Molecular rotation and lattice dynamical properties for cyclodextrin-ferrocene and some its ring-substituted derivative clathrates

This paper reports the unusual relaxation effect in the⁵⁷Fe Mössbauer spectra of -cyclodextrin(-cyclopentadienyl)(-ethylcyclopentadienyl)iron(II) clathrate. At low temperatures it consists of a simple quadrupole doublet. However, the Mössbauer spectrum collapses to a broad peak at 320 K. This behavior is interpreted in terms of a model that a ferrocene molecule in the cavity of clathrate lattices rotates as temperature is raised. The relaxation reaches a critical rate, a lifetime of the excited nuclear state. The relaxation time for the reorientation of (-cyclopentadienyl)(-ethylcyclopentadienyl)iron(II) in a cavity was 1.2×10^–7 s at 320 K and a barrier to rotation of about 8.8 KJ/mol was estimated.