NiCr2Se4 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 CrSe6 octahedra that share corners with six equivalent Ni(1)Se6 octahedra, edges with six equivalent Cr(1)Se6 octahedra, and  a faceface with one Ni(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-53°. Ni(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form NiSe6 octahedra that share corners with twelve equivalent Cr(1)Se6 octahedra, edges with two equivalent Ni(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 to three equivalent Cr(1) and two equivalent Ni(1) atoms to form a mixture of distorted corner and edge-sharing SeCr3Ni2 trigonal bipyramids. In the second Se site, Se(1) is bonded in a rectangular see-saw-like geometry to three equivalent Cr(1) and one Ni(1) atom.
NiCr2Se4 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 CrSe6 octahedra that share corners with six equivalent Ni(1)Se6 octahedra, edges with six equivalent Cr(1)Se6 octahedra, and  a faceface with one Ni(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-53°. There are two shorter (2.48 Å) and one longer (2.49 Å) Cr(1)-Se(1) bond length. There is one shorter (2.55 Å) and two longer (2.59 Å) Cr(1)-Se(2) bond lengths. Ni(1) is bonded to two equivalent Se(1) and four equivalent Se(2) atoms to form NiSe6 octahedra that share corners with twelve equivalent Cr(1)Se6 octahedra, edges with two equivalent Ni(1)Se6 octahedra, and faces with two equivalent Cr(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 49-53°. Both Ni(1)-Se(1) bond lengths are 2.51 Å. All Ni(1)-Se(2) bond lengths are 2.51 Å. There are two inequivalent Se sites. In the first Se site, Se(2) is bonded to three equivalent Cr(1) and two equivalent Ni(1) atoms to form a mixture of distorted corner and edge-sharing SeCr3Ni2 trigonal bipyramids. In the second Se site, Se(1) is bonded in a rectangular see-saw-like geometry to three equivalent Cr(1) and one Ni(1) atom.