Beyond Size Complementary Factors in Anion-Tetralactam Macrocycle Complexes: From Intrinsic Gas-Phase to...

The gas-phase affinities of different types of anions X^- (halogen anions, oxoanions, and hydrogenated anions) toward a model tetralactam-based macrocycle receptor (1), defined in terms of stability of an anion-receptor complex (1 + X^-) against its disintegration, were evaluated by dissociation studies using a mass spectrometry-based methodology and supported by theoretical calculations (density functional theory-PBE0). The gas-phase complex with Cl^- was found to be tailor-made for the macrocycle 1, while 1 + SA^- (SA^- = salicylate anion) and 1 + HSO₄^- were the weakest ones. Other complexes displayed a relatively low-stability dispersion (<1.2 kcal·mol^-1). The 1/ε_r approach of the electrostatic contribution scaling method was used to predict the stability trends in a dimethyl sulfoxide solvent from the gas-phase binding energy partition using the symmetry-adapted perturbation theory. High deformation energy and differences in solvation energies were suggested to be the main sources of inconsistency in the predicted and experimental stabilities of 1 + F^- and 1 + H₂PO₄^- complexes.