Discrete 1 : 1 complexes and higher order assemblies formed from aminobenzene sulphonate anions and a tetraimidazolium "molecular box".

Use of isomeric aminobenzene sulphonate anions in conjunction with a tetraimidazolium "molecular box" leads to self-assembled embedded structures. Simple 1 : 1 complexes are formed at low concentrations in DMSO when the host : guest ratio is 1.0. Higher order species are seen as the concentration is increased or the host-guest ratio is perturbed. The assembly and disassembly of the supramolecular aggregates can be controlled by application of various external stimuli, including changes in concentration, temperature, and protonation state of the guest species.

Post-synthetic modification of a macrocyclic receptor via regioselective imidazolium ring-opening.

A facile post-synthetic modification of a tetracationic tetraimidazolium macrocycle, 14+ (i.e., the "Texas-sized" molecular box (cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene)), is described. Under mild basic conditions, ring-opening of the imidazolium moieties occurs. This results in two new isomeric dicationic macrocycles. This simple yet efficient modification serves to alter the size of the molecular cavity, the charge of the macromolecular receptor, and the manner whereby it interacts with dianionic guest molecules. The isomeric mixture of imidazolium ring opened macrocycles can be synthesized in relatively high overall yield (86-93%). The reaction shows regioselectivity and the ratio of major to minor (i.e., trans : cis ring-opened products) was determined to be ca. 3 : 1 via1H NMR spectroscopy. The major isomer, trans-cyclo[2]((Z)-N-(2-((6-(1H-imidazol-1-yl)pyridin-2-yl)amino)vinyl)formamide)[2](1,4-bismethylbenzene) hexafluorophosphate (22+·2PF6-), was isolated in its pure form in 42% yield via recrystallization. The molecular recognition properties of 22+ were investigated using a series of dianionic guests (i.e., 2,6-naphthalenedicarboxylate (4), 2,6-naphthalenedisulfonate (5), and 1,5-naphthalenedisulfonate (6)) whose binding interactions with 14+ have been previously reported. This allowed us to evaluate how imidazolium ring-opening affects the inherent host/guest interactions of 14+. On the basis of solution spectroscopic studies (e.g., 1H NMR, 1H-1H COSY NMR, DOSY NMR, and NOESY NMR), in tandem with mass spectrometric analyses (ESI-MS) and single-crystal X-ray diffraction studies, we conclude that opening up the macrocyclic structure (i.e., converting 14+ to 22+) leads to considerable changes in the recognition behavior, with so-called outside binding or weak ion pair interactions, rather than pseudorotaxane formation, being favored both in solution and the solid-state. We postulate that methodologies such as those described herein could provide a means to control the molecular interactions of both free-standing macrocycles and those used to construct mechanically-interlocked molecules. Indeed, the application of hydroxide anion under the present conditions not only serves to effect the ring-opening of 14+, but also pseudorotaxane structures, such as, e.g., [14+·4] or [14+·5] derived there from.

Multicomponent Self-Assembled Metal-Organic [3]Rotaxanes.

A set of environmentally responsive metal-organic [3]rotaxanes is described. These mechanically interlocked macromolecules may be prepared in quantitative yield via a one-pot procedure involving treatment of a flexible tetracationic macrocycle, known as the Texas-sized molecular box, with tri-1,3,5-benzenetricarboxylate anion and silver cations (Ag(+)). The use of this three-component mixture gives rise to a metal-organic [3]rotaxane via a self-assembly process that occurs under ambient conditions in DMSO-d6 solution. The complex is stable in the presence of excess TFA. However, disassembly of the [3]rotaxane to produce anion-box associated entities may be triggered by adding a competitive counteranionic species (e.g., I(-)). Adding excess Ag(+) serves to reverse this decomplexation process. The nature of the [3]rotaxane complex could be fine-tuned via application of an external stimulus. Increasing the temperature or adding small molecules (e.g., D2O, methanol-d4, acetonitrile-d3, DMF-d7, acetone-d6, or THF-d8) to the initial DMSO-d6 solution induces conformational flipping of the macrocycle within the overall complex (e.g., from limiting chair to chairlike forms). Support for the molecular stimuli responsive nature of the various structures came from solution-phase one- and two-dimensional ((1)H, 1D and 2D NOESY) NMR spectroscopic studies carried out in DMSO-d6. The core metal-linked rotaxane unit was characterized via single-crystal X-ray diffraction analysis. Initial evidence that the present self-assembly process is not limited to the use of the Ag(+) cation came from studies involving Cd(2+); this replacement results in formation of 2D metal-organic rotaxane-containing frameworks (MORFs).

