Gd2HfS5 crystallizes in the orthorhombic Pnma space group. Gd(1) is bonded in a 8-coordinate geometry to two equivalent S(1), two equivalent S(2), two equivalent S(3), and two equivalent S(4) atoms. Hf(1) is bonded to one S(2), one S(3), one S(4), and four equivalent S(1) atoms to form distorted edge-sharing HfS7 pentagonal bipyramids. There are four inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Gd(1) and two equivalent Hf(1) atoms to form distorted SGd2Hf2 trigonal pyramids that share corners with four equivalent S(3)Gd4Hf square pyramids, corners with two equivalent S(2)Gd4Hf trigonal bipyramids, corners with two equivalent S(4)Gd4Hf trigonal bipyramids, corners with six equivalent S(1)Gd2Hf2 trigonal pyramids,  an edgeedge with one S(3)Gd4Hf square pyramid, edges with two equivalent S(2)Gd4Hf trigonal bipyramids, edges with two equivalent S(4)Gd4Hf trigonal bipyramids, and  an edgeedge with one S(1)Gd2Hf2 trigonal pyramid. In the second S site, S(2) is bonded to four equivalent Gd(1) and one Hf(1) atom to form distorted SGd4Hf trigonal bipyramids that share corners with five equivalent S(3)Gd4Hf square pyramids,  a cornercorner with one S(4)Gd4Hf trigonal bipyramid, corners with four equivalent S(2)Gd4Hf trigonal bipyramids, corners with four equivalent S(1)Gd2Hf2 trigonal pyramids, edges with two equivalent S(3)Gd4Hf square pyramids, edges with four equivalent S(4)Gd4Hf trigonal bipyramids, and edges with four equivalent S(1)Gd2Hf2 trigonal pyramids. In the third S site, S(3) is bonded to four equivalent Gd(1) and one Hf(1) atom to form SGd4Hf square pyramids that share corners with four equivalent S(4)Gd4Hf trigonal bipyramids, corners with five equivalent S(2)Gd4Hf trigonal bipyramids, corners with eight equivalent S(1)Gd2Hf2 trigonal pyramids, edges with two equivalent S(3)Gd4Hf square pyramids,  an edgeedge with one S(4)Gd4Hf trigonal bipyramid, edges with two equivalent S(2)Gd4Hf trigonal bipyramids, edges with two equivalent S(1)Gd2Hf2 trigonal pyramids, and  a faceface with one S(4)Gd4Hf trigonal bipyramid. In the fourth S site, S(4) is bonded to four equivalent Gd(1) and one Hf(1) atom to form distorted SGd4Hf trigonal bipyramids that share corners with four equivalent S(3)Gd4Hf square pyramids,  a cornercorner with one S(2)Gd4Hf trigonal bipyramid, corners with four equivalent S(4)Gd4Hf trigonal bipyramids, corners with four equivalent S(1)Gd2Hf2 trigonal pyramids,  an edgeedge with one S(3)Gd4Hf square pyramid, edges with four equivalent S(2)Gd4Hf trigonal bipyramids, edges with four equivalent S(1)Gd2Hf2 trigonal pyramids, and  a faceface with one S(3)Gd4Hf square pyramid.
Gd2HfS5 crystallizes in the orthorhombic Pnma space group. Gd(1) is bonded in a 8-coordinate geometry to two equivalent S(1), two equivalent S(2), two equivalent S(3), and two equivalent S(4) atoms. There is one shorter (2.86 Å) and one longer (2.87 Å) Gd(1)-S(1) bond length. There is one shorter (2.88 Å) and one longer (3.00 Å) Gd(1)-S(2) bond length. There is one shorter (2.86 Å) and one longer (2.87 Å) Gd(1)-S(3) bond length. There is one shorter (2.83 Å) and one longer (2.88 Å) Gd(1)-S(4) bond length. Hf(1) is bonded to one S(2), one S(3), one S(4), and four equivalent S(1) atoms to form distorted edge-sharing HfS7 pentagonal bipyramids. The Hf(1)-S(2) bond length is 2.66 Å. The Hf(1)-S(3) bond length is 2.71 Å. The Hf(1)-S(4) bond length is 2.58 Å. There are two shorter (2.51 Å) and two longer (2.65 Å) Hf(1)-S(1) bond lengths. There are four inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Gd(1) and two equivalent Hf(1) atoms to form distorted SGd2Hf2 trigonal pyramids that share corners with four equivalent S(3)Gd4Hf square pyramids, corners with two equivalent S(2)Gd4Hf trigonal bipyramids, corners with two equivalent S(4)Gd4Hf trigonal bipyramids, corners with six equivalent S(1)Gd2Hf2 trigonal pyramids,  an edgeedge with one S(3)Gd4Hf square pyramid, edges with two equivalent S(2)Gd4Hf trigonal bipyramids, edges with two equivalent S(4)Gd4Hf trigonal bipyramids, and  an edgeedge with one S(1)Gd2Hf2 trigonal pyramid. In the second S site, S(2) is bonded to four equivalent Gd(1) and one Hf(1) atom to form distorted SGd4Hf trigonal bipyramids that share corners with five equivalent S(3)Gd4Hf square pyramids,  a cornercorner with one S(4)Gd4Hf trigonal bipyramid, corners with four equivalent S(2)Gd4Hf trigonal bipyramids, corners with four equivalent S(1)Gd2Hf2 trigonal pyramids, edges with two equivalent S(3)Gd4Hf square pyramids, edges with four equivalent S(4)Gd4Hf trigonal bipyramids, and edges with four equivalent S(1)Gd2Hf2 trigonal pyramids. In the third S site, S(3) is bonded to four equivalent Gd(1) and one Hf(1) atom to form SGd4Hf square pyramids that share corners with four equivalent S(4)Gd4Hf trigonal bipyramids, corners with five equivalent S(2)Gd4Hf trigonal bipyramids, corners with eight equivalent S(1)Gd2Hf2 trigonal pyramids, edges with two equivalent S(3)Gd4Hf square pyramids,  an edgeedge with one S(4)Gd4Hf trigonal bipyramid, edges with two equivalent S(2)Gd4Hf trigonal bipyramids, edges with two equivalent S(1)Gd2Hf2 trigonal pyramids, and  a faceface with one S(4)Gd4Hf trigonal bipyramid. In the fourth S site, S(4) is bonded to four equivalent Gd(1) and one Hf(1) atom to form distorted SGd4Hf trigonal bipyramids that share corners with four equivalent S(3)Gd4Hf square pyramids,  a cornercorner with one S(2)Gd4Hf trigonal bipyramid, corners with four equivalent S(4)Gd4Hf trigonal bipyramids, corners with four equivalent S(1)Gd2Hf2 trigonal pyramids,  an edgeedge with one S(3)Gd4Hf square pyramid, edges with four equivalent S(2)Gd4Hf trigonal bipyramids, edges with four equivalent S(1)Gd2Hf2 trigonal pyramids, and  a faceface with one S(3)Gd4Hf square pyramid.