Recognition of nitrate by the ammonium derivative of a 20-membered dioxadiaza-calix[4]arene analog—solution and solid-state study of the anion binding properties

Abstract A 20-membered dioxadiaza-calix[4]arene analog ( 1 ) was combined with a series of inorganic acids to explore the anion-inclusion properties of the corresponding ammonium dication [ 1-H 2 ] 2+ . The neutral calix[4]arene analog  1 and six salts of the receptor in the mono- or diprotonated form, [ 1-H 2 ]Cl 2 ( 2 ), [ 1-H 2 ]Br 2 ( 3 ), [ 1-H 2 ][MeOSO 3 ] 2 ( 4 ), [ 1-H 2 ][NO 3 ] 2 ( 5 ), [ 1-H 2 ][ClO 4 ] 2 ( 6 ), and [ 1-H ][ClO 4 ] ( 6b ), were structurally characterized by single-crystal X-ray diffraction analysis, which enabled a detailed comparative analysis of the non-covalent interactions. The structural comparison showed that the different anions induce conformational changes of the macrocyclic structure, but only NO 3 − gave a true inclusion complex. Additionally, the tetramethylammonium derivative of 1 , [ 1-Me 4 ]I 2 ( 7 ), was prepared and structurally characterized. 1 H NMR titration studies of [ 1-H 2 ] 2+ in an aqueous–polar solvent mixture (H 2 O/MeOH, 9:1 v/v, pH 5.5) with a series of organic and inorganic anions gave association constants varying from 1.4 to 84.6 M −1 .