Ho2Se3 crystallizes in the tetragonal I-42d space group. There are three inequivalent Ho sites. In the first Ho site, Ho(1) is bonded in a 8-coordinate geometry to two equivalent Se(2), three equivalent Se(1), and three equivalent Se(3) atoms. In the second Ho site, Ho(2) is bonded in a 8-coordinate geometry to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms. In the third Ho site, Ho(3) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Ho(3), two equivalent Ho(2), and three equivalent Ho(1) atoms to form distorted SeHo6 octahedra that share corners with three equivalent Se(1)Ho6 octahedra, corners with five equivalent Se(2)Ho5 square pyramids, corners with seven equivalent Se(3)Ho5 square pyramids, edges with two equivalent Se(1)Ho6 octahedra,  an edgeedge with one Se(3)Ho5 square pyramid, edges with three equivalent Se(2)Ho5 square pyramids, faces with two equivalent Se(1)Ho6 octahedra,  a faceface with one Se(2)Ho5 square pyramid, and faces with two equivalent Se(3)Ho5 square pyramids. The corner-sharing octahedral tilt angles range from 18-50°. In the second Se site, Se(2) is bonded to one Ho(2), two equivalent Ho(1), and two equivalent Ho(3) atoms to form distorted SeHo5 square pyramids that share corners with five equivalent Se(1)Ho6 octahedra, corners with four equivalent Se(2)Ho5 square pyramids, corners with four equivalent Se(3)Ho5 square pyramids, edges with three equivalent Se(1)Ho6 octahedra,  an edgeedge with one Se(2)Ho5 square pyramid, edges with four equivalent Se(3)Ho5 square pyramids,  a faceface with one Se(1)Ho6 octahedra, and  a faceface with one Se(2)Ho5 square pyramid. The corner-sharing octahedral tilt angles range from 24-49°. In the third Se site, Se(3) is bonded to one Ho(2), one Ho(3), and three equivalent Ho(1) atoms to form distorted SeHo5 square pyramids that share corners with seven equivalent Se(1)Ho6 octahedra, corners with four equivalent Se(2)Ho5 square pyramids, corners with five equivalent Se(3)Ho5 square pyramids,  an edgeedge with one Se(1)Ho6 octahedra, edges with four equivalent Se(2)Ho5 square pyramids, faces with two equivalent Se(1)Ho6 octahedra, and  a faceface with one Se(3)Ho5 square pyramid. The corner-sharing octahedral tilt angles range from 15-53°.
Ho2Se3 crystallizes in the tetragonal I-42d space group. There are three inequivalent Ho sites. In the first Ho site, Ho(1) is bonded in a 8-coordinate geometry to two equivalent Se(2), three equivalent Se(1), and three equivalent Se(3) atoms. There is one shorter (2.84 Å) and one longer (3.12 Å) Ho(1)-Se(2) bond length. There are a spread of Ho(1)-Se(1) bond distances ranging from 2.87-3.27 Å. There are a spread of Ho(1)-Se(3) bond distances ranging from 2.86-3.09 Å. In the second Ho site, Ho(2) is bonded in a 8-coordinate geometry to two equivalent Se(2), two equivalent Se(3), and four equivalent Se(1) atoms. Both Ho(2)-Se(2) bond lengths are 2.87 Å. Both Ho(2)-Se(3) bond lengths are 3.09 Å. There are two shorter (2.87 Å) and two longer (3.14 Å) Ho(2)-Se(1) bond lengths. In the third Ho site, Ho(3) is bonded in a 8-coordinate geometry to two equivalent Se(1), two equivalent Se(3), and four equivalent Se(2) atoms. Both Ho(3)-Se(1) bond lengths are 3.22 Å. Both Ho(3)-Se(3) bond lengths are 2.88 Å. There are two shorter (2.88 Å) and two longer (3.09 Å) Ho(3)-Se(2) bond lengths. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Ho(3), two equivalent Ho(2), and three equivalent Ho(1) atoms to form distorted SeHo6 octahedra that share corners with three equivalent Se(1)Ho6 octahedra, corners with five equivalent Se(2)Ho5 square pyramids, corners with seven equivalent Se(3)Ho5 square pyramids, edges with two equivalent Se(1)Ho6 octahedra,  an edgeedge with one Se(3)Ho5 square pyramid, edges with three equivalent Se(2)Ho5 square pyramids, faces with two equivalent Se(1)Ho6 octahedra,  a faceface with one Se(2)Ho5 square pyramid, and faces with two equivalent Se(3)Ho5 square pyramids. The corner-sharing octahedral tilt angles range from 18-50°. In the second Se site, Se(2) is bonded to one Ho(2), two equivalent Ho(1), and two equivalent Ho(3) atoms to form distorted SeHo5 square pyramids that share corners with five equivalent Se(1)Ho6 octahedra, corners with four equivalent Se(2)Ho5 square pyramids, corners with four equivalent Se(3)Ho5 square pyramids, edges with three equivalent Se(1)Ho6 octahedra,  an edgeedge with one Se(2)Ho5 square pyramid, edges with four equivalent Se(3)Ho5 square pyramids,  a faceface with one Se(1)Ho6 octahedra, and  a faceface with one Se(2)Ho5 square pyramid. The corner-sharing octahedral tilt angles range from 24-49°. In the third Se site, Se(3) is bonded to one Ho(2), one Ho(3), and three equivalent Ho(1) atoms to form distorted SeHo5 square pyramids that share corners with seven equivalent Se(1)Ho6 octahedra, corners with four equivalent Se(2)Ho5 square pyramids, corners with five equivalent Se(3)Ho5 square pyramids,  an edgeedge with one Se(1)Ho6 octahedra, edges with four equivalent Se(2)Ho5 square pyramids, faces with two equivalent Se(1)Ho6 octahedra, and  a faceface with one Se(3)Ho5 square pyramid. The corner-sharing octahedral tilt angles range from 15-53°.