Unveiling the Dual Nature of the Smallest Aqueous Ferrocene Complex

The structure of the ferrocene-water ((Cp)₂Fe:H₂O) complex has been characterized by combining state of the art rotational spectroscopy and computational chemistry. Two structures have been retrieved experimentally where water interacts with two distinguished binding sites, the exo Cp π cloud and the planetary-like planar orbit around iron. The spectra of both conformers exhibit significant averaging effects due to the nearly free rotational dynamics of water. This is in good agreement with the exploration of the potential energy surface of (Cp)₂Fe:H₂O. For water interacting with the exo Cp π cloud, we found three axial conformers giving rise to twenty minima with small internal rotation barriers. Theoretical calculations reveal two minima for the observed equatorial complex. Water interacts with ferrocene quite strongly, exhibiting binding energies above -11 kJ/mol in all binding sites and contributing to small deformations in the structure of bare ferrocene.