CoCr2Se4 crystallizes in the monoclinic C2/m space group. Cr(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form distorted CrSe6 octahedra that share corners with six equivalent Co(1)Se6 octahedra, edges with six equivalent Cr(1)Se6 octahedra, and  a faceface with one Co(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-53°. Co(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form CoSe6 octahedra that share corners with twelve equivalent Cr(1)Se6 octahedra, edges with two equivalent Co(1)Se6 octahedra, and faces with two equivalent Cr(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-53°. There are two inequivalent Se sites. In the first Se site, Se(2) is bonded in a rectangular see-saw-like geometry to three equivalent Cr(1) and one Co(1) atom. In the second Se site, Se(1) is bonded to three equivalent Cr(1) and two equivalent Co(1) atoms to form a mixture of distorted corner and edge-sharing SeCr3Co2 square pyramids.
CoCr2Se4 crystallizes in the monoclinic C2/m space group. Cr(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form distorted CrSe6 octahedra that share corners with six equivalent Co(1)Se6 octahedra, edges with six equivalent Cr(1)Se6 octahedra, and  a faceface with one Co(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-53°. There is one shorter (2.60 Å) and two longer (2.61 Å) Cr(1)-Se(1) bond lengths. There are two shorter (2.49 Å) and one longer (2.50 Å) Cr(1)-Se(2) bond length. Co(1) is bonded to two equivalent Se(2) and four equivalent Se(1) atoms to form CoSe6 octahedra that share corners with twelve equivalent Cr(1)Se6 octahedra, edges with two equivalent Co(1)Se6 octahedra, and faces with two equivalent Cr(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-53°. Both Co(1)-Se(2) bond lengths are 2.47 Å. All Co(1)-Se(1) bond lengths are 2.50 Å. There are two inequivalent Se sites. In the first Se site, Se(2) is bonded in a rectangular see-saw-like geometry to three equivalent Cr(1) and one Co(1) atom. In the second Se site, Se(1) is bonded to three equivalent Cr(1) and two equivalent Co(1) atoms to form a mixture of distorted corner and edge-sharing SeCr3Co2 square pyramids.