Solvent and ligand effects on the structures of iron halide cations in the gas phase

The effects of the oxidation state, the ligand, and the solvent on structures and energetics of cationic iron complexes are investigated by means of electrospray-ionization mass spectrometry. Insights into the potential-energy surfaces of FeX+, FeX2+, and XFe(OCH3)(+) ions (X = F, Cl, Br, I) with a variable number of coordinated methanol molecules are obtained by means of collision experiments and complementary thermochemical considerations. It is shown that upon change of the halide ligand, the weakly solvated ions respond differentially to the increasing need for stabilization of the partial charge on the metal center. For example, whereas F2Fe(CH3OH)(n)(+) ions tend to lose mainly HF for n = 1-3, the loss of HBr is not observed at all for Br2Fe(CH3OH)(n)(+). Instead, the iron-bromide cations undergo reductive loss of atomic bromine. Cl2Fe(CH3OH)(n)(+) bears an intermediate position in that both reduction as well as elimination of HCl can occur.