Nitrate Anion Recognition in Organic–Aqueous Solvent Mixtures by a Bis(triazolium)acridine‐Containing [2]Rotaxane

Abstract

The synthesis of a novel [2]rotaxane host system containing a bis(triazolium)acridine-based axle component is reported. (1)H NMR anion-binding titrations reveal that the rotaxane is able to recognise selectively the NO3(-) anion over a range of more basic oxoanions (AcO(-), HCO3(-) and H2PO4(-)) in a competitive organic-aqueous solvent mixture.

[C–H⋯anion] interactions mediate the templation and anion binding properties of topologically non-trivial metal–organic structures in aqueous solutions

“…This motif is present in small anion binders such as the bisimidazoliums of the Maeda group,31 as well as the triazole-containing macrocycles and podands reported by Flood and coworkers 32–34. Previous examples of topologically interesting complexes in which this feature is present include Leigh's pentafoil knot,35–37 which is templated, in part, by a central chloride ion; and the chloride and nitrate-binding rotaxanes38,39 of the Beer group. Nevertheless, measurements of the anion binding affinities of molecular links and knots have rarely been reported 38,40.…”

Selective Nitrate Recognition by a Halogen‐Bonding Four‐Station [3]Rotaxane Molecular Shuttle

“…[22,23,55] Thes uperior nitrate recognition of this new generation of [3]rotaxanes is ascribed to the complementarity of the three-dimensional cavity resulting from the bidentate bis-triazolium site of the axle component and two hydrogen bond-donating isophthalamide macrocycles.T he importance of the macrocyclic wheel components was demonstrated by the significantly weaker binding of nitrate by the HB and XB axle components 1·(BF 4 ) 2 and 2·(BF 4 ) 2 in the same solvent mixture (K Ass = 163 and 216 m À1 respectively,F igures S23 and S24). [56] Ac omparison of the association constants for each [3]rotaxane crucially reveals the XB system to demonstrate superior anion binding,f or all anions,r elative to the HB analogue,c ourtesy of strong halogen bond formation to the anionic guest.…”

“…[7][8][9][10][11][12][13][14][15][16][17][18][19] Thec hallenge of developing synthetic receptors that can rival the anion recognition properties of biotic systems relies upon the arrangement of at hree-dimensional convergent array of numerous HB donor groups in an optimized geometry for recognition of the complementary guest. [20,21] To meet this challenge we have exploited anion-templation to construct interlocked host structures [22,23] whose unique threedimensional cavities encapsulate anionic guest species.While during the past two decades HB has been widely exploited in anion receptor design, halogen bonding (XB), [24][25][26][27] the attractive highly directional interaction between an electron-deficient halogen atom and aL ewis base,h as only recently begun to be utilised for anion recognition. Of the relatively few examples of XB anion receptors reported to date,i ti sn oteworthy that all display promising,a nd significantly contrasting, anion recognition behaviour when compared to HB analogues,byvirtue of their comparable bond strengths and more strict linear geometry preference.…”

“…[7][8][9][10][11][12][13][14][15][16][17][18][19] Thec hallenge of developing synthetic receptors that can rival the anion recognition properties of biotic systems relies upon the arrangement of at hree-dimensional convergent array of numerous HB donor groups in an optimized geometry for recognition of the complementary guest. [20,21] To meet this challenge we have exploited anion-templation to construct interlocked host structures [22,23] whose unique threedimensional cavities encapsulate anionic guest species.…”

Selective Nitrate Recognition by a Halogen‐Bonding Four‐Station [3]Rotaxane Molecular Shuttle

“…To meet this challenge we have exploited anion‐templation to construct interlocked host structures22, 23 whose unique three‐dimensional cavities encapsulate anionic guest species.…”