1 research outputs found
Role of the Multipolar Electrostatic Interaction Energy Components in Strong and Weak CationāĻ Interactions
Density
functional and MĆøllerāPlesset second-order
perturbation (MP2) calculations have been carried out on various model
cationāĻ complexes formed through the interactions of
Mg<sup>2+</sup>, Ca<sup>2+</sup>, and NH<sub>4</sub><sup>+</sup> cations
with benzene, <i>p</i>-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 cationāĻ
interactions. The binding energies of these complexes were computed
from the fully optimized structures using coupled cluster calculations
including triple excitations (CCSDĀ(T)) and Gaussian-G4-MP2 (G4MP2)
techniques. An analysis of the charge sharing between the donor (the
Ļ-systems) and the acceptors (the cations) together with the
partitioning of total interaction energies revealed that the strong
and weak cationāĻ interactions have similar electrostatic
interaction properties. Further decomposition of such electrostatic
terms into their multipolar components showed the importance of the
chargeādipole, chargeāquadrupole, and chargeāoctopole
terms in shaping the electrostatic forces in such interactions. The
computed vibrational spectra of the complexes were analyzed for the
specific cationāĻ interaction modes and have been shown
to contain the signature of higher order electrostatic interaction
energy components (quadrupole and octopole) in such interactions