CCL:G: Ferrocenium cation

["Dusan Petrovic" <dupet100,,hhu.de>]

 Sent to CCL by: "Dusan  Petrovic" [dupet100|hhu.de]
 Hi,
 While the calculation of ferrocene was rather straightforward (B3LYP/6-
 311++G** and LANL2DZ for iron), calculation of the ferrocenium ion (Fc+)
 generates problems.
 During Fc oxidation, one electron is removed from an orbital that formally
 belongs to iron (which should change iron's oxidation state from Fe+2 to
 Fe+3). Therefore, I expected that the partial charge on iron in Fc+ will be
 close to 1 (it was ~0 in Fc).
 Geometry optimization works well (I tried B3LYP, M06 and B97D functionals
 with either pure 6-311++G** or mixed 6-311++G**/ LANL2DZ with ECP in
 Gaussian). The cation multiplicity was set to 2, as the literature suggests
 a low spin state. However, calculated ESP charge on iron in Fc+ is negative,
 while hydrogen
 atoms have relatively high positive charge. Both restricted and unrestricted
 open shell calculations show very similar results (-0.033 for C, 0.165 for H
 and -0.315 for Fe).
 Contrary to that, semiempirical PM7 partial charges look more reasonable:
 -0.208 for C, 0.232 for H and 0.753 for Fe.
 What could be the cause of problems in the DFT calculations?
 Thanks,
 Dusan