RI-MP2 and MPWB1K Study of π-Anion-π′ Complexes: MPWB1K Performance and Some Additivity Aspects

Several sandwich complexes of hexafluorobenzene, trifluorobenzene, s-triazine, and trifluoro-s-triazine with halides, nitrate, and carbonate anions have been optimized at the RI-MP2/6-31++G** (full and frozen core), B3LYP/6-31++G**, and NOWB1K/6-31++G** levels of theory. All possible combinations of the a-systems and anions (to generate the sandwich pi-anion-pi' complexes) have been computed and analyzed using the aforementioned levels of theory. This allows us to evaluate the reliability and the performance of the MPWB1K functional to compute the binding energies of the anion-pi complexes and to analyze the additivity of the interaction in pi-anion-pi' complexes where the aromatic rings are of different nature (pi-acidity). We have also explored the Cambridge Structural Database and several interesting X-ray structures that support the theoretical calculations that have been found.