Halogen Bonding Interaction between Fluorohalides and Isocyanides

Hydrogen Bond versus Halogen Bond in Cation-Cation Complexes: Effect of the Solvent

Competition between hydrogen- (HB) and halogen-bonded (XB) 4-ammoniumpyridine and halogenammonium (NH_n F_3-n X⁺ ; n=0-3; X=F, Cl, Br, and I) cation-cation complexes are explored by means of DFT calculations. HB and XB minima structures are found for all systems in the gas phase. As the number of fluorine atoms increases, the HB complexes are more favored than those of XB. Proton transfer is generally observed in complexes with two, three, or four halogen atoms. The XB complexes evolve from traditional halogen bonds, to halogen-shared complexes, and to ionic complexes as the number of fluorine atoms increases. The dissociation transition states and their corresponding barriers are also characterized; the barriers increase as the number of fluorine atoms increases. The results if solvent effects are considered indicate that, even in an apolar solvent, such as n-hexane, most of the complexes have favorable binding energies. Atoms-in-molecules theory is used to analyze the complexes, and results in good correlations between electron density and total electron energy density (Η) values with the intermolecular bond length. According to the Η values obtained, the covalency of these interactions starts to manifest at distances around 72-74 % the sum of the van der Waals radii of the interacting atoms.

σ-Hole Bond vs π-Hole Bond: A Comparison Based on Halogen Bond

The σ-hole and π-hole are the regions with positive surface electrostatic potential on the molecule entity; the former specifically refers to the positive region of a molecular entity along extension of the Y-Ge/P/Se/X covalent σ-bond (Y = electron-rich group; Ge/P/Se/X = Groups IV-VII), while the latter refers to the positive region in the direction perpendicular to the σ-framework of the molecular entity. The directional noncovalent interactions between the σ-hole or π-hole and the negative or electron-rich sites are named σ-hole bond or π-hole bond, respectively. The contributions from electrostatic, charge transfer, and other terms or Coulombic interaction to the σ-hole bond and π-hole bond were reviewed first followed by a brief discussion on the interplay between the σ-hole bond and the π-hole bond as well as application of the two types of noncovalent interactions in the field of anion recognition. It is expected that this review could stimulate further development of the σ-hole bond and π-hole bond in theoretical exploration and practical application in the future.

Cooperative halogen bonds in V-shaped H3N·X1X2·X3Y (X1, X2, X3 = Cl and Br; Y = F, Cl and Br) complexes

The dihalogen molecule can simultaneously interact with NH₃ and another dihalogen molecule, forming a V-shaped trimer via cooperative halogen bonds.

Using beryllium bonds to change halogen bonds from traditional to chlorine-shared to ion-pair bonds

Dramatic synergistic cooperative effects between Be⋯F beryllium bonds and Cl⋯N halogen bonds in XYBe:FCl:N-base ternary complexes lead to changes in the halogen-bond type from traditional to chlorine-shared to ion-pair bonds.

Theoretical insights into the nature of halogen bonding in prereactive complexes

Benchmark quality geometries and interaction energies for the prereactive halogen-bonded complexes of dihalogens and ammonia, including hypothetical astatine containing dihalogens, have been produced via explicitly correlated coupled cluster methods. The application of local electron correlation partitioning reveals dispersion, electrostatics and ionic substitutions all contribute significantly to the interaction energy, with a linear relationship between the ionic substitutions and the degree of charge transfer. Potential energy curves for H3 N⋅⋅⋅ClF show that as the relative orientations of the two subunits are manipulated appreciable interactions can be found at considerably angular displaced geometries, signifying lower directionality in halogen bonding than previously supposed.

Insights into the strength and nature of carbene···halogen bond interactions: a theoretical perspective

Halogen-bonding, a noncovalent interaction between a halogen atom X in one molecule and a negative site in another, plays critical roles in fields as diverse as molecular biology, drug design and material engineering. In this work, we have examined the strength and origin of halogen bonds between carbene CH₂ and XCCY molecules, where X = Cl, Br, I, and Y = H, F, COF, COOH, CF₃, NO₂, CN, NH₂, CH₃, OH. These calculations have been carried out using M06-2X, MP2 and CCSD(T) methods, through analyses of surface electrostatic potentials V S(r) and intermolecular interaction energies. Not surprisingly, the strength of the halogen bonds in the CH₂···XCCY complexes depend on the polarizability of the halogen X and the electron-withdrawing power of the Y group. It is revealed that for a given carbene···X interaction, the electrostatic term is slightly larger (i.e., more negative) than the dispersion term. Comparing the data for the chlorine, bromine and iodine substituted CH₂···XCCY systems, it can be seen that both the polarization and dispersion components of the interaction energy increase with increasing halogen size. One can see that increasing the size and positive nature of a halogen's σ-hole markedly enhances the electrostatic contribution of the halogen-bonding interaction.