NMR spectroscopic characterization of the two isomers of [HFe4(CO)13]-

Article abstract of DOI:10.1021/om00083a019

Low-temperature ¹³C and ¹H NMR spectra of [HFe₄(CO)₁₃]^- demonstrate the presence of two distinct hydride species which are in equilibrium at room temperature. One of these displays a ¹H NMR resonance at -24.9 ppm and is assigned to a butterfly geometry for the Fe₄ framework while the other has a ¹H resonance at -16.9 ppm and appears to be due to a closed Fe₄ tetrahedron. Both species begin to equilibrate at approximately -30°C. The low-temperature, -80°C, ¹³C NMR spectrum of the species which is assigned the butterfly geometry is in full accord with the previously determined X-ray structure. The proposed tetrahedral isomer of [HFe₄(CO)₁₃]^- displays a single ¹³C resonance at 216.7 ppm, indicating rapid fluxional behavior down to the lowest temperatures studied (-80°C). ¹⁷O NMR spectra were obtained, but they do not provide further insight into the nature of the two isomers.