Coordination-Directed Construction of Molecular Links

Biomimetic Hierarchical Construction of Anti-Tumor Polyoxopalladates for Cancer Therapy

Inspired by the construction scheme of biomacromolecules, a hierarchical assembly based on the lacunary polyoxopalladate (POP) of [SrPd12O6(OH)3(PhAsO3)6(OAc)3]4- (SrPd12) has been achieved. As a structurally programmable molecular building block, SrPd12 is used to evolve from monomer via dimer to supramolecular aggregates in a controlled manner. In such process, the open-shell-type monomers are covalently integrated into bowl- or cage-like dimers via a direct or indirect splicing strategy. Upon that, hydrogen bond and hydrophobic effects are further hired to fabricate supramolecular aggregates of varied host-guest archetypes, thereby completing a hierarchical construction. In consideration of the combined advantages of noble metals and polyoxometalates in cancer treatment, both in vitro and in vivo anti-tumor assays of these SrPd12-derived POPs were studied in detail. A structure-dependent anti-tumor activitywas observed, originating from an imbalance of damage and repair of DNA as anti-tumor mechanism.

Step-by-Step Self-Assembly of a Double-Walled Knotted Cage With Increasing Topological Complexity

The self-assembly process of a double-walled cage formed from a semiflexible tripodal ligand and a Pd(II) 90-degree block was tracked by NMR and x-ray analysis. At least two intermediate structures with distinct topologies were observed prior to the formation of the final double-walled cage. By optimizing the self-assembly conditions (e.g., time, solvent, and concentration), these topological intermediates were successfully isolated and analyzed by x-ray crystallography. They are considered crucial metastable structures that navigate the shortest pathway to the final structure, demonstrating the critical role of molecular topology in guiding and controlling the kinetics of metal-directed self-assembly.

Restructuring of mortise-and-tenon frameworks at the molecular level

Restructuring of mortise-and-tenon frameworks at the molecular level has never been achieved. We report the first example of restructuring in molecular mortise-and-tenon joints (MTF-4 and MTF-5). The obtained cross-locking mortise-and-tenon framework of MTF-5 exhibits higher stability, better mechanical stiffness, and superior optical limiting (OL) performance.

One-Step Directed Self-Assembly of Molecular Closed Four-Link Chains and Borromean Links

Despite substantial advancements in the synthesis of mechanically interlocked molecules (MIMs), the efficient construction of higher order links remains a formidable challenge. Herein, we report the highly efficient one-step directed construction of a series of unprecedented molecular closed four-link chains (84 1 metalla-links), achieved through the synergistic assembly of coordination-driven and aromatic stacking interactions involving binuclear rhodium/iridium precursors and bis-dentate benzothiadiazole derivative ligands. Meanwhile, modulating the substituent positions of the pyridine groups in the ligand resulted in a change in topological structure, leading to the formation of two molecular Borromean links (6 2 3 ${6_2^3 }$ metalla-links). The molecular configurations of the abovementioned metalla-links were clearly identified through mass spectrometry, NMR, and single-crystal X-ray diffraction. Furthermore, structural transformation between the molecular Borromean links and corresponding monocycles was achieved through concentration effects, as validated by solution-state NMR spectroscopy investigations.

Modulation of Photoluminescence of BODIHY Dye Using Water-Soluble Coordination Cages With Different Shapes

The confinement of guest molecules within supramolecular hosts can alter their photophysical properties. However, the shapes of the hosts in regulating the guest's emission remains underexplored. Herein, we investigate how the shape of the host alters the emission behavior of boron difluoride hydrazone (BODIHY) (G1) dye encapsulated within two iso-stoichiometric water-soluble coordination cages: MC1 (double-square cage) and MC2 (octahedral cage). Encapsulation of G1 within MC1 results in a highly emissive solution, whereas similar confinement in MC2 leads to a non-emissive host-guest solution. A similar trend was observed with different sets of iso-stoichiometric cages MC3 (double-square cage) and MC4 (octahedral cage). Using a combination of femtosecond transient absorption and time-resolved fluorescence spectroscopy, we observed that the disparity in fluorescence behavior of BODIHY is attributed to charge transfer interactions between the guest and ligand panels of cages. The shape of the coordination cage dictates the preorganization of the guest within the cavity, thereby suppressing or promoting this charge transfer interactions. Moreover, we demonstrate a turn-on emission of BODIHY dye due to its preferential binding to a double-square cage. These findings provide fundamental insights into host-mediated modulation of the guest's photophysics and offer a blueprint for designing supramolecular systems with tunable emissive behavior.

Chiral ring-in-ring complexes with torsion-induced circularly polarized luminescence

We introduce a class of supramolecular precursors, termed 'folda-bonders', which utilize macrocycles to fold and precisely align reactive groups, effectively acting as bonding facilitators. This design enables highly efficient, selective, and mild 'click-like' reactions, making them particularly well-suited for the modular synthesis of complex structures. In this study, we highlight the versatility of folda-bonders in the one-pot aqueous synthesis of chiral ring-in-ring complexes exhibiting torsion-induced circularly polarized luminescence (CPL). Cucurbit[8]uril macrocycles facilitate the pseudostatic pre-folding of bis(4-phenyl pyridinium) derivatives, which act as folda-bonders, enabling efficient, purification-free covalent cyclization mediated by an axially chiral fragment. The single-crystal structure, obtained directly from the product solution, confirms the formation of a chiral ring-in-ring configuration. The macrocycle-imparted rigidity, combined with the tunable flexibility of alkyl linkers, drives the emergence of distinct chiroptical properties in the ring-in-ring complexes. Remarkably, torsion within the strained shorter alkyl linker is responsible for generating CPL, whereas longer linkers retain chirality, as evidenced by CD signals, but do not exhibit CPL. These findings demonstrate the potential of integrating noncovalent and covalent strategies to design sophisticated molecular architectures with tailored functional properties.

One-Pot 'Click' Synthesis of Ring-in-Rings Complexes with Customizable π-Stacked Dyads

We report an efficient one-pot aqueous synthesis of ring-in-rings complexes featuring customizable π-stacked dyads. Conventional methods for such complexes often suffer from poor solubility and low yields due to irreversible kinetically controlled reactions. To overcome these limitations, we developed a strategy combining noncovalent preassembly with efficient dynamic covalent bonding to secure a ring-in-rings complex as the exclusive thermodynamic product. Through complexation with cucurbit[8]uril (CB[8]), a folded conformation was induced in an aldehyde-functionalized bis(phenylpyridinium) derivative, predisposing the reactive aldehyde groups to promote acylhydrazone condensation with aromatic dihydrazides. The method achieves high conversion and purity, enabling direct single-crystal growth without the need for purification. We successfully synthesized π-stacked dyads across diverse aromatic moieties, including five distinct single-crystal structures demonstrating dimeric cofacial stacking. Kinetic analysis reveals that CB[8] complexation increases the ceiling temperature of the condensation reaction, rendering the process both thermodynamically and kinetically favorable. The modular nature of this strategy allows for precise tuning of photophysical properties by simply altering the linker lengths and the central aromatic cores, providing a facile platform for exploring structure-function relationships in ring-in-rings complexes and beyond.

