Theoretical Investigations of Anion−π Interactions: The Role of Anions and the Nature of π Systems

The nature of the anion−π interaction has been investigated by carrying out high level ab initio calculations of the complexes of halide (F-, Cl-, and Br-), linear organic (CN-, NC-), and trigonal planar organic (NO3- and CO32-) anions with different kinds of π systems, viz. olefinic (tetrafluoroethene), aromatic (hexafluorobenzene), and heteroaromatic (1,3,5-triazine). In an effort to comprehend the underlying basis of this interaction, we have also carried out a rigorous decomposition of the interaction energies using the symmetry adapted perturbational theory (SAPT) method. Contrary to our expectations, the results indicate that the magnitudes of total interation energies of anion−π and cation−π interactions are similar. In contrast to cation−π interactions, anion−π interactions are, however, marked by substantial contributions from dispersion energies. As in the case of cation−π interactions, the role of anions also have a marked influence on the nature and magnitude of the anion−π interaction with in...