A comparative view on the potential acting on an electron in a molecule and the electrostatic potential through the typical halogen bonds (original) (raw)
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Polarization plays the key role in halogen bonding: a point-of-charge-based quantum mechanical study
Theoretical Chemistry Accounts, 2018
The nature of the halogen bond has been under debate over the last decade. Herein, the nature of the halogen bond was reinvestigated using point-of-charge (PoC) approach in which a point of negative or positive charge was used to mimic a Lewis base or acid, respectively. Halogen bond strength was estimated in terms of stabilization energy of the halo molecule in the presence of PoC. Open-ended questions regarding halogen interaction via σ-hole were discussed. A number of fundamental physical terms including σ-node, − σ-hole and + σ-hole interactions were introduced to describe the unconventional behavior of the halogen's interactions. Several conflicts in the published results and explanations on the halogen bonding were highlighted and clarified. Based on PoC results, it may be claimed that: (i) halogen bond is mainly an electrostatic interaction and (ii) the polarization of the halogen is the key for understanding the reason behind the formation of halogen•••Lewis acid/ base interaction at halogen•••Lewis acid/base angle of 180°. A-X•••PoC angle and solvent effects on the molecular stabilization energy were estimated. Furthermore, electron correlation contribution to molecular stabilization energy was evaluated. Natural bonding orbital calculations were performed on the studied halo molecules. Finally, halogen bond test (σ n-hole test) was proposed as a theoretical calculation to examine the ability of a halo molecule to form a halogen bond.
A Molecular Electrostatic Potential Analysis of Hydrogen, Halogen, and Dihydrogen Bonds
Hydrogen, halogen, and dihydrogen bonds in weak, medium and strong regimes (<1 to ∼60 kcal/mol) have been investigated for several intermolecular donor−acceptor (D-A) complexes at ab initio MP4//MP2 method coupled with atoms-in-molecules and molecular electrostatic potential (MESP) approaches. Electron density ρ at bond critical point correlates well with interaction energy (E nb ) for each homogeneous sample of complexes, but its applicability to the entire set of complexes is not satisfactory. Analysis of MESP minimum (V min ) and MESP at the nuclei (V n ) shows that in all D-A complexes, MESP of A becomes more negative and that of D becomes less negative suggesting donation of electrons from D to A leading to electron donor−acceptor (eDA) interaction between A and D. MESP based parameter ΔΔV n measures donor−acceptor strength of the eDA interactions as it shows a good linear correlation with E nb for all D-A complexes (R 2 = 0.976) except the strongly bound bridged structures. The bridged structures are classified as donor−acceptor−donor complexes. MESP provides a clear evidence for hydrogen, halogen, and dihydrogen bond formation and defines them as eDA interactions in which hydrogen acts as electron acceptor in hydrogen and dihydrogen bonds while halogen acts as electron acceptor in halogen bonds. − (electron donors) with different electron acceptors. Throughout this paper, E nb represents the interaction energy calculated at MP4//MP2 method and the standard notations ρ and ∇ 2 ρ are used to indicate the electron density at the bond critical point (bcp) of the electron donor−acceptor bond and the Laplacian of the electron density at the bcp. Figure 7. Change in V min upon bond formation in electron donor−acceptor−donor complexes (a) F − ...IF and (b) F − ...IBr. The black dots represent the location of the most negative MESP-valued point and the corresponding V min values in kcal/mol are also depicted.
Journal of Molecular Modeling, 2013
In a previous study we investigated the effects of aromatic fluorine substitution on the strengths of the halogen bonds in halobenzene…acetone complexes (halo0 chloro, bromo, and iodo). In this work, we have examined the origins of these halogen bonds (excluding the iodo systems), more specifically, the relative contributions of electrostatic and dispersion forces in these interactions and how these contributions change when halogen σ-holes are modified. These studies have been carried out using density functional symmetry adapted perturbation theory (DFT-SAPT) and through analyses of intermolecular correlation energies and molecular electrostatic potentials. It is found that electrostatic and dispersion contributions to attraction in halogen bonds vary from complex to complex, but are generally quite similar in magnitude. Not surprisingly, increasing the size and positive nature of a halogen's σ-hole dramatically enhances the strength of the electrostatic component of the halogen bonding interaction. Not so obviously, halogens with larger, more positive σ-holes tend to exhibit weaker dispersion interactions, which is attributable to the lower local polarizabilities of the larger σ-holes.
