Redox properties of charged and neutral iron chlorides FeCl mn (m = 1–3; n = −1, 0, +1, and +2)

Abstract

Electron transfer in high-energy collision experiments is used to probe the redox chemistry of the iron chlorides FeCl m n (m = 1–3; n = −1, 0, +1, and +2). These experiments comprise charge inversion of FeCl m − anions ( m = 2–4) to cations, charge inversion of FeCl m + cations ( m = 1–3) to anions, charge stripping of FeCl m + monocations ( m = 1–3) to dications, and charge exchange of FeCl m 2+ dications ( m = 1, 2) to monocations. Ab initio calculations at the B3LYP/6-311+G∗ level of theory are used to evaluate the differences between adiabatic and vertical electron transfers; the accuracy of the calculated absolute energies for the associated electron-transfer processes predicted at this level of theory is doubted, however. The experimentally determined redox properties of the iron chlorides are in fair agreement with literature thermochemistry; new data derived in this work are: IE(FeCl 3) = 10.9 eV, IE(FeCl +) = 15.9 ± 0.4 eV, IE(FeCl 2 +) = 17.6 ± 0.7 eV, and IE(FeCl 3 +) = 16.0 ± 0.4 eV. In addition, evidence for the existence of the chlorine complexes Fe(Cl 2) + and Fe(Cl 2) 2+ is presented. According to the experimental data, diatomic FeCl 2+ is a thermochemically stable dication, whereas FeCl 2 2+ and FeCl 3 2+ are metastable with respect to the dissociations into FeCl ( m−1) + + Cl + and FeCl ( m−2) + + Cl 2 + ( m = 2, 3). Except for the dications, the dissociation behavior of the FeCl m n species ( m = 1–3; n = −1, 0, +1) is dominated by sequential losses of chlorine atoms rather than expulsion of molecular chlorine.