FeNi2S4 is Spinel-like structured and crystallizes in the orthorhombic Imma space group. Fe(1) is bonded to two equivalent S(1) and four equivalent S(2) atoms to form FeS6 octahedra that share corners with six equivalent Ni(1)S4 tetrahedra, edges with two equivalent Fe(1)S6 octahedra, and edges with four equivalent Ni(2)S6 octahedra. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form NiS4 tetrahedra that share corners with six equivalent Fe(1)S6 octahedra and corners with six equivalent Ni(2)S6 octahedra. The corner-sharing octahedral tilt angles range from 56-60°. 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 six equivalent Ni(1)S4 tetrahedra, edges with two equivalent Ni(2)S6 octahedra, and edges with four equivalent Fe(1)S6 octahedra. There are two inequivalent S sites. In the first S site, S(1) is bonded to one Fe(1), one Ni(1), and two equivalent Ni(2) atoms to form a mixture of distorted corner and edge-sharing SFeNi3 trigonal pyramids. In the second S site, S(2) is bonded in a rectangular see-saw-like geometry to two equivalent Fe(1), one Ni(1), and one Ni(2) atom.
FeNi2S4 is Spinel-like structured and crystallizes in the orthorhombic Imma space group. Fe(1) is bonded to two equivalent S(1) and four equivalent S(2) atoms to form FeS6 octahedra that share corners with six equivalent Ni(1)S4 tetrahedra, edges with two equivalent Fe(1)S6 octahedra, and edges with four equivalent Ni(2)S6 octahedra. Both Fe(1)-S(1) bond lengths are 2.25 Å. All Fe(1)-S(2) bond lengths are 2.25 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent S(1) and two equivalent S(2) atoms to form NiS4 tetrahedra that share corners with six equivalent Fe(1)S6 octahedra and corners with six equivalent Ni(2)S6 octahedra. The corner-sharing octahedral tilt angles range from 56-60°. Both Ni(1)-S(1) bond lengths are 2.16 Å. Both Ni(1)-S(2) bond lengths are 2.17 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 six equivalent Ni(1)S4 tetrahedra, edges with two equivalent Ni(2)S6 octahedra, and edges with four equivalent Fe(1)S6 octahedra. Both Ni(2)-S(2) bond lengths are 2.30 Å. All Ni(2)-S(1) bond lengths are 2.28 Å. There are two inequivalent S sites. In the first S site, S(1) is bonded to one Fe(1), one Ni(1), and two equivalent Ni(2) atoms to form a mixture of distorted corner and edge-sharing SFeNi3 trigonal pyramids. In the second S site, S(2) is bonded in a rectangular see-saw-like geometry to two equivalent Fe(1), one Ni(1), and one Ni(2) atom.