Giant Expanded Porous Metallo-Hexagons.

Molecular self-assembly is a widely recognized approach for fabricating biomimetic functional nanostructures. Here, we report the synthesis of two giant hollow coronoid-like supramolecular hexagons, H1 and H2. These hexagons feature large cavities, showcasing unique inner and outer hexagons fixed by specific connectivities for enhanced stability and high metal center density. H1 exhibits properties that can be transformed through the thermodynamic conversion of the metallopolymer formed by L1 and L2. With an edge length of 6.8 nm, H2 is one of the largest hexagons reported to date. 1D and 2D NMR, TEM, ESI-MS, and TWIM-MS experiments provided conclusive evidence for the composition and structure of the assembled hexagons. This work demonstrates the feasibility of constructing giant supramolecular architectures with precise control over their size and shape, opening up new possibilities for the design and synthesis of sophisticated supramolecules and nonbiological materials.

Segmented Template-Directed Self-Assembly of Giant Truncated Triangular Supramolecules.

The template-directed strategy has been extensively employed for the construction of supramolecular architectures. However, with the increase in the size and complexity of these structures, the synthesis difficulty of the templates escalates exponentially, thereby impeding the widespread application of this strategy. In this study, two truncated triangles T1 and T2 were successfully self-assembled through a novel segmented template strategy by segmenting the core triangular template into portions. Two metallo-organic ligands L2 and L3 were designed and synthesized by dividing the central stable triangle into three separate parts and incorporating them into the precursor ligands, which served as templates to guide the self-assembly process with ligands L1 and L4, respectively. The assembled structures were unambiguously characterized by multidimensional and multinuclear NMR (1H, COSY, NOESY), multidimensional mass spectrometry analysis (ESI-MS and TWIM-MS), and transmission electron microscopy (TEM). Moreover, we observed the formation of fiberlike nanotubes from single-molecule triangles by hierarchical self-assembly.

Synthesis of a Triangle-Fused Six-Pointed Star and Its Electrocatalytic CO2 Reduction Activity.

As electrocatalysts, molecular catalysts with large aromatic systems (such as terpyridine, porphyrin, or phthalocyanine) have been widely applied in the CO2 reduction reaction (CO2RR). However, these monomeric catalysts tend to aggregate due to strong π-π interactions, resulting in limited accessibility of the active site. In light of these challenges, we present a novel strategy of active site isolation for enhancing the CO2RR. Six Ru(Tpy)2 were integrated into the skeleton of a metallo-organic supramolecule by stepwise self-assembly in order to form a rhombus-fused six-pointed star R1 with active site isolation. The turnover frequency (TOF) of R1 was as high as 10.73 s-1 at -0.6 V versus reversible hydrogen electrode (vs RHE), which is the best reported value so far at the same potential to our knowledge. Furthermore, by increasing the connector density on R1's skeleton, a more stable triangle-fused six-pointed star T1 was successfully synthesized. T1 exhibits exceptional stability up to 126 h at -0.4 V vs RHE and excellent TOF values of CO. The strategy of active site isolation and connector density increment significantly enhanced the catalytic activity by increasing the exposure of the active site. This work provides a starting point for the design of molecular catalysts and facilitates the development of a new generation of catalysts with a high catalytic performance.

Microwave Flow Cytometric Detection and Differentiation of Escherichia coli.

Label-free measurement and analysis of single bacterial cells are essential for food safety monitoring and microbial disease diagnosis. We report a microwave flow cytometric sensor with a microstrip sensing device with reduced channel height for bacterial cell measurement. Escherichia coli B and Escherichia coli K-12 were measured with the sensor at frequencies between 500 MHz and 8 GHz. The results show microwave properties of E. coli cells are frequency-dependent. A LightGBM model was developed to classify cell types at a high accuracy of 0.96 at 1 GHz. Thus, the sensor provides a promising label-free method to rapidly detect and differentiate bacterial cells. Nevertheless, the method needs to be further developed by comprehensively measuring different types of cells and demonstrating accurate cell classification with improved machine-learning techniques.

Adjusting the Architecture of Heptagonal Metallo-Macrocycles by Embedding Metal Nodes into the Backbone.

