Comparison of Various Means of Evaluating Molecular Electrostatic Potentials for Noncovalent Interactions

Abstract

The various heterodimers formed by a series of Lewis acids with NH as Lewis base are identified. Lewis acids include those that can form chalcogen (HSF and HSBr), pnicogen (H PF and H PBr), and tetrel (H SiF and H SiBr) bonds, as well as H-bonds and halogen bonds. The molecular electrostatic potential (MEP) of each Lewis acid is considered in a number of ways. Pictorial versions show broad regions of positive and negative MEP, on surfaces that vary with respect to either the value of the chosen isopotential, or their distance from the nuclei. Specific points are identified where the MEP reaches a maximum on a particular isodensity surface (V ). The locations and values of V were evaluated on different isodensity surfaces, and compared to the stabilities of the various equilibrium geometries. As the chosen isodensity is decreased, and the MEP maxima drift away from the molecule, some points maintain their angular positions with respect to the molecule, whereas others undergo a reorientation. The lowering isodensity also causes some of the maxima to disappear. In general, there is a fairly good correlation between the energetic ordering of the equilibrium structures and the values of V . A number of possible Lewis acid sites on the heteroaromatic imidazole ring were also considered and presents some cautions about application of V as the principal criterion for predicting equilibrium geometries. © 2017 Wiley Periodicals, Inc.

Halogen, Chalcogen, and Pnicogen Bonding Involving Hypervalent Atoms

“…V s,max was thus recomputed for each monomer, on the isodensity surface corresponding to the ρ BCP of each complex listed in Table . Lying much closer to the nuclei, these maxima displayed in the final column of Table are of course much more positive . Nonetheless, they share many of the same trends as the 0.001 au maxima in the preceding column.…”

“…Lying much closer to the nuclei, these maximad isplayed in the final column of Ta ble 1 are of coursem uch more positive. [60] Nonetheless,t hey share many of the same trends as the 0.001 au maxima in the preceding column. The largestv alues are associated with the pnicogen bonds, and the smallest with the YF 6 chalcogen bonds.…”

Bond paths between distant atoms do not necessarily indicate dominant interactions

“…Therefore, as should be expected, the dominant intermolecular interaction will be indicated by the electrostatic energy and not the exchange energy, as is the case with molecules (where it indicates positions of covalent bonds). Of course, this fully justifies the search of dominant intermolecular interactions using some electrostatic indices as, e.g., atomic charges or molecular electrostatic potentials . This fact already indicates that the role of an intermolecular bond path as the indicator of the dominant intermolecular interaction becomes at least highly doubtful …”

“…It is clear that the electrostatic energy will dominate over the exchange one not only in magnitude but also in the choice of the dominate intermolecular interaction. For this reason, e.g., the molecular electrostatic potential is often used to visualize supposed dominant intermolecular interactions . Moreover, such an interpretationally problematic situation will arise especially when some other characteristics (geometric, spectroscopic, atomic charges, atomic electrostatic potentials, etc.)…”

In search for a hydride‐carbene bond

“…In order to verify this expectation, maps of the electrostatic potential have been prepared, and they are important proof of the suggested hydride‐carbene bonds. It is known that the electrostatic potential is often used to find areas of increased reactivity in molecules and dominant intermolecular interactions in dimers . For the purpose of yet deeper analysis of the hydride‐carbene bond in the presented dimers, the Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital (NBO) methods were also used—both are often utilized in the analysis of various intermolecular interactions.…”