Mössbauer spectra, structure, and bonding in iron carbonyl derivatives

Abstract

The Mössbauer spectra of the mono-, di-, tri- and tetra-nuclear iron carbonyl anions and carbonyl hydride anions are reported and compared with the known spectra of the neutral binary carbonyls. Increase in anionic charge in the sequence 0, –1, –2 results in progressively lower values of chemical isomer shift δ for each series. In addition, there is a systematic increase in δ as the co-ordination number of iron increases from 4 to 7. These trends are interpreted in terms of changes in the bonding in these compounds. Systematic variations in the quadrupole splitting Δ are also discussed. The effects on δ and Δ of substituting carbon monoxide by tertiary phosphines are investigated and the structure and bonding in the unusual new compound [(OC)₃FePMe₂Ph]₃ are discussed. The Mössbauer spectra of the tetrameric species [π-C₅H₅FeCO]₄ and [π-C₅H₅FeCO]⁺ ₄ are also investigated.