Beyond Size Complementary Factors in Anion–Tetralactam Macrocycle Complexes: From Intrinsic Gas-Phase to Solvent-Predicted Stabilities

Abstract

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). 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.