The fundamental importance of anions in a diverse range of biological and environmental processes has continued to serve as impetus for the development of synthetic host structures capable of their strong and selective recognition. Whilst considerable progress has been made in the field of anion recognition, wherein the past decades have witnessed a diverse range of host topologies employed and guest species targeted, the overwhelming majority of receptor systems reported to date principally rely on structural arrays of hydrogen bond (HB) donors to effect anion complexation. As such, there is exists a vast library of HB leitmotifs providing valuable insight into the electronic and structural factors that influence HB mediated anion recognition. By contrast the development of solution-phase sigma-hole mediated anion recognition strategies, such as halogen bonding (XB), has only emerged within recent years. To address the deficiency of structurally diverse XB donor arrays, we sought to investigate a new 1,2-bis-iodo-triazolium-triazole benzene based anion recognition motif, wherein convergent XB-anion interactions would facilitate strong anion complexation, with the ortho-benzene substitution pattern of the XB donors eliciting improved selectivity towards smaller anionic guests. Herein, we report the synthesis of a series of novel XB 1,2-iodotriazolium-triazole benzene receptors containing benzyl and perfluorophenyl substituents, and for comparison, HB 1,2-proto-triazolium-triazole benzene receptor analogues. One- and two-dimensional ¹H and ¹⁹F NMR spectroscopy delineate the steric and electronic consequences of proximal iodo-triazole XB donors, not observed in the HB proto-triazole analogues. ¹H NMR anion titration experiments and X-ray structural analysis provide insights into solution and solid state XB anion recognition induced receptor conformational changes and halide complexation modes.

Reference

T. Bunchuay, A. Docker, N. G. White and P. D. Beer, Polyhedron, 2021, 209, 115482.

(https://www.sciencedirect.com/science/article/pii/S0277538721004642?via%3Dihub)