Computational analysis of the nature and strength of the supramolecular contacts involved in the binding of chloride anions by imidazolium-based cyclic receptors.

The supramolecular bonding contacts driving the recognition of chloride ions by macrocyclic imidazolium-based receptors have been investigated by density functional theory calculations, both in vacuo and in solution (DMSO). This computational study reveals that the most stable host-guest complexes in vacuo and solution are different. While the anion interacts by means of two C-H···Cl(-) hydrogen bonds with the host molecule in vacuo (in a similar manner to that observed in the published single-crystal X-ray structure of the Cl-host complex), four C-H···Cl(-) contacts are clearly present in solution, as observed experimentally by earlier studies. In addition, the computed optimal Cl-host complex in solution confirms that the cavity of the host macrocycle, formed by four aromatic rings, does not includes the anions, which are located outside the cyclic receptor with which they interact through two CPh-H···Cl(-) hydrogen bonds and two unconventional (CIm-H)(+)···X(-) interactions.