Electrostatic Potential Differences and Halogen-Bond Selectivity
Crystal Growth & Design, 2016
Molecular electrostatic potential based guidelines for selectivity of halogen-bond interactions were explored via systematic co-crystallizations of 9 perfluorinated halogen-bond donors and 12 ditopic acceptors presenting two binding sites with different electrostatic potentials. A total of 89 of the 108 reactions resulted in co-crystal formation (as indicated by IR spectroscopy), and 35 new crystal structures were obtained. Methanol was exclusively used as a solvent for crystal growth in order to avoid any potential solvent−solute bias throughout these experiments. The structures were organized into three different groups depending upon the specific nature of the observed halogen-bond connectivities in each case. The electrostatic potential difference between the two acceptor sites on each molecule was defined as the ΔE value. Group 1 comprised acceptor molecules with a ΔE value below 35 kJ/mol units, and in this category halogen bonding took place on both binding sites in all co-crystals (9/9). Ditopic acceptor molecules in Group 2 were characterized by a ΔE value in the 35−65 kJ/mol range, and in this group half the structures showed halogen bonding to the best acceptor (11/22) and half the structures showed halogen bonding to both binding sites (11/22). In Group 3 the ΔE value was >167 kJ/mol, and in all of the co-crystals found herein (7/7), the halogen-bond donor favored the best acceptor site. These results allow us to propose some tentative guidelines and rationales for halogen-bond preferences in competitive systems. If ΔE < 35 kJ/mol, the electrostatic potential difference is not large enough to allow the donor molecules to form halogen bonds of sufficiently different thermodynamic strength to result in any pronounced molecular recognition preference (typically both, or several acceptors are then engaged in halogen bonding). Upon the basis of data produced in this study, in combination with relevant structures from the Cambridge Structural Database, it seems reasonable to suggest that if the ΔE value between two geometrically accessible halogen-bond acceptor sites is greater than 75 kJ/mol, the thermodynamic advantage of forming halogen bonds to the best acceptor provides a strong enough driving force that the best donor consistently interacts with the best acceptor; intermolecular selectivity is the result. However, if the ΔE resides between these two proposed boundaries, the outcome is unpredictable, and other factors are then likely to be responsible for the path that a particular supramolecular reaction will follow.
Halogen Bonding: A Study based on the Electronic Charge Density
The Journal of Physical Chemistry A, 2010
Density functional theory (DFT) and atoms in molecules theory (AIM) were used to study the characteristic of the noncovalent interactions in complexes formed between Lewis bases (NH 3 , H 2 O, and H 2 S) and Lewis acids (ClF, BrF, IF, BrCl, ICl, and IBr). In order to compare halogen and hydrogen bonds interactions, this study included hydrogen complexes formed by some Lewis bases and HF, HCl, and HBr Lewis acids. Ab initio, wave functions were generated at B3LYP/6-311++G(d,p) level with optimized structures at the same level. Criteria based on a topological analysis of the electron density were used in order to characterize the nature of halogen interactions in Lewis complexes. The main purpose of the present work is to provide an answer to the following questions: (a) why can electronegative atoms such as halogens act as bridges between two other electronegative atoms? Can a study based on the electron charge density answer this question? Considering this, we had performed a profound study of halogen complexes in the framework of the AIM theory. A good correlation between the density at the intermolecular bond critical point and the energy interaction was found. We had also explored the concentration and depletion of the charge density, displayed by the Laplacian topology, in the interaction zone and in the X-Y halogen donor bond. From the atomic properties, it was generally observed that the two halogen atoms gain electron population in response to its own intrinsic nature. Because of this fact, both atoms are energetically stabilized.
