Intermolecular interaction energies aromatic molecules

Electrostatic and dispersion interactions are important for the attraction and directionality of the intermolecular interactions of aromatic molecules [8-10,16]. Quantitative evaluation of electrostatic and dispersion energies is essential for understanding the intermolecular interactions of aromatic molecules. An accurate evaluation of electrostatic energy is not difficult, as DMA provides an accurate value ( es) [15]. On the other hand, an accurate evaluation of the dispersion energy is very difficult. An IMPT calculation using a large basis set is necessary. 

Static ( eie)> polarization ( poi), van der Waals ( vdw)> and total interacting energies were calculated when a fluorine ion approaches the hexafluoroben-zene molecule perpendicular to the center of the aromatic ring. The obtained results point out the importance of the polarization component, which is similar to the electrostatic term in the 2.0 to 3.0 A range, the equihbrium distance for the fluoride aryl centroid complex is 2.6 A. The authors mention the importance of the quadrupole moment for understanding intermolecular interactions of aromatic system but they do not elaborate on this issue in this work. 

DPT calculations are not suitable for evaluating the inter molecular interactions of aromatic molecules, as dispersion is the major source of the attraction in the interactions of aromatic molecules, with the exception of cation/TT interactions. DPT calculations using basis sets with polarization functions provide sufficiently accurate intermolecular interaction energies for the cation/TT interactions, as DPT calculations can reproduce electrostatic and induction energies sufficiently accurately. 

Table 4 Intermolecular interaction energies of aromatic molecules ...

There is a third geometrical type, in which parallel aromatic molecules are parallel but not offset, i.e., face-to-face (FF) or eclipsed. For the electrostatic reasons just outlined, this is not an energy minimum for a pair of identical molecules in a symmetrical motif and is rarely observed. However, if the two aromatic molecules in a motif are different, with complementary electron distributions, the FF motif can be the energy minimum. One of the better-known instances of this is the intermolecular interaction between a hydrous arene and a perfluorous arene. Due to the opposite polarization of the C-H and C-F bonds, the molecular quadrupoles of CgHe and CgFe are oppositely signed, and so the electrostatic intermolecular stabilization between them is maximized with FF geometry. 

There exist several intermolecular forces between an aromatic molecule and an interacting molecule [15]. Computational methods for their evaluation will be briefly explained in this section. Dispersion, electrostatic and exchange-repulsion interactions are the major intermolecular forces when the interacting molecules are both neutral. The dispersion contribution has paramoimt importance for the attraction in the tt/tt, OH/tt, NH/tt and CH/tt interactions [8-10,16] therefore, accurate calculation of the dispersion energy is essential for the quantitative evaluation of these interactions. On the other hand, electrostatic and induction (induced polarization) interactions are the major source of the attraction in the cation/TT interaction [17]. The contribution of the dispersion interaction is relatively small in the cation/TT interactions. 

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