FeNb2S4 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one S(2), two equivalent S(4), and three equivalent S(1) atoms to form distorted edge-sharing NbS6 octahedra. In the second Nb site, Nb(2) is bonded in a 7-coordinate geometry to one S(1), one S(4), two equivalent S(2), and three equivalent S(3) atoms. Fe(1) is bonded in a 7-coordinate geometry to one S(4), two equivalent S(1), two equivalent S(2), and two equivalent S(3) atoms. There are four inequivalent S sites. In the first S site, S(1) is bonded to one Nb(2), three equivalent Nb(1), and two equivalent Fe(1) atoms to form distorted SNb4Fe2 octahedra that share corners with three equivalent S(4)Nb3Fe trigonal pyramids, edges with four equivalent S(1)Nb4Fe2 octahedra, and edges with three equivalent S(4)Nb3Fe trigonal pyramids. In the second S site, S(2) is bonded in a 5-coordinate geometry to one Nb(1), two equivalent Nb(2), and two equivalent Fe(1) atoms. In the third S site, S(3) is bonded in a 5-coordinate geometry to three equivalent Nb(2) and two equivalent Fe(1) atoms. In the fourth S site, S(4) is bonded to one Nb(2), two equivalent Nb(1), and one Fe(1) atom to form SNb3Fe trigonal pyramids that share corners with three equivalent S(1)Nb4Fe2 octahedra, corners with two equivalent S(4)Nb3Fe trigonal pyramids, and edges with three equivalent S(1)Nb4Fe2 octahedra. The corner-sharing octahedral tilt angles range from 19-35°.
FeNb2S4 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one S(2), two equivalent S(4), and three equivalent S(1) atoms to form distorted edge-sharing NbS6 octahedra. The Nb(1)-S(2) bond length is 2.63 Å. Both Nb(1)-S(4) bond lengths are 2.49 Å. There are two shorter (2.56 Å) and one longer (2.62 Å) Nb(1)-S(1) bond length. In the second Nb site, Nb(2) is bonded in a 7-coordinate geometry to one S(1), one S(4), two equivalent S(2), and three equivalent S(3) atoms. The Nb(2)-S(1) bond length is 2.72 Å. The Nb(2)-S(4) bond length is 2.62 Å. Both Nb(2)-S(2) bond lengths are 2.61 Å. All Nb(2)-S(3) bond lengths are 2.52 Å. Fe(1) is bonded in a 7-coordinate geometry to one S(4), two equivalent S(1), two equivalent S(2), and two equivalent S(3) atoms. The Fe(1)-S(4) bond length is 2.31 Å. Both Fe(1)-S(1) bond lengths are 2.64 Å. Both Fe(1)-S(2) bond lengths are 2.48 Å. Both Fe(1)-S(3) bond lengths are 3.08 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded to one Nb(2), three equivalent Nb(1), and two equivalent Fe(1) atoms to form distorted SNb4Fe2 octahedra that share corners with three equivalent S(4)Nb3Fe trigonal pyramids, edges with four equivalent S(1)Nb4Fe2 octahedra, and edges with three equivalent S(4)Nb3Fe trigonal pyramids. In the second S site, S(2) is bonded in a 5-coordinate geometry to one Nb(1), two equivalent Nb(2), and two equivalent Fe(1) atoms. In the third S site, S(3) is bonded in a 5-coordinate geometry to three equivalent Nb(2) and two equivalent Fe(1) atoms. In the fourth S site, S(4) is bonded to one Nb(2), two equivalent Nb(1), and one Fe(1) atom to form SNb3Fe trigonal pyramids that share corners with three equivalent S(1)Nb4Fe2 octahedra, corners with two equivalent S(4)Nb3Fe trigonal pyramids, and edges with three equivalent S(1)Nb4Fe2 octahedra. The corner-sharing octahedral tilt angles range from 19-35°.