title: Likelihood of atom-atom contacts in crystal structures of halogenated organic compounds.
abstract: The likelihood of occurrence of intermolecular contacts in crystals of halogenated organic compounds has been analysed statistically using tools based on the Hirshfeld surface. Several families of small halogenated molecules (containing organic F, Cl, Br or I atoms) were analysed, based on chemical composition and aromatic or aliphatic character. The behaviour of crystal contacts was also probed for molecules containing O or N. So-called halogen bonding (a halogen making short interactions with O or N, or a π interaction with C) is generally disfavoured, except when H is scarce on the molecular surface. Similarly, halogen⋯halogen contacts are more rare than expected, except for molecules that are poor in H. In general, the H atom is found to be the preferred partner of organic halogen atoms in crystal structures. On the other hand, C⋯C interactions in parallel π-stacking have a high propensity to occur in halogenated aromatic molecules. The behaviour of the four different halogen species (F, Cl, Br, I) is compared in several chemical composition contexts. The analysis tool can be refined by distinguishing several types for a given chemical species, such as H atoms bound to O or C. Such distinction shows, for instance, that C-H⋯Cl and O-H⋯O are the preferred interactions in compounds containing both O and Cl.
authors.affiliation: CRM2, CNRS, Institut Jean Barriol, Université de Lorraine, Vandoeuvre les Nancy CEDEX, France.
authors.forename: Christian
authors.initials: C
authors.lastname: Jelsch
authors.affiliation: CRM2, CNRS, Institut Jean Barriol, Université de Lorraine, Vandoeuvre les Nancy CEDEX, France ; Faculté des Sciences de Bizerte, Laboratoire de Chimie des Matériaux, Université de Carthage, Zarzouna 7021, Tunisia.
authors.forename: Sarra
authors.initials: S
authors.lastname: Soudani
authors.affiliation: Faculté des Sciences de Bizerte, Laboratoire de Chimie des Matériaux, Université de Carthage, Zarzouna 7021, Tunisia.
authors.forename: Cherif
authors.initials: C
authors.lastname: Ben Nasr
keywords: Hirshfeld surface analysis; crystal packing; enrichment ratio; halogen bonding; halogenated organic compounds; intermolecular contacts; π-stacking interactions