AIM and NBO analyses of cation-π interaction

The nature of cation-π interaction has been investigated by carrying out high-level ab initio calculations of the complexes of (Li+, Na+, K+, H+, and NH4+) with π-systems such C2H2, C2H4 and C6H6. The interaction energies were calculated at MP2/6-311++G∗∗ level. The calculations suggest that the size of cation and the nature of π-system are two influential factors that affect the nature of interaction. It was found the proton-π interaction is much stronger than the interaction of other cations with π-system and it cannot be classified into the category of ordinary noncovalent cation-π interaction. AIM and NBO analyses of cation-π interaction indicate that the variation of densities and the extent of charge transfers upon complexation correlate well with the obtained interaction energies.