Metal atom motional anisotropy in iron organometallics: the Golʹdanskii–Karyagin effect in a dinuclear iron tetrahydrido complex Original Research Article

Temperature-dependent 57Fe Mössbauer effect spectroscopy has been used over the interval 4.2≤T≤300 K to determine the hyperfine interactions in [{(η5-C5(CH3)5)Fe}2(μ-H)4], and to elucidate the dynamical behavior of the two metal atoms in this solid. The isomer shift (IS) (at 90 K) is 0.27 mm s−1 smaller than that of ferrocene [(η5-C5H5)Fe] at the same temperature, diagnostic of a larger s-electron density at the Fe nucleus in the former, compared to the latter. The quadrupole splitting is nearly temperature independent over the above range. The iron atom motion is strongly anisotropic, even at low temperatures, and the temperature-dependent recoil-free fraction data and the corresponding intensity asymmetry data extracted from the Mössbauer spectra permit an evaluation of the difference in the mean-square-amplitude of vibration parallel and perpendicular to the molecular symmetry axis passing through the two Fe atoms and the two Cp rings.