Bonding, metal atom motion, and evidence for a phase transition in Fe metallocenes with a cyclo-P5 ligand

Temperature-dependent 57Fe Mössbauer spectroscopy has been employed to elucidate the relationship between the bonding, symmetry of the electrostatic field, and details of the metal atom motion between ferrocene (3) and two cyclo-pentaphospha homologues. Evidence is presented for the presence of a phase transition in solid [η5-Cp*Fe-η5-P5] (1) which is also observed in DSC scans over the appropriate temperature range. The dynamics of the ring motion in 1 is thought to account for the absence of long range order in this solid at room temperature. Differences in the electron distribution around the metal atom in several related ferrocene-type complexes are examined in detail.