A study of strong halogen bonding within three series of halogen-bonded complexes, derived from seven para-substituted pyridine derivatives and three N-halosuccinimides (iodo, bromo and chloro), has been undertaken with the aid of single-crystal diffraction, solution complexation and computational methods. The halogen bond was compared with the hydrogen bond in an equivalent series based on succinimide. The halogen-bond energies are in the range -60 to -20 kJ mol and change regularly with pyridine basicity and the Lewis acidity of the halogen. The halogen-bond energies correlate linearly with the product of charges on the contact atoms, which indicates a predominantly electrostatic interaction. The binding enthalpies in solution are around 19 kJ mol less negative due to solvation effects. The optimised geometries of the complexes in the gas phase are comparable to those of the solid-state structures, and the effects of the supramolecular surroundings in the latter are discussed. The bond energies for the hydrogen-bonded series are intermediate between the halogen-bond energies of iodine and bromine, although there are specific differences in the geometries of the halogen- and hydrogen-bonded complexes.

Over the past several decades, halogen bonding has become a standard ‘tool’ in supramolecular chemistry and particularly in crystal engineering. Traditionally, the study of halogen bonding has primarily been focused...

Six novel halogen-bonded cocrystals of active pharmaceutical ingredients with 1,4-diiodo- and 1,4-dibromotetrafluorobenzene have been synthesized.

A number of novel halogen-bonded aromatic amine cocrystals with 1,4-diiodotetrafluorobenzene have been synthesized via both mechanochemical and solution syntheses, offering valuable insight into potential halogen bond acceptor species.