Fig. 6: Ultra-strong binding capacity of the boroxine structure toward F⁻ in aqueous media.

a ¹H NMR spectra of HO‑PBA trimer (120 mmol L⁻¹) before (black) and after the addition of one molar equivalent of NaF (blue), NaCl (green), NaBr (purple), or NaI (yellow). b, c Photos (b) and ¹⁹F NMR spectra (c) of NaF (120 mmol L⁻¹) before (black) and after addition of one molar equivalent of PBA (red), or HO‑PBA trimer (blue). d ¹¹B NMR spectra of PBA (120 mmol L⁻¹) or HO‑PBA trimer (120 mmol L⁻¹) before and after addition of one molar equivalent NaF. All NMR measurements were carried out at room temperature using D₂O–DMSO−d₆ (1:6, v/v) mixtures as solvents.