Anion-directed self-assembly of a 2,6-bis(2-anilinoethynyl)pyridine bis(amide) scaffold

Abstract

Bis(sulfonamide) receptors based on the 2,6-bis(2-anilinoethynyl)pyridine scaffold form persistent dimers with water and halides in solution and in the solid-state. The structurally related bis(amide) receptor derived from 3,5-dinitrobenzoyl chloride is a dimer in the solid-state with two HCl molecules directing the self-assembly. The 2+2 dimer, with a twisted “S”-shaped backbone, is held together by six hydrogen bonds. Dissolution of the (H2+·Cl−)2 adduct in CHCl3 results, however, in a monomeric structure. DOSY and 1H NMR experiments were used to identify the dominance of monomer in solution for both 2 and H2+·Cl−. The ‘OFF-ON’ fluorescence response of 2, 6-bis(2-anilinoethynyl)pyridine is retained with amide arms.

Solution Studies of a Water-Stable, Trivalent Antimony Pnictogen Bonding Anion Receptor with High Binding Affinities for CN–, OCN–, and OAc–

“…Anion binding and recognition, an important subfield of host− guest interactions, is used to direct crystal engineering and molecular templating, 1,2 for selective sensing of anions 3,4 and for metal-free catalysis in organic synthesis. 5,6 Pnictogens have played an important role in anion binding in the +5 oxidation state.…”

“…Anion binding and recognition, an important subfield of host–guest interactions, is used to direct crystal engineering and molecular templating, , for selective sensing of anions , and for metal-free catalysis in organic synthesis. , Pnictogens have played an important role in anion binding in the +5 oxidation state. − This is largely due to the high Lewis acidity of the electron-deficient central pnictogen. Pnictogens in the +3 oxidation state are typically viewed as Lewis bases due to the presence of a lone pair. − The heaviest pnictogens are amphoteric in the +3 oxidation state, and by carefully choosing the chemical environment of the pnictogen, the scales can be tipped toward Lewis acidity allowing for anion binding mediated by pnictogens in the +3 oxidation state. − Figure depicts some of the examples where trivalent pnictogens have been purposefully used for anion binding.…”

“…Up to three of these sites can be induced. The stabilizing interaction that results from an electron donor interacting with this site has been termed a pnictogen bond (PnB), in analogy to the closely related halogen (XB) and chalcogen (ChB) bonds − which have been employed in the design of anion receptors. ,− ,− An important feature of these supramolecular interactions that distinguishes them from formal Lewis acids such as BX 3 , AlX 3 , or PnX 5 (Pn = pnictogen, X = halogen) is that they form with minimal geometric reorganization which results in reversible PnB, ChB, or XB formation without an activation barrier. , These receptors have been applied to form supramolecular capsules to mimic biological molecules, as cross-membrane anion transporting agents, ,,, and as catalysts in substitution reactions. , …”