Electrostatic field effects manifested in ferrocenyl metal complexes and the crystal structure of [Fe(η5-C5H5)(η5-C5H4CHNNHC5H4N)]·HCl

The structure of [Fe(η5-C5H5)(η5-C5H4CHNNHC5H4N)]·HCl (1·HCl) has been solved to R=0.05 and is described. The parent compound has been shown to act as a ligand for a range of M2+ cations in the form 1MCl2 (where M=Cd2+, Cu2+, Zn2+, Sn2+, Pd2+ and Fe2+). 57Fe Mössbauer spectroscopy has been used to probe the ferrocenyl iron electronic environments to give a ligandʹs eye view of the metal bonding. Two compounds of the formula [1M(H2O)4][PF6]2 where M=Fe2+ or Zn2+ were also prepared. The ferrocenyl quadrupole splittings of these two compounds were much smaller than those of the corresponding chloride. The change is explained in terms of the electric field experienced by the ferrocenyl iron atoms. In the chloride complexes the field from the M2+ is compensated by the chloride anions, whereas in the two [PF6]− salts the charge on the M2+ is not compensated in the first coordination sphere. The ferrocenyl iron is thus directly exposed to the M2+ charge and it is the effect of this that gives rise to the small quadrupole splitting value. This is the first time such a field effect has been observed on a ferrocenyl iron by Mössbauer spectroscopy. The coordination geometry of the inorganic iron(II) environment is also elucidated as tetrahedral in 1MCl2 and distorted octahedral in [LM(H2O)4][PF6]2.