Facile Self-Assembly of Metallo-Supramolecular Ring-in-Ring and Spiderweb Structures Using Multivalent Terpyridine Ligands

Stepwise construction of a metallocatenane based on non-labile bis(terpyridine)-CdII complexes

A series of metalloligands bearing homoleptic 2,2':6',2''-terpyridine (tpy)-CdII complexes has been successfully synthesized. The formation of ML1 was accomplished through a sequence of Suzuki-Miyaura coupling and complexation reactions, offering an alternative method to produce tpy-based metalloligands under relatively mild conditions. Moreover, the metallomacrocycle C1 and metallocatenane C2 were self-assembled from heteroleptic complexation reactions involving ML1 and suitable counterparts.

Ion Mobility Mass Spectrometry for Large Synthetic Molecules: Expanding the Analytical Toolbox

Understanding the composition, structure and stability of larger synthetic molecules is crucial for their design, yet currently the analytical tools commonly used do not always provide this information. In this perspective, we show how ion mobility mass spectrometry (IM-MS), in combination with tandem mass spectrometry, complementary techniques and computational methods, can be used to structurally characterize synthetic molecules, make and predict new complexes, monitor disassembly processes and determine stability. Using IM-MS, we present an experimental and computational framework for the analysis and design of complex molecular architectures such as (metallo)supramolecular cages, nanoclusters, interlocked molecules, rotaxanes, dendrimers, polymers and host-guest complexes.

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.

Evolution of Polynuclear Gold(I) Sulfido Complexes from Clusters and Cages to Macrocycles

Two unprecedented tetratriacontanuclear and tetraicosanuclear gold(I) sulfido clusters (denoted as Au34-LMe and Au24-LCbz) with different temperature-induced stimulus-responsive behavior and emission property have been constructed by taking advantage of the judiciously designed bidentate phosphine ligand. Au34-LMe represents the highest nuclearity of the gold(I) sulfido cluster with more than a thousand atoms in the molecule. Octagonal macrocycles based on metal-cluster nodes have been assembled for the first time. The self-assembly and temperature-induced stimulus-responsive processes were monitored by 1H and 31P{1H} NMR spectroscopy, and the identities of the discrete gold(I) complexes were established by single-crystal structural analysis and high-resolution electrospray ionization mass spectrometry data. The steric effects exerted by the substituents on the V-shaped 1,3-bis(diphenylphosphino)benzene ligand have been shown to govern the self-assembly from the 1D cluster and 3D cage to 2D macrocycles. This work not only offers a new strategy to construct and regulate the structure of 2D macrocyclic gold(I) sulfido complexes but also lays the foundation for the future precise design and controlled construction of higher polygonal and cluster-node macrocycles.

Stoichiometric Control of Guest Recognition of Self-Assembled Palladium(II)-Based Supramolecular Architectures

We report flexible [Pd(L)2 ]2+ complexes where there is self-recognition, driven by π-π interactions between electron-rich aromatic arms and the cationic regions they are tethered to. This self-recognition hampers the association of these molecules with aromatic molecular targets in solution. In one case, this complex can be reversibly converted to an 'open' [Pd2 (L)2 ]4+ macrocycle through introduction of more metal ion. This is accomplished by the ligand having two bidentate binding sites: a 2-pyridyl-1,2,3-triazole site, and a bis-1,2,3-triazole site. Due to favourable hydrogen bonding, the 2-pyridyl-1,2,3-triazole units reliably coordinate in the [Pd(L)2 ]2+ complex to control speciation: a second equivalent of Pd(II) is required to enforce coordination to bis-triazole sites and form the macrocycle. The macrocycle interacts with a molecular substrate with higher affinity. In this fashion we are able to use stoichiometry to reversibly switch between two different species and regulate guest binding.

