Anion Encapsulation with Micromolar Affinity on [Pd₂L₄]⁴⁺ Receptor Cage. Nature of Anion-Receptor Interaction and ¹H NMR Parameters from Dispersion-Corrected DFT Calculations

Anion recognition, leading to encapsulated species, remains a relevant issue in supramolecular chemistry. The recent characterization of [Pd₂L₄]⁴⁺ with L = 1,3-di(pyridine-3-yl)benzene, and partially fluorinated counterparts, denotes an important improvement in such characteristics, which are followed by variation of ¹H NMR patterns. In this report, we account for the interaction features promoting the binding properties, largely increased in comparison to other cavities such as bambusurils, denoting a high contribution from electrostatic character (82%), with complementary contribution from charge-transfer (12%), and London type interactions (6%). Chemical modification of the ligands with electron-withdrawing groups given by fluorinated decoration increases the electrostatic stabilization, enabling a rational strategy to increase the overall stabilization of the noncovalent aggregate. The resulting deshielding shift on ¹H NMR is evaluated in terms of the chemical shift anisotropy of the shielding tensor. Our results favor the rational design of further anion-receptor cavities, toward enhancing the receptor capabilities of the host cavity toward anions based on the balance between chemical characteristics and binding energies.