| Summary: | A series of ditopic ion pair receptors equipped with 4-nitrophenylurea and 1-aza-18-crown-6-ether linked by ortho-(<b>1</b>), meta-(<b>2</b>), and para-(<b>3</b>) substituted benzoic acid were readily synthesized in three steps from commercially available materials. The binding properties of these regioisomeric receptors were determined using UV-vis and <sup>1</sup>H NMR spectroscopy in MeCN and in the solid state by single-crystal X-ray diffraction crystallography. The solution studies revealed that, apart from carboxylates, all the anions tested formed stronger complexes in the presence of sodium cations. Receptors <b>2</b> and <b>3</b> were found to interact with ion pairs with remarkably higher affinity than <i>ortho</i>-substituted <b>1</b>. <sup>1</sup>H NMR titration experiments showed that both urea NH protons interacted with anions with comparable strength in the case of receptors <b>2</b> and <b>3</b>, but only one of the NHs was effective in anion binding in the case of receptor <b>1</b>. X-ray analysis of the crystal structure of receptor <b>1</b> and <b>1</b>·NaPF<sub>6</sub> complex showed that binding was hampered due to the formation of an intramolecular hydrogen bond. Analysis of the crystal structures of <b>2</b>·NaBr and <b>3</b>·NaBr complexes revealed that proper mutual orientation of binding domains was responsible for the improved binding of the sodium salts.
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