Bi-directional geometric constraints in the construction of giant dual-rim nanorings

In the field of metallo-supramolecular assemblies, supramolecular macrocycles have attracted considerable attention due to their guest recognition and catalytic properties. Herein, we report a novel strategy for the construction of giant hollow macrocyclic structures using a bi-directional geometric constraint strategy. We investigated the structural design of two terpyridine-based tetratopic organic ligands, whose inner and outer rims have different angles. Compared to conventional strategies of self-assembly using single angular orientation building blocks that typically generate small macrocyclic objects or polymers, the mutual interaction between the different angles of the ligands could promote the formation of giant hollow macrocyclic supramolecular architectures. The self-assembly mechanism and hierarchical self-assembly of giant supramolecular macrocycles have been characterized by NMR, ESI-MS and TEM experiments. The strategy used in this study not only advances the design of giant 2D macrocycles with large inner diameters but also gives insights into the mechanism of formation of large structures.

Supramolecular Shish Kebabs: Higher Order Dimeric Structures from Ring-in-Rings Complexes with Conformational Adaptivity

Use of abiotic chemical systems for understanding higher order superstructures is challenging. Here we report a ring-in-ring(s) system comprising a hydrogen-bonded macrocycle and cyclobis(paraquat-o-phenylene) tetracation (o-Box) or cyclobis(paraquat-p-phenylene) tetracation (CBPQT⁴⁺ , p-Box) that assembles to construct discrete higher order structures with adaptive conformation. As indicated by mass spectrometry, computational modeling, NMR spectroscopy, and single-crystal X-ray diffraction analysis, this ring-in-ring(s) system features the box-directed aggregation of multiple macrocycles, leading to generation of several stable species such as H4G (1 a/o-Box) and H5G (1 a/o-Box). Remarkably, a dimeric shish-kebab-like ring-in-rings superstructure H7G2 (1 a/o-Box) or H8G2 (1 a/p-Box) is formed from the coaxial stacking of two ring-in-rings units. The formation of such unique dimeric superstructures is attributed to the large π-surface of this 2D planar macrocycle and the conformational variation of both host and guest.

Hourglass-Shaped Nanocages with Concaved Structures Based on Selective Self-Complementary Coordination Ligands and Tunable Hierarchical Self-Assembly

Three-dimensional (3D) structures constructed via coordination-driven self-assemblies have recently garnered increasing attention due to the challenges in structural design and potential applications. In particular, developing new strategy for the convenient and precise self-assemblies of 3D supramolecular structures is of utmost interest. Introducing the concept of self-coordination ligands, herein the design and synthesis of two meta-modified terpyridyl ligands with selective self-complementary coordination moiety are reported and their capability to assemble into two hourglass-shaped nanocages SA and SB is demonstrated. Within these 3D structures, the meta-modified terpyridyl unit preferably coordinates with itself to serve as concave part. By changing the arm length of the ligands, hexamer (SA) and tetramer (SB) are obtained respectively. In-depth studies on the assembly mechanism of SA and SB indicate that the dimers could be formed first via self-complementary coordination and play crucial roles in controlling the final structures. Moreover, both SA and SB can go through hierarchical self-assemblies in solution as well as on solid-liquid interface, which are characterized by transmission electron microscope (TEM) and scanning tunneling microscopy (STM). It is further demonstrated that various higher-order assembly structures can be achieved by tuning the environmental conditions.

Mapping the Assembly of Neutral Tetrahedral Cages Tethered by Oximido Linkers and Their Guest Encapsulation Studies

A primary criterion for the design of polyhedral metal-organic cages is the requirement of geometrically matched pairs of metal ions and ligand moieties. However, understanding the pathway it takes to reach the final polyhedral structure can provide more insights into the self-assembly process and improved design strategies. In this regard, we report two neutral tetrahedral cages with the formulas {[Pd₃(NⁱPr)₃PO]₄(L¹)₆} (1-TD) and {[Pd₃(NⁱPr)₃PO]₄(L²)₆} (2-TD) starting from the acetate-bridged cluster {[Pd₃(NⁱPr)₃PO]₂(OAc)₂(OH)}₂·2(CH₃)₂SO (HEXA-Pd) and the respective oxamide precursors (L¹H₂: [C₂(NH₂)₂O₂]) and (L²H₂: (C₂(NHMe)₂O₂]). When subtle variations in the reaction conditions were made, two new tetrameric Pd₁₂ assemblies, {[Pd₃(NⁱPr)₃PO]₄(L¹)₂(OAc)₄(OMe)₄} (1-TM) and {[Pd₃(NⁱPr)₃PO]₄(L²)₂(OAc)₄(OMe)₄} (2-TM), were obtained from the same precursors. Detailed investigations using NMR, mass spectrometry, X-ray crystallography, and computational studies indicate that the macrocyclic complexes 1-TM and 2-TM are the reaction intermediates involved in the formation of the tetrahedral cages 1-TD and 2-TD, respectively. Moreover, the tetrahedral cages 1-TD and 2-TD exhibited intrinsic cavities of volume ∼85 ų. Guest encapsulation studies revealed that the cage 1-TD can encapsulate a wide range of guest molecules such as CH₂Cl₂, CHCl₃, CCl₄, C₆H₆, and C₆H₅F. Interestingly, 1-TD was shown to exhibit a preferential binding of C₆H₅F and C₆H₆ over other halogenated guest molecules, as determined from NMR titrations and computational studies.

