Tm3TaO7 crystallizes in the orthorhombic C222_1 space group. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to one O(1), one O(2), one O(4), two equivalent O(3), and two equivalent O(5) atoms to form distorted TmO7 pentagonal bipyramids that share corners with two equivalent Ta(1)O6 octahedra,  a cornercorner with one Tm(1)O7 pentagonal bipyramid, edges with two equivalent Ta(1)O6 octahedra, and edges with three equivalent Tm(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 39-50°. In the second Tm site, Tm(2) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms. Ta(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(5) 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 45°. There are five inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Tm(1) and two equivalent Ta(1) atoms to form distorted OTm2Ta2 tetrahedra that share corners with two equivalent O(1)Tm2Ta2 tetrahedra, corners with two equivalent O(4)Tm4 tetrahedra, corners with four equivalent O(5)Tm3Ta tetrahedra,  an edgeedge with one O(2)Tm4 tetrahedra, and edges with two equivalent O(5)Tm3Ta tetrahedra. In the second O site, O(2) is bonded to two equivalent Tm(1) and two equivalent Tm(2) atoms to form OTm4 tetrahedra that share corners with two equivalent O(2)Tm4 tetrahedra, corners with four equivalent O(5)Tm3Ta tetrahedra, corners with four equivalent O(4)Tm4 tetrahedra,  an edgeedge with one O(1)Tm2Ta2 tetrahedra,  an edgeedge with one O(4)Tm4 tetrahedra, and edges with two equivalent O(5)Tm3Ta tetrahedra. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Tm(1) and one Ta(1) atom. In the fourth O site, O(4) is bonded to two equivalent Tm(1) and two equivalent Tm(2) atoms to form OTm4 tetrahedra that share corners with two equivalent O(1)Tm2Ta2 tetrahedra, corners with two equivalent O(4)Tm4 tetrahedra, corners with four equivalent O(5)Tm3Ta tetrahedra, corners with four equivalent O(2)Tm4 tetrahedra,  an edgeedge with one O(2)Tm4 tetrahedra, and edges with two equivalent O(5)Tm3Ta tetrahedra. In the fifth O site, O(5) is bonded to one Tm(2), two equivalent Tm(1), and one Ta(1) atom to form distorted OTm3Ta tetrahedra that share corners with two equivalent O(1)Tm2Ta2 tetrahedra, corners with two equivalent O(5)Tm3Ta tetrahedra, corners with two equivalent O(2)Tm4 tetrahedra, corners with two equivalent O(4)Tm4 tetrahedra,  an edgeedge with one O(1)Tm2Ta2 tetrahedra,  an edgeedge with one O(5)Tm3Ta tetrahedra,  an edgeedge with one O(2)Tm4 tetrahedra, and  an edgeedge with one O(4)Tm4 tetrahedra.
Tm3TaO7 crystallizes in the orthorhombic C222_1 space group. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to one O(1), one O(2), one O(4), two equivalent O(3), and two equivalent O(5) atoms to form distorted TmO7 pentagonal bipyramids that share corners with two equivalent Ta(1)O6 octahedra,  a cornercorner with one Tm(1)O7 pentagonal bipyramid, edges with two equivalent Ta(1)O6 octahedra, and edges with three equivalent Tm(1)O7 pentagonal bipyramids. The corner-sharing octahedral tilt angles range from 39-50°. The Tm(1)-O(1) bond length is 2.38 Å. The Tm(1)-O(2) bond length is 2.17 Å. The Tm(1)-O(4) bond length is 2.26 Å. There is one shorter (2.20 Å) and one longer (2.39 Å) Tm(1)-O(3) bond length. There is one shorter (2.22 Å) and one longer (2.37 Å) Tm(1)-O(5) bond length. In the second Tm site, Tm(2) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(4), and two equivalent O(5) atoms. Both Tm(2)-O(2) bond lengths are 2.35 Å. Both Tm(2)-O(4) bond lengths are 2.28 Å. Both Tm(2)-O(5) bond lengths are 2.30 Å. Ta(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(5) 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 45°. Both Ta(1)-O(1) bond lengths are 1.98 Å. Both Ta(1)-O(3) bond lengths are 1.92 Å. Both Ta(1)-O(5) bond lengths are 2.02 Å. There are five inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Tm(1) and two equivalent Ta(1) atoms to form distorted OTm2Ta2 tetrahedra that share corners with two equivalent O(1)Tm2Ta2 tetrahedra, corners with two equivalent O(4)Tm4 tetrahedra, corners with four equivalent O(5)Tm3Ta tetrahedra,  an edgeedge with one O(2)Tm4 tetrahedra, and edges with two equivalent O(5)Tm3Ta tetrahedra. In the second O site, O(2) is bonded to two equivalent Tm(1) and two equivalent Tm(2) atoms to form OTm4 tetrahedra that share corners with two equivalent O(2)Tm4 tetrahedra, corners with four equivalent O(5)Tm3Ta tetrahedra, corners with four equivalent O(4)Tm4 tetrahedra,  an edgeedge with one O(1)Tm2Ta2 tetrahedra,  an edgeedge with one O(4)Tm4 tetrahedra, and edges with two equivalent O(5)Tm3Ta tetrahedra. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Tm(1) and one Ta(1) atom. In the fourth O site, O(4) is bonded to two equivalent Tm(1) and two equivalent Tm(2) atoms to form OTm4 tetrahedra that share corners with two equivalent O(1)Tm2Ta2 tetrahedra, corners with two equivalent O(4)Tm4 tetrahedra, corners with four equivalent O(5)Tm3Ta tetrahedra, corners with four equivalent O(2)Tm4 tetrahedra,  an edgeedge with one O(2)Tm4 tetrahedra, and edges with two equivalent O(5)Tm3Ta tetrahedra. In the fifth O site, O(5) is bonded to one Tm(2), two equivalent Tm(1), and one Ta(1) atom to form distorted OTm3Ta tetrahedra that share corners with two equivalent O(1)Tm2Ta2 tetrahedra, corners with two equivalent O(5)Tm3Ta tetrahedra, corners with two equivalent O(2)Tm4 tetrahedra, corners with two equivalent O(4)Tm4 tetrahedra,  an edgeedge with one O(1)Tm2Ta2 tetrahedra,  an edgeedge with one O(5)Tm3Ta tetrahedra,  an edgeedge with one O(2)Tm4 tetrahedra, and  an edgeedge with one O(4)Tm4 tetrahedra.