HgCr2S4 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one S(1), two equivalent S(4), and three equivalent S(2) atoms to form a mixture of corner and edge-sharing CrS6 octahedra. The corner-sharing octahedral tilt angles range from 49-54°. In the second Cr site, Cr(2) is bonded to one S(4), two equivalent S(1), and three equivalent S(3) atoms to form a mixture of corner and edge-sharing CrS6 octahedra. The corner-sharing octahedral tilt angles range from 49-54°. Hg(1) is bonded in a 7-coordinate geometry to one S(1), two equivalent S(2), two equivalent S(3), and two equivalent S(4) atoms. There are four inequivalent S sites. In the first S site, S(1) is bonded to one Cr(1), two equivalent Cr(2), and one Hg(1) atom to form distorted SCr3Hg trigonal pyramids that share corners with six equivalent S(3)Cr3Hg2 trigonal bipyramids, corners with two equivalent S(1)Cr3Hg trigonal pyramids, and  an edgeedge with one S(3)Cr3Hg2 trigonal bipyramid. In the second S site, S(2) is bonded in a 3-coordinate geometry to three equivalent Cr(1) and two equivalent Hg(1) atoms. In the third S site, S(3) is bonded to three equivalent Cr(2) and two equivalent Hg(1) atoms to form distorted SCr3Hg2 trigonal bipyramids that share corners with six equivalent S(1)Cr3Hg trigonal pyramids, edges with four equivalent S(3)Cr3Hg2 trigonal bipyramids, and  an edgeedge with one S(1)Cr3Hg trigonal pyramid. In the fourth S site, S(4) is bonded in a 5-coordinate geometry to one Cr(2), two equivalent Cr(1), and two equivalent Hg(1) atoms.
HgCr2S4 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one S(1), two equivalent S(4), and three equivalent S(2) atoms to form a mixture of corner and edge-sharing CrS6 octahedra. The corner-sharing octahedral tilt angles range from 49-54°. The Cr(1)-S(1) bond length is 2.51 Å. Both Cr(1)-S(4) bond lengths are 2.44 Å. There is one shorter (2.34 Å) and two longer (2.40 Å) Cr(1)-S(2) bond lengths. In the second Cr site, Cr(2) is bonded to one S(4), two equivalent S(1), and three equivalent S(3) atoms to form a mixture of corner and edge-sharing CrS6 octahedra. The corner-sharing octahedral tilt angles range from 49-54°. The Cr(2)-S(4) bond length is 2.49 Å. Both Cr(2)-S(1) bond lengths are 2.38 Å. There is one shorter (2.37 Å) and two longer (2.44 Å) Cr(2)-S(3) bond lengths. Hg(1) is bonded in a 7-coordinate geometry to one S(1), two equivalent S(2), two equivalent S(3), and two equivalent S(4) atoms. The Hg(1)-S(1) bond length is 2.74 Å. Both Hg(1)-S(2) bond lengths are 3.01 Å. Both Hg(1)-S(3) bond lengths are 2.93 Å. Both Hg(1)-S(4) bond lengths are 2.87 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded to one Cr(1), two equivalent Cr(2), and one Hg(1) atom to form distorted SCr3Hg trigonal pyramids that share corners with six equivalent S(3)Cr3Hg2 trigonal bipyramids, corners with two equivalent S(1)Cr3Hg trigonal pyramids, and  an edgeedge with one S(3)Cr3Hg2 trigonal bipyramid. In the second S site, S(2) is bonded in a 3-coordinate geometry to three equivalent Cr(1) and two equivalent Hg(1) atoms. In the third S site, S(3) is bonded to three equivalent Cr(2) and two equivalent Hg(1) atoms to form distorted SCr3Hg2 trigonal bipyramids that share corners with six equivalent S(1)Cr3Hg trigonal pyramids, edges with four equivalent S(3)Cr3Hg2 trigonal bipyramids, and  an edgeedge with one S(1)Cr3Hg trigonal pyramid. In the fourth S site, S(4) is bonded in a 5-coordinate geometry to one Cr(2), two equivalent Cr(1), and two equivalent Hg(1) atoms.