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.

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.

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.

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.

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.

Sierpinski Pyramids by Molecular Entanglement.

Planar, terpyridine-based metal complexes with the Sierpinski triangular motif and alkylated corners undergo a second self-assembly event to give megastructural Sierpinski pyramids; assembly is driven by the facile lipophilic-lipophilic association of the alkyl moieties and complementary perfect fit of the triangular building blocks. Confirmation of the 3D, pyramidal structures was verified and supported by a combination of TEM, AFM, and multiscale simulation techniques.

Monitoring Metallo-Macromolecular Assembly Equilibria by Ion Mobility-Mass Spectrometry.

Ion mobility-mass spectrometry (IM-MS) allows the separation of isomeric and isobaric species on the basis of their size, shape, and charge. The fast separation timescale (ms) and high sensitivity of these measurements make IM-MS an ideally suitable method for monitoring changes in macromolecular structure, such as those occurring in interconverting terpyridine-based metallosupramolecular self-assemblies. IM-MS is used to verify the elemental composition (size) and architecture (shape) of the self-assembled products. Additionally, this article demonstrates its applicability to the elucidation of concentration-driven association-dissociation (fusion-fission) equilibria between isobaric structures. IM-MS enables both quantitative separation and identification of the interconverting complexes as well as derivation of the corresponding equilibrium constants (i.e., thermodynamic information) from extracted IM-MS abundance data.

Terpyridine-Based, Flexible Tripods: From a Highly Symmetric Nanosphere to Temperature-Dependent, Irreversible, 3D Isomeric Macromolecular Nanocages.

A three-dimensional, highly symmetric sphere-like nanocage was synthesized using a terpyridine (tpy)-based, flexible tris-dentate ligand and characterized by single crystal X-ray analysis. To introduce more rigidity, one of the tpy units of the tris-dentate ligand was preblocked by stable connectivity to form the corresponding Ru2+-dimer. The complexation between Ru2+-dimer and Fe2+ demonstrates an unexpected temperature-dependent assembly between two irreversible isomeric 3D nanocages. Investigation of the coordination process and structural configurations of the metal-ligand framework, affected by the introduction of rigidity and in the presence of external stimuli (temperature), is reported.

Supercharged, Precise, Megametallodendrimers via a Single-Step, Quantitative, Assembly Process.

Synthesis of giant unimolecular dendrimers is challenging due, in part, to difficulties encountered at higher generations, in both convergent and divergent protocols because of the multistep construction/purification process. Herein, we report a hybrid synthetic procedure in which the core is constructed last. This quantitative assembly generated a metallodendrimer that is supercharged (120+), large (11.3 nm diameter), and its core was previously established. The series of complexes has been unequivocally characterized by NMR, ESI-IM-MS, and TEM techniques.

Controlled Interconversion of Superposed-Bistriangle, Octahedron, and Cuboctahedron Cages Constructed Using a Single, Terpyridinyl-Based Polyligand and Zn(2.).

Metallomacromolecular architectural conversion is expanded by the characterization of three different structures. A quantitative, single-step, self-assembly of a shape-persistent monomer, containing a flexible crown ether moiety, gives an initial Archimedean-based cuboctahedron that has been unequivocally characterized by 1D and 2D NMR spectroscopy, mass spectrometry, and collision cross section analysis. Both dilution and exchange of counterions, transforms this cuboctahedron into two identical octahedrons, which upon further dilution convert into four, superposed, bistrianglar complexes; increasing the concentration reverses the process. Ion binding studies using the cuboctahedral cage were undertaken.

Precise Molecular Fission and Fusion: Quantitative Self-Assembly and Chemistry of a Metallo-Cuboctahedron.

Inspiration for molecular design and construction can be derived from mathematically based structures. In the quest for new materials, the adaptation of new building blocks can lead to unexpected results. Towards these ends, the quantitative single-step self-assembly of a shape-persistent, Archimedean-based building block, which generates the largest molecular sphere (a cuboctahedron) that has been unequivocally characterized by synchrotron X-ray analysis, is described. The unique properties of this new construct give rise to a dilution-based transformation into two identical spheres (octahedra) each possessing one half of the molecular weight of the parent structure; concentration of this octahedron reconstitutes the original cuboctahedron. These chemical phenomena are reminiscent of biological fission and fusion processes. The large 6 nm cage structure was further analyzed by 1D and 2D NMR spectroscopy, mass spectrometry, and collision cross-section analysis. New routes to molecular encapsulation can be envisioned.

Probing a hidden world of molecular self-assembly: concentration-dependent, three-dimensional supramolecular interconversions.

A terpyridine-based, concentration-dependent, facile self-assembly process is reported, resulting in two three-dimensional metallosupramolecular architectures, a bis-rhombus and a tetrahedron, which are formed using a two-dimensional, planar, tris-terpyridine ligand. The interconversion between these two structures is concentration-dependent: at a concentration higher than 12 mg mL(-1), only a bis-rhombus, composed of eight ligands and 12 Cd(2+) ions, is formed; whereas a self-assembled tetrahedron, composed of four ligands and six Cd(2+) ions, appears upon sufficient dilution of the tris-terpyridine-metal solution. At concentrations less than 0.5 mg mL(-1), only the tetrahedron possessing an S4 symmetry axis is detected; upon attempted isolation, it quantitatively reverts to the bis-rhombus. This observation opens an unexpected door to unusual chemical pathways under high dilution conditions.

Construction of a highly symmetric nanosphere via a one-pot reaction of a tristerpyridine ligand with Ru(II).

