Anion Receptors Based on Highly Fluorinated Aromatic Scaffolds

Mono-, di-, and tri-pentafluorobenzyl-substituted hexafluorobenzene (HFB) scaffolds, viz., R_I, R_II, and R_III are proposed as promising receptors for molecules of chemical, biological, and environmental relevance, viz., N₂, O₃, H₂O, H₂O₂, F^–, Cl^–, BF₄^–, NO₃^–, ClO^–, ClO₂^–, ClO₃^–, ClO₄^–, and SO₄^2–. The receptor–guest complexes modeled using M06L/6-311++G­(d,p) DFT show a remarkable increase in the complexation energy (E_int) with an increase in the number of fluorinated aromatic moieties in the receptor. Electron density analysis shows that fluorinated aromatic moieties facilitate the formation of large number of lone pair−π interactions around the guest molecule. The lone pair strength of the guest molecules quantified in terms of the absolute minimum (V_min) of molecular electrostatic potential show that E_int strongly depends on the electron deficient nature of the receptor as well as strength of lone pairs in the guest molecule. Compared to HFB, R_I exhibits 1.1–2.5-fold, R_II shows 1.6–3.6-fold, and the bowl-shaped R_III gives 1.8–4.7-fold increase in the magnitude of E_int. For instance, in the cases of HFB···F^–, R_I···F^–, R_II···F^–, and R_III···F^– the E_int values are −21.1, −33.7, −38.1, and −50.5 kcal/mol, respectively. The results strongly suggest that tuning lone pair−π interaction provides a powerful strategy to design receptors for small molecules and anions.