Anion Template Research Articles

Silver(I)−Ethynide Clusters Constructed with Phosphonate-Functionized Polyoxovanadates

Two neutral silver(I)-phenylethynide clusters incorporating the [((t)BuPO(3))(4)V(4)O(8)](4-) unit as an integral shell component, namely {(NO(3))(2)@Ag(16)(C≡CPh)(4)[((t)BuPO(3))(4)V(4)O(8)](2)(DMF)(6)(NO(3))(2)}·DMF·H(2)O and {[(O(2))V(2)O(6)](3)@Ag(43)(C≡CPh)(19)[((t)BuPO(3))(4)V(4)O(8)](3)(DMF)(6)}·5DMF·2H(2)O, have been isolated and characterized by X-ray crystallography. The central cavities of the Ag(16) and Ag(43) clusters are occupied by two NO(3)(-) and three [(O(2))V(2)O(6)](4-) template anions, respectively.

Chloride Anion Templated Synthesis and Crystal Structure of a Handcuff Catenane

Chloride, you're nicked! A novel handcuff catenane was prepared by anion templation and π–π stacking interactions. In addition, the first crystal structure determination of such a catenane is reported.

Kinetic Studies Exploring the Role of Anion Templation in the Slippage Formation of Rotaxane-Like Structures

The first examples of the slippage formation of rotaxane-like structures in the presence of an anion template are reported between a macrocycle, synthesised by exploiting Eglinton coupling, and stoppered pyridinium axle components. The role of the anion template in the slippage process has been explored by kinetic studies. (1)H NMR spectroscopic investigations reveal the slippage species formed are not rotaxanes but pseudorotaxanes with some rotaxane character. The anion template significantly influences the amount of rotaxane character and the rate of slippage. Importantly, the fastest slippage rates, k(on), are achieved with the non-coordinating hexafluorophosphate anion, whereas the slowest slippage off rates, k(off), are observed in the presence of coordinating anions, such as chloride. Since the k(off) rates are significantly smaller than the k(on) rates in the presence of coordinating anions, these anions act as templates favouring formation of the slippage species thermodynamically. Consequently, the resulting pseudorotaxanes with coordinating anions have greater rotaxane character. Two strategies for converting the slippage pseudorotaxanes into rotaxanes using hydrogenation or complexation with cobalt carbonyl are investigated.

Anion templated assembly of [2]catenanes capable of chloride anion recognition in aqueous solvent media

An anion templated double cyclization strategy to synthesize [2]catenanes in which two identical acyclic pyridinium receptor motifs interweave around a chloride anion template is described. Ring closing metathesis (RCM) of the preorganized orthogonal precursor chloride complex facilitates the isolation of [2]catenanes in very high yields. X-ray crystal structures provide an insight of the supramolecular forces responsible for chloride anion templated efficacy and recognition. Removal of the chloride anion template generates topologically unique interlocked binding cavities for anions. 1H NMR anion binding investigations demonstrate the catenanes to be highly selective hosts for chloride in preference to more basic monocharged oxoanions. In aqueous solvent media containing 30% water, such catenanes exclusively bind chloride, under which conditions no binding of acetate or dihydrogen phosphate is observed. Molecular dynamic simulations in the solution phase are used to account for the catenanes’ anion recognition properties.

Polyoxometalate-templated lanthanide–organic hybrid layers based on 63-honeycomb-like 2D nets

