Hyperfine Interactions and Metal Atom Dynamic Effects of Pentafluorophenyl Substituents on Ferrocene Complexes

Abstract

Seven ferrocenyl complexes, in which one or more of the Cp ring protons have been substituted by strongly electron-withdrawing pentafluorophenyl groups, have been examined by temperature-dependent ⁵⁷Fe Mössbauer spectroscopy (MES) to determine both the electronic and dynamic effects of such substitution. The mean-square-vibrational-amplitudes of the metal atom have been expressed in terms of the dimensionless parameter ₣_z,T=k²<x_ave²>, where z=M for the Mössbauer data, z=X for the X-ray data, k is the wave vector of the gamma radiation, and <x_ave²> is the mean square amplitude of the metal atom vibration. The differences between the M and X values can be related to the effects of local (atomic) and non-local (molecular) contributions to the metal atom dynamics. The MES data also elucidate the vibrational anisotropy of the metal atom motion, which in all of the complexes examined is isotropic within the experimental error.