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.

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.

Assembling Shape-Persistent High-Order Sierpinski Triangular Fractals.

Fractals are a series of intricate patterns with aesthetic, mathematic, and philosophic significance. The Sierpinski triangles have been known for more than one hundred years, but only recently discrete shape-persistent low-generation (mainly ST-1) fractal supramolecules have been realized. Herein, we report a retro-assembly pathway to the nanometer-scale, supra-macromolecular second-generation Sierpinski triangle and its third-generation saturated counterpart (Pascal's triangle). These gigantic triangular assemblies are unambiguously confirmed by NMR, DOSY, ESI-MS, TWIM-MS, TEM, and AFM analyses. Notably, the dense-packed counterions of these discrete triangular architectures could further form supramolecular hydro-gels in water. This work not only provides a fundamental chemical pathway to explore various giant supramolecular constructs and further overcome the synthetic limitation of complicated molecular fractals, but also presents a new type of supramolecular hydro-gels with potential in controlled release applications.

Author Correction: Intra- and intermolecular self-assembly of a 20-nm-wide supramolecular hexagonal grid.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Intra- and intermolecular self-assembly of a 20-nm-wide supramolecular hexagonal grid.

For the past three decades, the coordination-driven self-assembly of three-dimensional structures has undergone rapid progress; however, parallel efforts to create large discrete two-dimensional architectures-as opposed to polymers-have met with limited success. The synthesis of metallo-supramolecular systems with well-defined shapes and sizes in the range of 10-100 nm remains challenging. Here we report the construction of a series of giant supramolecular hexagonal grids, with diameters on the order of 20 nm and molecular weights greater than 65 kDa, through a combination of intra- and intermolecular metal-mediated self-assembly steps. The hexagonal intermediates and the resulting self-assembled grid architectures were imaged at submolecular resolution by scanning tunnelling microscopy. Characterization (including by scanning tunnelling spectroscopy) enabled the unambiguous atomic-scale determination of fourteen hexagonal grid isomers.

Giant Truncated Metallo-Tetrahedron with Unexpected Supramolecular Aggregation Induced Emission Enhancement.

The artificial synthesis of giant, three-dimensional, and shell-like architectures with growing complexity and novel functionalities is an especially challenging task for chemists. Fullerenes and self-assembled cages are remarkable examples that are proven milestones in the field of functional materials. Herein, we present another unique system: a giant terpyridine-based truncated metallo-tetrahedral architecture that includes densely-packed ionic pairs with a significant internal cavity. This huge metallo-tetrahedron with a molecular weight up to 70 000 Da was self-assembled simultaneously with 64 components: 12 large antler-shaped ligands (5), 4 star-shaped ligands (6), and 48 Cd2+ ions. Surprisingly, the giant tetrahedron shows broad visible emission (400-640 nm) and aggregation induced emission enhancement (AIEE) via a hierarchical assembly into highly-ordered nanoaggregates. A tunable emission color and near white-light emission in mixed solvent systems were also achieved. The present work not only affords an effective approach to the creation of giant shell-like architectures that can be used to mimic biological viruses and chemical frameworks but also provides a new class of functional metallo-architectures.

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.

Vertical Assembly of Giant Double- and Triple-Decker Spoked Wheel Supramolecular Structures.

The double- or triple-decker 3D metallo-hexagons were obtained by self-assembly of multitopic tris-terpyridines with Cd2+ ions in near-quantitative yield. Comprising up to 72 ionic pairs, the multiple spoked wheels display characteristic reversible gelation properties under thermodynamic conditions. The supramolecular metallo-nanoarchitectures were characterized by 1 H NMR, 2D NMR (COSY and NOESY), and diffusion-ordered spectroscopy (DOSY) and HR-ESI-MS, traveling-wave ion mobility mass spectrometry (TWIM-MS), TEM, and AFM. For the first time, the self-assembly of 45 units at once was demonstrated to yield exceptional giant triple-decker hexagons of up to circa 42 000 Da.

Supramolecular arrays by the self-assembly of terpyridine-based monomers with transition metal ions.

