LAUSR

Weakening and leveling of the halogen bond (XB) between diiodoperfluoroalkane (DIPFA) and halide anions (X−, X = Cl, Br and I) are imposed by solvent polarity. The solvents involved in this system are classified into three groups according to the acceptor number (AN) and solvent HB acidity (α) and were studied in detail. In non-competitive solvents, the strength of C–I···X− XB is strongest, decreasing with electrostatic interaction in the order: C–I···Cl− > C–I···Br− > C–I···I−. However, in weakly competitive solvents, the XB strength is largely weakened. Further, in strongly competitive solvents, the XB strength is leveled with no change occurring with X−. This phenomenon can be attributed to the solvent effect. That is, the solvent can destabilize the DIPFA···X− XB. This was confirmed by the experiment showing that the XB was destroyed as very small amounts of water was added into the CH3CN solution of DIPFA and X−.