Structure and Dynamics of Iron Pentacarbonyl

The dynamics of CO ligand scrambling in Fe­(CO)₅ has been investigated by linear infrared spectroscopy in supercritical xenon solution. The activation barrier for the Berry pseudorotation in Fe­(CO)₅ was determined experimentally to be E_a = 2.5 ± 0.4 kcal mol^–1 by quantitative analysis of the temperature-dependent spectral line shape. This compares well with the range of E_a/(kcal mol^–1) = 2.0 to 2.3 calculated by various DFT methods and the value of 1.6 ± 0.3 previously obtained from 2D IR measurements by Harris et al. (Science 2008, 319, 1820). The involvement of Fe­(CO)₅···Xe interactions in the ligand scrambling process was tested computationally at the BP86-D3/AE2 level and found to be negligible.