On the importance of the inclusion of the basis set superposition error counterpoise correction during optimization of ion-π complexes

Several complexes of hexafluorobenzene and trifluorobenzene with halide anions have been optimized using the HF, B3LYP and MP2 methods and either the 6-31++G∗∗ or 6-311++G∗∗ basis sets. The BSSE (basis set superposition error) counterpoise correction (CP) was included during the geometry optimization for all complexes at the six levels of theory. The results were compared with cation-π complexes of benzene and trifluorobenzene. The effect of inclusion of BSSE-CP correction during the optimization is very important in some anion-π complexes.