The anionic recognition mechanism based on polyol and boronic acid receptors

Abstract

Anion selective recognition plays pivotal roles in the environmental field. The polyol and boronic acid receptor classes are investigated here to recognize the chloride (Cl⁻); fluoride (F⁻); dihydrogen phosphate (H₂PO₄⁻); acetate (AcO⁻); bromide (Br⁻); and hydrogen sulfate (HSO₄⁻) anions. Energy Decomposition Analysis (EDA) shows that the anion–receptor interactions are predominantly electrostatic. Interestingly, the increase of the number of –CF₃ groups or of the carbonic chain in the polyol structure favors Cl⁻ recognition. The polyol–Cl⁻ interactions are more attractive than the boronic acid–Cl⁻ bond. Boronic acid recognizes F⁻ and H₂PO₄⁻ with the most attractive energies. The Quantum Theory of Atoms in Molecules (QTAIM) method elucidated that the recognition of AcO⁻, Cl⁻, Br⁻, and HSO₄⁻ by the receptors is maintained through hydrogen bonds, while the recognition of F⁻ and H₂PO₄⁻ by boronic acid involves B⋯F⁻ and B⋯O⁻–P bonds, respectively, showing a larger covalent character compared to other boronic acid–anion bonds, but with a primarily electrostatic nature.