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.

Self-Assembly Methods for Recently Reported Discrete Supramolecular Structures Based on Terpyridine

In this Review, self-assembly methods of discrete metallo-supramolecules based on 2,2' : 6',2''-terpyridine (tpy) are comprehensively summarized. With the development of self-assembly, strategies for discrete 2D and 3D supramolecular architectures have boomed, including the geometry-directed method, template-driven method, and stepwise method. Ligand geometry-directed method mainly depends on the geometry of ligands (i. e., angle, geometric strain, and rigidity), and it is suitable for dual-component systems, while the template-driven method can guide the self-assembly of predesigned supramolecules by the introduction of specific templates. Meanwhile, stepwise method, breaking the inherent self-sorting of ligands and reducing the probability of mismatch, is suitable for multicomponent systems to yield predesigned supramolecules. This review focuses on self-assembly methods and aims to provide a guideline for constructing supramolecular architectures using a suitable approach.

Stimuli-Responsive Topological Transformation of a Molecular Borromean Ring via Controlled Oxidation of Thioether Moieties

A Cp*-Rh based D-shaped binuclear metallacycle and a template-free molecular Borromean ring (BR) were obtained in high yield using the semi-rigid thioether dipyridyl ligand 1,4-bis[(pyridin-4-ylthio)methyl]benzene (Bptmb). The topological transformation from a binuclear metallacycle and a BR to tetranuclear metallacycles was realized via the controlled oxidation of thioethers. The strategy used in this work can be regarded as a new form of stimuli-responsive post-synthesis modification (PSM).

Construction of Hybrid Bimetallic Uranyl Compounds Based on a Preassembled Terpyridine Metalloligand

Six hybrid uranyl-transition metal compounds [UO₂ Ni(cptpy)₂ (HCOO)₂ (DMF)(H₂ O)] (1), [UO₂ Ni(cptpy)₂ (BTPA)₂ ] (2), [UO₂ Fe(cptpy)₂ (HCOO)₂ (DMF)(H₂ O)] (3), [UO₂ Fe(cptpy)₂ (BTPA)₂ ] (4), [UO₂ Co(cptpy)₂ (HCOO)₂ (DMF)(H₂ O)] (5), and [UO₂ Co(cptpy)₂ (BTPA)₂ ] (6), based on bifunctional ligand 4'-(4-carboxyphenyl)-2,2':6',2''-terpyridine (Hcptpy) are reported (H₂ BTPA = 4,4'-biphenyldicarboxylic acid). Single-crystal XRD revealed that all six compounds feature similar metalloligands, which consist of two cptpy^- anions and one transition metal cation. The metalloligand M(cptpy)₂ can be considered to be an extended linear dicarboxylic ligand with length of 22.12 Å. Compounds 1, 3, and 5 are isomers, and all of them feature 1D chain structures. The adjacent 1D chains are connected together by hydrogen bonds and π-π interactions to form a 3D porous structure, which is filled with solvent molecules and can be exchanged with I₂ . Compounds 2, 4, and 6 are also isomers, and all of them feature 2D honeycomb (6,3) networks with hexagonal units of dimensions 41.91×26.89 Å, which are the largest among uranyl compounds with honeycomb networks. The large aperture allows two sets of equivalent networks to be entangled together to result in a 2D+2D→3D polycatenated framework. Remarkably, these uranyl compounds exhibit high catalytic activity for cycloaddition of carbon dioxide. Moreover, the geometric and electronic structures of compounds 1 and 2 are systematically discussed on the basis of DFT calculations.