The reaction of a double-betaine-containing ligand with LnPMo(12)O(40)·nH(2)O (Ln = Dy, Tb and Er) led to the isolation of new polyoxometalate-templated lanthanide-organic hybrid layers with the molecular formula [Ln(L)(1.5)(H(2)O)(5)][PMo(12)O(40)]·1.5CH(3)CN·2H(2)O (Ln = Dy (1), Tb (2) and Er (3); L = 1,4-bis(pyridinil-4-carboxylato)-l,4-dimethylbenzene). All compounds were characterized by elemental analyses, TG analyses, IR and the single-crystal X-ray diffraction. Compounds 1-3 are isostructural and possess a 2D undulating cationic network [Ln(L)(1.5)(H(2)O)(5)](n)(3n+) with the honeycomb-like cavities. Interestingly, the interval 2D networks are further connected by the H-bonds to form a 3D supramolecular framework. Moreover, two of such identical supramolecular frameworks are 2-fold interpenetrated with each other and encapsulate the α-Keggin-type [PMo(12)O(40)](3-) anionic templates and the solvent molecules. These composite compounds display both luminescent properties (induced by organic ligands and/or lanthanide ions) and electrocatalytic activities towards the reduction of nitrite.

Clipping and stoppering anion templated synthesis of a [2]rotaxane host system

A new [2]rotaxane host system containing nitro-isophthalamide macrocycle and polyether functionalised pyridinium axle components is prepared via clipping and stoppering synthetic methodologies using chloride anion templation. After removing the chloride anion template, (1)H NMR titration experiments reveal the unique interlocked host cavity to be highly selective for binding chloride and bromide in preference to basic oxoanions in competitive aqueous solvent mixtures. The rotaxane host system proved to be a superior anion complexant in comparison to the individual macrocycle and axle components. The anion binding affinity of the novel rotaxane is also investigated via molecular dynamics simulations and in general the structural data obtained corroborates the experimental solution anion recognition behaviour.

Structurally disfavoured pseudopeptidic macrocycles through anion templation

An anionic dicarboxylate is able to template the formation of geometrically disfavoured macrocycles from a dynamic covalent mixture of open chain oligoimines.

A ferrocene functionalized rotaxanehost system capable of the electrochemical recognition of chloride

A ferrocene appended rotaxane is prepared by chloride anion templation and ring closing metathesis. Upon removal of the chloride template, the rotaxane is demonstrated to be selective for chloride over more basic oxoanions by (1)H NMR spectroscopy and electrochemistry, in marked contrast to an acyclic analogue--the first example of a solution based redox-active interlocked host system capable of the electrochemical recognition of anions.

A redox-active [3]rotaxane capable of binding and electrochemically sensing chloride and sulfate anions

A ferrocene functionalised redox-active [3]rotaxane which contains two interlocked anion recognition sites has been prepared by chloride anion templation. With chloride two equivalents of anion are bound, one in each of the interlocked cavities, while sulfate forms a 1:1 stoichimetric sandwich type complex; the rotaxane can also electrochemically sense the two anions in acetonitrile.

Cation-induced molecular motion of spring-like [2]catenanes

The syntheses and cation recognition studies of two novel heteroditopic [2]catenanes that are capable of reversible rotary motion are described. Prepared by chloride anion templation, both catenanes possess a calixdiquinone unit able to bind Na+, K+, NH4+ and Ba2+ cations. Following characterization of the chloride salts of both catenanes by NMR, mass spectrometry and crystal structure determination, hexafluorophosphate salts were investigated for their behaviour upon addition of cations. Ba2+ complexation caused a partial intra-ring rotation of the two macrocycles in both species, which was reversed upon addition of the sequestering SO42− anion.

A new synthetic route to chloride selective [2]catenanes

A novel anion templation route has been developed to synthesise two new catenanes, which are observed to selectively complex chloride in protic solvent media.

A novel arenedisulfonate-templated 1D silver ladder constructed from 4-aminobenzonitrile ligand

A novel infinite 1D Ag(I)-abn ladder, [nds⊂Ag2(abn)4]n (1, H2nds = 1,5-naphthalenedisulfonic acid, abn = 4-aminobenzonitrile), was synthesized based on a nds anionic template which was encapsulated in the 1D ladder through N–H⋯O hydrogen bonds and weak C–H⋯π interactions. In contrast, using X [X = NO3− (2), ClO4− (3), PF6− (4), CF3COO− (5)] as counteranions, four 2D wavy 63-hcb nets (2–5) were obtained, which unambiguously indicates that nds anion plays the role of template in the formation of 1. The photoluminescence behaviour of 1–5 were also discussed.

