HfTe3Se8 crystallizes in the triclinic P-1 space group. Hf(1) is bonded to one Se(1), one Se(5), two equivalent Se(6), and two equivalent Se(7) atoms to form distorted HfSe6 pentagonal pyramids that share  a cornercorner with one Te(2)Se5 trigonal bipyramid, edges with two equivalent Hf(1)Se6 pentagonal pyramids, and  an edgeedge with one Te(2)Se5 trigonal bipyramid. There are three inequivalent Te sites. In the first Te site, Te(1) is bonded in a distorted see-saw-like geometry to one Se(2), one Se(8), and two equivalent Se(3) atoms. In the second Te site, Te(2) is bonded to one Se(1), one Se(3), one Se(4), one Se(7), and one Se(8) atom to form distorted TeSe5 trigonal bipyramids that share  a cornercorner with one Hf(1)Se6 pentagonal pyramid and  an edgeedge with one Hf(1)Se6 pentagonal pyramid. In the third Te site, Te(3) is bonded in a 5-coordinate geometry to one Se(2), one Se(4), one Se(5), and two equivalent Se(6) atoms. There are eight inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted L-shaped geometry to one Hf(1) and one Te(2) atom. In the second Se site, Se(2) is bonded in a water-like geometry to one Te(1) and one Te(3) atom. In the third Se site, Se(3) is bonded in a 3-coordinate geometry to one Te(2) and two equivalent Te(1) atoms. In the fourth Se site, Se(4) is bonded in a bent 120 degrees geometry to one Te(2) and one Te(3) atom. In the fifth Se site, Se(5) is bonded in a distorted water-like geometry to one Hf(1) and one Te(3) atom. In the sixth Se site, Se(6) is bonded in a 4-coordinate geometry to two equivalent Hf(1) and two equivalent Te(3) atoms. In the seventh Se site, Se(7) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Hf(1) and one Te(2) atom. In the eighth Se site, Se(8) is bonded in a water-like geometry to one Te(1) and one Te(2) atom.
HfTe3Se8 crystallizes in the triclinic P-1 space group. Hf(1) is bonded to one Se(1), one Se(5), two equivalent Se(6), and two equivalent Se(7) atoms to form distorted HfSe6 pentagonal pyramids that share  a cornercorner with one Te(2)Se5 trigonal bipyramid, edges with two equivalent Hf(1)Se6 pentagonal pyramids, and  an edgeedge with one Te(2)Se5 trigonal bipyramid. The Hf(1)-Se(1) bond length is 2.55 Å. The Hf(1)-Se(5) bond length is 2.67 Å. There is one shorter (2.62 Å) and one longer (2.76 Å) Hf(1)-Se(6) bond length. There is one shorter (2.75 Å) and one longer (2.86 Å) Hf(1)-Se(7) bond length. There are three inequivalent Te sites. In the first Te site, Te(1) is bonded in a distorted see-saw-like geometry to one Se(2), one Se(8), and two equivalent Se(3) atoms. The Te(1)-Se(2) bond length is 2.66 Å. The Te(1)-Se(8) bond length is 2.66 Å. There is one shorter (2.60 Å) and one longer (3.04 Å) Te(1)-Se(3) bond length. In the second Te site, Te(2) is bonded to one Se(1), one Se(3), one Se(4), one Se(7), and one Se(8) atom to form distorted TeSe5 trigonal bipyramids that share  a cornercorner with one Hf(1)Se6 pentagonal pyramid and  an edgeedge with one Hf(1)Se6 pentagonal pyramid. The Te(2)-Se(1) bond length is 2.81 Å. The Te(2)-Se(3) bond length is 2.97 Å. The Te(2)-Se(4) bond length is 2.67 Å. The Te(2)-Se(7) bond length is 2.74 Å. The Te(2)-Se(8) bond length is 2.74 Å. In the third Te site, Te(3) is bonded in a 5-coordinate geometry to one Se(2), one Se(4), one Se(5), and two equivalent Se(6) atoms. The Te(3)-Se(2) bond length is 2.72 Å. The Te(3)-Se(4) bond length is 2.73 Å. The Te(3)-Se(5) bond length is 2.61 Å. There is one shorter (3.06 Å) and one longer (3.17 Å) Te(3)-Se(6) bond length. There are eight inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted L-shaped geometry to one Hf(1) and one Te(2) atom. In the second Se site, Se(2) is bonded in a water-like geometry to one Te(1) and one Te(3) atom. In the third Se site, Se(3) is bonded in a 3-coordinate geometry to one Te(2) and two equivalent Te(1) atoms. In the fourth Se site, Se(4) is bonded in a bent 120 degrees geometry to one Te(2) and one Te(3) atom. In the fifth Se site, Se(5) is bonded in a distorted water-like geometry to one Hf(1) and one Te(3) atom. In the sixth Se site, Se(6) is bonded in a 4-coordinate geometry to two equivalent Hf(1) and two equivalent Te(3) atoms. In the seventh Se site, Se(7) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Hf(1) and one Te(2) atom. In the eighth Se site, Se(8) is bonded in a water-like geometry to one Te(1) and one Te(2) atom.