A Covalent Organic Helical Cage with Remarkable Chiroptical Amplification

Purely organic shape‐persistent chiral cages are designed through the use of rigid chiral axes. Covalent dimerization of a tripodal fragment bearing chiral allenes forms a molecular twisted prism with loop‐like lateral edges presenting 10‐fold chiroptical amplification compared to its isolated building blocks. The expected geometry of covalent organic helical cage (M,M)₃‐ 1 was confirmed by X‐ray crystal structure analysis. Comparison of the chiroptical responses of this shape‐persistent molecular container with more flexible analogues highlights how the control of the conformational freedom of the molecule can be used to obtain molecular cages with strong chiroptical responses. Selective inclusion‐complex formation with ferrocenium ions [(P,P)₃‐ 1 @Fc⁺] was confirmed and quantified with HR‐ESI‐MS and NMR spectroscopy.     

A Polymorphic Azobenzene Cage for Energy-Efficient and Highly Selective p-Xylene Separation

Developing the competence of molecular sorbents for energy-saving applications, such as C8 separations, requires efficient, stable, scalable, and easily recyclable materials that can readily transition to commercial implementation. Herein, we report an azobenzene-based cage for the selective separation of p-xylene isomer across a range of C8 isomers in both vapor and liquid states with selectivity that is higher than the reported all-organic sorbents. The crystal structure shows non-porous cages that are separated by p-xylene molecules through selective CH–π interactions between the azo bonds and the methyl hydrogen atoms of the xylene molecules. This cage is stable in solution and can be regenerated directly under vacuum to be used in multiple cycles. We envisage that this work will promote the investigation of the azo bond as well as guest-induced crystal-to-crystal phase transition in non-porous organic solids for energy-intensive separations.     

Counterion Dynamics in an Interpenetrated Coordination Cage Capable of Dissolving AgCl

In solution, the eight BF₄^? counterions of a positively charged D₄‐symmetric interpenetrated [Pd₄ligand₈]⁸⁺ double cage ( 1 ) are localized in distinct positions. At low temperatures, one BF₄^? ion is encapsulated inside the central pocket of the supramolecular structure, two BF₄^? ions are bound inside the equivalent outer pockets, and the remaining five BF₄^? ions are located outside the cage structure (expressed by the formula [3 BF₄@ 1 ][BF₄]₅). On warming, the two BF₄^? ions in the outer pockets are found to exchange with the exterior ions in solution whereas the central BF₄^? ion stays locked inside the central cavity (here written as [BF₄@ 1 ][BF₄]₇). The exchange kinetics were determined by exchange spectroscopy (EXSY) NMR experiments and line‐shape fitting in different solvents. The tremendously high affinity of this double cage for the binding of two chloride ions inside the outer pockets allows for complete exchange of two BF₄^? ions by the addition of solid AgCl to give [2 Cl+BF₄@ 1 ][BF₄]₅. The uptake of the two chloride ions is allosteric and is thus accompanied by a structural rearrangement (compression along the Pd₄ axis) of the double cage structure. An analysis by using 900 MHz NOESY NMR spectroscopy shows that this compression of about 3.3 % is associated with a helical twist of 8°, which together resemble a screw motion. As a consequence of squeezing each of the outer two pockets by 53 %, the volume of the central pocket is increased by 43 %, which results in an increase of 36 % in the ¹⁹F spin‐lattice relaxation time (T₁) of the central BF₄^? ion. The packing coefficients (PC) for the ions in the outer pockets (103 % for BF₄^? and 96 % for Cl^?) were calculated.     

A Reduced-Symmetry Heterobimetallic [PdPtL4]4+ Cage: Assembly,Guest Binding,and Stimulus-Induced Switching

A strategy is presented that enables the quantitative assembly of a heterobimetallic [PdPtL₄]⁴⁺ cage. The presence of two different metal ions (Pd^II and Pt^II) with differing labilities enables the cage to be opened and closed selectively at one end upon treatment with suitable stimuli. Combining an inert Pt^II tetrapyridylaldehyde complex with a suitably substituted pyridylamine and Pd^II ions led to the assembly of the cage. ¹H and DOSY NMR spectroscopy and ESI mass spectrometry data were consistent with the quantitative formation of the cage, and the heterobimetallic structure was confirmed using single-crystal X-ray crystallography. The structure of the host–guest adduct with a 2,6-diaminoanthraquinone guest molecule was determined. Addition of N,N′-dimethylaminopyridine (DMAP) resulted in the formation of the open-cage [PtL₄]²⁺ compound and [Pd(DMAP)₄]²⁺ complex. This process could then be reversed, with the reformation of the cage, upon addition of p-toluenesulfonic acid (TsOH).     

