engleski

Evolution of supramolecular halogen-bonded structures in cocrystallisation via grinding: from a finite assembly to an infinite chain

Halogen bonds, involving an electron-defficient halogen atom (I, Br) and an electron donor (e.g. N, O or S atoms) have recently been recognised as alternatives to hydrogen bonds in the planned construction of supramolecular architectures. Typical halogen bonds are similar to hydrogen bonds both in terms of length (2.7-3.0 Å) and directionality. We, along with others, have recently begun exploring halogen bonds as design elements for the synthesis of cocrystals, i.e. crystalline solids consisting of more than one sort of chemical species. We now report grinding as a method to construct halogen-bonded solids in high yields and in absence of solvent. 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 (Figure 1). 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

halogen-bonded cocrystalls; solid-state grinding; mechanochemical methods

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