Halogen bond tunability II: the varying roles of electrostatic and dispersion contributions to attraction in halogen bonds (original) (raw)
Related papers
Journal of Molecular Modeling, 2011
In the past several years, halogen bonds have been shown to be relevant in crystal engineering and biomedical applications. One of the reasons for the utility of these types of noncovalent interactions in the development of, for example, pharmaceutical ligands is that their strengths and geometric properties are very tunable. That is, substitution of atoms or chemical groups in the vicinity of a halogen can have a very strong effect on the strength of the halogen bond. In this study we investigate halogen-bonding interactions involving aromatically-bound halogens (Cl, Br, and I) and a carbonyl oxygen. The properties of these halogen bonds are modulated by substitution of aromatic hydrogens with fluorines, which are very electronegative. It is found that these types of substitutions have dramatic effects on the strengths of the halogen bonds, leading to interactions that can be up to 100% stronger. Very good correlations are obtained between the interaction energies and the magnitudes of the positive electrostatic potentials (σ-holes) on the halogens. Interestingly, it is seen that the substitution of fluorines in systems containing smaller halogens results in electrostatic potentials resembling those of systems with larger halogens, with correspondingly stronger interaction energies. It is also shown that aromatic fluorine substitutions affect the optimal geometries of the halogen-bonded complexes, often as the result of secondary interactions.
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.
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.
Halogen Bonding: A Halogen-Centered Noncovalent Interaction Yet to Be Understood
Inorganics, 2019
In addition to the underlying basic concepts and early recognition of halogen bonding, this paper reviews the conflicting views that consistently appear in the area of noncovalent interactions and the ability of covalently bonded halogen atoms in molecules to participate in noncovalent interactions that contribute to packing in the solid-state. It may be relatively straightforward to identify Type-II halogen bonding between atoms using the conceptual framework of σ-hole theory, especially when the interaction is linear and is formed between the axial positive region (σ-hole) on the halogen in one monomer and a negative site on a second interacting monomer. A σ-hole is an electron density deficient region on the halogen atom X opposite to the R–X covalent bond, where R is the remainder part of the molecule. However, it is not trivial to do so when secondary interactions are involved as the directionality of the interaction is significantly affected. We show, by providing some specifi...
The journal of physical chemistry. A, 2016
Geometries of benzene complexes with C6F5X, C6H5X, and CF3X (X is I, Br, Cl, and F) were optimized, and their interaction energies were evaluated. The CCSD(T) interaction energies at the basis set limit (Eint) of C6F5X (X is I, Br, Cl, and F) with benzene were -3.24, -2.88, -2.31, and -0.92 kcal mol(-1). Eint of C6H5X (X is I, Br, and Cl) with benzene were -2.31, -1.97, and -1.48 kcal mol(-1). The fluorination of halobenzenes slightly enhances the attraction. Eint of CF3X (X is I, Br, Cl, and F) with benzene (-3.11, -2.74, -2.22, and -0.71 kcal mol(-1)) were very close to Eint of corresponding C6F5X with benzene. In contrast to the halogen bond of iodine and bromine with pyridine (n-type halogen bond acceptor) where the main cause of the attraction is the electrostatic interactions, that of halogen bond with benzene (p-type acceptor) is dispersion interaction. In the halogen bonds with p-type acceptors (halogen-π interactions), the electrostatic interactions and induction interactio...
Journal of computational chemistry, 2018
This work considers the features of the electrostatic potential (ESP), and the potential acting on an electron in a molecule (PAEM) for the series of isolated dihalide molecules and for their molecular complexes. The joint analysis of these functions enriches the vision of atomic predispositions to the halogen bond formation and reveals details for their characterization. The account for the exchange-correlation interaction in PAEM retains the specific anisotropy of the ESP, which is commonly used for the halogen bonding explanation within σ-hole concept. Along the halogen bonds, the curvatures of PAEM and ESP functions are opposite. Being jointly mapped on the closed isosurfaces of the reduced density gradient, placed between bound atoms, they are significantly differed from the side facing the halogen atom and from the side looking at the electron donor atom. © 2017 Wiley Periodicals, Inc.
2013
Halogenated compounds are gaining an increasing importance in medicinal chemistry and materials science. Ab initio quantum chemistry (QC) has unraveled the existence of a ' 'sigma hole' ' along the CAX (X ¼ F, Cl, Br, I) bond, namely, a depletion of electronic density prolonging the bond, concomitant with a build-up on its sides, both of which are enhanced along the F < Cl < Br < I series. We have evaluated whether these features were intrinsically built-in in an anisotropic, polarizable molecular mechanics (APMM) procedure such as SIBFA (sum of interactions between fragments ab initio computed). For that purpose, we have computed the interaction energies of fluoro-, chloro-, and bromobenzene with two probes: a divalent cation, Mg(II), and water approaching X through either one H or its O atom. This was done by parallel QC energy-decomposition analyses (EDA) and SIBFA computations. With both probes, the leading QC contribution responsible for the existence of the sigma hole is the Coulomb contribution E c . For all three halogenated compounds, and with both probes, the in-and out-of-plane angular features of E c were closely mirrored by the SIBFA electrostatic multipolar contribution (E MTP ). Resorting to such a contribution thus dispenses with empirically-fitted ' 'extra' ' , off-centered partial atomic charges as in classical molecular mechanics/dynamics.
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.