Mechanical and Covalent Tailoring of Copper Catenanes for Selective Aqueous Nitrate-to-Ammonia Electrocatalysis

Electrocatalytic nitrate reduction reaction (NO3RR) for the selective generation of ammonia (NH3) enables the removal of deleterious nitrate pollutants while simultaneously upcycling them into a value-added fertilizer. The development of nonprecious metal-derived catalysts such as those featuring copper (Cu) as earth-abundant alternatives for the state-of-the-art precious metal catalysts is of urgent need yet suffering from the activity-selectivity-durability trilemma. Rational design of molecular Cu complexes with well-defined coordination structures permitting systematic structure-activity relationship (SAR) investigations is key to addressing the challenge. Here, a series of molecular Cu(I) complexes with [2]catenane ligands are developed as NO3RR electrocatalysts for the first time. By engineering multiple cationic ammoniums on the catenane backbone, acceptance of the anionic nitrate substrate as well as the release of the cationic ammonium product are promoted, thereby facilitating a higher Faradaic efficiency and product selectivity toward ammonia via an 8e- pathway. Of note, the mutual Coulombic repulsion between the multiply charged ligands is overcome by the mechanical interlocking such that the catalyst integrity can be maintained under practical conditions. This report highlights the promise of employing mechanically interlocked ligands as a platform for customizing metal complexes as catalysts for redox processes involving multiple proton-coupled electron transfer steps.

Box-like Molecules-Induced Discrete Ring-in-Rings Assembly of Hydrogen-Bonded Aramide Macrocycles

The controlled formation of ring-in-ring(s) assemblies is highly desirable as precursors for constructing higher order supramolecular architectures. We report our findings that this goal can be achieved by balancing molecular structures and conformational adaptivity through an interplay of multiple non-covalent bonding interactions. With hydrogen-bonded (H-bonded) aramide macrocycles and box-like molecules including naph-Box, m-Box and p4p-Box, ring-in-rings assembling systems with 4 : 1 stoichiometry are preferentially created. The formation of such assemblies with a defined number of rings threaded on a Box molecule is unprecedented using 2D shape-persistent macrocycles. The unusual assembly behaviors are rationalized by the aid of NMR spectroscopy, mass spectrometry, X-ray crystallography, and xTB computation. In sharp contrast to the use of o-Box and p-Box in forming ring-in-rings complexes where a distribution of various assembled species is observed, the box-like molecules all afford monodisperse compact assemblies. Conformational adaptivity is deemed as one of the major factors that is accountable for the selectivity observed, which is driven mainly by cooperative action of multiple non-covalent bonding interactions including H-bonding and π-π stacking interactions. Using pyrimidyl-incorporated H-bonded macrocycles and box-like molecules to form ring-in-rings assembling structures may provide opportunities for designing more sophisticated and topologically unique supramolecular systems with potential functions.

Single step site-selective reaction to construct a Ag2Au2 ← Ag4 supramolecular assembly from hybrid N-heterocyclic carbene (NHC): synthesis, structures and optoelectronic properties

Two supramolecular complex assemblies, [Ag4(1)2][PF6]4·4MeCN 2 and Ag(i)-Au(i) mixed metal complex [Ag2Au2(1)2][PF6]4·4MeCN 3, have been prepared from 3-(pyridylmethyl)imidazo[1,5-a]pyridin-4-ylium hexafluorophosphate (1 HPF6), which is the precursor of N-heterocyclic carbene (NHC). These complexes were subsequently analyzed using various spectroscopic techniques to confirm their structural and chemical properties. Transmetallation of Au(i) onto the Ag4 macrocycle results in the formation of an Ag2Au2 macrocyclic assembly. Au(i) selectively binds with the soft donor Ccarbene, whereas Ag(i) binds with comparatively hard donor Npy (py = pyridine). The geometries of 2 and 3 were established by single-crystal X-ray diffraction studies. Both molecules form a 2D network through M-M and several non-covalent interactions. Electrical conductivity measurements revealed that Ag(i) complex 2 is better conductor than Au(i) complex 3. Optoelectronic studies revealed the utility of complexes 2 and 3 as photovoltaic devices. Furthermore, MS-junction potential measurements show that they are suitable for semiconductor devices, with complex 2 being more efficient than complex 3. Finally, in this study, we aimed to explore the scope of (i) the development of heterobimetallic supramolecular organometallic complexes (SOC), (ii) the charge transport behaviour of SOCs, and (iii) the modification of intrinsically conductive SOCs-based electronics.

The Interplay Between Component Denticity and Flexibility Promotes the Formation of [AgI⋅⋅⋅AgI]-stabilised Links and Knots

A subtle interplay between the flexibility of the 2,2'-bipyridyl-based diamine and the denticity of the coordination domain formed upon self-assembly enabled the formation of four distinct topologies stabilised by [Ag⋅⋅⋅Ag]2+ pairs. The reactions utilising 2,6-diformylpyridine resulted in the formation of silver(I)-stabilised molecular tweezer, trefoil knot, and Solomon link. The 1,8-naphthyridine-based dialdehyde promoted the formation of [2]catenanes and trefoil knot, demonstrating very close AgI⋅⋅⋅AgI distances. Two of the studied assemblies demonstrated interesting luminescent properties in the solid state.

Control of Interlocking Mode in Pd4L8 Cage Catenanes

Precise control over the catenation process in interlocked supramolecular systems remains a significant challenge. Here, we report a system in which a lantern-shaped Pd2L4 cage can dimerize to form two distinct Pd4L8 catenanes with different interlocking degree: a previously described quadruply interlocked double cage motif of D4 symmetry and an unprecedented triply interlocked structure of C2h symmetry. While the former structure features a linear arrangement of four Pd(II) centers, separated by three mechanically linked pockets, the new motif has a staggered shape. Both assemblies are topological isomers, coexisting in equilibrium in solution. The triply interlocked species is thermodynamically more stable due to extended noncovalent interactions between the ligands, as supported by X-ray structure analysis and electronic structure calculations. Notably, the degree of interlocking in the double cage system can be controlled by a change of temperature and through anion exchange. Cage-to-cage transformations were followed by NMR, MS and TIMS methods.

Chemo-Selective Transformation of Anthracene Derivative within Water-Soluble Coordination Cages Having Different Cavities

Coordination cages with specific properties and functionalities are utilized as reaction vessels for the desired chemical transformation of substrates. The symmetry and inherent cavity of coordination cages can influence the host-guest interactions and the reaction outcome in their confined space. However, the impact of the cage shape on different transformations remains unclear. In this chapter, we report the chemo-selective transformation of anthracene derivative using three geometrically distinct Pd6 cages (CC2, CC3, and CC4). Photoirradiation of 9-bromoanthracene (G3) in the distorted double-square cage (CC2) yields anthracene-9,10-dione, while the known double-square cage (CC3) forms a [4 + 4] cycloaddition product. The same reaction in a known Pd6 bowl-shaped cage (CC4) resulted in the oxidized product. Through a combination of experimental and computational studies, we demonstrate that the shape and cavity size of coordination cages can significantly influence the reaction pathways of the encapsulated anthracene derivative, leading to chemo-selectivity. Furthermore, we observe that the encapsulation of 9-bromoanthracene (G3) in the cage cavities (CC2 and CC4) leads to a significant enhancement in the rate of photooxidation of G3. This work underscores the versatility of water-soluble coordination cages as reaction vessels in synthetic chemistry, offering interesting avenues for chemo-selective chemical transformation.