Aromatic sulfonate anion-induced pseudorotaxanes: environmentally benign synthesis, selectivity, and structural characterization.

Anion-induced molecular threading is an emerging strategy for generating mechanically interlocked molecular architectures. Herein, we report the preparation of two pseudorotaxane structures generated from aromatic sulfonate anions and a tetraimidazolium-containing macrocycle in organic media, as well as under environmentally benign aqueous conditions.

Correction: Aromatic sulfonate anion-induced pseudorotaxanes: environmentally benign synthesis, selectivity, and structural characterization.

Correction for 'Aromatic sulfonate anion-induced pseudorotaxanes: environmentally benign synthesis, selectivity, and structural characterization' by Han-Yuan Gong et al., Chem. Commun., 2015, DOI: .

Reversible anion-induced cross-linking of well-defined calix[4]pyrrole-containing copolymers.

Reversible addition/fragmentation chain-transfer polymerization is used to generate a calix[4]pyrrole methacrylate-derived copolymer. The material is found to undergo supramolecular cross-linking upon exposure to select dianionic species (e.g., pyrophosphate and terephthalate salts), altering the viscoelastic properties of the copolymer in solution and in the solid state. The copolymeric material is also used for selective differentiation of mono- and bis-anions under conditions of liquid/liquid extraction.

"Texas-sized" molecular boxes: building blocks for the construction of anion-induced supramolecular species via self-assembly.

It was previously established that the flexible tetraimidazolium macrocycle cyclo[2](2,6-bis(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene) (1(4+)) is capable of stabilizing higher-order supramolecular structures via both anion and cation recognition. Described herein is a set of structurally related imidazolium macrocycles (2(4+)-4(4+)) that contain modified central cores. The flexible nature of these new constructs is highlighted by the isolation of several independent crystalline forms for the same basic structure. Each of the individual receptors was found to bind the 2,6-naphthalenedicarboxylate dianion and to stabilize the formation of self-associated structures. The observed binding modes and resulting supramolecular organizational forms were found to differ dramatically depending on the nature of the bridging group present in the imidazolium macrocycle. This finding was established by solution studies involving, inter alia, one- and two-dimensional ((1)H, (1)H-(1)H COSY, DOSY, and NOESY) NMR spectroscopy as well as electrospray ionization mass spectrometry. The new systems in this report serve to expand the available "tool box" for the construction of complex self-assembled materials while providing insights into the determinants that regulate the formation of specific supramolecular structures from flexible receptors capable of adopting multiple stable conformations.

Rare-earth cation effects on three-dimensional metal-organic rotaxane framework (MORF) self assembly.

A set of metal-organic rotaxane frameworks (MORFs) are constructed with the use of a tetraimidazolium macrocycle, the terephthalate dianion, and the trivalent lanthanide metal cations Nd(III), Sm(III), Eu(III) or Tb(III) and are reported herein. The specific choice of the metal cation allows for control of the structure and luminescent properties of the resulting molecular frameworks.

The "Texas-sized" molecular box: a versatile building block for the construction of anion-directed mechanically interlocked structures.

