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Control over the integrative self-sorting of metallo-supramolecular assemblies opens up possibilities for introducing increased complexity and function into a single self-assembled architecture. Herein, the relationship between the geometry of three ligand components and morphology of three self-sorted heteroleptic [Pd₂L₂L′₂]⁴⁺ cages is examined. Pd-mediated assembly of two bis-monodentate pyridyl ligands with native bite angles of 75° and 120° affords a cis-[Pd₂L₂L′₂]⁴⁺ cage while the same reaction with two ligands with bite angles of 75° and 60° gives an unprecedented, self-penetrating structural motif; a trans-[Pd₂(anti-L)₂L′₂]⁴⁺ heteroleptic cage with a “doubly bridged figure eight” topology. Each heteroleptic assembly can be formed by cage-to-cage conversion of the homoleptic precursors and morphological control of [Pd₂L₂L′₂] cages is achieved by selective ligand displacement transformations in a system of three ligands and at least six possible cage products.

A doubly bridged figure eight: Integrative self-sorting of geometrically distinct ligands and cages is regulated to form new [Pd₂L₂L′₂] structures. For one example, X-ray analysis reveals a doubly bridged figure-eight topology which is an unprecedented motif for metallo-supramolecular structures. Furthermore, morphological control of a system of cages is achieved by highly selective ligand displacement transformations.

We have adopted the concept of “cage to frameworks” to successfully produce a Na–N connected coordination networked cage Na-NC1 by using a [3+6] porous imine-linked organic cage NC1 (Nanjing Cage 1) as the precursor. It is found that Na-NC1 exhibits hierarchical porosity (inherent permanent voids and interconnected channel) and gas sorption measurements reveal a significantly enhanced CO₂ uptake (1093 cm³ g⁻¹ at 23 bar and 273 K) than that of NC1 (162 cm³ g⁻¹ under the same conditions). In addition, Na-NC1 exhibits very low CO₂ adsorption enthalpy making it a good candidate for porous materials with both high CO₂ storage and low adsorption enthalpy.

Networking: Hierarchically porous structures are prepared by linking discrete shape-persistent porous organic cages with sodium ions. The resulting cage network has an excellent CO₂ storage capacity along with low adsorption enthalpy compared to the discrete cage precursor.

We report an autonomous oscillatory micromotor system in which active colloidal particles form clusters, the size of which changes periodically. The system consists of an aqueous suspension of silver orthophosphate microparticles under UV illumination, in the presence of varying concentrations of hydrogen peroxide. The colloid particles first attract each other to form clusters. After a short delay, these clusters abruptly disperse and oscillation begins, alternating between clustering and dispersion of particles. After a cluster oscillation initiates, the oscillatory wave propagates to nearby clusters and eventually all the clusters oscillate in phase-shifted synchrony. The oscillatory behavior is governed by an electrolytic self-diffusiophoretic mechanism which involves alternating electric fields generated by the competing reduction and oxidation of silver. The oscillation frequency is tuned by changing the concentration of hydrogen peroxide. The addition of inert silica particles to the system results in hierarchical sorting and packing of clusters. Densely packed Ag₃PO₄ particles form a non-oscillating core with an oscillating shell composed largely of silica microparticles.

Tunable colloidal oscillations: An autonomous oscillatory system involves Ag₃PO₄ colloidal particles under UV illumination in the presence of hydrogen peroxide. The particles oscillate between clustered and dispersed states, exhibiting signal propagation and synchronization. The behavior follows an electrolytic self-diffusiophoretic mechanism based on the redox chemistry of silver.

Chains of hydrogen bonds such as those found in water and proteins are often presumed to be more stable than the sum of the individual H bonds. However, the energetics of cooperativity are complicated by solvent effects and the dynamics of intermolecular interactions, meaning that information on cooperativity typically is derived from theory or indirect structural data. Herein, we present direct measurements of energetic cooperativity in an experimental system in which the geometry and the number of H bonds in a chain were systematically controlled. Strikingly, we found that adding a second H-bond donor to form a chain can almost double the strength of the terminal H bond, while further extensions have little effect. The experimental observations add weight to computations which have suggested that strong, but short-range cooperative effects may occur in H-bond chains.