The Flexibility of Tetra(N-Heterocyclic Carbene) Ligands Controls the Nuclearity and Geometry of Polynuclear MI‒NHC Assemblies

A series of tetrakisimidazolium salts bearing two di(phenylimidazolium)amine groups linked by differently substituted anthracenes has been prepared. These are H4-1a(PF6)4 (anthracene bridge), H4-1b(PF6)4 (phenyl-anthracene-phenyl bridge), H4-1c(PF6)4 (anthracene-phenyl bridge), and H4-1d(PF6)4 (anthracene-phenyl-anthracene bridge). X-ray crystallography showed that those ligand precursors having the di(phenylimidazolium)amine connected directly to the anthracene experience restricted rotation about the N─Canthracene bond. Depending on their flexibility, the reaction of the tetrakisimidazolium salts with Ag2O followed by transmetalation with [AuCl(THT)] yielded octanuclear ([Au8(1a)4](PF6)8), tetranuclear ([Au4(1b)2](PF6)4), hexanuclear ([Au6(1c)3](PF6)6), or octanuclear ([Au8(1d)4](PF6)8) assemblies, demonstrating the direct bonding strategy can be employed for the selective synthesis of polynuclear poly-NHC (NHC = N-heterocyclic carbene) metallosupramolecular assemblies.

Fine-Tuning of the Sequential Self-Assembly of Entangled Polyhedra by Exploiting the Side-Chain Effect

The control of the sequential self-assembly processes of highly entangled (Ag3L2)n (n=2,4,6,8) and Ag21L12 coordination polyhedra using side-chain effects was studied via the introduction of linear or branched side chains into the tripodal ligands. In addition to changes in the intermediate polyhedral species affording the multi- pathway process, disruption of the kinetic control of the sequential self-assembly was observed, thus demonstrating the utility of steric control for the construction of 3D-entangled molecular materials on the 5 nm scale with high molecular complexity.

Metal Coordination-Induced Structural Regulation of Twisted Cucurbit[14]uril-Based Supramolecular Assemblies for Mercury Ions Detection on Smart Platform

The high selectivity and reversibility of metal coordination enable precise modulation of the structural morphology of supramolecular assemblies, which is essential for the development and intelligent application of functionalized materials. In this study, sheet-like supramolecular assemblies (Pyr-O@tQ[14]) constructed by twisted cucurbit[14]urils (tQ[14]) and pyrene derivatives (Pyr-O) through host-guest interactions, which exhibit excellent optical properties, achieves highly sensitive detection of Hg2+ by fluorescence quenching, with a limit of detection of 0.177 μM. A novel smart platform, compatible with smartphones, is developed to enhance the detection efficiency and practicality for practical applications. From a microscopic structural perspective, adjusting the concentration of Hg2+ can change the structural morphology of Pyr-O@tQ[14] from lamellar to square and finally to spherical, demonstrating the dynamic control of the assembly structure in response to environmental stimuli. This study not only presents a novel and efficient intelligent quantitative sensing platform for Hg2+ detection but also highlights the unique advantages of tQ[14] in constructing supramolecular assemblies with tunable, responsive structures, opening new avenues for the design and synthesis of advanced smart materials.

Highly Selective Construction of Unique Cyclic [4]Catenanes Induced by Multiple Noncovalent Interactions

The synthesis of high-ordered mechanically interlocked supramolecular structures is an extremely challenging topic. Only two linear [4]catenanes have been reported so far and there is no defined strategy to obtain cyclic [4]catenane. Herein, two unprecedented cyclic [4]catenanes, 1 and 2, were prepared in high yields. The syntheses rely on the strategic selection of naphthalenediimide (NDI) based Cp*Rh/Ir building blocks E1/E2 (Cp*=pentamethyl-cyclopentadienyl) and nonlinear diimidazole ligand precursor L1, exhibiting large conjugate plane, appropriate coordination angles, and freely rotating imidazole units, thereby enabling multiple π⋅⋅⋅π stacking interactions to maintain the supramolecular structures. The use of other Cp*Rh building blocks E3, E4 or E5 featuring slightly shorter metal-to-metal distances than E1/E2 and different chemical properties led to the formation of a complex 3 and two metallamacrocycles 4 or 5, respectively. The structures of these assemblies were confirmed by X-ray crystallographic analysis, ESI-TOF-MS and NMR spectroscopy. Complex 1, exhibiting a broad-band absorption in the UV/Vis to NIR regions and a remarkable photothermal conversion was thereafter used to build the new 1 membrane. The solar power-induced water steam generation performance of 1 membrane was investigated, reaching a value of 2.37 kg ⋅ m-2 ⋅ h-1, making it suitable for collection of fresh water via desalination and wastewater.

Stimuli Induced Reversible Switching Between a Self-Assembled 2-Catenane and the Constituent Coordination Rings

A pair of comparable sized C-shaped bis-monodentate ligands (L1 and L22+) and a linear bis-monodentate ligand (L3) complementing to the terminal-lengths of the C-shaped ligands have been identified. One-pot combination of cis-Pd(tmeda)2+, L1 and L3 (2 : 1 : 1 ratio) in water resulted an octa-cationic 2-catenane, [Pd2(tmeda)2(L1)(L3)]2 8+ in which two identical tetra-cationic macromonocyclic coordination rings are interlocked; however, a guest bound coordination ring was formed in presence of a selected di-anionic guest. Complexation of cis-Pd(tmeda)2+ with a mixture of L22+ and L3 (2 : 1 : 1 ratio) in water resulted the hexa-cationic macromonocyclic coordination ring, [Pd2(tmeda)2(L2)(L3)]6+ whereas a guest bound coordination ring was formed in the presence of the di-anionic guest. Addition of the guest to the preformed octa-cationic catenane caused ring separation to favour the guest-bound ring. This guest bound ring could be reverted to the 2-catenane by sequestering the bound guest using the relatively electron deficient hexa-cationic coordination ring. Thus, a design principle for reversible switching between a 2-catenane and the constituent macromonocyclic-rings using anion-binding/-sequestering as the core concept has been established.

Sensitive detection of formaldehyde via a luminescent distorted Eu4L4 tetrahedral cage

A distorted low-symmetry Eu4L4 tetrahedral cage was fabricated through the self-assembly of europium ions and C3-symmetric bowl-shaped ligands containing a phosphangulene core. X-ray crystallography confirmed its unique architecture, featuring significant structural distortion and solvent-accessible coordination sites. This cage showcases exceptional luminescence-based sensitivity for formaldehyde detection compared to other analogs, achieving an impressive detection limit of 19.4 ppb.

Functional Post-Synthetic Chemistry of Metal-Organic Cages According to Molecular Architecture and Specific Geometry of Origin

Metal-organic cages (MOCs) are discrete supramolecular entities consisting of metal nodes and organic connectors or linkers; MOCs are noted for their high porosity and processability. Chemically, they can be post-synthetically modified (PSM) and new functional groups can be introduced, presenting attractive qualities, and it is expected that their new properties will differ from those of the original compound. This is why they are highly regarded in the fields of biology and chemistry. The present review deals with the current PSM strategies used for MOCs, including covalent, coordination, and noncovalent methods and their structural benefits. The main emphasis of this review is to show to what extent and under what circumstances a MOC can be designed to obtain a tailored geometric architecture. Although sometimes unclear when examining supramolecular systems, particularizing the design of and systematic approaches to the development and characterization of families of MOCs provides new insights into structure-function relationships, which will guide future developments.

