FeCu3S8 is Pyrite-derived structured and crystallizes in the monoclinic P2_1/c space group. Fe(1) is bonded to two equivalent S(1), two equivalent S(2), and two equivalent S(4) atoms to form FeS6 octahedra that share corners with four equivalent Cu(2)S6 octahedra, corners with eight equivalent Cu(1)S6 octahedra, corners with two equivalent S(3)Cu3S tetrahedra, corners with two equivalent S(1)FeCu2S tetrahedra, and corners with two equivalent S(2)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 64-65°. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one S(1), one S(2), two equivalent S(3), and two equivalent S(4) atoms to form CuS6 octahedra that share corners with four equivalent Fe(1)S6 octahedra, corners with four equivalent Cu(1)S6 octahedra, corners with four equivalent Cu(2)S6 octahedra,  a cornercorner with one S(1)FeCu2S tetrahedra,  a cornercorner with one S(2)FeCu2S tetrahedra, corners with two equivalent S(3)Cu3S tetrahedra, and corners with two equivalent S(4)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 64-71°. In the second Cu site, Cu(2) is bonded to two equivalent S(1), two equivalent S(2), and two equivalent S(3) atoms to form CuS6 octahedra that share corners with four equivalent Fe(1)S6 octahedra, corners with eight equivalent Cu(1)S6 octahedra, corners with two equivalent S(1)FeCu2S tetrahedra, corners with two equivalent S(2)FeCu2S tetrahedra, and corners with two equivalent S(4)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 64-70°. There are four inequivalent S sites. In the first S site, S(1) is bonded to one Fe(1), one Cu(1), one Cu(2), and one S(1) atom to form distorted SFeCu2S tetrahedra that share  a cornercorner with one Fe(1)S6 octahedra,  a cornercorner with one Cu(1)S6 octahedra,  a cornercorner with one Cu(2)S6 octahedra, corners with two equivalent S(1)FeCu2S tetrahedra, corners with four equivalent S(3)Cu3S tetrahedra, corners with four equivalent S(4)FeCu2S tetrahedra, and corners with five equivalent S(2)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 69-79°. In the second S site, S(2) is bonded to one Fe(1), one Cu(1), one Cu(2), and one S(2) atom to form distorted SFeCu2S tetrahedra that share  a cornercorner with one Fe(1)S6 octahedra,  a cornercorner with one Cu(1)S6 octahedra,  a cornercorner with one Cu(2)S6 octahedra, corners with two equivalent S(2)FeCu2S tetrahedra, corners with four equivalent S(3)Cu3S tetrahedra, corners with four equivalent S(4)FeCu2S tetrahedra, and corners with five equivalent S(1)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 69-79°. In the third S site, S(3) is bonded to one Cu(2), two equivalent Cu(1), and one S(4) atom to form SCu3S tetrahedra that share  a cornercorner with one Fe(1)S6 octahedra, corners with two equivalent Cu(1)S6 octahedra, corners with three equivalent S(3)Cu3S tetrahedra, corners with four equivalent S(1)FeCu2S tetrahedra, corners with four equivalent S(2)FeCu2S tetrahedra, and corners with four equivalent S(4)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 71-78°. In the fourth S site, S(4) is bonded to one Fe(1), two equivalent Cu(1), and one S(3) atom to form distorted SFeCu2S tetrahedra that share  a cornercorner with one Cu(2)S6 octahedra, corners with two equivalent Cu(1)S6 octahedra, corners with three equivalent S(4)FeCu2S tetrahedra, corners with four equivalent S(3)Cu3S tetrahedra, corners with four equivalent S(1)FeCu2S tetrahedra, and corners with four equivalent S(2)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 71-76°.
