Studies of the bonding in iron(II) cyclopentadienyl and arene sandwich compounds. Part 2. Correlations and interpretations of carbon-13 and iron-57 nuclear magnetic resonance and iron-57 mössbauer data
Carbon-13 NMR data for [Fe(η-C5H5)(η-C5H4X)] and [Fe(η-C5H5)(η-C6H5X)]+ and 57Fe NMR data for neutral substituted ferrocenes, ferrocenyl carbenium ions and ferrocenophanes have been analysed and correlations between these data sets and those of the 57Fe Mössbauer quadrupole splitting (q.s.) are discussed on the basis of concepts put forward previously. For substituted neutral ferrocenes there is a linear relationship between q.s. and chemical shift δ(57Fe). For ferrocenyl carbenium ions the relationship suggests a change in structure and bonding from species like [Fe(η-C5H5)(η-C5H4[graphic omitted]CMe2)] to the more fulvenoid structure [Fe(η-C5H5)(C5H4CH2)]+. Bridged ferrocenes (ferrocenophanes) show effects which are associated with ring tilting.