Tuning the Intercage Distance in Charge-Regulated Blackberry-Type Assemblies through Host–Guest Chemistry

Charged or neutral adamantane guests can be encapsulated into the cavity of cationic metal–organic M₆L₄ (bpy-cage, M=Pd^II(2,2′-bipyridine), L=2,4,6-tri(4-pyridyl)-1,3,5-triazine) cages through hydrophobic interaction. These encapsulations can provide an approach to control the net charge on the resulting cage–guest complexes and regulate their charge-dominated assembly into hollow spherical blackberry-type assemblies in dilute solutions: encapsulation of neutral guests will hardly influence their self-assembly process, including the blackberry structure size, which is directly related to the intercage distance in the assembly; whereas encapsulating negatively (positively) charged guests resulted in a shorter (longer) intercage distance with larger (smaller) assemblies formed. Therefore, the host–guest chemistry approach can be used to tune the intercage distance accurately.     

Host–Guest Recognition and Fluorescence of a Tetraphenylethene‐Based Octacationic Cage

We report the synthesis and characterization of a three‐dimensional tetraphenylethene‐based octacationic cage that shows host–guest recognition of polycyclic aromatic hydrocarbons (e.g. coronene) in organic media and water‐soluble dyes (e.g. sulforhodamine 101) in aqueous media through CH???π, π–π, and/or electrostatic interactions. The cage?coronene exhibits a cuboid internal cavity with a size of approximately 17.2×11.0×6.96 ų and a “hamburger”‐type host–guest complex, which is hierarchically stacked into 1D nanotubes and a 3D supramolecular framework. The free cage possesses a similar cavity in the crystalline state. Furthermore, a host–guest complex formed between the octacationic cage and sulforhodamine 101 had a higher absolute quantum yield (Φ_F=28.5 %), larger excitation–emission gap (Δλ_ex‐em=211 nm), and longer emission lifetime (τ=7.0 ns) as compared to the guest (Φ_F=10.5 %; Δλ_ex‐em=11 nm; τ=4.9 ns), and purer emission (Δλ_FWHM=38 nm) as compared to the host (Δλ_FWHM=111 nm).     

A Triphasic Sorting System: Coordination Cages in Ionic Liquids

Host–guest chemistry is usually carried out in either water or organic solvents. To investigate the utility of alternative solvents, three different coordination cages were dissolved in neat ionic liquids. By using ¹⁹F NMR spectroscopy to monitor the presence of free and bound guest molecules, all three cages were demonstrated to be stable and capable of encapsulating guests in ionic solution. Different cages were found to preferentially dissolve in different phases, allowing for the design of a triphasic sorting system. Within this system, three coordination cages, namely Fe₄L₆ 2 , Fe₈L₁₂ 3 , and Fe₄L₄ 4 , each segregated into a distinct layer. Upon the addition of a mixture of three different guests, each cage (in each separate layer) selectively bound its preferred guest.     

Flexible Cyclooligosaccharides: Guest-Binding and Regio-selective Modification

Modified -cyclodextrin in which one glucopyranose unit is converted into analtropyranose unit showed a guest-induced fit behavior in the inclusion of globular orplanar-shaped guests and brought about, as the result, the regioselective sulfonylationon 2-OH of the altropyranose unit.     

