Mechanochemical reactions of cocrystals: comparing theory with experiment in the making and breaking of halogen bonds in the solid state.

Mechanochemical re-investigation of the halogen-bonded cocrystallisation of 1,4-diazabicyclo[2.2.2]-octane and 1,2-diiodotetrafluorobenzene revealed an unexpectedly complex system with three distinct cocrystal compositions, one of which also exhibits temperature-dependent polymorphism. This provided an opportunity to experimentally test the ability of dispersion-corrected periodic density functional theory (DFT) to not only explain the formation, but also predict the interconversion between halogen-bonded cocrystals of different stoichiometries.