Coordination-driven self-assembly has been extensively employed for the bottom-up construction of discrete metallo-macrocycles. However, the prevalent use of benzene rings as the backbone limits the formation of large metallo-macrocycles with more than six edges. Herein, by embedding metal nodes into the ligand backbone, we successfully regulated the ligand arm angle and assembled two giant heptagonal metallo-macrocycles with precise control. The angle between two arms at position 4 of the central terpyridine (tpy) extended after complexation with metal ions, leading to ring expansion of the metallo-macrocycle. The assembled structures were straightforwardly identified through multi-dimensional NMR spectroscopy (1 H, COSY, NOESY), multidimensional mass spectrometry analysis (ESI-MS and TWIM-MS), transmission electron microscopy (TEM), as well as scanning tunneling microscopy (STM). In addition, the catalytic performances of metallo-macrocycles in the oxidation of thioanisole were studied, with both supramolecules exhibiting good conversion rates. Furthermore, fiber-like nanostructures were observed from single-molecule heptagons by hierarchical self-assembly.

Strain-Induced Heteromorphosis Multi-Cavity Cages: Tension-Driven Self-Expansion Strategy for Controllable Enhancement of Complexity in Supramolecular Assembly.

Coordinative supramolecular cages with adjustable cavities have found extensive applications in various fields, but the cavity modification strategies for multi-functional structures are still challenging. Here, we present a tension-driven self-expansion strategy for construction of multi-cavity cages with high structural complexity. Under the regulation of strain-induced capping ligands, unprecedented heteromorphosis triple-cavity cages S2 /S4 were obtained based on a metallo-organic ligand (MOL) scaffold. The heteromorphosis cages exhibited significant higher cavity diversity than the homomorphous double-cavity cages S1 /S3 ; all of the cages were thoroughly characterized through various analytical techniques including (1D and 2D) NMR, ESI-MS, TWIM-MS, AFM, and SAXS analyses. Furthermore, the encapsulation of porphyrin in the cavities of these multi-cavity cages were investigated. This research opens up new possibilities for the architecture of heteromorphosis supramolecular cages via precisely controlled "scaffold-capping" assembly with preorganized ligands, which could have potential applications in the development of multifunctional structures with higher complexity.

Crystalline Metallo-Organic Cage by Triphenylene-Cored Hexaterpyridine for Fast Iodine Capture.

In recent years, radioactive iodine capture has played an important role in nuclear waste treatment. However, most of the adsorbents possess low economic efficiency and undesirable reutilization in practical application. In this work, a terpyridine-based porous metallo-organic cage was assembled for iodine adsorption. Through synchrotron X-ray analysis, the metallo-cage was found to have a porous hierarchical packing mode with inherent cavity and packing channel. By taking advantage of polycyclic aromatic units and charged ⟨tpy-Zn2+-tpy⟩ (tpy = terpyridine) coordination sites in the structure, this nanocage exhibits an excellent ability to capture iodine in both the gas phase and aqueous medium, and the crystal state of the nanocage shows an ultrafast kinetic process of capturing I2 in aqueous solution within 5 min. The calculated maximum sorption capacities for I2 based on the Langmuir isotherm models are 1731 and 1487 mg g-1 for amorphous and crystalline nanocages, which is noticeably higher than most of the reported iodine sorbent materials in the aqueous phase. This work not only provides a rare example of iodine adsorption by a terpyridyl-based porous cage but also expands the applications of terpyridine coordination systems into iodine capture.

Steric Hindrance Effect as a Decisive Factor for the Self-Assembly of Metallocages.

In the past decades, many supramolecular cages with different sizes and shapes have been achieved through coordination-driven self-assembly. However, the strategy of topology adjustment by using a steric hindrance effect has not been fully developed. In this Article, we report the synthesis of ligand LA with rotatable arms, ligand LB with restricted arms, and their precisely controlled self-assembly to tetramer cage T1 and dimer cage D1, respectively, under the same conditions. By utilizing the steric hindrance of the ligands, the shapes and sizes of metallosupramolecular cages have been successfully adjusted. The metallocages were characterized by NMR spectroscopy (1H, 13C, COSY, NOESY, and DOSY), mass spectrometry (ESI-MS, TWIM-MS), transmission electron microscopy, and atomic force microscopy. This synthetic method would have the potential to be a general strategy for the design and self-assembly of diverse cages with tunable shape, size, and applicable properties.

