Structures for hypervalent anions KF3- and KF2- have been optimized at MP4SD(T)(full) and CCSD(T) with both 6-311+G(d) and 6-311+G(3df) basis sets. Anion KF3- is T-shaped and KF2- is linear. The calculated vertical electron detachment energy (VDE) for KF3- (6.83eV) is higher than that of the classical superhalogen anion KF2- (5.52eV). The lowest dissociation pathways are for KF3-, ΔH0°=23.3kcalmol −1 (products KF2- plus F) and for KF2-, ΔH0°=49.6kcalmol −1 (products KF plus F − ). KF32- (D 3h symmetry) is in a shallow minimum with a barrier to dissociation of 4.5kcalmol −1 (products KF2- plus F − ) and an overall exothermicity of 40.6kcalmol −1 .