Interaction between some anions and deficient olefinic and aromatic centers

The anion-π interaction between Br−, Cl−, F− and H− anions and para-chloranil (P-CA) and ortho-chloranil (O-CA) have been studied by means of ab initio methods. The geometries were fully optimized at B3LYP, and MP2/6-31++G∗∗ levels by standard and counterpoise corrected (CP-corrected) methods. The binding energies obtained by standard method were corrected for basis set superposition error (EBSSE) and zero point energy (EZPE). Also, the B3LYP results were corrected by single point calculation at B3LYP/aug-cc-PVTZ level of theory. Although the distance between anion and ring is generally higher in CP-corrected method, the complexation energies obtained for CP-corrected structures are higher in comparison with BSSE corrected results obtained by standard method. The O-CA···X− dimers show higher complexation energies. The trends in the stability of complexes are alike in two series. Topological properties of electron density were determined using atoms in molecules (AIM) method on the wave functions obtained at MP2/6-31++G(d,p) level. The number and the nature of critical points (CPs) depend on aromatic ring and anion. Natural bond orbital analysis indicates that nX → π∗CO is the most important interaction in these complexes.