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A stepwise mechanism for the mechanochemical synthesis of halogen-bonded cocrystal architectures

The synthesis of multi-component crystals (cocrystals) has been recognized as a versatile approach to construct functional organic solids for pharmaceutical, optical and electronic applications, as well as for organic synthesis. With our interest in the interplay of different halogen bond acceptors in the solid state, we have synthesized cocrystals of ortho- (o-DITFB) and para-diiodotetrafluorobenzene (p-DITFB) with thiomorpholine, a non-symmetrical acceptor. This contribution will present experimental results obtained by investigating different grinding times and reactant stoichiometries on the outcome of the mechanochemical cocrystallisation. The results reveal that mechanochemical cocrystal synthesis is most likely a stepwise process. The first step is the formation of strong I...N halogen bonds, leading to finite three- (in case of p-DITFB) or five-membered (in case of o-DITFB) assemblies. These are the first cases of finite halogen-bonded assemblies characterised in the solid state. Further grinding leads to the transformation of finite assemblies into infinite linear or zig-zag halogen-bonded chains.

mechanochemical synthesis; halogen-bond; cocrystal architectures; stepwise mechanism; tetrafluoro-1; 4-diiodobenzene; tetrafluoro-1; 2-diiodobenzene

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