Knowledge Bank

The molecular structure of iron pentacarbonyl has been studied by the gas-phase electron diffraction method. The conformation was found to be that of a trigonal bipyramid, in agreement with several earlier investigations. The axial Fe-C bonds were found to be shorter than the trigonal by 0.045 {\AA}; the values being $r(axial)=1.797$ {\AA} and $r(trigonal)=1.842$ {\AA}. The mean value of the $C=O$ bond lengths was found to be $1.136\pm 0.003$ {\AA}. It was found that the existence of shorter axial bonds is corroborated by the results of both X-ray crystallographic and vibrational spectroscopic studies. Considerations of the possible bonding situations in the molecule seem to be consistent with the existence of shorter axial Fe-C bonds.