The role of halogen bonding in the interaction landscape directing the crystal packing in a homologous series of halogenated coumarin derivatives

Abstract

The role of halogen bonding as a supramolecular directing interaction was investigated in a series of ten 3-halogenocoumarin derivatives using X-ray diffraction analysis. Halogen bonds might not be as strong as classical hydrogen bonds in molecules such as substituted coumarins but are nevertheless expected to play a certain role in the supramolecular assemblies. Hirshfeld surface analysis, full interaction maps and quantum calculations are used to identify halogen interactions such as X···O, X···π or interhalogen contacts of type I and II, where X is a halogen atom. The halogen interactions in this series appear to be in competition with other supramolecular interactions which leads to a larger structural diversity than expected. This might be due to the steric shielding by the ortho substituents of the halogen atom in the 3-position on the lactone ring of the coumarin motif which are themselves strong hydrogen bond acceptors or donors, but also to the relatively abundant presence of π- π interactions between the aromatic coumarin moieties.