Crystallographic and theoretical evidence of anion–pi and hydrogen-bonding interactions in a squaramide-nitrate salt

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- and hydrogen-bonding interactions in the crystal packing of this compound in relation to those found in the free squaramide solid structure.