Multi-functionalized Metallo-Supramolecular Spoked Wheels: Their Emission-Tunable Hierarchically Assembled System with Dye Molecules.

Supramolecular architectures with multiple emissive units are especially appealing due to their desired properties, such as artificial light harvesting and white-light emission. But fully achieving multi-wavelength photoluminescence in a single supramolecular architecture remains a challenge. In this paper, functionalized supramolecular architectures containing twelve metal centers and six pyrene moieties were nearly quantitatively synthesized by multi-component self-assembly and fully characterized by 1D and 2D nuclear magnetic resonance, dynamic light scattering, electrospray ionization mass spectrometry, traveling-wave ion mobility mass spectrometry, and transmission electron microscopy. Moreover, the hierarchical nano-assemblies were prepared by introducing anionic dyes to the positively charged self-assembled framework, which contained three luminescence centers, namely, pyrene, tpy-Cd coordination parts, and Sulforhodamine B anions. Such a hierarchically assembled system displayed tunable emission by taking full advantage of aggregation-induced emission enhancement, aggregation-caused quenching, and fluorescence resonance energy transfer effects and showed the diverse emission colors. This research provides a new insight for constructing multiple emissive metallo-supramolecular assemblies.

Tpy-Mn(II)-Tpy (Tpy = 2,2':6',2″-terpyridine)-Based Pentagonal Prism for Green Photodriven Oxidation.

In coordination-driven metal-organic cages, the transition metal ions are generally utilized as linkages. Employment of its unique properties with the aim of achieving specific applications still presents great challenges. Herein, we report a decametric metal-organic cage named pentagonal prism (Mn20LC10) based on Tpy-Mn(II)-Tpy connectivity (Tpy = 2,2':6',2″-terpyridine) in which Mn(II) serves as a linker and endows the resulting metal-organic cage with good photosensitivity. In the photooxidation of benzaldehyde, pentagonal prism Mn20LC10 showed a significantly increased level of 1O2 production, the fastest conversion time, good recyclability, and substrate versatility due to its greatly improved intersystem crossing ability. Notably, the abundant active sites of metal pentagonal prism Mn20LC10 enable its photooxidation under solvent-free and daylight conditions. This work provides approaches for the development of inexpensive, green, and low-cost photosensitizer systems.

Heteroleptic/Heterometallic Sierpinski Triangle with Room Temperature Fluorescence Emission and Photocatalytic Amine Oxidation Activity.

As a result of their optical and redox properties, bipyridyl (bpy) and terpyridyl (tpy) ruthenium complexes play vital roles in numerous domains. Herein, the design and synthesis of two bipyridyl and terpyridyl ruthenium(II) building units L1 and L2 are explained. A [Ru(bpy)3]2+ functionalized triangle S1 and a Sierpinski triangle S2 were synthesized in almost quantitative yields by the self-assembly of L1 with Zn2+ ions and by the heteroleptic self-assembly of L1 and L2 with Zn2+ ions, respectively. The Sierpinski triangle S2 contains the coordination metals [Ru(bpy)3]2+, [Ru(tpy)2]2+, and [Zn(tpy)2]2+. According to research on the catalytic activity of amine oxidation on supramolecules S1 and S2, the benzylamine substrates were nearly entirely transformed to N-benzylidenebenzylamine derivatives after 1 h under a Xe lamp. Furthermore, the observed ruthenium-containing terpyridyl supramolecule S2 maintains high luminous performance at ambient temperature. This discovery opens up new possibilities for the rational molecular design of terpyridyl ruthenium fluorescent materials and catalytic functional materials.

Coordination-Driven Tetragonal Prismatic Cage and the Investigation on Host-Guest Complexation.

A coordination-driven host has been reported to encapsulate guests by noncovalent interactions. Herein, we present the design and synthesis of a new type of prism combining porphyrin and terpyridine moieties with a long cavity. The prism host can contain bisite or monosite guests through axial coordination binding of porphyrin and aromatic π interactions of terpyridine. The ligands and prismatic complexes were characterized by electrospray ionization mass spectrometry (ESI-MS), TWIM-MS, NMR spectrometry, and single-crystal X-ray diffraction analysis. The guest encapsulation was investigated through ESI-MS, NMR spectrometry, and transient absorption spectroscopy analysis. The binding constant and stability were determined by UV-Vis spectrometry and gradient tandem MS (gMS2) techniques. Based on the prism, a selectively confined condensation reaction was also performed and detected by NMR spectrometry. This study provides a new type of porphyrin- and terpyridine-based host that could be used for the detection of pyridyl- and amine-contained molecules and confined catalysis.