Hierarchical construction of a highly ordered supramolecular array has been, in general, a challenge due to the complexation of building blocks and the hard-to-control weak interactions. Herein, we present a type of well-ordered nanoribbon, which was self-assembled via shape complimentary and hydrophobic effects from the bowl-shaped supramolecular components, which were synthesized by combining designer terpyridine-based monomers and two different metal ions (Ru2+, Zn2+). Interestingly, switching counter ions or changing monomer concentrations, a transformation between a uniform nanosphere and nanoribbon occurred. This opens a door to fabricate readily tailorable, large-scale, supramacromolecular materials.

Terpyridine-based metallosupramolecular constructs: tailored monomers to precise 2D-motifs and 3D-metallocages.

This overview represents a comprehensive summary of the recent developments in the growing field of terpyridine-based, discrete metallosupramolecular architectures. The N-heteroaromatic ligand [2,2':6',2'']terpyridine (tpy) presents a convergent N,N',N''-chelating donor set and has the ability to bind diverse metal ions to form stable pseudo-octahedral tpy-M2+-tpy bonds. Use of tpy-M2+-tpy connectivity for the edges and directed organic vertices has opened the door to diverse, dynamic, utilitarian macromolecular materials. New strategies have been employed to synthesize a range of 2D- and 3D-fractals as well as novel macrocyclic constructs by employing new designer strategies, such as: triangle-based frameworks, hexagonal fractal designs, flexible polyterpyridine linkers, and noncovalent interactions for spontaneous quantitative self-assembly. Numerous examples of heteroleptic self-assembly have been described along with the synthesis of heterometallic conjugates using step-wise protocols. Utilizing multiplanar, directed spacer units in the polyterpyridine vertices, new 3D-polyhedra were obtained facilitating the assembly of hybrid fractal-dendritic materials. These constructs are shown to undergo tunable conformational transformations by responding to specific stimuli such as concentration, temperature, and counter ions. The increasing ability to exploit hierarchical self-assembly of complex, higher order supramolecular nanomaterials is discussed.

Concentration dependent supramolecular interconversions of triptycene-based cubic, prismatic, and tetrahedral structures.

The quantitative, single step, self-assembly of a shape-persistent, three-dimensional C3v-symmetric, triptycene-based tris-terpyridinyl ligand initially gives a platonic-based cubic architecture, which was unequivocally characterized by 1D and 2D NMR spectroscopy, mass spectrometry, and single crystal X-ray structural analysis. The unique metal-ligand binding properties of the Cd2+ analogue of this construct give rise to a concentration-dependent dynamic equilibrium between cube, prism, and tetrahedron-shaped architectures. Dilution transforms this cube into two identical tetrahedra through a stable prism-shaped intermediate; increasing the concentration reverses the process.

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.

Metallosupramolecular 3D assembly of dimetallic Zn4[RuL2]2 and trimetallic Fe2Zn2[RuL2]2.

A novel metallo-organic ligand [RuL2] with four uncomplexed coordination sites was created, and upon treatment with Zn2+ generated a dimetallic 3D metallosupramolecule in nearly quantitative yield. This self-assembly process gave stable intermediates, opening the pathway to the first 3D metallo-assembly possessing two Ru2+, two Fe2+, and two Zn2+ ions precisely located in the different edges. This strategy opens the door to novel designer 3D polymetallic constructs capable of diverse applications.

Constructing High-Generation Sierpinski Triangles by Molecular Puzzling.

Three generations of metalated trigonal supramolecular architectures, so-called metallo-triangles, were assembled from terpyridine (tpy) complexes. The first generation (G1) metallo-triangles were directly obtained by reacting a bis(terpyridinyl) ligand with a 60° bite angle and ZnII ions. The direct self-assembly of G2 and G3 triangles by mixing organic ligands and ZnII , however, only generated a mixture of G1 and G2, as well as a trace amount of insoluble polymer-like precipitate. Therefore, a modular strategy based on the connectivity of ⟨tpy-Ru2+ -tpy⟩ was employed to construct two metallo-organic ligands for the assembly of G2 and G3 Sierpinski triangles. The metallo-organic ligands LA and LB with multiple free terpyridines were obtained through Suzuki cross-coupling of the RuII complexes, and then assembled with ZnII or CdII to obtain high-generation metallo-triangular architectures in nearly quantitative yield. The G1-G3 architectures were characterized by NOESY and DOSY NMR spectroscopy, ESI-MS, TWIM-MS, and transmission electron microscopy.

