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.