Controlled Construction of Heteroleptic [Pd2 (LA )2 (LB )(LC )]4+ Cages: A Facile Approach for Site-Selective endo-Functionalization of Supramolecular Cavities.

Construction of supramolecular structures with internal functionalities is a promising approach to build enzyme-like cavities. The endo-functionalized [Pd12 L24 ] and [Pd2 L4 ] coordination cages represent the most successful systems in this regard. However, these systems mainly contain one type of endo-moiety. We herein provide a solution for the controlled endo-functionalization of [Pd2 L4 ] cages. Site-selective introduction of the endo-functional group was achieved through the formation of heteroleptic [Pd2 (LA )2 (LB )(LC )] cages. Using two orthogonal steric control elements is the key for the selective formation of the hetero-assemblies. We demonstrated the construction of two hetero-cages with a single internal functional group as well as a hetero-cage with two distinct endohedral functionalities. The endo-functionalized hetero-cages bound sulfonate guests with fast-exchange dynamics. This strategy provides a new solution for the controlled endo-functionalization of supramolecular cavities.

Anion-Regulated Hierarchical Self-Assembly and Chiral Induction of Metallo-Tetrahedra.

The precise control over hierarchical self-assembly of superstructures relying on the elaboration of multiple noncovalent interactions between basic building blocks is both elusive and highly desirable. We herein report a terpyridine-based metallo-cage T with a tetrahedral motif and utilized it as an efficient building block for the controlled hierarchical self-assembly of superstructures in response to different halide ions. Initially, the hierarchical superstructure of metallo-cage T adopted a hexagonal close-packed structure. By adding Cl- /Br- or I- , drastically different hierarchical superstructures with highly-tight hexagonal packing or graphite-like packing arrangements, respectively, have been achieved. These unusual halide-ion-triggered hierarchical structural changes resulted in quite distinct intermolecular channels, which provided new insights into the mechanism of three-dimensional supramolecular aggregation and crystal growth based on macromolecular construction. In addition, the chiral induction of the metallo-cage T can be realized with the addition of chiral anions, which stereoselectively generated either PPPP- or MMMM-type enantiomers.

The Marriage of Sierpinski Triangles and Platonic Polyhedra.

Fractal structures with self-similarity are of fundamental importance in the fields of aesthetic, chemistry and mathematics. Here, by taking advantage of constructs the rational geometry-directed precursor design, we report the construction of two fascinating Platonic solids, the Sierpinski tetrahedron ST-T and the Sierpinski octahedron ST-O, in which each possesses a fractal Sierpinski triangle on their independent faces. These two discrete complexes are formed in near-quantitative yield from the multi-component self-assembly of truncated Sierpinski triangular kernel L1 with tribenzotriquinacene-based hexatopic and anthracene-based tetratopic terpyridine ligands (L3 and L4 ) in the presence of metal ions, respectively. The enhanced stabilities of the 3D discrete structures were investigated by gradient tandem mass spectrometry (gMS2 ). This work provides new constructs for the imitation of complex virus assemblies and for the molecular encapsulation of giant guest molecules.

An Imidazole-Based Triangular Macrocycle for Visual Detection of Formaldehyde.

Highly selective detection of formaldehyde utilizing supramolecules has promising applications in both environmental monitoring and biomonitoring areas. Herein we present a new class of imidazole-based, coordination-driven, self-assembled triangular macrocycles with specific recognition of formaldehyde. The visible fluorescence change to the naked eye from yellow to green-yellow occurs via an unusual reversible hydroxymethylation reaction of imidazole, whereas the corresponding imidazole ligands show no fluorescence change. This study provides a new method for efficient formaldehyde detection by utilizing imidazole-based coordination supramolecules.

Tetratopic Terpyridine Building Unit as a Precursor to Wheel-Like Metallo-Supramolecules.