Over the last two decades, researchers have focused on the synthesis and development of mechanically interlocked molecules (MIMs). The intramolecular motion of mechanical bonds and the ability to induce this effect with the choice of the proper external stimuli has prompted the development of macromolecular systems that possess the ability to "perform work" at the molecular level. Currently, researchers are working to incorporate interlocked species into complex structural systems, such as molecular frameworks and nanoparticles, and to create ever more elegant noncovalent architectures. This effort provides an incentive to generate new building blocks for the construction of MIMs. In this Account, we describe progress in the development of a new cationic building block inspired by the "blue box" of Stoddart and collaborators. The blue box (cylcobis(paraquat-p-phenylene) or CBPQT(4+)) is a tetracationic, electron-deficient macrocycle widely recognized for its role in the construction of MIMs. This venerable receptor displays a high affinity for a variety of π-donor guests, and researchers have used them to construct a wide range of molecular and supramolecular structures, including rotaxanes, catenanes, pseudorotaxanes, polypseudorotaxanes, pseudo[n]polyrotaxanes, and electrochemically switchable molecules. To date, several synthetic analogues of the basic CBPQT(4+) structure have been reported, including systems containing biphenylene linkers and chiral tetracationic cyclophanes. However, researchers have not yet fully generalized the promise of the blue box. In this Account, we chronicle the development of a larger, more flexible tetracationic macrocycle, referred to as the "Texas-sized" molecular box. To highlight its relatively increased size and to distinguish it from CBPQT(4+), we have chosen to color this new receptor burnt orange. The Texas-sized box (cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene), 1(4+)·4PF(6)(-)) acts as a dynamic molecular receptor that displays an ability to adjust its shape and conformation to accommodate anionic guests of different size and charge within its central core. The use of different guests can favor different binding modes and promote the formation of different macromolecular aggregates. Furthermore, the proper selection of the guest allows for the "turning on" or "turning off" of molecular threading and can be used to produce new kinds of threaded species. This dynamic behavior is a special feature of the Texas-sized molecular box, as is its ability to stabilize a range of polypseudorotaxanes, rotaxane-containing metal-organic frameworks (MORFs), and rotaxane-based supramolecular organic frameworks (RSOFs).

Neutral and anionic guests and their effect on the formation of pseudorotaxanes by using a flexible tetracationic imidazolium macrocycle.

The ability to control and direct molecular assembly has important implications in the design of environmentally responsive materials. Reported here is the use of competitive neutral- and anionic-guest recognition to control the formation, disruption, replacement-based construction and higher-order assembly properties of pseudorotaxane structures involving a large, cationic tetraimidazolium receptor. In particular, we showed that the chloride anion (as the tetrabutylammonium (TBA(+)) salt) serves to replace directly the 2,6-naphthalene dicarboxylate dianion from the preformed complex, involving this dianion. In contrast, the addition of the nitrate anion (as the TBA(+) salt) serves to effect displacement of a pre-bound 2,6-naphthalene dicarboxylate dianion in a stepwise manner allowing for stabilization of a so-called "outside"-binding mode under appropriate conditions. We have also found that by using biphenyl-3,4,3',4'-tetraamine as the guest, a 1D-donor-acceptor-donor coordination polymer can be stabilized, whereas the addition of 6-amino-naphthalene-2-sulfonate anion to the pre-formed complex between the tetraimidazolium receptor and the 2,6-naphthalene dicarboxylate dianion produces a new pseudorotaxane complex. This guest-based competition and subsequent molecular translocation is supported by solution-state NMR spectroscopic studies as well as solid-state single-crystal X-ray structural analyses. The results described herein provide initial evidence that guest competition can be used to control molecular "switching" and substrate binding within an appropriately designed anion receptor.

Multi component self-assembly: supramolecular organic frameworks containing metal-rotaxane subunits (RSOFs).

A facile, one-pot synthesis of rotaxanated supramolecular organic frameworks (RSOFs) is reported. These systems consist of bis-carboxylate anions threaded through the core of tetraimidazolium macrocycles. Trivalent metal cations, yttrium(III) and smaller lanthanides, are used to "lock" the threaded strut in place. This results in the formation of three-dimensional RSOFs.

Oligopyrrole macrocycles: receptors and chemosensors for potentially hazardous materials.

