Ho3TaO7 crystallizes in the orthorhombic Cmme space group. There are two inequivalent Ho sites. In the first Ho site, Ho(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form distorted corner-sharing HoO6 octahedra. The corner-sharing octahedral tilt angles are 70°. In the second Ho site, Ho(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(3), and four equivalent O(2) atoms. Ta(1) is bonded in a body-centered cubic geometry to four equivalent O(2) and four equivalent O(3) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ho(1) and two equivalent Ho(2) atoms to form OHo4 tetrahedra that share corners with two equivalent O(1)Ho4 tetrahedra, corners with four equivalent O(3)Ho2Ta2 tetrahedra, corners with eight equivalent O(2)Ho3Ta tetrahedra, and edges with four equivalent O(2)Ho3Ta tetrahedra. In the second O site, O(2) is bonded to one Ho(1), two equivalent Ho(2), and one Ta(1) atom to form OHo3Ta tetrahedra that share corners with two equivalent O(1)Ho4 tetrahedra, corners with four equivalent O(3)Ho2Ta2 tetrahedra, corners with eight equivalent O(2)Ho3Ta tetrahedra,  an edgeedge with one O(1)Ho4 tetrahedra, edges with two equivalent O(3)Ho2Ta2 tetrahedra, and edges with two equivalent O(2)Ho3Ta tetrahedra. In the third O site, O(3) is bonded to two equivalent Ho(2) and two equivalent Ta(1) atoms to form distorted OHo2Ta2 tetrahedra that share corners with two equivalent O(1)Ho4 tetrahedra, corners with four equivalent O(3)Ho2Ta2 tetrahedra, corners with eight equivalent O(2)Ho3Ta tetrahedra, edges with two equivalent O(3)Ho2Ta2 tetrahedra, and edges with four equivalent O(2)Ho3Ta tetrahedra.
Ho3TaO7 crystallizes in the orthorhombic Cmme space group. There are two inequivalent Ho sites. In the first Ho site, Ho(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form distorted corner-sharing HoO6 octahedra. The corner-sharing octahedral tilt angles are 70°. Both Ho(1)-O(1) bond lengths are 2.26 Å. All Ho(1)-O(2) bond lengths are 2.27 Å. In the second Ho site, Ho(2) is bonded in a 7-coordinate geometry to one O(1), two equivalent O(3), and four equivalent O(2) atoms. The Ho(2)-O(1) bond length is 2.24 Å. There is one shorter (2.08 Å) and one longer (2.56 Å) Ho(2)-O(3) bond length. There are two shorter (2.25 Å) and two longer (2.45 Å) Ho(2)-O(2) bond lengths. Ta(1) is bonded in a body-centered cubic geometry to four equivalent O(2) and four equivalent O(3) atoms. All Ta(1)-O(2) bond lengths are 2.16 Å. All Ta(1)-O(3) bond lengths are 2.18 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ho(1) and two equivalent Ho(2) atoms to form OHo4 tetrahedra that share corners with two equivalent O(1)Ho4 tetrahedra, corners with four equivalent O(3)Ho2Ta2 tetrahedra, corners with eight equivalent O(2)Ho3Ta tetrahedra, and edges with four equivalent O(2)Ho3Ta tetrahedra. In the second O site, O(2) is bonded to one Ho(1), two equivalent Ho(2), and one Ta(1) atom to form OHo3Ta tetrahedra that share corners with two equivalent O(1)Ho4 tetrahedra, corners with four equivalent O(3)Ho2Ta2 tetrahedra, corners with eight equivalent O(2)Ho3Ta tetrahedra,  an edgeedge with one O(1)Ho4 tetrahedra, edges with two equivalent O(3)Ho2Ta2 tetrahedra, and edges with two equivalent O(2)Ho3Ta tetrahedra. In the third O site, O(3) is bonded to two equivalent Ho(2) and two equivalent Ta(1) atoms to form distorted OHo2Ta2 tetrahedra that share corners with two equivalent O(1)Ho4 tetrahedra, corners with four equivalent O(3)Ho2Ta2 tetrahedra, corners with eight equivalent O(2)Ho3Ta tetrahedra, edges with two equivalent O(3)Ho2Ta2 tetrahedra, and edges with four equivalent O(2)Ho3Ta tetrahedra.