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

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-H2]2+. The neutral calix[4]arene analog 1 and six salts of the receptor in the mono- or diprotonated form, [1-H2]Cl2 (2), [1-H2]Br2 (3), [1-H2][MeOSO3]2 (4), [1-H2][NO3]2 (5), [1-H2][ClO4]2 (6), and [1-H][ClO4] (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 NO3− gave a true inclusion complex. Additionally, the tetramethylammonium derivative of 1, [1-Me4]I2 (7), was prepared and structurally characterized.1H NMR titration studies of [1-H2]2+ in an aqueous–polar solvent mixture (H2O/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.

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