The origins of the directionality of noncovalent intermolecular interactions^#

Abstract

The recent σ-hole concept emphasizes the contribution of electrostatic attraction to noncovalent bonds, and implies that the electrostatic force has an angular dependency. Here a set of clusters, which includes hydrogen bonding, halogen bonding, chalcogen bonding, and pnicogen bonding systems, is investigated to probe the magnitude of covalency and its contribution to the directionality in noncovalent bonding. The study is based on the block-localized wavefunction (BLW) method that decomposes the binding energy into the steric and the charge transfer (CT) (hyperconjugation) contributions. One unique feature of the BLW method is its capability to derive optimal geometries with only steric effect taken into account, while excluding the CT interaction. The results reveal that the overall steric energy exhibits angular dependency notably in halogen bonding, chalcogen bonding, and pnicogen bonding systems. Turning on the CT interactions further shortens the intermolecular distances. This bond shortening enhances the Pauli repulsion, which in turn offsets the electrostatic attraction, such that in the final sum, the contribution of the steric effect to bonding is diminished, leaving the CT to dominate the binding energy. In several other systems particularly hydrogen bonding systems, the steric effect nevertheless still plays the major role whereas the CT interaction is minor. However, in all cases, the CT exhibits strong directionality, suggesting that the linearity or near linearity of noncovalent bonds is largely governed by the charge-transfer interaction whose magnitude determines the covalency in noncovalent bonds.

The intricacies of the stacking interaction in a pyrrole–pyrrole system

“…They play a key role in supramolecular chemistry which is defined as ''chemistry beyond the molecule'' and are without doubt the dominant type of interaction in maintaining the three-dimensional structure of large systems such as proteins, nucleic acids and other large molecules [1][2][3][4][5][6][7][8]. In these systems, NCI involving aromatic rings can be distinguished and those are for instance: p-stacking, cation/p, anion-p, C-H/p and N-H/p interactions [9][10][11][12][13][14].…”

Electrostatic Potential and a Simple Extended Electric Dipole Model of Hydrogen Fluoride as Probes of Non-Bonding Electron Pairs in the Cyclic Ethers 2,5-Dihydrofuran, Oxetane and Oxirane

“…As stated earlier, the rules for predicting angular geometries are electrostatic in origin in the sense that unperturbed electric charge distributions are assumed to define the angular geometry assumed by the interacting pair of molecules, i.e., the effects of polarisation of one molecule by the other and of charge transfer are assumed negligible. In fact, recently there has been considerable controversy and much discussion about the role of polarization [20] and that of charge transfer [21,22] in determining angular geometry in complexes formed through the various types of non-covalent interaction. The effects of the interplay between charge transfer and rehybridization in the two subunits brought about by non-covalent interaction have also been discussed [23].…”

On the Interplay between Charge‐Shift Bonding and Halogen Bonding

“…Many correlations were established between the maximum value of the molecular electrostatic potential, V s,max , calculated at the σ-hole and the stabilisation energies of the corresponding XBs. [28][29][30][31][32][33][34][35][36][37] The controversy remains strong, as can be noted from the recent literature on the emblematic case of the Y 3 CÀ I halogenbond donor. [19,27] Some authors opposed other contributions, including dispersion, charge transfer (leading to partial covalent bond formation), and the repulsive component resulting from the Pauli exclusion principle.…”