTb4 tetrahedra that share corners with six equivalent O(1)Tb4 tetrahedra, corners with eight equivalent O(2)Tb3Nb trigonal pyramids,  an edgeedge with one O(1)Tb4 tetrahedra, and edges with four equivalent O(2)Tb3Nb trigonal pyramids. In the second O site, O(2) is bonded to one Tb(2), two equivalent Tb(1), and one Nb(1) atom to form distorted OTb3Nb trigonal pyramids that share corners with four equivalent O(1)Tb4 tetrahedra, corners with eight equivalent O(2)Tb3Nb trigonal pyramids, edges with two equivalent O(1)Tb4 tetrahedra, and edges with two equivalent O(2)Tb3Nb trigonal pyramids. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to two equivalent Tb(1) and two equivalent Nb(1) atoms.
Tb3NbO7 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to one O(3), two equivalent O(1), and four equivalent O(2) atoms to form distorted TbO7 pentagonal bipyramids that share corners with two equivalent Nb(1)O6 octahedra, corners with three equivalent Tb(1)O7 pentagonal bipyramids, edges with two equivalent Nb(1)O6 octahedra, and edges with two equivalent Tb(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 42°. The Tb(1)-O(3) bond length is 2.64 Å. There is one shorter (2.22 Å) and one longer (2.27 Å) Tb(1)-O(1) bond length. There are two shorter (2.32 Å) and two longer (2.40 Å) Tb(1)-O(2) bond lengths. In the second Tb site, Tb(2) is bonded in a body-centered cubic geometry to four equivalent O(1) and four equivalent O(2) atoms. All Tb(2)-O(1) bond lengths are 2.37 Å. All Tb(2)-O(2) bond lengths are 2.65 Å. Nb(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Tb(1)O7 pentagonal bipyramids, and edges with four equivalent Tb(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 33°. Both Nb(1)-O(3) bond lengths are 1.98 Å. All Nb(1)-O(2) bond lengths are 2.01 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Tb(1) and two equivalent Tb(2) atoms to form OTb4 tetrahedra that share corners with six equivalent O(1)Tb4 tetrahedra, corners with eight equivalent O(2)Tb3Nb trigonal pyramids,  an edgeedge with one O(1)Tb4 tetrahedra, and edges with four equivalent O(2)Tb3Nb trigonal pyramids. In the second O site, O(2) is bonded to one Tb(2), two equivalent Tb(1), and one Nb(1) atom to form distorted OTb3Nb trigonal pyramids that share corners with four equivalent O(1)Tb4 tetrahedra, corners with eight equivalent O(2)Tb3Nb trigonal pyramids, edges with two equivalent O(1)Tb4 tetrahedra, and edges with two equivalent O(2)Tb3Nb trigonal pyramids. In the third O site, O(3) is bonded in a distorted bent 150 degrees geometry to two equivalent Tb(1) and two equivalent Nb(1) atoms.