Comparison of isomeric meta- and para-diiodotetrafluorobenzene as halogen bond donors in crystal engineering

Abstract

The ability of meta- and para-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.

Abstract

We provide a systematic investigation of the structures and composition of halogen-bonded cocrystals involving the bent ( meta) halogen bond donor 1,3-diiodotetrafluorobenzene ( 1,3-tfib), in comparison to analogous systems based on its linear ( para) 1,4-isomer. In particular, whereas 1,4-tfibhas now been established as an archetypal, ubiquitous example of a halogen bond donor, its meta-isomer has remained almost completely unexplored. This study investigates the structures of 14 new cocrystals of 1,3-tfiband 9 new, analogous cocrystals of 1,4-tfib, with 9 monotopic and 7 ditopic nitrogen-based aliphatic and aromatic halogen bond acceptors. Combined with previously reported structures of cocrystals of 1,4-tfib,the results of our study indicate that whereas halogen bond lengths and the thermal stability of the investigated cocrystals are similar, the change in molecular shape between the two halogen bond donors brings about important consequences in supramolecular architectures and preferred stoichiometric compositions of otherwise analogous cocrystals. These preliminary results suggest that the principal factor responsible for such differences might be the different abilities of the cocrystals based on 1,3-tfiband 1,4-tfibto form close-packed structures.