A series of meso-tetraaryl calixpyrrole receptors have been used as a model system to quantify chloride- interactions in solution (see picture; green balls are chloride ions). The free energy values are generally indicative of a repulsive interaction; their magnitude depends on the substituent on the aromatic ring.
Quantitative evaluation of anion-pi interactions in solution
Angew. Chem. Int. Ed. 2008, 47, 4114-4118.