Controlled Self-Assembly and Multistimuli-Responsive Interconversions of Three Conjoined Twin-Cages

Stimuli-responsive structural transformations between discrete coordination supramolecular architectures not only are essential to construct smart functional materials but also provide a versatile molecular-level platform to mimic the biological transformation process. We report here the controlled self-assembly of three topologically unprecedented conjoined twin-cages, i.e., one stapled interlocked Pd₁₂L₆ cage (2) and two helically isomeric Pd₆L₃ cages (3 and 4) made from the same cis-blocked palladium corners and a new bis-bidentate ligand (1). While cage 2 features three mechanically coupled cavities, cages 3 and 4 are topologically isomeric helicate-based twin-cages based on the same metal/ligand stoichiometry. Sole formation of cage 2 or a dynamic mixture of cages 3 and 4 can be controlled by changing the solvents employed during the self-assembly. Structural conversions between cages 3 and 4 can be triggered by changes in both temperature/solvent and induced-fit guest encapsulations. Well-controlled interconversion between such topologically complex superstructures may lay a solid foundation for achieving a variety of functions within a switchable system.

Self-Assembly of Metallo-Supramolecules with Dissymmetrical Ligands and Characterization by Scanning Tunneling Microscopy

Asymmetrical and dissymmetrical structures are widespread and play a critical role in nature and life systems. In the field of metallo-supramolecular assemblies, it is still in its infancy for constructing artificial architectures using dissymmetrical building blocks. Herein, we report the self-assembly of supramolecular systems based on two dissymmetrical double-layered ligands. With the aid of ultra-high-vacuum, low-temperature scanning tunneling microscopy (UHV-LT-STM), we were able to investigate four isomeric structures corresponding to four types of binding modes of ligand LA with two major conformations complexes A. The distribution of isomers measured by STM and total binding energy of each isomer obtained by density functional theory (DFT) calculations suggested that the most abundant isomer could be the most stable one with highest total binding energy. Finally, through shortening the linker between inner and outer layers and the length of arms, the arrangement of dissymmetrical ligand LB could be controlled within one binding mode corresponding to the single conformation for complexes B.

Clover leaf-shaped supramolecules assembled using a predesigned metallo-organic ligand

A series of clover-like supramolecular structures were designed and synthesized using a combination of Ru–Zn, Ru–Co, Ru–Mn or Ru–Ni metal ions. These structures with distinct redox properties may have further applications as functional materials.

Customized self-assembled molecules: rim adjustable coronal polygons with multiple-folds symmetry

Three desired discrete metallomacrocyclic wreaths with four-, five- and six-fold symmetry were successfully realized in a controlled fashion.

Self-Assembly of Metallo-Supramolecules under Kinetic or Thermodynamic Control: Characterization of Positional Isomers Using Scanning Tunneling Spectroscopy

Coordination-driven self-assembly has been extensively employed to construct a variety of discrete structures as a bottom-up strategy. However, mechanistic understanding regarding whether self-assembly is under kinetic or thermodynamic control is less explored. To date, such mechanistic investigation has been limited to distinct, assembled structures. It still remains a formidable challenge to study the kinetic and thermodynamic behavior of self-assembly systems with multiple assembled isomers due to the lack of characterization methods. Herein, we use a stepwise strategy which combined self-recognition and self-assembly processes to construct giant metallo-supramolecules with 8 positional isomers in solution. With the help of ultrahigh-vacuum, low-temperature scanning tunneling microscopy and scanning tunneling spectroscopy, we were able to unambiguously differentiate 14 isomers on the substrate which correspond to 8 isomers in solution. Through measurement of 162 structures, the experimental probability of each isomer was obtained and compared with the theoretical probability. Such a comparison along with density functional theory (DFT) calculation suggested that although both kinetic and thermodynamic control existed in this self-assembly, the increased experimental probabilities of isomers compared to theoretical probabilities should be attributed to thermodynamic control.

