Atomic and Molecular Motion in Iron Organometallics

Abstract

Temperature-dependent ⁵⁷Fe Mössbauer effect studies have been carried out on organge needle-shaped crystals of acetyl ferrocene over the range 90≤T≤350 K in an effort to elucidate the motional behavior of the metal atom up to temperatures near the melting point (359K). The spectra consist of one well resolved doublet at all temperatures, with an isomer shift of 0.554±0.002 and 0.438±0.001 mm s^-1 at 90 and 298K, respectively. The temperature dependence of the isomer shift corresponds to an effective vibrating mass of 74±2 daltons, and, in conjunction with the temperature dependence of the recoil-free fraction, to a Mössbauer lattice temperature of 134K. There is a small but significant vibrational anisotropy of the metal atom motion evident in the spectroscopic data above ∼ 200K.