In an effort to construct molecules with distinct shapes and functions, the design and synthesis of multitopic ligands are often able to play an important role. Here, we report the synthesis of a novel tetratopic organic ligand LA, which can be viewed as a bis-tenon with successive angular orientations in space. The particular ligand has been treated with different tailored metal-organic ligands to afford new members of the molecular wheel family (multi-rhomboidal-shaped wheel and bis-trapezium-shaped wheel) that show enhanced stability. Two-dimensional (2D) diffusion nuclear magnetic resonance (NMR) spectroscopy (DOSY), electrospray ionization (ESI) mass spectrometry, traveling wave ion mobility (TWIM), and gradient tandem mass spectrometry (gMS2) experiments, as well as molecular modeling, have been employed to provide structural information and differentiate the isomeric separation process. In addition, considering that LA has rotational properties, it is expected to open the door to functional supramolecules and stimuli-responsive materials.

Modular Construction of a Tessellated Octahedron, its Hierarchical Spherical Aggregate Behavior, and Electrocatalytic CO2 Reduction Activity.

Coordination-driven self-assembly has led to the formation of various aesthetical polyhedrons and compounds with advanced functions. Whereas two-dimensional supramolecules with complex and giant skeletons are plentiful, the constructions of polyhedrons are limited by using basic polygons as the panels. Herein, we report the modular synthesis of a tessellated triangle and tessellated octahedron with metal-organic modules as the panels and formed via template-driven self-assembly. These architectures have diameters on the order of 10.9 nm and molecular weights greater than 84 kDa. Interestingly, fiber and spherical-like nanostructures could be formed from the tessellated triangles and octahedrons, respectively, through hierarchical self-assembly. In addition, after hybridization with carbon nanotubes, the supramolecules exhibit electrochemical reduction activity for CO2 to CO.

Russian-Doll-Like Molecular Cubes.

Nanosized cage-within-cage compounds represent a synergistic molecular self-assembling form of three-dimensional architecture that has received particular research focus. Building multilayered ultralarge cages to simulate complicated virus capsids is believed to be a tough synthetic challenge. Here, we synthesize two large double-shell supramolecular cages by facile self-assembly of presynthesized metal-organic hexatopic terpyridine ligands with metal ions. Differing from the mixture of prisms formed from the inner tritopic ligand, the redesigned metal-organic hexatopic ligands bearing high geometric constraints that led to the exclusive formation of discrete double-shell structures. These two unique nested cages are composed of inner cubes (5.1 nm) and outer huge truncated cubes (12.0 and 13.2 nm) with six large bowl-shape subcages distributed on six faces. The results with molecular weights of 75 232 and 77 667 Da were among the largest synthetic cage-in-cage supramolecules reported to date. The composition, size and shape were unambiguously characterized by a combination of 1H NMR, DOSY, ESI-MS, TWIM-MS, TEM, AFM, and SAXS. This work provides an interesting model for functional recognition, delivery, and detection of various guest molecules in the field of supramolecular materials.

Construction of Macromolecular Pinwheels Using Predesigned Metalloligands.

Developing a methodology to build target structures is one of the major themes of synthetic chemistry. However, it has proven to be immensely challenging to achieve multilevel elaborate molecular architectures in a predictable way. Herein, we describe the self-assembly of a series of pinwheel-shaped starlike supramolecules through three rationally preorganized metalloligands L1-L3. The key octa-uncomplexed terpyridine (tpy) metalloligand L3, synthesized with an 8-fold Suzuki coupling reaction to metal-containing complexes, has four different types of terpyridines connected with three ⟨tpy-Ru2+-tpy⟩ units, making this the most subunits known so far for a preorganized module. Based on the principle of geometric complementation and the high "density of coordination sites", these metalloligands were assembled with Zn2+ ions to form a pinwheel-shaped star trigon P1, pentagram P2, and hexagram P3 with precisely controlled shapes in nearly quantitative yields. With molecular weights ranging from 16756 to 56053 Da and diameters of 6.7-13.6 nm, the structural composition, shape, and rigidity of these pinwheel-shaped architectures have been fully characterized by 1D and 2D (NMR), electrospray ionization mass spectrometry, traveling-wave ion mobility mass spectrometry, and transmission electron microscopy.