Molecular Structures and Electronic Structures of Transition-Metal Mixed-Sandwich Complexes, [CpFe(II)(PhX)](+1) and Ferrocene

The local structures of the transition-metal mixed-sandwich complexes, [CpFe(Il)(PhX)](+1), (Cp =η5- cyclopentadienyl ; PhX =η6-benzene and its derivatives), have been studied by EXAFS and density-functional theory (DFT). Fe K-edge EXAFS spectra were measured at 10K and analysed by a two-shell model, and DFT calculations were made to predict more detailed molecular structures. Both methods give the Fe-C distance of ferrocene in good agreement with electron diffraction in gas phase. For the mixed-sandwich complexes, EXAFS and DFT provide similar structures that the Fe-C distance in the Ph-pyramid is slightly longer than that in the Cp-pyramid for all the derivatives except the [CpFe(C6(CH3)6)](+) complex. It is found by DFT that the Fe-C(X) distance in the PhX-pyramid changes depending on whether the substituent X is an electron donnor or an electron acceptor. We discuss the dependence from the valence MO's and the Mulliken population analysis