Systematic Ligand Effects in the Reactions of Fe+(6D) and FeX+(5Δ) with CF3X (X = Cl, Br, I). Ion Mobility Measurements of FeX+(5Δ) (X = F, Cl, Br, I) in He.

The gas phase reactions of Fe+(6D) and FeX+(5Δ) with CF3X (X = Cl, Br, I) were examined using a selected-ion drift cell reactor under near-thermal energetic conditions. All reactions were carried out in a uniform electric field at a total pressure of 3.5 Torr at room temperature. In addition, reduced zero-field mobilities were measured for FeX+(5Δ) (X = F, Cl, Br, I) in He, yielding values of 14.2 ± 0.4, 13.7 ± 0.3, 13.3 ± 0.2, and 13.0 ± 0.3 cm2·V-1·s-1, respectively. Fe+(6D) reacts slowly with CF3Cl and CF3Br, producing an adduct exclusively with the former and FeBr+ with the latter. Conversely, Fe+(6D) exhibits efficient chemistry with CF3I to yield FeI+, FeCF3+, and FeFI+ in parallel reactions. Dependent on the halogen, FeX+(5Δ) reactions display one or more of four different processes: F- abstraction, X- abstraction, halogen switching, and association. In general, the presence of the halogen ligand enhances the rate of reaction over that of Fe+(6D) with the same molecular substrate. With CF3Cl, this ligand effect is observed to vary systematically with the electron-withdrawing capability of the halogen. This is illustrated by the correlation between reaction efficiency and the charge distribution on FeX+(5Δ) as determined from DFT calculations. Specific reaction outcomes for the FeX+(5Δ) reactions lead to upper and lower bounds on XFe-Y bond strengths (X, Y = F, Cl, Br, I) that are generally consistent with one another and with known trends.