Stepwise, multicomponent assembly of a molecular trapezoid possessing three different metals.

A novel terpyridine-based, trapezoidal architecture was synthesized by a coordination-driven multicomponent assembly and features three different tpy-M2+-tpy bonds (M2+ = Ru2+, Fe2+, and Zn2+) in the macrocyclic ring. This trimetallic macrocycle introduces the construction of polymetallosupramolecular assemblies possessing multiple, differing metal centers in an ordered, predetermined pattern. Characterization was accomplished by NMR spectroscopy, mass spectrometry, and UV-Vis spectroscopy.

Self-assembly of a supramolecular hexagram and a supramolecular pentagram.

Five- and six-pointed star structures occur frequently in nature as flowers, snow-flakes, leaves and so on. These star-shaped patterns are also frequently used in both functional and artistic man-made architectures. Here following a stepwise synthesis and self-assembly approach, pentagonal and hexagonal metallosupramolecules possessing star-shaped motifs were prepared based on the careful design of metallo-organic ligands (MOLs). In the MOL design and preparation, robust ruthenium-terpyridyl complexes were employed to construct brominated metallo-organic intermediates, followed by a Suzuki coupling reaction to achieve the required ensemble. Ligand LA (VRu2+X, V=bisterpyridine, X=tetraterpyridine, Ru=Ruthenium) was initially used for the self-assembly of an anticipated hexagram upon reaction with Cd2+ or Fe2+; however, unexpected pentagonal structures were formed, that is, [Cd5LA5]30+ and [Fe5LA5]30+. In our redesign, LB [V(Ru2+X)2] was synthesized and treated with 60° V-shaped bisterpyridine (V) and Cd2+ to create hexagonal hexagram [Cd12V3LB3]36+ along with traces of the triangle [Cd3V3]6+. Finally, a pure supramolecular hexagram [Fe12V3LB3]36+ was successfully isolated in a high yield using Fe2+ with a higher assembly temperature.

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.

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.

3D helical and 2D rhomboidal supramolecules: stepwise self-assembly and dynamic transformation of terpyridine-based metallo-architectures.

A Ru(2+)-connected, metallo-organic ligand (L) with three free terpyridines was designed and synthesized. L was assembled with Zn(2+) to generate a helical structure; however, when mixing L with a 1,2,3-tristerpyridine ligand (T), a thermodynamically stable 2D rhombus was assembled. Furthermore, this 2D rhomboidal structure can also be achieved through the dynamic transformation of preassembled helix H with T and Zn(2+) at room temperature.

Mono- and Bis-Terpyridine-Based Dimer and Metallo-Organic Polymers as Ionic Templates for Preparation of Multi-Metallic Au Nanocluster and Nanowires.

The preparation of multi-metallic Au nanocluster and nanowires has been achieved using terpyridine-based metallo-organic polymers as multi-ionic templates through a straightforward counterion exchange with aqueous NaAuCl4 followed by a mild reduction in-situ with sodium citrate. The mild reduction of the [TpyFeTpy]2+ x 2[AuCl4]- complex, derived from [TpyFeTpy]2+ x 2Cl- 1 (tpy = 2,2':6',2"-terpyridine), led to the formation of Au nanoclusters (Au NC) with diameters ranging from 7.5-88 nm. Each Au NC alone contained multiple nanoparticles, with diameters ranging from 2.5-4.5 nm. 1,4-bis-terpyridine based metallo-oraganic polymer [-TpyFeTpy-TpyFeTpy-]n(2n+) x [Cl]2n- 2 was found to generate a multi-ionic metallo-polymer with AuCl4- as the counterion, after mild reduction with sodium citrate, resulting in irregular zigzag shaped Au nanowires (Au NW). The prepared Au NW from the di-metallic complex 3 should find applications within electronic devices. Both Au NC and NW were also found to possess excellent catalytic properties.