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The synthesis and anion binding properties of novel halogen-bonding (XB) bis-iodotriazole-pyridinium-containing acyclic and [2]catenane anion host systems are described. The XB acyclic receptor displays selectivity for acetate over halides with enhanced anion recognition properties compared to the analogous hydrogen-bonding (HB) acyclic receptor. A reversal in halide selectivity is observed in the XB [2]catenane, in comparison to the acyclic XB receptor, due to the interlocked host's unique three-dimensional binding cavity, and no binding is observed for oxoanions. Notable halide anion association constant values determined for the [2]catenane in competitive organic-aqueous solvent mixtures demonstrate considerable enhancement of anion recognition as compared to the HB catenane analogue. X-ray crystallographic analysis of a series of halide catenane complexes reveal strong XB interactions in the solid state. These interactions were studied using Cl and Br K-edge X-ray Absorption Spectroscopy (XAS) indicating intense pre-edge features characteristic of charge transfer from the halide to its bonding partner (σ(AX←X(-))(*) ← X1s), and providing a direct measure of the degree of covalency in the halogen bond(s). The data reveal that the degree of covalency is similar to that which is observed in transition metal coordinate covalent bonds. These results are supported by DFT results, which correlate well with the experimental data.

Iodotriazole and triazole anion recognition groups have been integrated into a picket-fence zinc(ii)-metalloporphyrin scaffold to produce receptors for anion recognition and sensing applications. (1)H NMR and UV/visible spectroscopic investigations reveal both host systems exhibit strong anion binding affinities in a range of solvent media. Importantly, the halogen-bonding iodotriazole-containing porphyrin-based host displays halide binding affinities substantially larger than the protic-functionalised analogue concomitant with a reduced strength of oxoanion complexation.

We report the first use of solution-phase halogen bonding to control and facilitate the assembly of an interlocked structure through the bromide anion-templated formation of a rotaxane based upon an iodotriazolium axle. The incorporation of a halogen atom into the rotaxane host cavity dramatically improves the anion-recognition capabilities of the interlocked receptor, giving unusual iodide selectivity in a competitive aqueous medium.

We attempted to use hydrogen, iodo and seleno 3,5-bis(triazolyl)pyridinium (btp) motifs to form 3D supramolecular frameworks assembled by hydrogen, halogen or chalcogen bonding to anions. Initially, we prepared flexible ditopic and tetratopic receptors where the pyridinium nitrogen atom was functionalised with a benzylic group but were unable to crystallise extended frameworks. We subsequently developed the use of Zincke methodology to prepare rigid ditopic and tetratopic hydrogen and halogen bonding tectons, and were able to crystallise the sulfate derivative of a tetratopic receptor, although unfortunately this did not have the desired open framework. Several crystal structures were obtained with the receptors and monovalent anions, including one containing an unusually short iodotriazole⋯Cl− halogen bond. Generally, the btp triazole groups show a tendency to rotate away from the desired conformation and it appears that this may contribute to difficulties in obtaining 3D frameworks even when the receptors have a rigid core. [ABSTRACT FROM AUTHOR]

In this work four new tripodal tris(halopyridinium) receptors containing potentially halogen bonding groups were prepared. The ability of the receptors to bind anions in competitive CD3CN/d6-DMSO was studied using 1H NMR titration experiments, which revealed that the receptors bind chloride anions more strongly than more basic acetate or other halide ions. The solid state self-assembly of the tripodal receptors with halide anions was investigated by X-ray crystallography. The nature of the structures was dependent on the choice of halide anion, as well as the crystallisation solvent. Halogen bond lengths as short as 80% of the sum of the van der Waals radii were observed, which is shorter than any halogen bonds involving halopyridinium receptors in the Cambridge Structural Database. [ABSTRACT FROM AUTHOR]

Neutral heteroditopic [2]rotaxane ion-pair host systems were synthesised via a Cu(ii) directed passive metal template strategy. Each rotaxane contains discrete, axle-separated interlocked binding sites for a guest anion and a transition metal countercation. The anion binding sites are composed of convergent X–H (X = C, N) hydrogen bond donor groups, or mixed X–H and C–I hydrogen and halogen bond donor groups, whereas an equivalent three-dimensional array of amine, pyridine and carbonyl oxygen donor groups comprise the transition metal binding site. 1H NMR titrations experiments in CDCl3/CD3OD or CDCl3/CD3OD/D2O solvent mixtures reveal that the heteroditopic [2]rotaxane host systems are capable of cooperative anion recognition in the presence of a co-bound Zn(ii) cation. [ABSTRACT FROM AUTHOR]

A series of halogen bonding (XB) acyclic anion receptors based on a novel 1,2-iodo-triazolium-triazole benzene motif is reported. The halide anion recognition properties of this new XB donor array are investigated by a suite of techniques including; one- and two-dimensional 1H and 19F NMR spectroscopy and X-ray crystal structure analysis. [Display omitted] The synthesis of a series of halogen bonding (XB) acyclic anion receptors based on a novel 1,2-iodo-triazolium-triazole benzene motif is reported. A combination of one- and two-dimensional 1H and 19F NMR spectroscopic techniques elucidate key conformational effects associated with the incorporation of ortho -substituted iodo-triazole based XB donors. 1H NMR anion titration experiments highlight the anion recognition potency of a mono-cationic XB iodo-triazolium-triazole benzene receptor, remarkably forming stronger halide complexes in comparison to a dicationic hydrogen bonding (HB) bis-proto-triazolium receptor analogue. X-ray crystal structure analysis provide insights into halide binding induced conformational changes and coordination modes, revealing the unique electronic and steric consequences associated with multidentate XB donor arrays. [ABSTRACT FROM AUTHOR]