Introducing Seven Transition Metal Ions into Terpyridine-Based Supramolecules: Self-Assembly and Dynamic Ligand Exchange Study

In coordination-driven self-assembly, 2,2':6',2″-terpyridine (tpy) has gained extensive attention in constructing supramolecular architectures on the basis of ⟨tpy-M-tpy⟩ connectivity. In direct self-assembly of large discrete structures, however, the metal ions were mainly limited to Cd(II), Zn(II), and Fe(II) ions. Herein, we significantly broaden the spectrum of metal ions with seven divalent transition metal ions M(II) (M = Mn, Fe, Co, Ni, Cu, Zn, Cd) to assemble a series of supramolecular fractals. In particular, Mn(II), Co(II), Ni(II), and Cu(II) were reported for the first time to form such large and discrete structures with ⟨tpy-M-tpy⟩ connectivity. In addition, the structural stabilities of those supramolecules in the gas phase and the kinetics of the ligand exchange process in solution were investigated using mass spectrometry. Such a fundamental study gave the relative order of structural stability in the gas phase and revealed the inertness of coordination in solution depending on the metal ions. Those results would guide the future study in tpy-based supramolecular chemistry in terms of self-assembly, characterization, property, and application.

Ditopic Chiral Pineno-Fused 2,2':6',2″-Terpyridine: Synthesis, Self-Assembly, and Optical Properties

The syntheses of 4'-substituted chiral 2,2':6',2″-terpyridine (tpy) ligands with predetermined configurations and directionalities are rather limited in the supramolecular chemistry field. In this study, a carbazole-linked ditopic chiral ligand L was synthesized using 4'-bromo-substituted pineno-fused tpy 5 as the precursor. Upon complexation with Cd(NO₃)₂·4H₂O and Zn(NO₃)₂·6H₂O, two enantiomerically pure metallosupramolecules, [Cd₃L₃] and [Zn₄L₄], have been self-assembled and characterized by NMR, electrospray ionization-mass spectrometry, traveling wave ion mobility-mass spectrometry, and DOSY analysis. In addition, their optical properties are characterized by UV-vis, fluorescence, circular dichroism, and circularly polarized luminescence, suggesting an efficiency transmission and amplification of chirality from the ligand to metal center via self-assembly.

One-Pot Self-Assembly of Stellated Metallosupramolecules from Multivalent and Complementary Terpyridine-Based Ligands

A series of stellated metallosupramolecular architectures have been assembled through three-component integrative self-sorting. Building on the complementary ligand pairing, the initial attempts to synthesize the hexagram complex from a combination of X-shaped tetrakis- and V-shaped bis-terpyridine ligands, and Cd^II ions, resulted in an unprecedented mixture of stellated octanuclear and dodecanuclear metallocages, which were further isolated by column chromatography. To overcome the unexpected obstacle, the multivalent ligand design along with spontaneous heteroleptic complexation was applied to realization of the one-pot synthesis of the intricate topology. A centrally situated triangle served as a prop for quantitative formation of the six-pointed stellated complex. Notably, in the absence of the triangular prop, a four-pointed star was produced.

Dictating Nanoparticle Assembly via Systems-Level Control of Molecular Multivalency

Nanoparticle assembly can be controlled by multivalent binding interactions between surface ligands, indicating that more precise control over these interactions is important to design complex nanoscale architectures. It has been well-established in natural materials that the arrangement of different molecular species in three dimensions can affect the ability of individual supramolecular units to coordinate their binding, thereby regulating the strength and specificity of their collective molecular interactions. However, in artificial systems, limited examples exist that quantitatively demonstrate how changes in nanoscale geometry can be used to rationally modulate the thermodynamics of individual molecular binding interactions. As a result, the use of nanoscale design features to regulate molecular bonding remains an underutilized design handle to control nanomaterials synthesis. Here we demonstrate a polymer-coated nanoparticle material where supramolecular bonding and nanoscale structure are used in conjunction to dictate the thermodynamics of their multivalent interactions, resulting in emergent bundling of supramolecular binding groups that would not be expected on the basis of the molecular structures alone. Additionally, we show that these emergent phenomena can controllably alter the superlattice symmetry by using the mesoscale particle arrangement to alter the thermodynamics of the supramolecular bonding behavior. The ability to rationally program molecular multivalency via a systems-level approach therefore provides a major step forward in the assembly of complex artificial structures, with implications for future designs of both nanoparticle- and supramolecular-based materials.

