An All‐Halogen Bonding Rotaxane for Selective Sensing of Halides in Aqueous Media

Abstract

The synthesis and anion binding properties of the first rotaxane host system to bind and sense anions purely through halogen bonding, is described. Through a combination of polarized iodotriazole and iodotriazolium halogen bond donors, a three-dimensional cavity is created for anion binding. This rotaxane incorporates a luminescent rhenium(I) bipyridyl metal sensor motif within the macrocycle component, thus enabling optical study of the anion binding properties. The rotaxane topology was confirmed by single-crystal X-ray structural analysis, demonstrating halogen bonding between the electrophilic iodine atoms and chloride anions. In 50 % H 2 O/CH 3 CN solvent mixtures the rotaxane host exhibits strong binding affinity and selectivity for chloride, bromide, and iodide over a range of oxoanions.

The Halogen Bond

“…In this case both the axle and the macrocycle integrated XB donor units, namely, two iodotriazole and two iodotriazolium motifs, respectively ( Figure 70 , top). 550 The cooperative and convergent XB interaction with chloride allowed for the formation of the interlocked adduct as confirmed by X-ray analysis.…”

“… 1109 This was, for example, the case for directionality when allowing some XBs to outperform stronger HBs in writing surface-relief gratings on thin films of supramolecular polymers, 489 , 855 , 859 or for donor atom size when altering by the heavy-atom effect the light-emitting properties of halogenated dyes by promoting singlet-to-triplet intersystem crossing. 997 Many other examples of specific advantages brought up by the use of XB have been demonstrated in quite different fields spanning from material sciences (e.g., liquid crystals 844 , 854 , 1110 and gels 83 ) to separation and sensing (e.g., anion recognition 550 , 657 , 719 and transport 213 , 214 ).…”

“…Its cationic form also has a good XB donor ability and has been recently used in anion recognition processes driven by XB in solution. 550 …”

Anion Recognition in Water by Charge-Neutral Halogen and Chalcogen Bonding Foldamer Receptors

“…A small hypsochromic shift of emission maximum from 564 nm to 558 nm was also observed. This significant 'turn-on' emission observed upon Iaddition is especially noteworthy, as the 'heavy atom effect' associated with this anion 81 often results in dramatic fluorescence attenuation 82 or small changes in intensity. 47,83 The main reason for the fluorescence enhancement is most likely the restriction of intramolecular motion 84 upon Icomplex formation.…”

Contrasting anion recognition behaviour exhibited by halogen and hydrogen bonding rotaxane hosts

“…[10][11][12][13][14][15][16] In an effort to overcome the challenge of recognising anions in competitive protic solvent media we have constructed interlocked rotaxane and catenane host structures containing unique three dimensional cavities decorated with an array of convergent HB donors and shown such systems to be effective hosts in solvent media of this nature. [21][22][23][24][25] For example, a rotaxane containing a XB 5-iodo-1,2,3-triazolium functionalised axle component binds halides strongly in aqueous solvent media, with a preference for iodide. [21][22][23][24][25] For example, a rotaxane containing a XB 5-iodo-1,2,3-triazolium functionalised axle component binds halides strongly in aqueous solvent media, with a preference for iodide.…”