Infrared, 57Fe Mössbauer, and 31P NMR Spectroscopic Characterization of Fe(CO)4L (L = Phosphine and Phosphite)

Abstract

A series of trigonal bipyramidal Fe(CO)4L complexes has been prepared and characterized by infrared, 57Fe Mössbauer and 31P NMR spectroscopy. A linear correlation, with a negative slope, between the CO stretching frequencies and the isomer shifts demonstrates that the triple bond nature of the carbonyl ligands is strengthened with increasing iron-to-phosphorus back donation. The linear dependence of the quadrupole splittings on the isomer shifts with a positive slope has revealed that the σ-donor capability of the phosphine or phosphite ligand is offset by the π-acceptor capability. The formation of Fe(CO)4L complexes from the corresponding free ligands is accompanied by a downfield shift of 31P NMR chemical shifts. The coordination shifts are linearly correlated with the Mössbauer isomer shifts. © 1987, IEEE. All rights reserved.