Redox properties of charged and neutral iron chlorides FeClmn (m = 1-3; n = -1, 0, +1, and +2)

Electron transfer in high-energy collision experiments is used to probe the redox chemistry of the iron chlorides FeClmn (m = 1-3; n = - 1, 0, + 1, an d + 2). These experiments comprise charge inversion of FeClm- anions (m = 2 -4) to cations, charge inversion of FeClm+ cations (m = 1-3) to anions, cha rge stripping of FeClm+ monocations (m = 1-3) to dications, and charge exch ange of FeClm2+ 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 cal culated absolute energies for the associated electron-transfer processes pr edicted at this level of theory is doubted, however. The experimentally det ermined redox properties of the iron chlorides are in fair agreement with l iterature thermochemistry; new data derived in this work are: IE(FeCl3) = 1 0.9 eV, IE(FeCl+) = 15.9 +/- 0.4 eV, IE(FeCl2+) = 17.6 +/- 0.7 eV, and IE(F eCl3+) = 16.0 +/- 0.4 eV. In addition, evidence for the existence of the ch lorine complexes Fe(Cl-2)(+) and Fe(Cl-2)(2+) is presented. According to th e experimental data, diatomic FeCl2+ is a thermochemically stable dication, whereas FeCl22+ and FeCl32+ are metastable with respect to the dissociatio ns into FeCl(m - 1)+ + Cl+ and FeCl(m - 2)+ + Cl-2(+) (m = 2, 3). Except fo r the dications, the dissociation behavior of the FeClmn species (m = 1-3; n = -1, 0, + 1) is dominated by sequential Posses of chlorine atoms rather than expulsion of molecular chlorine. (C) 1999 Elsevier Science B.V.