Suppression of background sites in molecularly imprinted polymersviaurea-urea monomer aggregation

The molecular imprinting process provides a synthetically efficient route to polymers with tailored recognition properties. However, the binding properties of the templated binding sites are often masked by the more prevalent background binding sites. Therefore, a strategy for reducing the number of background binding sites was developed and evaluated that uses functional monomer aggregation to suppress the formation of background sites. A series of imprinted and non-imprinted polymers was formed using crosslinking urea monomer and were evaluated for their ability to rebind the anionic template, tetrabutylammonium diphenyl phosphate (TBA-DPP). The urea monomer was shown to form linear hydrogen bonded aggregates in solution and in the solid state. Functional monomer aggregation in the polymerization solution was shown to dramatically reduce the numbers of background binding sites by occupying and blocking the urea recognition groups that were not bound to the template molecule. Despite the low aggregation constant of the urea monomer (3.5 M(-1) in chloroform), the number of background sites was reduced by more than 60%. We predict that this strategy of using monomers that aggregate to reduce background binding sites is a general one for MIPs and other types of polymers with tailored recognition properties. The key is to identify self-assembling monomers where the guest binding processes are stronger than the aggregation processes.

ChemInform Abstract: New Strategy and Methods for Constructing Artificial Macrocyclic Anion Receptors. Selective Binding of Tetrahedral Oxoanions

AbstractReview: 41 refs.

Synthesis and Characterization of Chloride-incorporated Dodecavanadate from Dicopper Complex of Macrocyclic Octadecavanadate

Abstract A chloride-incorporated dodecavanadate, [V12O32(Cl)]5− (1) has been synthesized from a dicopper macrocyclic complex, [Cu2V8O24]4− (2). By using hydrogen cyanide with a chloride guest anion, two copper cations are removed and the presence of chloride anion template affords a new bowl-shaped dodecavanadate, 1, with chloride anion at the center. The 1:1 mixture of 1 and [V12O32(CH3CN)]4− (3) in acetonitrile shows no 51V NMR signal scrambling at room temperature suggesting the tight binding of the chloride anion inside the anionic bowl molecule. The dissociation of the chloride anion was only observed at higher temperatures.

Reversible Anion Exchange and Catalytic Properties of Two Cationic Metal−Organic Frameworks Based on Cu(I) and Ag(I)

We report the synthesis and characterization of two Ag(I)/Cu(I)-based cationic metal-organic frameworks and their application in both heterogeneous catalysis and anion exchange. The Cu(I)-based material was designed from our previously reported Ag(I) cationic topology. Both structures consist of cationic layers with pi-pi stacked chains of alternating metal and 4,4'-bipyridine. Alpha,omega-alkanedisulfonate serves as an anionic template, electrostatically bonding to the cationic layers. Due to weak interaction between the sulfonate template and cationic extended framework, both materials display reversible anion exchange for a variety of inorganic species. Indeed, the Ag(I)-based material exhibits highly efficient uptake of permanganate and perrhenate anion trapping, a model for pertechnetate trapping. The materials also display heterogeneous Lewis acidity, likely due to the coordinatively unsaturated metal sites which only bind to two bipy nitrogens and a weak interaction with one sulfonate oxygen. A comparative study on the influence of structure versus size selectivity and reusability for both exchange and catalysis is discussed.