A three-dimensional, highly symmetric, terpyridine-based, spherical complex was synthesized via the coordination of four novel, trisdentate ligands and six Ru(2+) ions, and it exhibits excellent stability over a wide range of pH values (1-14). Structural confirmation was obtained by NMR and ESI-TWIM-MS.

Towards molecular construction platforms: synthesis of a metallotricyclic spirane based on bis(2,2':6',2"-terpyridine)RuII connectivity.

The design and construction of the first multicomponent stepwise assembly of a -based (tpy=terpyridine), three-dimensional, propeller-shaped trismacrocycle, 8, are reported. Key steps in the synthesis involve the preparation of a hexaterpyridinyl triptycene and its reaction with dimeric, 60°-directional, bisterpyridine-Ru(II) building blocks. Characterization includes ESI- and ESI-TWIM-MS and TEM, along with 1D and 2D (1) H NMR spectroscopy.

One ligand in dual roles: self-assembly of a bis-rhomboidal-shaped, three-dimensional molecular wheel.

A facile high yield, self-assembly process that leads to a terpyridine-based, three-dimensional, bis-rhomboidal-shaped, molecular wheel is reported. The desired coordination-driven supramolecular wheel involves eight structurally distorted tristerpyridine (tpy) ligands possessing a 60° angle between the adjacent tpy units and twelve Zn(2+) ions. The tpy ligand plays dual roles in the self-assembly process: two are staggered at 180° to create the internal hub, while six produce the external rim. The wheel can be readily generated by mixing the tpy ligand and Zn(2+) in a stoichiometric ratio of 2:3; full characterization is provided by ESI-MS, NMR spectroscopy, and TEM imaging.

Metal-ion-determined geometrical configurations of metallo-cages with different emission properties.

The formation of metallo-cages is affected by a variety of factors such as the ligands, metals, and anions, among which the impact of metals with different binding capacities is particularly important, but has rarely been studied in three-dimensional metallo-cages. Herein, we report the design of truxene-centered terpyridine ligands and the self-assembly of a series of tetrameric metallo-cages. The utilization of metal ions with strong (Zn2+, Fe2+) or weak (Cd2+) binding strength afforded 3D metallo-cages with low symmetry or highly symmetric metallo-tetrahedra, respectively, possessing totally different geometrical configurations. In addition, their photophysical properties and host-guest chemical properties were investigated.

Multiple-stimuli fluorescent responsive metallo-organic helicated cage arising from monomer and excimer emission.

Effectively regulating monomer and excimer emission in a singular supramolecular luminous platform is challenging due to high difficulty of precise control over its aggregation and dispersion behavior when subjected to external stimuli. Here, we show a metallo-cage (MTH) featuring a triple helical motif that displays a unique dual emission. It arises from both intramolecular monomer and intermolecular excimer, respectively. The distorted molecular conformation and the staggered stacking mode of MTH excimer are verified through single crystal X-ray diffraction analysis. These structural features facilitate the switch between monomer and excimer emission, which are induced by changes in concentration and temperature. Significantly, adjusting the equilibrium between these two states in MTH enables the production of vibrant white light emission in both solution and solid state. Moreover, when combined with a PMMA (polymethyl methacrylate) substrate, the resulting thin films can serve as straightforward fluorescence thermometer and thermally activated information encryption materials.

A truncated triangular prism constructed by using imidazole-terpyridine building blocks.

The construction of low-symmetry topological supramolecular structures using bistable building blocks remains challenging. We report an unusual truncated triangular prismatic cage with D3h symmetry using a ligand with both cis- and trans-configurations upon coordination with metal. This work provides new ideas and methods for the future synthesis of low-symmetry topological supramolecules.

Supramolecular cuboctahedra with aggregation-induced emission enhancement and external binding ability.

Beyond the AIE (aggregation-induced emission) phenomenon in small molecules, supramolecules with AIE properties have evolved in the AIE family and accelerated the growth of supramolecular application diversity. Inspired by its mechanism, particularly the RIV (restriction of intramolecular vibrations) process, a feasible strategy of constructing an AIE-supramolecular cage based on the oxidation of sulfur atoms and coordination of metals is presented. In contrast to previous strategies that used molecular stacking to limit molecular vibrations, we achieved the desired goal using the synergistic effects of coordination-driven self-assembly and oxidation. Upon assembling with zinc ions, S1 was endowed with a distinct AIE property compared with its ligand L1, while S2 exhibited a remarkable fluorescence enhancement compared to L2. Also, the single cage-sized nanowire structure of supramolecules was obtained via directional electrostatic interactions with multiple anions and rigid-shaped cationic cages. Moreover, the adducts of zinc porphyrin and supramolecules were investigated and characterized by 2D DOSY, ESI-MS, TWIM-MS, UV-vis, and fluorescence spectroscopy. The protocol described here enriches the ongoing research on tunable fluorescence materials and paves the way towards constructing stimuli-responsive luminescent supramolecular cages.

An organic-Ru2+ cluster-initiated dendritic faced metallo-octahedron and its unpredictable photoactivity.

Herein, a novel 3D metal-organic ligand consisting of a folded Ru(II)-connected tetrameric cycle and two sets of 60° juxtaposed bisterpyridine arms was synthesized and its complexation with Zn2+ gave rise to dendritic-faced metallo-octahedron 6. Remarkably, octahedron 6 displayed unexpected photosensitization ability that could produce singlet oxygen (1O2) under white light irradiation.