A Reduced‐Symmetry Heterobimetallic [PdPtL4]4+ Cage: Assembly,Guest Binding,and Stimulus‐Induced Switching

A strategy is presented that enables the quantitative assembly of a heterobimetallic [PdPtL₄]⁴⁺ cage. The presence of two different metal ions (Pd^II and Pt^II) with differing labilities enables the cage to be opened and closed selectively at one end upon treatment with suitable stimuli. Combining an inert Pt^II tetrapyridylaldehyde complex with a suitably substituted pyridylamine and Pd^II ions led to the assembly of the cage. ¹H and DOSY NMR spectroscopy and ESI mass spectrometry data were consistent with the quantitative formation of the cage, and the heterobimetallic structure was confirmed using single‐crystal X‐ray crystallography. The structure of the host–guest adduct with a 2,6‐diaminoanthraquinone guest molecule was determined. Addition of N,N′‐dimethylaminopyridine (DMAP) resulted in the formation of the open‐cage [PtL₄]²⁺ compound and [Pd(DMAP)₄]²⁺ complex. This process could then be reversed, with the reformation of the cage, upon addition of p‐toluenesulfonic acid (TsOH).     

Distribution of Butane in the Host Water Cage of Structure II Clathrate Hydrates

To understand host–guest interactions of hydrocarbon clathrate hydrates, we investigated the crystal structure of simple and binary clathrate hydrates including butane (n‐C₄H₁₀ or iso‐C₄H₁₀) as the guest. Powder X‐ray diffraction (PXRD) analysis using the information on the conformation of C₄H₁₀ molecules obtained by molecular dynamics (MD) simulations was performed. It was shown that the guest n‐C₄H₁₀ molecule tends to change to the gauche conformation within host water cages. Any distortion of the large 5¹²6⁴ cage and empty 5¹² cage for the simple iso‐C₄H₁₀ hydrate was not detected, and it was revealed that dynamic disorder of iso‐C₄H₁₀ and gauche‐nC₄H₁₀ were spherically extended within the large 5¹²6⁴ cages. It was indicated that structural isomers of hydrocarbon molecules with different van der Waals diameters are enclathrated within water cages in the same way owing to conformational change and dynamic disorder of the molecules. Furthermore, these results show that the method reported herein is applicable to structure analysis of other host–guest materials including guest molecules that could change molecular conformations.     

Anisotropic Expansion of an M2L4 Coordination Capsule: Host Capability and Frame Rearrangement

Anisotropic expansion of a spherical M₂L₄ coordination capsule through the elongation of the ligand led to a new M₂L′₄ capsule. The expanded capsule provides an elliptical cavity encircled by polyaromatic frameworks with large openings and thereby can encapsulate elliptical fullerene C₇₀ and monofunctionalized fullerene C₆₀ in high yields. In addition, selective formation of a new M₂L₂L′₂ capsule occurs by mixing the original M₂L₄ and expanded M₂L′₄ capsules in a 1:1 ratio upon addition of C₆₀ or monofunctionalized C₆₀ as a template molecule.     

Trackable Supramolecular Fusion: Cage to Cage Transformation of Tetraphenylethylene-Based Metalloassemblies

Herein, the trackable supramolecular transformation of a two-component molecular cage to a three-component cage through supramolecular fusion with another two-component molecular square is described. The use of tetraphenylethene (TPE), a chromophore with aggregation-induced emission (AIE) character, as a component for the molecular cages enables facile fluorescence monitoring of the transformation process: while both cages exhibit fluorescence emission via the restriction of intramolecular motion of the TPE motif, the interactions between TPE and 4,4′-bipyridine introduced in the supramolecular fusion process result in partial fluorescence quenching and shifts in the emission maximum. This study provides a simple and efficient approach towards complex supramolecular cages with emergent functions and demonstrates that AIE features could provide unique opportunities for the characterization of complex, dynamic supramolecular transformation processes.     

Highly Efficient Chirality Transfer from Diamines Encapsulated within a Self‐Assembled Calixarene–Salen Host

A calix[4]arene host equipped with two bis‐[Zn(salphen)] complexes self‐assembles into a capsular complex in the presence of a chiral diamine guest with an unexpected 2:1 ratio between the host and the guest. Effective chirality transfer from the diamine to the calix–salen hybrid host is observed by circular dichroism (CD) spectroscopy, and a high stability constant K_2,1 of 1.59×10¹¹ M ^?2 for the assembled host–guest ensemble has been determined with a substantial cooperativity factor α of 6.4. Density functional calculations are used to investigate the origin of the stability of the host–guest system and the experimental CD spectrum compared with those calculated for both possible diastereoisomers showing that the M,M isomer is the one that is preferentially formed. The current system holds promise for the chirality determination of diamines, as evidenced by the investigated substrate scope and the linear relationship between the ee of the diamine and the amplitude of the observed Cotton effects.     