Unchained: Experiments and calculations show that the energies (ΔG) of hydrogen bonds can double upon formation of a chain of hydrogen bonds, but further extension of the chain results in a surprisingly negligible additional cooperative effect (A=H-bond acceptor).

We present the self-assembly of redox-responsive polymer nanocontainers comprising a cyclodextrin vesicle core and a thin reductively cleavable polymer shell anchored via host–guest recognition on the vesicle surface. The nanocontainers are of uniform size, show high stability, and selectively respond to a mild reductive trigger as revealed by dynamic light scattering, transmission electron microscopy, atomic force microscopy, a quantitative thiol assay, and fluorescence spectroscopy. Live cell imaging experiments demonstrate a specific redox-responsive release and cytoplasmic delivery of encapsulated hydrophilic payloads, such as the pH-probe pyranine, and the fungal toxin phalloidin. Our results show the high potential of these stimulus-responsive nanocontainers for cell biological applications requiring a controlled delivery.

Inside and outside the box: A new concept for the self-assembly of redox-responsive polymer nanocontainers is based on the stabilization of a cyclodextrin vesicle core by a reductively cleavable polymer shell anchored via host–guest recognition. Controlled release of cargo from the container is possible by a redox trigger.

The development of foldamer-based receptors is driven by the design of monomers with specific properties. Herein, we introduce a pyridazine-pyridine-pyridazine diacid monomer and its incorporation into helical aromatic oligoamide foldamer containers. This monomer codes for a wide helix diameter and can sequester metal ions on the inner wall of the helix cavity. Crystallographic studies and NMR titrations show that part of the metal coordination sphere remains available and may then promote the binding of a guest within the cavity. In addition to metal coordination, binding of the guest is assisted by cooperative interactions with the helix host, thereby resulting in significant enhancements depending on the foldamer sequence, and in slow guest capture and release on the NMR time scale. In the absence of metal ions, the pyridazine-pyridine-pyridazine monomer promotes an extended conformation of the foldamer that results in aggregation, including the formation of an intertwined duplex.

Better together: Combined contributions from organic and inorganic components promote guest binding in helical containers formed from aromatic foldamers (red). Pyridazine-pyridine-pyridazine diacid building blocks can sequester metal ions on the inner wall of the helix cavity that may promote the binding of a guest within the cavity. In addition to metal coordination, binding of the guest is assisted by cooperative interactions with the helix host.

We report on the synthesis and the structure elucidation of the elusive azafullerene pentachloride C₅₉NCl₅, which was obtained by high temperature halogenation of (C₅₉N)₂. The exceptionally strong host–guest interaction of the title compound in the solid is discussed.

Snuggle right up: The elusive heterofullerene chloride C₅₉NCl₅ was accomplished by high temperature halogenation of (C₅₉N)₂ with TiCl₄/Br₂. The geometry of C₅₉NCl₅ involves a perfect host–guest interaction by nestling the ball-shaped fullerene subunit into the cavity formed by five chlorine atoms of an adjacent molecule. Quantum chemical calculations revealed that cumulative effect results in a very strong supramolecular binding.

The mechanochemical cycloreversion of 1,2,3-triazole compounds, which serve as unusually stable building blocks in materials and biomolecular chemistry as a result of mild “click chemistry”, remains puzzling. We show that the hitherto discussed straight-forward retro-click mechanism of the 1,4-disubstituted isomer, even if Cu^I catalyzed, can be ruled out in view of more favorable activation free energies of destructive pathways. In stark contrast, the 1,5-regioiomer can undergo cycloreversion under rather mild mechanochemical conditions owing to its favorable response to the external force in conjunction with standard Ru^II catalysis.

Mechanochemical unclicking reactions of 1,2,3-triazoles have been a topic of controversy. Based on isotensional quantum-chemical calculations, it is shown that their 1,5-regioisomers easily undergo cycloreversion reactions under standard sonication conditions if they are Ru^II catalyzed.

