Tm3TaO7 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to one O(3), two equivalent O(1), and four equivalent O(2) atoms to form distorted TmO7 pentagonal bipyramids that share corners with two equivalent Ta(1)O6 octahedra, corners with three equivalent Tm(1)O7 pentagonal bipyramids, edges with two equivalent Ta(1)O6 octahedra, and edges with two equivalent Tm(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 42°. In the second Tm site, Tm(2) is bonded in a body-centered cubic geometry to four equivalent O(1) and four equivalent O(2) atoms. Ta(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with four equivalent Tm(1)O7 pentagonal bipyramids, and edges with four equivalent Tm(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 37°. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Tm(1) and two equivalent Tm(2) atoms to form a mixture of corner and edge-sharing OTm4 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Tm(2), two equivalent Tm(1), and one Ta(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Tm(1) and two equivalent Ta(1) atoms.
Tm3TaO7 crystallizes in the orthorhombic Cmcm space group. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to one O(3), two equivalent O(1), and four equivalent O(2) atoms to form distorted TmO7 pentagonal bipyramids that share corners with two equivalent Ta(1)O6 octahedra, corners with three equivalent Tm(1)O7 pentagonal bipyramids, edges with two equivalent Ta(1)O6 octahedra, and edges with two equivalent Tm(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 42°. The Tm(1)-O(3) bond length is 2.60 Å. There is one shorter (2.18 Å) and one longer (2.24 Å) Tm(1)-O(1) bond length. There are two shorter (2.25 Å) and two longer (2.38 Å) Tm(1)-O(2) bond lengths. In the second Tm site, Tm(2) is bonded in a body-centered cubic geometry to four equivalent O(1) and four equivalent O(2) atoms. All Tm(2)-O(1) bond lengths are 2.33 Å. All Tm(2)-O(2) bond lengths are 2.63 Å. Ta(1) is bonded to two equivalent O(3) and four equivalent O(2) atoms to form TaO6 octahedra that share corners with two equivalent Ta(1)O6 octahedra, corners with four equivalent Tm(1)O7 pentagonal bipyramids, and edges with four equivalent Tm(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 37°. Both Ta(1)-O(3) bond lengths are 1.96 Å. All Ta(1)-O(2) bond lengths are 1.99 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Tm(1) and two equivalent Tm(2) atoms to form a mixture of corner and edge-sharing OTm4 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Tm(2), two equivalent Tm(1), and one Ta(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to two equivalent Tm(1) and two equivalent Ta(1) atoms.