The small binding energies of the negative cluster ions: SF5−(SF6)1, SF6−(SF6)1 and F−(SF6)n (n = 1 and 2), in the gas phase

The gas-phase clustering reactions of SF5−, SF6− and F− ions with SF6 were measured using a high-pressure mass spectrometer. The bond energies of SF5−(SF6)1 and SF6−(SF6)1 were estimated to be ⩽2.3 kcal/mol. The bond energies of F−(SF6)n with n = 1 and 2 were determined to be 5.4 and ≈4.1 kcal/mol, respectively. This result indicates that the SF6 molecule is the weakest electrophilic reagent toward F− ever reported. This is mainly due to the exchange repulsion between the negative ions and fluorine atoms surrounding the reactive S atom. The structure of the cluster ion F−(SF6)1 whose binding energy was surrrisingly small was investigated by ab initio MO calculations.