We report the synthesis of a tetracationic macrocycle which contains two N,N′-bis(methylene)naphthalenediimide units inserted in between the pyridinium rings of the bipyridinium units in cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺ or “blue box”) and describe the investigation of its potential use in materials for organic electronics. The incorporation of the two naphthalenediimide (NDI) units into the constitution of CBPQT⁴⁺, not only changes the supramolecular properties of the tetracation in the solid state, but also has a profound influence on the electrochemical and electronic behavior of the resulting tetracationic macrocycle. In particular, the solid-state (super)structure, investigated by single-crystal X-ray diffraction, reveals the formation of a three-dimensional (3D) supramolecular framework with ca. 2.8 nm diameter one-dimensional (1D) hexagonal channels. Electrochemical studies on solid-state thin films of the macrocycle show that they exhibit semiconducting properties with a redox-conductivity of up to 7.6×10⁻⁴ S m⁻¹. Moreover, EPR and ENDOR spectroscopies show that charge is equally shared between the NDIs within the one-electron reduced state of the NDI-based macrocycle on the time scale of these techniques.

Organic electronics: A tetracationic macrocyle containing two naphthalenediimide (NDI) units and four pyridinium rings was synthesized and investigated for its potential use as an organic semiconductor. The incorporation of the NDI units into the constitution of cyclobis(paraquat-p-phenylene) has resulted in a macrocyle that exhibits a boat-shape conformation and assembles into an ultralarge-pore supramolecular framework with semiconducting properties.

Go Aggies! Go Chemikers! The word “gig” applies to a multipronged metal tool for hunting frogs and fish. It constitutes part of a rallying cry, “gig ’em” that inspires Texas A&M Aggies to victory in athletic and academic competitions. This Highlight examines recent victories in the C C cleavage of benzene made possible by a four-pronged iridium gig that yields a “spring-loaded” norbornadiene-like structure with significant ring strain.

The synthesis of alternating donor–acceptor [12] and [16]cycloparaphenylenes (CPPs) has been achieved by the rhodium-catalyzed intermolecular cross-cyclotrimerization followed by imidation and/or aromatization. These alternating donor–acceptor CPPs showed positive solvatofluorochromic properties and smaller HOMO–LUMO gaps compared with nonfunctionalized CPPs, which was confirmed by the theoretical study.

Catherine wheels: The synthesis of alternating donor–acceptor [12] and [16]cycloparaphenylenes (CPPs) has been achieved by the rhodium-catalyzed intermolecular cross-cyclotrimerization followed by imidation and/or aromatization. The alternating donor–acceptor CPPs showed positive solvatofluorochromic properties and smaller HOMO–LUMO gaps compared with nonfunctionalized CPPs, which was confirmed by the theoretical study.

Controllable manipulation of self-organized dynamic superstructures of functional molecular materials by external stimuli is an enabling enterprise. Herein, we have developed a thermally driven, self-organized helical superstructure, i.e., thermoresponsive cholesteric liquid crystal (CLC), by integrating a judiciously chosen thermoresponsive chiral molecular switch into an achiral liquid crystalline medium. The CLC in lying state, in both planar and twisted nematic cells, exhibits reversible in-plane orthogonal switching of its helical axis in response to the combined effect of temperature and electric field. Consequently, the direction of the cholesteric grating has been observed to undergo 90° switching in a single cell, enabling non-mechanical beam steering along two orthogonal directions. The ability to reversibly switch the cholesteric gartings along perpendicular directions by appropriately adjusting temperature and electric field strength could facilitate their applications in 2D beam steering, spectrum scanning, optoelectronics and beyond.

Controllable manipulation of self-organized dynamic superstructures of functional molecular materials by external stimuli is an enabling enterprise. Here, reversible in-plane orthogonal switching of a thermoresponsive cholesteric liquid crystal is demonstrated, and dynamic control of cholesteric gratings between two perpendicular directions in a single cell by appropriately adjusting the temperature and electric field is achieved.