Ultra-High Metal-Ion Selectivity Induced by Intramolecular Cation-π Interactions for the One-Pot Synthesis of Precise Heterometallic Architectures

Heterometallic supramolecules, known for their unique synergistic effects, have shown broad applications in photochemistry, host-guest chemistry, and catalysis. However, there are great challenges to precisely construct heterometallic supramolecules rather than a statistical mixture, due to the limited metal-ion selectivity of coordination units. In particular, heterometallic architectures precisely encoded with different metal ions usually fail to form in a one-pot method when only one type of coordinated motif exists due to its poor metal-ion selectivity. Herein, we propose an effective intramolecular cation-π (ICπ) strategy and successfully constructed the heterometallic supramolecule Zn2Cu4L34 by the one-pot self-assembly of tritopic terpyridyl ligand L3 with Zn(II) and Cu(II), following a clear self-assembly mechanism in which only thermodynamic dimers ZnL12 and Cu2L22 were constructed with model ligands L1, L2, Zn(II) and Cu(II) with perfect self-sorting and an ultra-high metal-selectivity feature. The successful construction of the heterometallic supramolecule Zn2Cu4L34, in which the definite sequence of metal ions Zn(II) and Cu(II) is encoded in the one-pot method, will offer a novel approach to precisely construct heterometallic architectures.

Programming Bifunctional Metal-Organic Frameworks to Integrate Multiple Triboelectric Nanogenerators for Green Electronics toward Effective Self-Powered Photocatalytic System

Programming and synthesizing bifunctional materials for regulating the output of triboelectric nanogenerators (TENGs) and their photocatalytic efficiency is a promising strategy for energy harvesting to build self-powered systems. Herein, we tackle this challenge by introducing metal-organic frameworks (MOFs) as molecular catalysts and triboelectric layers for self-powered photocatalytic systems. A zeolite-like mixed-valence MOF (CuICuII-1) and a ladder-structured MOF (CuII-2) were obtained through structural transformation. Due to the excellent charge-trapping capability and surface potential of CuICuII-1, the outputs of CuICuII-1-TENG (a short-circuit current (Isc) of 30.4 μA and an open-circuit voltage (Voc) of 524.1 V) were significantly superior to those of CuII-2-TENG. The incorporation of CuICuII-1 with ethylcellulose (EC) to form CuICuII-1@EC composite films greatly improved the TENG outputs, and the 10% CuICuII-1@EC-TENG offered the maximum Isc (57.2 μA) and Voc (986.8 V). Furthermore, multiple 10% CuICuII-1@EC-TENG devices were integrated in parallel to assemble multiple TENG devices (M-TENG) to harvest biomechanical energy, which displayed significant potential to continuously power blue LEDs, generating blue-light irradiation to trigger the photocatalytic C(sp)-H/Si-H cross-coupling reactions of aromatic alkyne and trimethylsilane for alkynylsilane over the photocatalysts CuICuII-1 and CuII-2. The results revealed that CuICuII-1 achieved a cooperative effect on remarkable catalytic selectivity and activity. This work demonstrates that bifunctional MOFs can serve as friction electrode materials for the large-scale integration and assembly of MOF-based TENG, and photocatalysts for achieving self-powered photocatalytic systems.

Weak Coupling Strategy to Construct High-Performance Sm/Tb-Doped Lanthanide Coordination Polymer Luminescent Sensor for D2O Detection

Accurate measurement of the purity and content of heavy water is of great concern in nuclear energy, the chemical industry, and biomedicine. Since the physical and chemical properties of D2O and H2O are very similar, achieving luminescent detection is challenging. Due to the difference in the vibrational frequency of the O-D and the O-H bonds, the quenching efficiency of the excited state of Ln3+ is different, which leads to a significant difference in the optical properties of Ln3+. Based on this theory, we composed a weak coupling strategy to strengthen the luminescence difference of Ln3+. Then, we demonstrated the weak coupling effect and how to improve detection performance by analyzing L1-Eu0.14Tb0.86(C22H20Eu0.14Tb0.86N3O10) and L1-Sm0.45Tb0.55(C22H20Sm0.45Tb0.55N3O10). The structure and performance of the two sensors were characterized in detail. A series of heavy water detection luminescence sensing experiments show that L1-Sm0.45Tb0.55 and L1-Eu0.14Tb0.86 can not only qualitatively distinguish D2O and H2O with the naked eye but also quantitatively detect any concentration of H2O in D2O. The prepared composite films L1-Sm0.45Tb0.55@PMMA and L1-Eu0.14Tb0.86@PMMA have practical application value. The application of Sm/Tb-doped lanthanide coordination polymers for detecting the H2O content in D2O has not been reported.

Chiral Self-Assembly of Twisted Prisms, Cuboids, and Polyhedral Capped Cages with Tartrate Ligands

Homochiral triangular prisms, cuboid cages, and capped polyhedral cages are successfully synthesized via coordination-driven self-assembly. Typical tartrate ligands demonstrated notable torsional flexibility and variable coordination numbers, allowing for diverse coordination patterns, including saturated chelation and terminal mono-coordination with half-sandwich rhodium and iridium fragments. The ligand lengths, molar ratios, and metal vertices are meticulously designed and fine-tuned to yield chiral cages with entirely distinct architectures. Tartrate ligand exhibits abundant hydrogen bonding interactions and chiral induction capabilities, these supramolecular assemblies are characterized by single-crystal X-ray diffraction, nuclear magnetic resonance, and circular dichroism spectroscopy. An efficient method is developed for constructing chiral structurally versatile cage-like entities, facilitating self-assembly in complicated multi-component systems.

Recent Developments in the Metal-Catalyzed Synthesis of Nitrogenous Heterocyclic Compounds

Metal-catalyzed cyclization reactions have become a powerful and efficient approach for the stereoselective construction of both carbocyclic and heterocyclic ring systems. Transition metal complexes, with their ability to activate and selectively functionalize organic substrates, have revolutionized various areas of synthetic chemistry. This review highlights recent advancements in metal-catalyzed cyclization reactions, especially in the synthesis of nitrogen-containing heterocycles like imidazoles, pyridines, pyrimidines, and indoles. These advancements have significantly impacted fields such as natural product synthesis, pharmaceuticals, functional materials, and organic electronics. Novel catalytic systems, ligand designs, and reaction conditions continue to expand the capabilities of these reactions, driving further the progress made in synthetic organic chemistry. This review provides a comprehensive overview of recent research.

General and Modular Synthesis of Covalent Organic Cages for Efficient Molecular Recognition

Cage-type structures based on coordination and dynamic covalent chemistry have the characteristics of facile and efficient preparation but poor stability. Chemically stable organic cages, generally involving fragment coupling and multi-step reactions, are relatively difficult to synthesize. Herein, we offer a general and modular strategy to customize covalent organic cages with diverse skeletons and sizes. First, one skeleton (S) module with three extension (E) modules and three reaction (R) modules are connected by one- or two-step coupling to get the triangular monomer bearing three reaction sites. Then one-pot Friedel-Crafts condensation of the monomer and linking module of paraformaldehyde produces the designed organic cages. The cage forming could be regulated by the geometrical configuration of monomeric blocks. The S-E-R angles in the monomer is crucial; only 120° (2,4-dimethoxyphen as reaction module) or 60° (2,5-dimethoxyphen as reaction module) angle between S-E-R successfully affords the resulting cages. By the rational design of the three modules, a series of organic cages have been constructed. In addition, the host-guest properties show that the representative cages could strongly encapsulate neutral aromatic diimide guests driven by solvophobic interactions in polar solvents, giving the highest association constant of (2.58±0.18)×105 M-1.

