A computational study of arene coordination to singly- and doubly-charged iron atoms

Abstract

Ab initio calculations at the B3LYP level of theory are reported on a set of mono- and doubly-charged complexes [Fe(L)(L′)]+,2+, where L, L′ = benzene (Bz) or pyridine (Py). Benzene is found to bind via its π electrons, with pyridine forming σ complexes, although local minima have been found with π-bonded pyridine. Overall, a reasonable agreement is found with available experimental data, with two possible interesting exceptions where the error may be with the mass spectrometric experiments. Thus, the kinetic method applied to the metastable decomposition of the [Fe(Bz)(Py)]+ cation predicts the Fe+ bond energies to Bz and Py to be nearly identical. Computation suggests that Py is bound 10 to 30 kJ mol−1 more strongly to Fe+ than is Bz. A more confident prediction from theory is that charge-stripping determination of second ionisation energies for large monocations such as [Fe(Bz)2]+ and [Fe(Py)2]+ tends to give overestimated results; the discrepancy between our computed values and the experimental values, of roughly 2 eV, exceeds the likely inaccuracy of the computations.