# Bonding, multiplicity and quantum chemistry for FeP2

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?
• 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. – tschoppi Apr 13 '14 at 16:51
• P.S. Welcome to Chem.SE! – tschoppi Apr 13 '14 at 16:52
• 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. – Karol Apr 16 '14 at 3:35
• 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. – permeakra Jun 29 '15 at 16:01
• Your reference also specifically states that Fe has $d4$ configuration, it corresponds to +4 oxidation state. – permeakra Jun 29 '15 at 16:05