A New Biscarbazole-Based Metal–Organic Framework for Efficient Host–Guest Energy Transfer

A new metal–organic framework (MOF), [Zn₆L₄(Me₂NH₂⁺)₄⋅3 H₂O] ( 1 ) was constructed based on [9, 9′-biscarbazole]-3, 3′, 6, 6′-tetracarboxylic acid (H₄L) and Zn²⁺ ions. The porous framework and intense blue fluorescence of the MOF based on the biscarbazole moiety of the ligand could facilitate efficient host to guest energy transfer, which makes it an ideal platform for the tuning of luminescence.     

Post-Synthetic Modification of a Porous Hydrocarbon Cage to Give a Discrete Co24 Organometallic Complex**

A new alkyne-based hydrocarbon cage was synthesized in high overall yield using alkyne-alkyne coupling in the cage forming step. The cage is porous and displays a moderately high BET surface area (546 m² g⁻¹). The cage loses crystallinity on activation and thus is porous in its amorphous form, while very similar cages have been either non-porous, or retained crystallinity on activation. Reaction of the cage with Co₂(CO)₈ results in exhaustive metalation of its 12 alkyne groups to give the Co₂₄(CO)₇₂ adduct of the cage in good yield.     

Wide‐Ranging Host Capability of a PdII‐Linked M2L4 Molecular Capsule with an Anthracene Shell

This article reports that an M₂L₄ molecular capsule is capable of encapsulating various neutral molecules in quantitative yields. The capsule was obtained as a single product by mixing a small number of components; two Pd^II ions and four bent bispyridine ligands containing two anthracene panels. Detailed studies of the host capability of the Pd^II‐linked capsule revealed that spherical (e.g., paracyclophane, adamantanes, and fullerene C₆₀), planar (e.g., pyrenes and triphenylene), and bowl‐shaped molecules (e.g., corannulene) were encapsulated in the large spherical cavity, giving rise to 1:1 and 1:2 host–guest complexes, respectively. The volume of the encapsulated guest molecules ranged from 190 to 490 ų. Within the capsule, the planar guests adopt a stacked‐dimer structure and the bowl‐shaped guests formed an unprecedented concave‐to‐concave capsular structure, which are fully shielded by the anthracene shell. Competitive binding experiments of the capsule with a set of the planar guests established a preferential binding series for pyrenes≈phenanthrene>triphenylene. Furthermore, the capsule showed the selective formation of an unusual ternary complex in the case of triphenylene and corannulene.     

客体诱导LiCl/FER沸石客/主体材料主体相变行为的研究

用热扩散法将客体LiCl组装进入主体FER沸石孔道生成的客/主体材料中, 客体与主体骨架在一定温度下发生相互作用, 诱导该沸石发生相转变. XRD, FT-IR, TG/DTA/DTG等方法表征该客/主体材料相变过程证明, 相变起始温度500 ℃, 500～600 ℃生成LiAlSi₃O₈, 800 ℃的相变产物主要为β-石英, LiAlSi₃O₈的相对含量随LiCl的组装量增多而增加.     

Hexabenzocoronene Graphitic Nanocoils Appended with Crown Ethers: Supramolecular Chirality Induced by Host–Guest Interaction

We have designed and synthesized two new achiral hexa-peri-hexabenzocoronene (HBC) derivatives, HBC^CE and HBC^TEG-CE , which bear the crown ether as the pendant for the amino acid binding site. The HBC^CE self-assembled into a racemic mixture of P- and M-handed helical nanocoils, however, in the presence of chiral amino acid guests, it formed helical nanocoils with one-handed screw sense. The effects of the concentration, type and configuration of the guests on the induced circular dichroism (ICD) during the co-assembly of HBC^CE with chiral amino acids were also investigated. Additionally, after complete removal of the chiral guests, the optically active nanocoils did not racemize, even in the presence of excess amino acids with the opposite configuration. In contrast, HBC^TEG-CE with a long triethylene glycol (TEG) chain between the crown ether group and the HBC unit did not exhibit ICD during the co-assembly with chiral amino acids.