Heterometallic-Organic Cages with Customized Cavities: Constructed by Bottom-Up Step-Wise Coordination-Driven Self-Assembly

Accurately synthesizing coordination-driven metal-organic cages with customized shape and cavity remains a great challenge for chemists. In this work, a bottom-up step-wise coordination-driven self-assembly approach was put forward. Employing this strategy, three terpyridyl heterometallic-organic truncated tetrahedral cages with different sizes and cavity were precisely synthesized. Firstly, the coordination of tripodal organic ligands with Ru2+ afforded dendritic metal-organic ligands L1-L3. Then the Ru building blocks complexed with Fe2+ and shrunk to form the desired heterometallic-organic cages (C1-C3). These discrete heterometallic-organic supramolecular cages were fully characterized and displayed the large and open cavities varied from 7205 Å3 to 9384 Å3. Notably, these cages could not be directly constructed by single-step assembly process using initial organic ligands or dimeric metal-organic ligands, indicative of the irreplaceability of a bottom-up step-wise assembly strategy for size-customized architectures. This work paves a new way for precisely constructing metal-organic cages with well-defined cavities.

Solvent- and Concentration-Induced Topological Transformation of a Ruthenium(II)-Based Trigonal Prism to a Triply Interlocked [2] Catenane

Synthesis of interlocked supramolecular cages has been a growing field of interest due to their structural diversity. Herein, we report the template-free synthesis of a Ru(II) triply interlocked [2] catenane using coordination-driven self-assembly. The self-assembly of a triazine-based tripyridyl donor L (2,4,6-tris(5-(pyridin-4-yl)thiophen-3-yl)-1,3,5-triazine) with a dinuclear Ru(II) acceptor M (Ru2(dhnq)(η6-p-cymene)2)(CF3SO3)2) yielded two distinct structures depending on the solvent and concentration. In methanol, a triply interlocked metalla [2] catenane (MC2) was formed, whereas in nitromethane, a non-interlocked cage (MC1) was obtained. The non-interlocked cage MC1 was gradually converted to MC2 in nitromethane by the increase in the concentration of cage MC1 from 0.5 to 9 mM. The interlocked cage (MC2) was stable after formation and was unaffected by the change in concentration. Notably, the free cage (MC1) exhibited host-guest interactions with polycyclic aromatic aldehydes, stabilizing the non-interlocked structure even at higher concentrations. In contrast, the triply interlocked [2] catenane (MC2) remains stable due to self-penetration and does not encapsulate guest molecules. This work showcases the stimuli-induced irreversible structural transformation of a triangular prismatic cage to its triply interlocked [2] catenane by employing metal-ligand coordination chemistry.

Pyrene-Functionalized Ru-Catenated Metallacycles: Conversion of Catenated System to Monorectangle through Aging

Molecular transformation behavior within a mechanically interlocked system is often assisted by chemical manipulation, such as the inclusion of guest molecules, variation in the solution concentration, or swapping of solvents. We present in this report the synthesis of ruthenium metal and π-conjugated pyrene-based (2 + 2)2 catenated rectangles. Additionally, we discuss the structural conversion of these catenated rectangles into monorectangles through adjustments in concentration and solvent composition. In the presence of a methanol solution, a transformation into monorectangles was observed as the concentration declined. However, interestingly, in the presence of a nitromethane solution, an alteration in conformation to monorectangles was noted by just standing at room temperature for a few hours without any chemical manipulation. Furthermore, theoretical calculations were studied to provide insights into the formation of catenated structures over other potential ring-in-ring or Borromean-ring-type structures. The computational study with the GFN2-xTB method combined with density functional theory (DFT) calculations showed that the lower binding energy within the rectangles favors a catenated structure over other potential ring-in-ring or Borromean-ring-type structures. This work represents a new example of an intertwined structure that self-assembles into a catenated ring rather than a ring-in-ring or Borromean ring and transforms into a monorectangle in nitromethane without the use of any template, alteration in solution concentration, or exchange of solvents, but simply by standing at room temperature.

Interwoven Trimeric Cage-Catenanes with Topological Chirality

Catenanes have gained increasing attention for their unique features such as topological chirality. To date, the majority of works have focused on catenanes comprising monocyclic rings. Due to the lack of efficient synthetic strategy, catenanes of multiannulated monomers remain scarce. Here, we report the one-pot synthesis of an interwoven trimeric cage-catenane in high yield by dynamic imine condensation between diamine linkers of suitable length and trialdehyde panels in stoichiometry. The formation of cage-catenane is driven by the efficient 6-fold π-π stacking of panels. The monomeric cage and trimeric cage-catenane are interconvertible with reversible imine chemistry, with the latter thermodynamically being more favored. Using a topology-based statistical model, we first reveal that the formation probability of the interwoven catenane surpasses that of its chain-like isomer by 20%. When this pure mathematical model is refined by taking into account the strong template effect provided by the π-π stacking of aromatic panels, it shows that the interwoven structure emerges as the dominant species, almost ruling out the formation of the latter. Although composed of achiral cage monomers, the topological chirality of the interwoven trimeric catenane is unraveled by chiral-high-performance liquid chromatography (HPLC) and circular dichroism (CD) spectroscopy, and single-crystal X-ray diffraction (XRD) analysis of the interwoven cage-catenane also reveals a pair of two topological enantiomers. Our probability analysis-aided rationale would provide a design rationale for guiding the efficient synthesis of topologically sophisticated structures.

Supramolecular and molecular capsules, cages and containers

Stemming from early seminal notions of molecular recognition and encapsulation, three-dimensional, cavity-containing capsular compounds and assemblies have attracted intense interest due to the ability to modulate chemical and physical properties of species encapsulated within these confined spaces compared to bulk environments. With such a diverse range of covalent motifs and non-covalent (supramolecular) interactions available to assemble building blocks, an incredibly wide-range of capsular-type architectures have been developed. Furthermore, synthetic tunability of the internal environments gives chemists the opportunity to engineer systems for uses in sensing, sequestration, catalysis and transport of molecules, just to name a few. In this tutorial review, an overview is provided into the design principles, synthesis, characterisation, structural facets and properties of coordination cages, porous organic cages, supramolecular capsules, foldamers and mechanically interlocked molecules. Using seminal and recent examples, the advantages and limitations of each system are explored, highlighting their application in various tasks and functions.

Mechanically interlocked host systems for ion-pair recognition

The ever-increasing interest directed towards the construction of host architectures capable of the strong and selective recognition of various ionic species of biological, medical and environmental importance has identified mechanically interlocked molecules (MIMs), such as rotaxanes and catenanes, as potent host systems, owing to their unique three-dimensional topologically preorganised cavity recognition environments. Ion-pair receptors are steadily gaining prominence over monotopic receptor analogues due to their enhanced binding strength and selectivity, demonstrated primarily through acyclic and macrocyclic heteroditopic host systems. Exploiting the mechanical bond for ion-pair recognition through the strategic design of neutral heteroditopic MIMs offers exciting opportunities to accomplish potent and effective binding while mitigating competing interactions from the bulk solvent and counter-ions. This review details the design and ion-pair recognition capabilities of rotaxanes and catenanes employing hydrogen bonding (HB) and halogen bonding (XB) motifs, providing valuable insight into the burgeoning field and inspiration for future research.

