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I’m trying to do some quantum chemical calculations for the linear molecule $\ce{FeP2}$ in the gas phase as well as its crystal (orthorhombic symmetry like here). I am lead to believe that in both cases iron has an oxidation state of +6, and phosphorous has an oxidation state of −3. My questions are:

  • Are such oxidation states a reasonable assumption for this molecule?
  • Would the molecule normally be a singlet (multiplicity of one)?
  • What quantum chemistry methods would be appropriate for this system?
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    $\begingroup$ While I find your question interesting, I'd also very much like to see your thoughts on the questions you pose and where exactly you have problems. $\endgroup$ – tschoppi Apr 13 '14 at 16:51
  • $\begingroup$ P.S. Welcome to Chem.SE! $\endgroup$ – tschoppi Apr 13 '14 at 16:52
  • $\begingroup$ Are my problems not clear from the question? I am mainly concerned with the oxidation state and spin configuration that could be assigned to this system, and aslo what minimal method from quantum chemistry I should use to tackle it. $\endgroup$ – Karol Apr 16 '14 at 3:35
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    $\begingroup$ The reference you provided states that FeP2 has marcasite-like structure. Marcasite is FeS2 polymorf with S2 units and Fe(II), so marcasite-type FeP2 likely has Fe(IV) This is a high value, but reasonably common for Fe-Ni in sulfide neighborhood, so FeP2 may have said formal oxidation state (since P is close neighboor of S). I would be very hesitant to use it for any consideration, though, since P is not very electronegative, so the real charge of Fe is likely very low. $\endgroup$ – permeakra Jun 29 '15 at 16:01
  • $\begingroup$ Your reference also specifically states that Fe has $d4$ configuration, it corresponds to +4 oxidation state. $\endgroup$ – permeakra Jun 29 '15 at 16:05
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Admittedly it is vacuum phase, but are you certain about your oxidation state assignments? "nearly temperature independent susceptibility of -(8.8±0.7)centerdot10-6SI (at room temperature)"

doi:10.1016/j.jpcs.2013.04.015
https://sciborg.uwaterloo.ca/~lfnazar/publications/Electrochem_Solid-State_Lett_6_8_A162-A165_2003.pdf
doi:10.1021/ja301173q
http://www.staff.uni-bayreuth.de/~bt220235/refs/HPR_29_235.pdf
doi:10.1088/0031-8949/4/3/010 (given)

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  • $\begingroup$ No, I am not sure at all. That is why I would like to do some calculations, and also why I raised the question... any other suggestions? $\endgroup$ – Karol Apr 13 '14 at 20:55
  • $\begingroup$ You might write an orbital diagram for the elements and push electron population into reasonable configurations. I'm happier with Fe(II). Elemental phosphorus is not a strong oxidizing agent. However, Vacuum phase has its own rules. $\endgroup$ – Uncle Al Apr 15 '14 at 19:48
  • $\begingroup$ Can phosphorous have an oxidation state of -1 in such phosphides? $\endgroup$ – Karol Apr 16 '14 at 3:32

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