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

Z. Naturforsch. 42b, 573-578 (1987); eingegangen am 8. Januar 1987 Phosphinetetracarbonyliron, Phosphitetetracarbonyliron, IR Spectra, P NMR Spectra, Fe Mössbauer Spectra A series of trigonal bipyramidal Fe(CO)4L complexes has been prepared and characterized by infrared, Fe Mössbauer and P 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 cr-donor capability of the phosphine or phosphite ligand is offset by the ^•-acceptor capability. The formation of Fe(CO)4L complexes from the corresponding free ligands is accompanied by a downfield shift of P NMR chemical shifts. The coordination shifts are linearly correlated with the Mössbauer isomer shifts.