Synergizing Steric Hindrance and Stacking Interactions To Facilitate the Controlled Assembly of Multiple 41 Metalla-Knots and Pseudo-Solomon Links

In this work, a noncoplanar terphenyl served as a building block to synthesize a novel 3,3'-substituted bipyridyl ligand (L1) which further reacted with binuclear half-sandwich units A/B, giving rise to two aesthetic 41 metalla-knots in high yields via a coordination-driven self-assembly strategy. Furthermore, given the inherent compactness of the 41 metalla-knots, it creates favorable conditions for the emergence of steric repulsion. We focused on progressively introducing nitrogen atoms featuring a lone pair of electrons (LPEs) into ligand L1 to manipulate the balance of H⋅⋅⋅H/LPEs⋅⋅⋅LPEs steric repulsion during the assembly process, ultimately achieving controlled assembly from 41 metalla-knots to the pseudo-Solomon link and then to molecular tweezer-like assembly facilitated by stacking interactions. All the assemblies were well characterized by solution-state NMR techniques, ESI-TOF/MS, and single-crystal X-ray diffraction. The evolutionary process of the topological architectures is equivalent to visualizing the synergistic effect of steric hindrance and stacking interactions on structural assembly, providing a new avenue for achieving the controlled synthesis of different topologies.

Synthesis of a Metalla[2]catenane, Metallarectangles and Polynuclear Assemblies from Di(N-Heterocyclic Carbene) Ligands

The 2,7-fluorenone-linked bis(6-imidazo[1,5-a]pyridinium) salt H2-1(PF6)2 reacts with Ag2O in CH3CN to yield the [2]catenane [Ag4(1)4](PF6)4. The [2]catenane rearranges in DMF to yield two metallamacrocycles [Ag2(1)2](PF6)2. 2,7-Fluorenone-bridged bis-(imidazolium) salts H2-L(PF6)2 (L=2 a, 2 b) react with Ag2O in CH3CN to yield metallamacrocycles [Ag2(L)2](PF6)2 with interplanar distances between the fluorenone rings too small for [2]catenane formation. Intra- and intermolecular π⋅⋅⋅π interactions between the fluorenone groups were observed by X-ray crystallography. The strongly kinked 2,7-fluorenone bridged bis(5-imidazo[1,5-a]pyridinium) salt H2-4(PF6)2 reacts with Ag2O to yield [Ag2(4)(CN)](PF6), while the tetranuclear assembly [Ag4(4)2(CO3)](PF6)2 was obtained in the presence of K2CO3.

One-, two- and three-dimensional interlocked polymers based on hybrid inorganic-organic rotaxanes

We report three new polymers, based on mechanically interlocked inorganic-organic rotaxanes. They are made in very mild conditions and involve pyrimidine head groups binding to copper(ii) linking units. A two-dimensional 6,3 net and a three-dimensional 10,3b net are found depending on the solvent used in the reaction.

Host-Guest Interactions Induced Enhancement in Oxidase-Like Activity of a Benzothiadiazole Dye Inside an Aqueous Pd8L4 Barrel

The effect of host-guest interactions on the chemistry of encapsulated molecules is a fascinating field of research that has gained momentum in recent years. Much of the work in this field has been focused on the effect of such interactions on catalysis and photoluminescence of encapsulated dyes. However, the effect of such interactions on related photoinduced processes, such as photoregulated oxidase-mimicking activity, has not been explored much. Herein, we report a unique example of enhancement of oxidase-like activity of a benzothiadiazole dye (G1) in water through encapsulation within a M8L4 molecular barrel (1). Favorable host-guest interactions helped the encapsulated guest G1 to have better photoinduced electron transfer to molecular oxygen leading to increased production of superoxide radical anions and oxidase-like activity. Furthermore, encapsulation inside 1 also caused a change in the redox potentials of the guest (G1) which after photoinduced electron transfer produced a better oxidizing agent than free G1. These phenomena combined to enhance the oxidase-like activity of dye G1 upon encapsulation inside cage 1. The present report demonstrates a unique effect of host-guest chemistry on photoregulated processes.

Breaking New Ground towards Innovative Synthesis of Palladacycles: The Electrochemical Synthesis of a Tetranuclear Thiosemicarbazone-[C,N,S] Palladium(II) Complex

The electrochemical oxidation of anodic metals (M = nickel and palladium) in an acetonitrile solution of the thiosemicarbazone ligands (E)-2-(1-(4-methoxyphenyl)ethylidene)-N-methylhydrazine-1-carbothioamide (a), (E)-2-(1-(p-tolyl)ethylidene)hydrazine-1-carbothioamide (b), and (E)-N-phenyl-2-(1-(p-tolyl)ethylidene)hydrazine-1-carbothioamide (c) yielded the homoleptic complexes [ML2], 1a, 1b, 1c, and 2c and [M4L4], 2a as air-stable solids. The crystal structures for 1a, 1b, 1c, and 2c show the ligands in a transoid disposition with the [S,S] and [N,N] donor atom pairs occupying cis positions on the nearly square planar coordination plane of the metal. The structure for 2a of S4 symmetry comprises a tetranuclear palladacycle where the metalated ligands are arranged around a central Pd4S4 environment: a crown ring with alternating palladium and sulfur atoms. The latter complex is the first example of an electrochemical preparation of a cyclometalated palladium compound, marking a milestone in the chemistry of such species. The compounds have been fully characterized by elemental microanalysis, mass spectrometry, infrared (IR), and 1H nuclear magnetic resonance (NMR) spectra.

Stimuli-Mediated Structural Interchange Between Pd6 and Pd12 Architectures: Selective Recognition of E-Stilbene by the Pd6 Architecture and its Photoprotection

The dynamic behaviour of metal-ligand bonding cultivates stimuli-mediated structural transformations in self-assembled molecular architectures. The propensity of synthetically designed self-assembled systems to interchange between higher-order architectures is increased multi-fold when the building blocks have higher conformational degrees of freedom. Herein, we report a new ligand, (2,7-bis(di(pyridin-4-yl)amino)-9H-fluoren-9-one) (L), which, upon self-assembly with a cis-[(ethylene-1,2-diamine)Pd(NO3)2] acceptor (M), resulted in the formation of a M6L3 trifacial barrel (C1) in water. Interestingly, during crystallization, a rare M12L6 triangular orthobicupola architecture (C2) was generated along with C1. C2 could also be generated in solution via the application of several stimuli. C1 in aqueous media could stabilize one trans-stilbene (tS) or cis-stilbene (cS) molecule in its cavity, with a selectivity for the former from their mixture. Moreover, C1 acted as an effective host to prevent the otherwise facile photoisomerization of tS to cS inside its hydrophobic cavity under UV irradiation. Conversely, the visible-light-induced reverse isomerization of encapsulated cS to encapsulated tS could be achieved readily due to the better stabilization of tS within the cavity of C1 and its transparency to visible light. A multi-functional system was therefore designed, which at the same time is stimuli-responsive, shows isomer selectivity, and photo-protects trans-stilbene.

