Reconciling Experiment and Theory in the Use of Aryl-Extended Calix[4]pyrrole Receptors for the Experimental Quantification of Chloride<br>π Interactions in Solution

In this manuscript we consider from a theoretical point of view the recently reported experimental quantification of anionπ interactions (the attractive force between electron deficient aromatic rings and anions) in solution using aryl extended calix[4]pyrrole receptors as model systems. Experimentally, two series of calix[4]pyrrole receptors functionalized, respectively, with two and four aryl rings at the meso positions, were used to assess the strength of chlorideπ interactions in acetonitrile solution. As a result of these studies the contribution of each individual chlorideπ interaction was quantified to be very small (π interaction. In addition, the obtained theoretical results also suggest that the chloride-calix[4]pyrrole complex used as reference to dissect experimentally the contribution of the chlorideπ interactions to the total binding energy for both the two and four-wall aryl-extended calix[4]pyrrole model systems is probably not ideal