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Oxidation States in Fe and Cu Sulfides: Electroneutrality Requirements

This study explores the oxidation states of Fe and Cu in sulfides, specifically focusing on heazlewoodite, greigite, and cubanite. The findings challenge the conventional understanding of stoichiometry and oxidation states in sulfides.

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Oxidation States in Fe and Cu Sulfides: Electroneutrality Requirements

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  1. Bonded interactions in Fe and Cu Sulfides;Do electroneutrality requirements hold in the classical sense for sulfides? G.V. Gibbs1, David F. Cox2, Kevin M. Rosso3, Nancy L. Ross1 and Robert T. Downs4 1Department of Geosciences, Virginia Tech, Blacksburg, VA 24061 2Department of Chemical Engineering, Virginia Tech, Blacksburg, VA 24061 3William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratories, Richland, Washington 99352 4Department of Geosciences, University of Arizona, Tucson, AZ, 85721.

  2. A representative block of the heazlerwoodite structure: Three NiS4 tetrahedra sharing a common edge S 2.498Å Chemical Formula Ni3S2 Ni Ni-Ni bond path Bulk Ni metal R(Ni-Ni) 2.492Å What are the oxidation states of Ni and S? Gibbs, Cox, Ross, Rosso, Downs and Prewitt (2005) J. Phys. Chem.,

  3. Ni-S Ni-Ni S-S Comparison of experimental and theoretical bond critical points properties for the Ni-S, Ni-Ni and S-S bonded interactions for heazlewoodite, Ni3S2 Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (2007) Spackman, Gibbs and Downs (Experimental, In prep.)

  4. S Fe2+ S2 dimer connected by bond path with a bond critical point Fe2+ marcasite, FeS2 ls pyrite, FeS2 ls Fe2+,Fe3+ Fe3+ Fe2+ hs troilite, FeS greigite, Fe3+Fe2+Fe3+S4

  5. Smythite Fe3S4

  6. Cu Fe Cu Fe cubanite, CuFe2S3 chalcopyrite, CuFeS2

  7. Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted) VIFehs2+- S IVFehs2+?- S VIFels2+- S IVFehs3+- S

  8. Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted) VIFehs2+- S IVFehs2+?- S VIFels2+- S IVFehs3+- S

  9. Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted) VIFehs2+- S IVFehs2+?- S VIFels2- - S IVFehs3+- S

  10. X-ray photoemission and L2,3 - edge X-ray absorption spectra recently determined by Pearse et al. (2006) show that the Fe atom in chalcopyrite is unequivocally Fe3+ ‘Given that Fe is trivalent in chalcopyrite, ‘What are the oxidation states of the Fe atoms comprising greigite and cubanite?’

  11. Hoggins and Steinfink (1976) predicted the oxidation state for the Fe atom in greigite to be Fe3.92+ and that for chalcopyrite and cubanite to be Fe2.79+ and Fe2.77+, respectively.

  12. Bob Shannon (1981) observed that a Fe-S bond valence-bond length connection predicts a IVFe4+-S bond length of 2.144 Å compared with that observed 2.147Å for greigite. He concluded that the oxidation state of Fe atom in greigite is Fe4+

  13. Fe4+ is known but it is rare and an unlikely state! But there exist materials like FeS2 and Ba3FeS5 which must contain Fe4+ if electrical neutrality requirements hold and (2) only S-2 anions are only present.

  14. Neutron diffraction and Mössbauer studies show that the two edge sharing tetrahedra in cubanite are inversion center equivalent. Mössbauer spectrum indicates that the Fe atom in cubanite has an oxidation state of Fe2.5+ with a chemical formula CuFe2.5+Fe2.5+S3. (McCammon, 1995)

  15. Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted) VIFehs2+- S IVFehs2.5?- S Fels2+ - S IVFehs3+- S IVFehs4+?- S

  16. H4Fe4+S4 H S R(H-S) = 1.349 Å <S –Fe –S = 108.30o 2x <S –Fe –S = 110.06o 4x <Fe –S –H = 99.70o R(Fe-S) (opt) = 2.130 Å Fe4+ R(Fe-S) (greigite) = 2.147Å Structure of the molecule (S4 point group) geometry optimized at the B3LYP/6-311++G(2d,p) level.

  17. Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted) VIFehs2+- S IVFehs2.5+?- S VIFels2+- S IVFehs3+- S IVFehs4+?- S

  18. Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted) VIFehs2+- S IVFehs2.5+?- S VIFels2+- S IVFehs3+ - S IVFehs4+?- S

  19. Gibbs, Cox, Ross, Rosso and Downs, J. Phys. Chem. (accepted) VIFehs2+- S IVFehs2.5+?- S IVFehs3+- S VIFels2+- S IVFehs4+?- S

  20. Comments The properties of low spin VIFe-S bonded interactions are distinct from those of high spin VIFe-S bonded interactions. For the low spin VIFe-S bonded interactions, (1) Fe-S bond lengths are shorter, (2) ρ(rc ) is larger, (3) the bonded radii are smaller, (4) the Fe and S atomic charges are smaller.

  21. The presence of Fe4+ in greigite is consistent with • the metastability of greigite, • (2) the difficulty of its synthesis, • (3) the predicted oxidation state of 3.92+, • (4) its short observed IVFe-S bond length and • (5) the properties calculated for the H4Fe4+S4.

  22. What is the status of the Fe atom in cubanite? CuFe2.5+Fe2.5+S3? CuFe2+Fe3+S3 with Fe2+,Fe3+ disorder? None of the above?

  23. The evidence suggests that a simple connection between stoichiometry and oxidation state is not always a virtue of sulfides in the classical sense!

  24. Congratulations Alex for the many elegant contributions that you have made to our science. 

  25. Gibbs, Cox, Ross, Rosso (2006) J. Chemical Physics Shared bonded interaction Intermediate bonded interaction IVFe4+?-S ViFe2+-S IVFe3+?-S Closed-shell bonded interaction

  26. Gibbs, Cox, Ross, Rosso (2006) J. Chemical Physics G(rc) Mg-O Na-O Si-O P-O H(rc) Al-O V(rc) S-O

  27. Gibbs, Cox, Ross, Rosso (2006) J. Chemical Physics IVFe4+-S VIFe2+-S IVFe3+-S

  28. Given that a bonded interaction is shared when ¼2(rc) = 2G(rc) + V(rc)  0 and that a bonded interaction is closed when H(rc) = G(rc) + V(rc) ≥ 0. then 2G(rc) + V(rc)= 0 |V(rc)| /G(rc) ≥ 2 and G(rc) + V(rc)= 0,  |V(rc)| /G(rc)  1. A bonded interaction is classified as shared when |V(rc)| /G(rc) ≥ 2, closed-shell when |V(rc)| /G(rc)  1 and intermediate when 1 < |V(rc)| /G(rc)< 2.

  29. S Fe-S bcp Fe2+ S-S bcp

  30. Gibbs, Jayatililaka, Spackman, Cox and Rosso (2006) J. Phys. Chem.

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