Exploitation of the Menshutkin Reaction for the Controlled Assembly of Halogen Bonded Architectures Incorporating 1,2-Diiodotetrafluorobenzene and 1,3,5-Triiodotrifluorobenzene

1,4-Diazabicyclo­[2.2.2]­octane (DABCO) forms well-defined
co-crystals
with 1,2-diiodotetrafluorobenzene (1,2-DITFB), [(1,2-DITFB)2DABCO], and 1,3,5-triiodotrifluorobenzene, [(1,3,5-TITFB)2DABCO]. Both systems exhibited lower-than-expected supramolecular
connectivity, which inspired a search for polymorphs in alternative
crystallization solvents. In dichloromethane solution, the Menshutkin
reaction was found to occur, generating chloride anions and quaternary
ammonium cations through the reaction between the solvent and DABCO.
The controlled in situ production of chloride ions facilitated the
crystallization of new halogen bonded networks, DABCO–CH2Cl­[(1,2-DITFB)­Cl] (zigzag X-bonded chains) and (DABCO–CH2Cl)3[(1,3,5-TITFB)2Cl3]·CHCl3 (2D pseudo-trigonal X-bonded nets displaying
Borremean entanglement), propagating with charge-assisted C–I···Cl– halogen bonds. The method was found to be versatile,
and substitution of DABCO with triethylamine (TEA) gave (TEA-CH2Cl)3[(1,2-DITFB)­Cl3]·4­(H2O) (mixed halogen bond hydrogen bond network with 2D supramolecular
connectivity) and TEA-CH2Cl­[(1,3,5-TITFB)­Cl] (tightly packed
planar trigonal nets). The co-crystals were typically produced in
high yield and purity with relatively predictable supramolecular topology,
particularly with respect to the connectivity of the iodobenzene molecules.
The potential to use this synthetic methodology for crystal engineering
of halogen bonded architectures is demonstrated and discussed.