Oligopyrroles represent a diverse class of molecular receptors that have been utilized in a growing number of applications. Recently, these systems have attracted interest as receptors and chemosensors for hazardous materials, including harmful anionic species, high-valent actinide cations, and nitroaromatic explosives. These versatile molecular receptors have been used to develop rudimentary colorimetric and fluorimetric assays for hazardous materials.

Anion-directed assembly of a three-dimensional metal-organic rotaxane framework.

A three-dimensional extended, metal-organic rotaxane framework (MORF) that incorporates encircled "struts" has been synthesized through a one-pot self-assembly process involving a macrocyclic tetraimidazolium "molecular box", naphthalene dicaboxylate dianion, and Zn(II) cations. The present system represents progress towards controlling the features of three-dimensional metal-organic frameworks.

Environmentally responsive threading, dethreading, and fixation of anion-induced pseudorotaxanes.

The tetracationic macrocycle cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene) hexafluorophosphate (1(4+)·4PF(6)(-)) acts as a large, flexible "molecular box" that supports the formation of environmentally responsive anion-induced pseudorotaxanes, as well as other extended structures, including metal-linked supramolecular polyrotaxanes. Specifically, the combination of the tetracation 1(4+) and bis-carboxylate guests derived from 4,4'-biphenyldicarboxylic acid and 2,6-naphthalenedicarboxylic acid results in the formation of pseudorotaxanes that respond to changes in environmental stimuli, including pH and temperature. The resulting structures can be "locked into place" via the addition of a metal-linker in the form of Ag(I); this gives rise to an ordered metal-linked polyrotaxane. The interpenetrated constructs described in this article were characterized in solution and in the solid state by one- and two-dimensional ((1)H and NOESY) NMR spectroscopy, as well as by mass spectrometry (ESI-MS) and single-crystal X-ray diffraction methods.

Covalent Polymers Containing Discrete Heterocyclic Anion Receptors.

This chapter covers recent advances in the development of polymeric materials containing discrete heterocyclic anion receptors, and focuses on advances in anion binding and chemosensor chemistry. The development of polymers specific for anionic species is a relatively new and flourishing area of materials chemistry. The incorporation of heterocyclic receptors capable of complexing anions through non-covalent interactions (e.g., hydrogen bonding and electrostatic interactions) provides a route to not only sensitive but also selective polymer materials. Furthermore, these systems have been utilized in the development of polymers capable of extracting anionic species from aqueous environments. These latter materials may lead to advances in water purification and treatment of diseases resulting from surplus ions.

A 'Texas-sized' molecular box that forms an anion-induced supramolecular necklace.

The 'blue box' (cyclobis(paraquat-p-phenylene) or CBPQT(4+)), developed by Stoddart and colleagues, forms effective charge transfer complexes with a variety of electron-rich species and has been used to support the formation of a wide range of interlocked structures. However, little effort seems to have been devoted to generalizing the blue box concept. We describe a new flexible tetracationic macrocycle-a 'Texas-sized' molecular box. This positively charged receptor is capable of binding the mono-terephthalate anion, forming pseudorotaxanes. These pseudorotaxanes self-assemble into short supramolecular pseudo-oligorotaxanes in solution and more extended pseudo-polyrotaxanes in the solid state. The supramolecular oligomers formed in solution are environmentally responsive; they undergo deaggregation as the overall concentration of the cationic and anionic constituents is reduced, the temperature is increased, or the protonation state of the threading mono-terephthalate anion is changed.

Substituent effects on the structure and supramolecular assembly of bis(dioxaborole)s.

Solid-state and solution analysis shows that dialkyl substituents on the central phenyl ring of bis(dioxaborole)s, such as , do not have an appreciable effect on the planarity but do significantly alter the supramolecular assembly of these compounds.

Self-repairing polymers: poly(dioxaborolane)s containing trigonal planar boron.

The molecular weight of poly(dioxaborolane)s can be controlled during the polymerization reaction or through post-polymerization processing in such a manner that hydrolytic damage to these materials may be repaired, thereby regenerating the polymer.