Synthesis and Anion Recognition by a 1,8-Disulfonamidocarbazole-Isophthalamide Hybrid Macrocycle and Its Thioamide...

Novel 1,8-disulfonamidocarbazole-isophthalamide hybrid macrocycle 1 and its thioamide analogue 2 containing ortho-substituted benzyl spacers are reported, together with their anion recognition properties as determined by ¹H NMR and UV-vis titration studies conducted in a dimethyl sulfoxide solution and X-ray crystallographic analyses. Notable differences in their anion affinity and selectivity were observed for these two macrocyclic receptors. In particular, thioamide-bearing macrocycle 2 demonstrated nearly 20- and 30-fold improvement in its affinities for PhCOO^- and H₂PO₄^-, respectively, as compared to those of amide-containing macrocycle 1. In contrast, the conversion of amides into thioamides within the discussed macrocycles proved to be exceptionally unfavorable for AcO^- binding, as supported by a reduction in affinity by a factor of at least 27. Moreover, the 1:1 binding complexes formed by macrocycle 1 with Cl^- and macrocycle 2 with AcO^- in the solid state were unambiguously confirmed via single-crystal X-ray diffraction analysis. These findings provide deeper insight into the contrasting anion recognition behaviors of thioamide-based anion receptors versus their amide counterparts.