Role of the multipolar electrostatic interaction energy components in strong and weak cation-π interactions

J Phys Chem A. 2013 Aug 22;117(33):7989-8000. doi: 10.1021/jp404245q. Epub 2013 Aug 13.

Abstract

Density functional and Møller-Plesset second-order perturbation (MP2) calculations have been carried out on various model cation-π complexes formed through the interactions of Mg(2+), Ca(2+), and NH4(+) cations with benzene, p-methylphenol, and 3-methylindole. Partial hydration of the metal cations was also considered in these model studies to monitor the effect of hydration of cations in cation-π interactions. The binding energies of these complexes were computed from the fully optimized structures using coupled cluster calculations including triple excitations (CCSD(T)) and Gaussian-G4-MP2 (G4MP2) techniques. An analysis of the charge sharing between the donor (the π-systems) and the acceptors (the cations) together with the partitioning of total interaction energies revealed that the strong and weak cation-π interactions have similar electrostatic interaction properties. Further decomposition of such electrostatic terms into their multipolar components showed the importance of the charge-dipole, charge-quadrupole, and charge-octopole terms in shaping the electrostatic forces in such interactions. The computed vibrational spectra of the complexes were analyzed for the specific cation-π interaction modes and have been shown to contain the signature of higher order electrostatic interaction energy components (quadrupole and octopole) in such interactions.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Ammonium Compounds / chemistry*
  • Benzene / chemistry
  • Calcium / chemistry*
  • Cations / chemistry
  • Cresols / chemistry
  • Magnesium / chemistry*
  • Quantum Theory*
  • Skatole / chemistry
  • Static Electricity

Substances

  • Ammonium Compounds
  • Cations
  • Cresols
  • 4-cresol
  • Skatole
  • Magnesium
  • Benzene
  • Calcium