Dual Role of the 1, 2, 3‐Triazolium Ring as a Hydrogen‐Bond Donor and Anion–π Receptor in Anion‐Recognition Processes. Issue 27 (1st June 2015)

• Record Type: Journal Article
• Authors: Zapata, Fabiola; Gonzalez, Lidia; Caballero, Antonio; Alkorta, Ibón; Elguero, Jose; Molina, Pedro
• Is Part Of: Chemistry. Volume 21:Issue 27(2015)
• Page Start: 9797
• Page End: 9808
• Publication Date: 2015-06-01
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201500231
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Several bis(triazolium)‐based receptors have been synthesized as chemosensors for anion recognition. The central naphthalene core features two aryltriazolium side‐arms. NMR experiments revealed differences between the binding modes of the two triazolium rings: one triazolium ring acts as a hydrogen‐bond donor, the other as an anion–π receptor. Receptors <bold>9<sup>2+</sup>⋅2BF<sub>4</sub></bold><sup><bold>−</bold></sup> (C<sub>6</sub>H<sub>5</sub>), <bold>11<sup>2+</sup>⋅2BF<sub>4</sub></bold><sup><bold>−</bold></sup> (4‐NO<sub>2</sub>C<sub>6</sub>H<sub>4</sub>), and <bold>13<sup>2+</sup>⋅2BF<sup>4−</sup></bold> (ferrocenyl) bind HP<sub>2</sub>O<sub>7</sub><sup>3−</sup> anions in a mixed‐binding mode that features a combination of hydrogen‐bonding and anion–π interactions and results in strong binding. On the other hand, receptor <bold>10<sup>2+</sup>⋅2 BF<sub>4</sub></bold><sup><bold>−</bold></sup> (4‐CH<sub>3</sub>OC<sub>6</sub>H<sub>4</sub>) only displays combined Csp<sub>2</sub>H/anion–π interactions between the two arms of the receptors and the bound anion rather than triazolium (CH)<sup>+</sup>⋅⋅⋅anion hydrogen bonding. All receptors undergo a downfield shift of the triazolium protons, as well as the inner naphthalene protons, in the presence of H<sub>2</sub>PO<sub>4</sub><sup>−</sup> anions. That suggests that only hydrogen‐bonding interactions exist between the binding site and the bound anion, and involve a combination of cationic (triazolium) and neutral (naphthalene) CH donor interactions. Theoretical calculations relate the electronic structure of the substituent on the aromatic group with the interaction energies and provide a minimum‐energy conformation for all the complexes that explains their measured properties.</p> </abstract>