CoNi2S4 crystallizes in the monoclinic P2/m space group. Co(1) is bonded to two equivalent S(2) and four equivalent S(1) atoms to form CoS6 octahedra that share corners with four equivalent Ni(2)S6 octahedra, edges with two equivalent Co(1)S6 octahedra, edges with four equivalent Ni(1)S6 octahedra, and faces with two equivalent Ni(2)S6 octahedra. The corner-sharing octahedral tilt angles are 49°. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent S(1) and four equivalent S(2) atoms to form NiS6 octahedra that share corners with eight equivalent Ni(2)S6 octahedra, edges with two equivalent Ni(1)S6 octahedra, and edges with four equivalent Co(1)S6 octahedra. The corner-sharing octahedral tilt angles are 49°. In the second Ni site, Ni(2) is bonded to two equivalent S(2) and four equivalent S(1) atoms to form NiS6 octahedra that share corners with four equivalent Co(1)S6 octahedra, corners with eight equivalent Ni(1)S6 octahedra, edges with two equivalent Ni(2)S6 octahedra, and faces with two equivalent Co(1)S6 octahedra. The corner-sharing octahedral tilt angles are 49°. There are two inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Co(1), one Ni(1), and two equivalent Ni(2) atoms to form distorted SCo2Ni3 square pyramids that share corners with five equivalent S(1)Co2Ni3 square pyramids, corners with four equivalent S(2)CoNi3 trigonal pyramids, edges with four equivalent S(1)Co2Ni3 square pyramids, and edges with four equivalent S(2)CoNi3 trigonal pyramids. In the second S site, S(2) is bonded to one Co(1), one Ni(2), and two equivalent Ni(1) atoms to form distorted SCoNi3 trigonal pyramids that share corners with four equivalent S(1)Co2Ni3 square pyramids, corners with six equivalent S(2)CoNi3 trigonal pyramids, edges with four equivalent S(1)Co2Ni3 square pyramids, and  an edgeedge with one S(2)CoNi3 trigonal pyramid.
CoNi2S4 crystallizes in the monoclinic P2/m space group. Co(1) is bonded to two equivalent S(2) and four equivalent S(1) atoms to form CoS6 octahedra that share corners with four equivalent Ni(2)S6 octahedra, edges with two equivalent Co(1)S6 octahedra, edges with four equivalent Ni(1)S6 octahedra, and faces with two equivalent Ni(2)S6 octahedra. The corner-sharing octahedral tilt angles are 49°. Both Co(1)-S(2) bond lengths are 2.25 Å. All Co(1)-S(1) bond lengths are 2.30 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent S(1) and four equivalent S(2) atoms to form NiS6 octahedra that share corners with eight equivalent Ni(2)S6 octahedra, edges with two equivalent Ni(1)S6 octahedra, and edges with four equivalent Co(1)S6 octahedra. The corner-sharing octahedral tilt angles are 49°. Both Ni(1)-S(1) bond lengths are 2.41 Å. All Ni(1)-S(2) bond lengths are 2.26 Å. In the second Ni site, Ni(2) is bonded to two equivalent S(2) and four equivalent S(1) atoms to form NiS6 octahedra that share corners with four equivalent Co(1)S6 octahedra, corners with eight equivalent Ni(1)S6 octahedra, edges with two equivalent Ni(2)S6 octahedra, and faces with two equivalent Co(1)S6 octahedra. The corner-sharing octahedral tilt angles are 49°. Both Ni(2)-S(2) bond lengths are 2.35 Å. All Ni(2)-S(1) bond lengths are 2.37 Å. There are two inequivalent S sites. In the first S site, S(1) is bonded to two equivalent Co(1), one Ni(1), and two equivalent Ni(2) atoms to form distorted SCo2Ni3 square pyramids that share corners with five equivalent S(1)Co2Ni3 square pyramids, corners with four equivalent S(2)CoNi3 trigonal pyramids, edges with four equivalent S(1)Co2Ni3 square pyramids, and edges with four equivalent S(2)CoNi3 trigonal pyramids. In the second S site, S(2) is bonded to one Co(1), one Ni(2), and two equivalent Ni(1) atoms to form distorted SCoNi3 trigonal pyramids that share corners with four equivalent S(1)Co2Ni3 square pyramids, corners with six equivalent S(2)CoNi3 trigonal pyramids, edges with four equivalent S(1)Co2Ni3 square pyramids, and  an edgeedge with one S(2)CoNi3 trigonal pyramid.