Noncovalent interaction or chemical bonding between alkaline earth cations and benzene? A quantum chemistry study using MP2 and density-functional theory methods

Calculations on alkaline earth metal ion–benzene complexes were performed using the density-functional theory (DFT) B3LYP and ab initio MP2 methods. They showed that the interaction is very strong, of the order of magnitude of a normal chemical bond. Electrostatic interaction is not the dominant component, and both charge transfer and induction make a significant contribution. Analysis of molecular orbital interactions indicated that binding of the alkaline earth metal ions to benzene may be attributed to s–π and p–π interactions, which are significantly stronger than those between alkali cations and benzene.