Modulating Chalcogen Bonding and Halogen Bonding Sigma-Hole Donor Atom Potency and Selectivity for Halide Anion Recognition.

A series of acyclic anion receptors containing chalcogen bond (ChB) and halogen bond (XB) donors integrated into a neutral 3,5-bis-triazole pyridine scaffold are described, in which systematic variation of the electronic-withdrawing nature of the aryl substituents reveal a dramatic modulation in sigma-hole donor atom potency for anion recognition. Incorporation of strongly electron-withdrawing perfluorophenyl units appended to the triazole heterocycle telluro- or iodo- donor atoms, or directly linked to the tellurium donor atom dramatically enhances the anion binding potency of the sigma-hole receptors, most notably for the ChB and XB receptors displaying over thirty-fold and eight-fold increase in chloride anion affinity, respectively, relative to unfluorinated analogues. Linear free energy relationships for a series of ChB based receptors reveal the halide anion recognition behaviour of the tellurium donor is highly sensitive to local electronic environments. This is especially the case for those directly appended to the Te centre (3⋅ChB), where a remarkable enhancement of strength of binding and selectivity for the lighter halides is observed as the electron-withdrawing ability of the Te-bonded aryl group increases, highlighting the exciting opportunity to fine-tune anion affinity and selectivity in ChB-based receptor systems.