Advances in Anion Supramolecular Chemistry: From Recognition to Chemical Applications

Abstract

Since the start of this millennium, remarkable progress in the binding and sensing of anions has been taking place, driven in part by discoveries in the use of hydrogen bonding, as well as the previously under-exploited anion-π interactions and halogen bonding. However, anion supramolecular chemistry has developed substantially beyond anion recognition, and now encompasses a diverse range of disciplines. Dramatic advance has been made in the anion-templated synthesis of macrocycles and interlocked molecular architectures, while the study of transmembrane anion transporters has flourished from almost nothing into a rapidly maturing field of research. The supramolecular chemistry of anions has also found real practical use in a variety of applications such as catalysis, ion extraction, and the use of anions as stimuli for responsive chemical systems.

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

“…[1][2][3] Thenitrate anion in particular is an environmental pollutant when leeched into lakes and rivers resulting from anthropogenic overuse of fertilizers or by acid rain.…”

“…[1][2][3] Thenitrate anion in particular is an environmental pollutant when leeched into lakes and rivers resulting from anthropogenic overuse of fertilizers or by acid rain. [4] Medically,a no ver exposure to nitrate via contaminated drinking water is associated with the formation of carcinogenic nitrosamines and ar ange of diseases such as methemoglobinemia (blue baby syndrome) in infants.…”

“…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. [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] Importantly in as ignificant step forward for highlighting the potential importance of halogen bonding in anion supramolecular chemistry,w eh ave recently demonstrated the first examples of solution phase halogen bonding being exploited to control and facilitate the anion-templated assembly of interlocked structures [43][44][45][46][47] and demonstrated that the incorporation of halogen bond donor atoms into a [ 2]rotaxane host cavity dramatically improves the anion recognition capabilities of the XB interlocked receptor. [48][49][50][51] Herein, we report the synthesis of the first halogen bonding [3]rotaxane host system, containing ab is-iodo triazolium-bis-naphthalene diimide four station axle component, which employs multiple cooperative XB and HB interactions to exhibit enhanced recognition of anions relative to an all-HB analogue and, impressively,i sf ound to be selective for nitrate over other oxoanions and chloride.…”

“…Thereaction of two equivalents of bis-vinyl-functionalised macrocyclic precursor 3 with the appropriate HB, 1·(Cl) 2 or XB, 2·(Cl) 2 axle in the presence of Grubbs II catalyst in dry dichloromethane afforded, after purification by preparative silica thin-layer chromatography,the desired HB and XB [3]rotaxanes, 4·(Cl) 2 and 5·(Cl) 2 respectively (Scheme 1).…”

“…Cross coupling correlations between the mechanically bonded macrocycle (H g,g' and H e,e' )a nd diagnostic protons of the bis triazolium station of the axle components (H n ,H k, H l and H o )i ndicate both macrocycles symmetrically occupying the central recognition site courtesy of convergent HB and/or XB to each of the chloride counter anions ( Figures S1 and S2). An absence of cross coupling between the macrocycle and NDI station protons (Figures S1 and S2) and small differences between d(H e,e' )inthe 1 HNMR spectra of [3]rotaxanes 4·(Cl) 2 and 5·(Cl) 2 and the bis-chloride salts of their corresponding axles indicates there are negligible interactions between macrocycles and the NDI stations ( Figures S3 and S4).…”