Intermolecular interactions in weak donor-acceptor complexes from symmetry-adapted perturbation and coupled-cluster theory: tetracyanoethylene-benzene and tetracyanoethylene-p-xylene.
The interactions in the complexes of tetracyanothylene (TCNE) with benzene and p-xylene, often classified as weak electron donor-acceptor (EDA) complexes, are investigated by a range of quantum chemical methods including intermolecular perturbation theory at the DFT-SAPT (symmetry-adapted perturbation theory combined with density functional theory) level and explicitly correlated coupled-cluster theory at the CCSD(T)-F12 level. The DFT-SAPT interaction energies for TCNE-benzene and TCNE-p-xylene are estimated to be -35.7 and -44.9 kJ mol(-1), respectively, at the complete basis set limit. The best estimates for the CCSD(T) interaction energy are -37.5 and -46.0 kJ mol(-1), respectively. It is shown that the second-order dispersion term provides the most important attractive contribution to the interaction energy, followed by the first-order electrostatic term. The sum of second- and higher-order induction and exchange-induction energies is found to provide nearly 40 % of the total interaction energy. After addition of vibrational, rigid-rotor, and translational contributions, the computed internal energy changes on complex formation approach results from gas-phase spectrophotometry at elevated temperatures within experimental uncertainties, while the corresponding entropy changes differ substantially.
Fakultät für Chemie, Universität Duisburg-Essen, Universitätsstraße 5, 45117 Essen, Germany.
Dennis
D
Kuchenbecker
Georg
G
Jansen