FeCu3S8 is Pyrite-derived structured and crystallizes in the monoclinic P2_1/c space group. Fe(1) is bonded to two equivalent S(1), two equivalent S(2), and two equivalent S(4) atoms to form FeS6 octahedra that share corners with four equivalent Cu(2)S6 octahedra, corners with eight equivalent Cu(1)S6 octahedra, corners with two equivalent S(3)Cu3S tetrahedra, corners with two equivalent S(1)FeCu2S tetrahedra, and corners with two equivalent S(2)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 64-65°. Both Fe(1)-S(1) bond lengths are 2.30 Å. Both Fe(1)-S(2) bond lengths are 2.30 Å. Both Fe(1)-S(4) bond lengths are 2.30 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one S(1), one S(2), two equivalent S(3), and two equivalent S(4) atoms to form CuS6 octahedra that share corners with four equivalent Fe(1)S6 octahedra, corners with four equivalent Cu(1)S6 octahedra, corners with four equivalent Cu(2)S6 octahedra,  a cornercorner with one S(1)FeCu2S tetrahedra,  a cornercorner with one S(2)FeCu2S tetrahedra, corners with two equivalent S(3)Cu3S tetrahedra, and corners with two equivalent S(4)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 64-71°. The Cu(1)-S(1) bond length is 2.47 Å. The Cu(1)-S(2) bond length is 2.50 Å. There is one shorter (2.39 Å) and one longer (2.40 Å) Cu(1)-S(3) bond length. There is one shorter (2.46 Å) and one longer (2.49 Å) Cu(1)-S(4) bond length. In the second Cu site, Cu(2) is bonded to two equivalent S(1), two equivalent S(2), and two equivalent S(3) atoms to form CuS6 octahedra that share corners with four equivalent Fe(1)S6 octahedra, corners with eight equivalent Cu(1)S6 octahedra, corners with two equivalent S(1)FeCu2S tetrahedra, corners with two equivalent S(2)FeCu2S tetrahedra, and corners with two equivalent S(4)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 64-70°. Both Cu(2)-S(1) bond lengths are 2.46 Å. Both Cu(2)-S(2) bond lengths are 2.46 Å. Both Cu(2)-S(3) bond lengths are 2.44 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded to one Fe(1), one Cu(1), one Cu(2), and one S(1) atom to form distorted SFeCu2S tetrahedra that share  a cornercorner with one Fe(1)S6 octahedra,  a cornercorner with one Cu(1)S6 octahedra,  a cornercorner with one Cu(2)S6 octahedra, corners with two equivalent S(1)FeCu2S tetrahedra, corners with four equivalent S(3)Cu3S tetrahedra, corners with four equivalent S(4)FeCu2S tetrahedra, and corners with five equivalent S(2)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 69-79°. The S(1)-S(1) bond length is 2.09 Å. In the second S site, S(2) is bonded to one Fe(1), one Cu(1), one Cu(2), and one S(2) atom to form distorted SFeCu2S tetrahedra that share  a cornercorner with one Fe(1)S6 octahedra,  a cornercorner with one Cu(1)S6 octahedra,  a cornercorner with one Cu(2)S6 octahedra, corners with two equivalent S(2)FeCu2S tetrahedra, corners with four equivalent S(3)Cu3S tetrahedra, corners with four equivalent S(4)FeCu2S tetrahedra, and corners with five equivalent S(1)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 69-79°. The S(2)-S(2) bond length is 2.09 Å. In the third S site, S(3) is bonded to one Cu(2), two equivalent Cu(1), and one S(4) atom to form SCu3S tetrahedra that share  a cornercorner with one Fe(1)S6 octahedra, corners with two equivalent Cu(1)S6 octahedra, corners with three equivalent S(3)Cu3S tetrahedra, corners with four equivalent S(1)FeCu2S tetrahedra, corners with four equivalent S(2)FeCu2S tetrahedra, and corners with four equivalent S(4)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 71-78°. The S(3)-S(4) bond length is 2.05 Å. In the fourth S site, S(4) is bonded to one Fe(1), two equivalent Cu(1), and one S(3) atom to form distorted SFeCu2S tetrahedra that share  a cornercorner with one Cu(2)S6 octahedra, corners with two equivalent Cu(1)S6 octahedra, corners with three equivalent S(4)FeCu2S tetrahedra, corners with four equivalent S(3)Cu3S tetrahedra, corners with four equivalent S(1)FeCu2S tetrahedra, and corners with four equivalent S(2)FeCu2S tetrahedra. The corner-sharing octahedral tilt angles range from 71-76°.