Cation–π complexes between alkali metal cation andpara-halogenophenols. Structures, binding energies and thermodynamic properties: DFT study and CCSD(T) complete basis set limit calculations

Density functional (B3LYP) studies have been undertaken on the molecular structures, binding energies and thermodynamic properties of π type complexes formed by alkali metal cations (Li+, Na+, K+) with phenol (Ph), and para-halogenophenols, p-XPh (X = F, Cl, Br). The performance of the DFT procedure for M+(phenol) complexes was verified by performing the complete basis set limit calculations at the CCSD(T) level. The DFT stabilization energies for the Li+ and Na+ complexes agree well with earlier accurately determined energies, while those for K+ complexes are underestimated by about 30%. This is explained by the role of electron correlation effects (mainly dispersion energy), which are neglected at the DFT level. The effect of the halogen para-substituent on the strength of cation binding to the π face of the phenol ring is discussed. The calculated Gibbs free energy (▵G) has revealed that all the investigated complexes are stable under standard conditions. Results show that the binding energies of these complexes vary in the range from −36.8 to −11.5 kcal/mol. Natural Bond Orbital (NBO) analysis has provided detailed insight into the nature of the electronic interactions in these systems.