σ-Holes vs. Buildups of Electronic Density on the Extensions of Bonds to Halogen Atoms
Inorganics, 2019
Our discussion focuses upon three possible features that a bonded halogen atom may exhibit on its outer side, on the extension of the bond. These are (1) a region of lower electronic density (a σ-hole) accompanied by a positive electrostatic potential with a local maximum, (2) a region of lower electronic density (a σ-hole) accompanied by a negative electrostatic potential that also has a local maximum, and (3) a buildup of electronic density accompanied by a negative electrostatic potential that has a local minimum. In the last case, there is no σ-hole. We show that for diatomic halides and halogen-substituted hydrides, the signs and magnitudes of these maxima and minima can be expressed quite well in terms of the differences in the electronegativities of the halogen atoms and their bonding partners, and the polarizabilities of both. We suggest that the buildup of electronic density and absence of a σ-hole on the extension of the bond to the halogen may be an operational indication...
Molecules
In this study, we present results of a detailed topological analysis of electron density (ED) of 145 halogen-bonded complexes formed by various fluorine-, chlorine-, bromine-, and iodine-containing compounds with trimethylphosphine oxide, Me3PO. To characterize the halogen bond (XB) strength, we used the complexation enthalpy, the interatomic distance between oxygen and halogen, as well as the typical set of electron density properties at the bond critical points calculated at B3LYP/jorge-ATZP level of theory. We show for the first time that it is possible to predict the XB strength based on the distance between the minima of ED and molecular electrostatic potential (ESP) along the XB path. The gap between ED and ESP minima exponentially depends on local electronic kinetic energy density at the bond critical point and tends to be a common limiting value for the strongest halogen bond.
Journal of Molecular Modeling, 2019
A series of 20 halogen bonded complexes of the types R-Br•••Br − (R is a substituted methyl group) and R´-C≡C-Br•••Br − are investigated at the M06-2X/6-311+G(d,p) level of theory. Computations using a point-charge (PC) model, in which Br − is represented by a point charge in the electronic Hamiltonian, show that the halogen bond energy within this set of complexes is completely described by the interaction energy (ΔE PC) of the point charge. This is demonstrated by an excellent linear correlation between the quantum chemical interaction energy and ΔE PC with a slope of 0.88, a zero intercept, and a correlation coefficient of R 2 = 0.9995. Rigorous separation of ΔE PC into electrostatics and polarization shows the high importance of polarization for the strength of the halogen bond. Within the data set, the electrostatic interaction energy varies between 4 and −18 kcal mol-1 , whereas the polarization energy varies between −4 and −10 kcal mol-1. The electrostatic interaction energy is correlated to the sum of the electron-withdrawing capacities of the substituents. The polarization energy generally decreases with increasing polarizability of the substituents, and polarization is mediated by the covalent bonds. The lower (more favorable) ΔE PC of CBr 4-Br − compared to CF 3 Br•••Br − is found to be determined by polarization as the electrostatic contribution is more favorable for CF 3 Br•••Br −. The results of this study demonstrate that the halogen bond can be described accurately by electrostatics and polarization without any need to consider charge transfer.
On The Nature of the Halogen Bond
Journal of Chemical Theory and Computation, 2014
The wide-ranging applications of the halogen bond (X-bond), notably in self-assembling materials and medicinal chemistry, have placed this weak intermolecular interaction in a center of great deal of attention. There is a need to elucidate the physical nature of the halogen bond for better understanding of its similarity and differences vis-a-vis other weak intermolecular interactions, for example, hydrogen bond, as well as for developing improved force-fields to simulate nano-and biomaterials involving X-bonds. This understanding is the focus of the present study that combines the insights of a bottom-up approach based on ab initio valence bond (VB) theory and the block-localized wave function (BLW) theory that uses monomers to reconstruct the wave function of a complex. To this end and with an aim of unification, we studied the nature of X-bonds in 55 complexes using the combination of VB and BLW theories. Our conclusion is clear-cut; most of the X-bonds are held by charge transfer interactions (i.e., intermolecular hyperconjugation) as envisioned more than 60 years ago by Mulliken. This is consistent with the experimental and computational findings that X-bonds are more directional than H-bonds. Furthermore, the good linear correlation between charge transfer energies and total interaction energies partially accounts for the success of simple force fields in the simulation of large systems involving X-bonds.