Theoretical analysis of an anion-π complex: I−·C6F6.

Recently, Anstöter and co-workers [J. Am. Chem. Soc. 141, 6132 (2019)] have provided the first photoelectron spectroscopic determination of the anion-π bond strength (D_e) using iodide-hexafluorobenzene (I⁻·C₆F₆) as the archetypical system. In combination with an equation-of-motion coupled cluster theory, namely EOM-IP-CCSD(dT), using Dunning's aug-cc-pVDZ (aVDZ) basis set, D_e in I⁻·C₆F₆ was found to be −0.53 eV with an uncertainty less than 0.03 eV. The interaction was claimed to arise for a large part from correlation forces (41%) with only a 23% contribution from electrostatic forces. In the present work, we performed the coupled-cluster with single and double and perturbative triple excitations, CCSD(T), calculations. We found that CCSD(T)/aVDZ can have an uncertainty up to 0.113 eV due to the basis set incompleteness. Our calculations disclosed that the previous calculations on the electrostatic contribution are concealed by the contributions from the exchange and Pauli repulsion. The electrostatic contribution is actually determinant, being more than double of the correlation contribution in the I⁻·C₆F₆ complex at the equilibrium binding distance. [ABSTRACT FROM AUTHOR]