Pyrazino[2.3‐g]quinoxaline‐Bridged Indole‐Based Building Blocks: Design, Synthesis, Anion‐Binding Properties, and Phosphate‐Directed Assembly in the Solid State

Strategies for exploring anionic templates to direct sophisticated supramolecular assembly have attracted attention. Herein, a series of new anion receptors 1-3 containing two indole-based binding sites bridged by linking spacer pyrazino[2.3-g]quinoxaline (PQ) have been rationally designed and prepared from the precursors 2,3-diindol-3'-yl quinoxaline (DIQ) and 5,6-dihydrodiindolo[3,2-a:2',3'-c]phenazine (DIPZ). X-ray analyses showed a self-connected network and dimeric packing through hydrogen bonding and π-π stacking interaction in the solid state in the structures of 1 and 2, respectively. All three receptors exhibited a series of prominent absorption bands from the expanded π system. The indole-based expanded receptors were found to strongly and selectively bind F(-), AcO(-), and H2PO4(-) among the tested anions (F(-), Cl(-), Br(-), AcO(-), H2PO4(-), HSO4(-), NO3(-), and ClO4(-)), and operated as efficient colorimetric sensors for naked-eye detection of fluoride anions in DMSO. These tailored building blocks captured two anions located at far-spaced binding sites, and adopted noninterfering anion-binding processes to guarantee the anion-binding affinity, topology, and dimensionality. Solid-state studies elucidated that the neutral 1-3 interacted with the tetrahedral dihydrogen phosphate anion in proper proportions and designed topologies, thus leading to the formation of a series of multidimensional networks by self-assembly in the solid state. The observations showed a well-characterized phosphate-directed assembly of multidimensional metal-free coordination polymers in the solid state, in which the formed phosphate aggregates, including dimer encapsulated in an indole-mediated hydrogen-bonded pocket and an infinite chain, behaved as anionic templates to direct the self-assembly. However, no evidence proved the presence of such phosphate-directed infinite coordination polymers in solution.

Synthetic Strategies for the Construction of Threaded and Interlocked Molecules

This review summarizes the different synthetic strategies based on chemical templation for the construction of threaded and interlocked molecules (rotaxanes, pseudorotaxanes and catenanes). The chemical templates or intermolecular interactions used to bring together in an organised fashion the different component parts of the threaded or interlocked structures can be divided into: anionic and cationic templates, hydrogen bonding interactions, π-stacking and charge-transfer interactions and hydrophobic interactions. Examples of the most common structures displaying these interactions will be discussed. Keywords: Catenanes, rotaxanes, pseudorotaxanes, template synthesis, self-assembly

Calix[4]arene‐Based Rotaxane Host Systems for Anion Recognition

The synthesis, structure and anion binding properties of the first calix[4]arene-based [2]rotaxane anion host systems are described. Rotaxanes 9.Cl and 12.Cl, consisting of a calix[4]arene functionalised macrocycle wheel and different pyridinium axle components, are prepared via adaption of an anion templated synthetic strategy to investigate the effect of preorganisation of the interlocked host's binding cavity on anion binding. Rotaxane 12.Cl contains a conformationally flexible pyridinium axle, whereas rotaxane 9.Cl incorporates a more preorganised pyridinium axle component. The X-ray crystal structure of 9.Cl and solution phase (1)H NMR spectroscopy demonstrate the successful interlocking of the calix[4]arene macrocycle and pyridinium axle components in the rotaxane structures. Following removal of the chloride anion template, anion binding studies on the resulting rotaxanes 9.PF(6) and 12.PF(6) reveal the importance of preorganisation of the host binding cavity on anion binding. The more preorganised rotaxane 9.PF(6) is the superior anion host system. The interlocked host cavity is selective for chloride in 1:1 CDCl(3)/CD(3)OD and remains selective for chloride and bromide in 10 % aqueous media over the more basic oxoanions. Rotaxane 12.PF(6) with a relatively conformationally flexible binding cavity is a less effective and discriminating anion host system although the rotaxane still binds halide anions in preference to oxoanions.

Hydrolytic synthesis and structural characterization of five hexanuclear oxo-hydroxo lanthanideclusters

Five hexanuclear oxo-hydroxo lanthanide clusters are synthesized by hydrolysis of the lanthanide ions together with 4-amido-3,5-dimethyl-1,2,4-triazole (L). They all have a [Ln6(µ6–O)(µ3–OH)8]8+ core structure and the triazole groups stabilize the core structure in different fashions. The oxo group functions as an anion template to induce the self-assembly of lanthanide ions.