Crystallographic and Theoretical Evidence of Anion–π and Hydrogen‐Bonding Interactions in a Squaramide–Nitrate Salt

Abstract Synthetic anionic receptors are fundamental to the understanding of the mechanism of recognition phenomena, which is the basis of many fundamental biological processes. Recognition studies and X‐ray crystallography techniques provide accurate information on the structure of the molecular complexes and the nature of the interactions involved. Here, we present the first example of a squaramide–nitrate salt. X‐ray crystallography and theoretical studies show the important roles of anion–π and hydrogen‐bonding interactions in the crystal packing of this compound in relation to those found in the free squaramide solid structure.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)