Selective sodium halide over potassium halide binding and extraction by a heteroditopic halogen bonding [2]catenane

The synthesis and ion-pair binding properties of a heteroditopic [2]catenane receptor exhibiting highly potent and selective recognition of sodium halide salts are described. The receptor design consists of a bidentate halogen bonding donor motif for anion binding, as well as a di(ethylene glycol)-derived cation binding pocket which dramatically enhances metal cation affinity over previously reported homo[2]catenane analogues. 1H NMR cation, anion and ion-pair binding studies reveal significant positive cooperativity between the cation and anion binding events in which cation pre-complexation to the catenane subsequently 'switches-on' anion binding. Notably, the heteroditopic catenane displayed impressive selectivity for sodium halide recognition over the corresponding potassium halides. We further demonstrate that the catenane is capable of extracting solid alkali metal salts into organic media. Crucially, the observed solution phase binding selectivity for sodium halides translates to superior functional extraction capabilities of these salts relative to potassium halides, overcoming the comparatively higher lattice enthalpies NaX > KX dictated by the smaller alkali metal sodium cation. This is further exemplified in competitive solid-liquid experiments which revealed the exclusive extraction of sodium halide salts from solid mixtures of sodium and potassium halide salts.

Mechanically Interlocked Water-Soluble Pd6 Host for the Selective Separation of Coal Tar-Based Planar Aromatic Molecules

Research on the synthesis of catenated cages has been a growing field of interest in the past few years. While multiple types of catenated cages with different structures have been synthesized, the application of such systems has been much less explored. Specifically, the use of catenated cages in the separation of industrially relevant molecules that are present in coal tar has not been explored before. Herein, we demonstrate the use of a newly synthesized interlocked cage 1 [C184H240N76O48Pd6] (M6L4), formed through the self-assembly of ligand L.HNO3 (tris(4-(1H-imidazole-1-yl)benzylidene)hydrazine-1-carbohydrazonhydrazide) with acceptor cis-[(tmchda)Pd(NO3)2] [tmchda = ±N,N,N',N'-tetramethylcyclohexane-1,2-diamine] (M). The interlocked cage 1 was able to separate the isomers (anthracene and phenanthrene) using a simple solvent extraction technique. Using the same technique, the much more difficult separation of structurally and physiochemically similar compounds acenaphthene and acenaphthylene was performed for the first time with 1 as the host. Other noninterlocked hexanuclear Pd6 cages having a wider cavity proved inefficient for such separation, demonstrating the uniqueness of the interlocked cage 1 for such challenging separation.

Triply Interlocked [2]catenanes: Rational Synthesis, Reversible Conversion Studies and Unprecedented Application in Photothermal Responsive Elastomer

Triply interlocked [2]catenane complexes featuring two identical, mechanically interlocked units are extraordinarily rare chemical compounds, whose properties and applications remain open to detailed studies. Herein, we introduce the rational design of a new ligand precursor, L1, suitable for the synthesis of six triply interlocked [2]catenanes by coordination-driven self-assembly. The interlocked compounds can be reversibly converted into the corresponding simple triangular prism metallacage by addition of H2O or DMF solvents to their CH3OH solutions, thereby demonstrating the importance of π⋅⋅⋅π stacking and hydrogen bonding interactions in the formation of triply interlocked [2]catenanes. Moreover, extensive studies have been conducted to assess the remarkable photothermal conversion performance. Complex 6 a, exhibiting outstanding photothermal conversion performance (conversion efficiency in solution : 31.82 %), is used to prepare novel photoresponsive elastomer in combination with thermally activated liquid crystal elastomer. The resultant material displays robust response to near-infrared (NIR) laser and the capability of completely reforming the shape and reversible actuation, paving the way for the application of half-sandwich organometallic units in photo-responsive smart materials.

Non-threaded and rotaxane-type threaded wheel-axle assemblies consisting of dinickel(II) metallomacrocycle and dibenzylammonium axle

Rotaxanes are typically prepared using covalent bonds to trap a wheel component onto an axle molecule, and rotaxane-type wheel-axle assembly using only noncovalent interactions has been far less explored. Here we show that a dinickel(II) metallomacrocycle forms two different types of wheel-axle assemblies with a dibenzylammonium axle molecule based only on noncovalent interactions. The non-threaded assembly was obtained by introduction of Ni2+ into the macrocycle before the complexation with the axle molecule (metal-first method). The non-threaded assembly was in rapid equilibrium with each of the components in solution. The threaded assembly was obtained by introduction of Ni2+ after the formation of a pseudorotaxane from the non-metalated wheel and the axle molecule (axle-first method). The threaded assembly was not in equilibrium with the dissociated species even though it was maintained only by noncovalent interactions. Thus, formation of one of the non-threaded and threaded wheel-axle assemblies over the other is governed by the assembly pathway.

Water and Air Stable Copper(I) Complexes of Tetracationic Catenane Ligands for Oxidative C-C Cross-Coupling

Aqueous soluble and stable Cu(I) molecular catalysts featuring a catenane ligand composed of two dicationic, mutually repelling but mechanically interlocked macrocycles are reported. The ligand interlocking not only fine-tunes the coordination sphere and kinetically stabilizes the Cu(I) against air oxidation and disproportionation, but also buries the hydrophobic portions of the ligands and prevents their dissociation which are necessary for their good water solubility and a sustained activity. These catenane Cu(I) complexes can catalyze the oxidative C-C coupling of indoles and tetrahydroisoquinolines in water, using H2O2 as a green oxidant with a good substrate scope. The successful use of catenane ligands in exploiting aqueous Cu(I) catalysis thus highlights the many unexplored potential of mechanical bond as a design element for exploring transition metal catalysis under challenging conditions.

The codriven assembly of molecular metalla-links ([Formula: see text], [Formula: see text]) and metalla-knots ([Formula: see text], [Formula: see text]) via coordination and noncovalent interactions

Although mechanically interlocked molecules (MIMs) display unique properties and functions associated with their intricate connectivity, limited assembly strategies are available for their synthesis. Herein, we presented a synergistic assembly strategy based on coordination and noncovalent interactions (π-π stacking and CH⋯π interactions) to selectively synthesize molecular closed three-link chains ([Formula: see text] links), highly entangled figure-eight knots ([Formula: see text] knots), trefoil knot ([Formula: see text] knot), and Borromean ring ([Formula: see text] link). [Formula: see text] links can be created by the strategic assembly of nonlinear multicurved ligands incorporating a furan or phenyl group with the long binuclear half-sandwich organometallic Cp*RhIII (Cp* = η5-pentamethylcyclopentadienyl) clip. However, utilizing much shorter binuclear Cp*RhIII units for union with the 2,6-naphthyl-containing ligand led to a [Formula: see text] knot because of the increased π-π stacking interactions between four consecutive stacked layers and CH⋯π interactions. Weakening such π-π stacking interactions resulted in a [Formula: see text] knot. The universality of this synergistic assembly strategy for building [Formula: see text] knots was verified by utilizing a 1,5-naphthyl-containing ligand. Quantitative conversion between the [Formula: see text] knot and the simple macrocycle species was accomplished by adjusting the concentrations monitored by NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). Furthermore, increasing the stiff π-conjugated area of the binuclear unit afforded molecular Borromean ring, and this topology is a topological isomer of the [Formula: see text] link. These artificial metalla-links and metalla-knots were confirmed by single-crystal X-ray diffraction, NMR and ESI-MS. The results offer a potent strategy for building higher-order MIMs and emphasize the critical role that noncovalent interactions play in creating sophisticated topologies.

