Cation–π complexes between alkali metal cation and para -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 pi 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 pi face of the phenol ring is discussed. The calculated Gibbs free energy (Delta 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.