title: Role of the multipolar electrostatic interaction energy components in strong and weak cation-π interactions.
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.
authors.affiliation: Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland.
authors.forename: Pawel
authors.initials: P
authors.lastname: Kadlubanski
authors.forename: Katherine
authors.initials: K
authors.lastname: Calderón-Mojica
authors.forename: Weyshla A
authors.initials: WA
authors.lastname: Rodriguez
authors.forename: D
authors.initials: D
authors.lastname: Majumdar
authors.forename: Szczepan
authors.initials: S
authors.lastname: Roszak
authors.forename: Jerzy
authors.initials: J
authors.lastname: Leszczynski
mesh_terms: D064751:Ammonium Compounds / Q000737:chemistry*; D001554:Benzene / Q000737:chemistry; D002118:Calcium / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D003408:Cresols / Q000737:chemistry; D008274:Magnesium / Q000737:chemistry*; D011789:Quantum Theory; D012862:Skatole / Q000737:chemistry; D055672:Static Electricity
chemical_list: D064751:Ammonium Compounds; D002412:Cations; D003408:Cresols; C032538:4-cresol; D012862:Skatole; D008274:Magnesium; D001554:Benzene; D002118:Calcium