The Topological Transformation of Trefoil Knots to Solomon Links via Diels-Alder Click Reaction

The quest for more efficient, user-friendly, and less wasteful topological transformations remains a significant challenge in the realm of postassembly modifications. In this article, high yields of two molecular trefoil knots (Rh-1, Ir-1) were obtained using ligand 3,6-bis(3-(pyridin-4-yl)phenyl)-1,2,4,5-tetrazine (L1) with reactive tetrazine units and binuclear half-sandwich organometallic units [Cp*2M2(μ-TPPHZ)(OTf)2](OTf)2 (Rh-B, M = RhIII; Ir-B, M = IrIII). 2,5-Norbornadiene was used as an inducer of the Diels-Alder click reaction to modulate rapidly and efficiently the transformation of Trefoil knots to Solomon links. However, the key to achieving this topological structural change is the subtle increase in site steric of the pyridazine fragments (L2), which allows the molecular structures to spread and bend in three-dimensional space, as confirmed by single-crystal X-ray diffraction, ESI-TOF/MS, elementary analysis and detailed solution-state NMR techniques.

Self-Assembly of a Water-Soluble Pd16 Square Bicupola Architecture and Its Use in Aerobic Oxidation in Aqueous Medium

Designing supramolecular architectures with uncommon geometries has always been a key goal in the field of metal-ligand coordination-driven self-assembly. It acquires added significance if functional building units are employed in constructing such architectures for fruitful applications. In this report, we address both these aspects by developing a water-soluble Pd16L8 coordination cage 1 with an unusual square orthobicupola geometry, which was used for selective aerobic oxidation of aryl sulfides. Self-assembly of a benzothiadiazole-based tetra-pyridyl donor L with a ditopic cis-[(tmeda)Pd(NO3)2] acceptor [tmeda = N,N,N',N'-tetramethylethane-1,2-diamine] produced 1, and the geometry was determined by single-crystal X-ray diffraction study. Unlike the typically observed tri- or tetrafacial barrel, the present Pd16L8 coordination assembly features a distinctive structural topology and is a unique example of a water-soluble molecular architecture with a square orthobicupola geometry. Efficient and selective aerobic oxidation of sulfides to sulfoxides is an important challenge as conventional oxidation generally leads to the formation of sulfoxide along with toxic sulfone. Cage 1, designed with a ligand containing a benzothiadiazole moiety, demonstrates an ability to photogenerate reactive oxygen species (ROS) in water, thus enabling it to serve as a potential photocatalyst. The cage showed excellent catalytic efficiency for highly selective conversion of alkyl and aryl sulfides to their corresponding sulfoxides, therefore without the formation of toxic sulfones and other byproducts, under visible light in aqueous medium.

Advancements and strategic approaches in catenane synthesis

Catenanes, a distinctive category of mechanically interlocked molecules composed of intertwined macrocycles, have undergone significant advancements since their initial stages characterized by inefficient statistical synthesis methods. Through the aid of molecular recognition processes and principles of self-assembly, a diverse array of catenanes with intricate structures can now be readily accessed utilizing template-directed synthetic protocols. The rapid evolution and emergence of this field have catalyzed the design and construction of artificial molecular switches and machines, leading to the development of increasingly integrated functional systems and materials. This review endeavors to explore the pivotal advancements in catenane synthesis from its inception, offering a comprehensive discussion of the synthetic methodologies employed in recent years. By elucidating the progress made in synthetic approaches to catenanes, our aim is to provide a clearer understanding of the future challenges in further advancing catenane chemistry from a synthetic perspective.

Efficient and Selective Construction of 41 2 Metalla-links Using Weak C-H⋅⋅⋅Halogen Interactions

Through a coordination-driven self-assembly method, four4 1 2 ${4_1^2 }$ metalla-links and one tetranuclear monocycle were constructed with high selectivity and yield by adjusting the substituent species of the building blocks, as evidenced using X-ray crystallographic analysis, electrospray ionization-time-of-flight/mass spectrometry (ESI-TOF/MS), elemental analysis and detailed solution-state nuclear magnetic resonance (NMR) spectroscopy. Based on X-ray crystallographic analysis and independent gradient model analysis, a significant factor leading to the formation of4 1 2 ${4_1^2 }$ metalla-links was the introduction of F, Cl, Br and I atoms, which generated additional weak C-H⋅⋅⋅X (X=F, Cl, Br and I) interactions. Furthermore, the dynamic conversion of4 1 2 ${4_1^2 }$ metalla-links to monocyclic rings in methanol solution was systematically investigated using quantitative 1H NMR techniques.

Endowing Metal-Organic Coordination Materials with Chiroptical Activity by a Chiral Anion Strategy

Recently, chiral metal-organic coordination materials have emerged as promising candidates for a wide range of applications in chiroptoelectronics, chiral catalysis, and information encryption, etc. Notably, the chiroptical effect of coordination chromophores makes them appealing for applications such as photodetectors, OLEDs, 3D displays, and bioimaging. The direct synthesis of chiral coordination materials using chiral organic ligands or complexes with metal-centered chirality is very often tedious and costly. In the case of ionic coordination materials, the combination of chiral anions with cationic, achiral coordination compounds through noncovalent interactions may endow molecular materials with desirable chiroptical properties. The use of such a simple chiral strategy has been proven effective in inducing promising circular dichroism and/or circularly polarized luminescence signals. This concept article mainly delves into the latest advances in exploring the efficacy of such a chiral anion strategy for transforming achiral coordination materials into chromophores with superb photo- or electro-chiroptical properties. In particular, ionic small-molecular metal complexes, metal clusters, coordination supramolecular assemblies, and metal-organic frameworks containing chiral anions are discussed. A perspective on the future opportunities on the preparation of chiroptical materials with the chiral anion strategy is also presented.

Intramolecular Cation-π Interactions Organize Bowl-Shaped, Luminescent Molecular Containers

Molecules with nonplanar architectures are highly desirable due to their unique topological structures and functions. We report here the synthesis of two molecular containers (1 ⋅ 3Br- and 1 ⋅ 3Cl-), which utilize intramolecular cation-π interactions to enforce macrocylic arrangements and exhibit high binding affinity and luminescent properties. Remarkably, the geometry of the cation-π interaction can be flexibly tailored to achieve a precise ring arrangement, irrespective of the angle of the noncovalent bonds. Additionally, the C-H⋅⋅⋅Br- hydrogen bonds within the container are also conducive to stabilizing the bowl-shaped conformation. These bowl-shaped conformations were confirmed both in solution through NMR spectroscopy and in the solid state by X-ray studies. 1 ⋅ 3Br- shows high binding affinity and selectivity: F->Cl-, through C-H⋅⋅⋅X- (X=F, Cl) hydrogen bonds. Additionally, these containers exhibited blue fluorescence in solution and yellow room-temperature phosphorescence (RTP) in the solid state. Our findings illustrate the utility of cation-π interactions in designing functional molecules.