Recognition of nitrate by the ammonium derivative of a 20-membered dioxadiaza-calix[4]arene analogdsolution and solid-state study of the anion binding properties Ram  on Moreno-Corral a , Herbert H € opfl b, * , Anatoly K. Yatsimirsky c , Juan Carlos G  alvez-Ruiz a, d , Karen O. Lara a, * a Departamento de Investigaci on en Polímeros y Materiales, Universidad de Sonora, Rosales y Encinas s/n, Col. Centro, C.P. 83000 Hermosillo, Sonora, Mexico b Centro de Investigaciones Químicas, Universidad Aut onoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, C.P. 62209 Cuernavaca, Morelos, Mexico c Facultad de Química, Universidad Nacional Aut onoma de M exico, Ciudad Universitaria, Circuito Exterior, C.P. 04510 M exico D.F., Mexico d Departamento de Ciencias Químico Biol ogicas, Universidad de Sonora, Rosales y Encinas s/n, Col. Centro, C.P. 83000 Hermosillo, Sonora, Mexico article info Article history: Received 21 October 2014 Received in revised form 18 December 2014 Accepted 5 January 2015 Available online 9 January 2015 Keywords: Calixarene analog Cyclophane Hosteguest chemistry Anion recognition Nitrate receptor X-ray structure analysis 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 ] 2þ . 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 com- parative 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 ] 2þ in an aqueousepolar 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 . Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Anion recognition has emerged as an important topic in modern supramolecular chemistry as a consequence of the key role anions play in biological processes, agriculture, food technology, and en- vironmental chemistry. The most common hosts for the recogni- tion of anion guest molecules are neutral and charged acyclic, macrocyclic, and cage-like receptors. 1 An alternative approach for anion binding consists in the construction of receptors containing Lewis acidic metal centers. 2 Among macrocyclic receptors, cyclophanes, 3 calix[n]arenes 4 and related molecules 5 have received attention because of the in- herent cavity and conformational flexibility that allows them to adapt to the steric and electronic requirements of the guest. This is particularly important for the inclusion of anions because of their larger variation in size and geometry compared with cations. Initially, azonia-bridged cyclophanes and calixarene derivatives have been employed only for the formation of inclusion complexes with neutral and negatively charged aromatic guest molecules, 6 but more recently these studies have been extended to the recognition of inorganic anions. 7,8 Starting from salicylaldehyde and salicylic acid, a large family of oxaazamacrocycles can be prepared, whose properties and struc- tural frames can be modified easily by varying the size and/or functionality of the bridging groups. 9,10 This includes also hetero- atom bridged calix[4]arene analogs, which can be obtained by employing proper building blocks. 10g These systems are interesting candidates for binding inorganic and organic anions of diverse nature because they can provide multiple hydrogen bonding in- teractions, which can be accomplished further through additional interactions, such as CeH/X  and p/p contacts. 11 Additionally, the electrostatic interaction between the host and the guest can be significantly enhanced by transforming the neutral macrocycles into the corresponding ammonium salts, either via protonation or alkylation. 1jem The resulting cationic macrocycles are frequently soluble in water. 3c,d * Corresponding authors. Fax: þ52 777 329 7997 (H.H); fax: þ52 662 259 2216 (K.O.L); e-mail addresses: hhopfl@uaem.mx (H. H€ opfl), karenol@polimeros.uson.mx (K.O. Lara). Contents lists available at ScienceDirect Tetrahedron journal homepage: www.elsevier.com/locate/tet http://dx.doi.org/10.1016/j.tet.2015.01.005 0040-4020/Ó 2015 Elsevier Ltd. All rights reserved. Tetrahedron 71 (2015) 1232e1240