Characterisation of the weak halogen bond in N2⋯ICF3 by pure rotational spectroscopy

Comparison of isomericmeta- andpara-diiodotetrafluorobenzene as halogen bond donors in crystal engineering

The ability ofmeta- andpara-diiodotetrafluorobenzene to act as halogen bond donors in crystal engineering has been compared by the synthesis and crystal structure analysis of a family of 20 novel halogen-bonded cocrystals with simple monotopic and ditopic nitrogen-based acceptors.

Halogen Bonds Formed between Substituted Imidazoliums and N Bases of Varying N-Hybridization

Heterodimers are constructed containing imidazolium and its halogen-substituted derivatives as Lewis acid. N in its sp³, sp² and sp hybridizations is taken as the electron-donating base. The halogen bond is strengthened in the Cl < Br < I order, with the H-bond generally similar in magnitude to the Br-bond. Methyl substitution on the N electron donor enhances the binding energy. Very little perturbation arises if the imidazolium is attached to a phenyl ring. The energetics are not sensitive to the hybridization of the N atom. More regular patterns appear in the individual phenomena. Charge transfer diminishes uniformly on going from amine to imine to nitrile, a pattern that is echoed by the elongation of the C-Z (Z=H, Cl, Br, I) bond in the Lewis acid. These trends are also evident in the Atoms in Molecules topography of the electron density. Molecular electrostatic potentials are not entirely consistent with energetics. Although I of the Lewis acid engages in a stronger bond than does H, it is the potential of the latter which is much more positive. The minimum on the potential of the base is most negative for the nitrile even though acetonitrile does not form the strongest bonds. Placing the systems in dichloromethane solvent reduces the binding energies but leaves intact most of the trends observed in vacuo; the same can be said of ∆G in solution.

The Halogen Bond

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

Building a Better Halide Receptor: Optimum Choice of Spacer, Binding Unit, and Halosubstitution

Quantum calculations are used to measure the binding of halides to a number of bipodal dicationic receptors, constructed as a pair of binding units separated by a spacer group. A number of variations are studied. A H atom on each binding unit (imidazolium or triazolium) is replaced by Br or I. Benzene, thiophene, carbazole, and dimethylnaphthalene are considered as spacer groups. Each receptor is paired with halides F(-) , Cl(-) , Br(-) , and I(-) . Substitution with I on the binding unit yields a large enhancement of binding, as much as 13 orders of magnitude; a much smaller increase occurs for substitution with Br. Imidazolium is a more effective binding agent than is triazolium. Benzene and dimethylnaphthalene represent the best spacers, followed by thiophene and carbazole. F(-) binds much more strongly than do the other halides, which obey the order Cl(-) >Br(-) >I(-) .