Geometrically Complementary Self-Assembly of a Hexarhomboid Architecture from Two Ruthenium(II)-Organic Building Blocks

A shape-persistent metallosupramolecular multirhomboid that inlays a hexarhomboid polygon in a three-lobed flat structure was prepared by means of coordination-driven self-assembly. The key ligands were synthesized by a "reaction on complex" strategy that becomes accessible to troublesome metalloorganic ligand L3. The formation here consists of four different starting components and two metal ions. Complementarity of the shape and size drives molecular puzzling and results in the multicomponent, quantitative self-assembled construct.

Stepwise Self-Assembly and Dynamic Exchange of Supramolecular Snowflakes

Snowflake, a highly symmetrical hexagram figure, is challenging to be expressed by chemistry/supramolecular chemistry due to the complex structure. Herein, we have constructed super snowflake supramolecules using terpyridine (tpy)-based metal-organic building blocks with <tpy-Ru(II)-tpy> and <tpy-Zn(II)-tpy> connectivities through stepwise strategies in high yield. The structures were characterized by multi-dimensional mass spectrometry and multi-dimensional NMR spectrometry. In order to address the stability/tolerance of our designed super snowflake structures, ligand exchange behaviors between different supramolecules with various arm length were fully investigated by mass spectrometry. The study revealed that three modes could exist in such binary systems, including full exchange, partial exchange and self-sorting (no exchange) depending on the length difference of ligands.

Facile synthesis of multicomponent heterobimetallic metallomacrocycles through selective metal–ligand coordination

Through selective coordination, three heterobimetallic Zn^II–Pd^II/Pt^II metallomacrocycles have been constructed by either a stepwise or a one-pot self-assembly protocol.

Self-Assembly of Supramolecular Fractals from Generation 1 to 5

In the seeking of molecular expression of fractal geometry, chemists have endeavored in the construction of molecules and supramolecules during the past few years, while only a few examples were reported, especially for the discrete architectures. We herein designed and constructed five generations of supramolecular fractals (G1-G5) based on the coordination-driven self-assembly of terpyridine ligands. All the ligands were synthesized from triphenylamine motif, which played a central role in geometry control. Different approaches based on direct Sonogashira coupling and/or ⟨tpy-Ru(II)-tpy⟩ connectivity were employed to prepare complex Ru(II)-organic building blocks. Fractals G1-G5 were obtained in high yields by precise coordination of organic or Ru(II)-organic building blocks with Zn(II) ions. Characterization of those architectures were accomplished by 1D and 2D NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), traveling-wave ion mobility mass spectrometry (TWIM-MS), and transmission electron microscopy (TEM). Furthermore, the two largest fractals also hierarchically self-assemble into ordered supramolecular nanostructures either at solid/liquid interface or in solution on the basis of their well-defined scaffolds.

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.

Truncated Sierpiński Triangular Assembly from a Molecular Mortise-Tenon Joint

The amalgamation of different components into a giant and intricate structure that makes quantitative and spontaneous assembly through molecular design is indispensable but challenging. To construct novel metallo-supramolecular architectures, here we present an architectural design principle based on multicomponent self-assembly. Using a carefully designed hexatopic terpyridine-based metallo-organic ligand (MOL), [Ru₂T₂K], we report on the formation of supramolecular trapezoid Zn₅[Ru₂T₂K]V₂, hollow hexagon Zn₁₅[Ru₂T₂K]₃K₃, and giant star-shaped supramolecule Zn₁₈[Ru₂T₂K]₃[Ru₂X₂V]₃, all of which were assembled by one-pot, nearly quantitative assembly of [Ru₂T₂K] with the ditopic 60°-directed bisterpyridine V, tetrakisterpyridine K, and MOL [Ru₂X₂V], respectively. The complementary ligands were selected on the basis of the size- and shape-fit principles, actually similar to the mortise-tenon joint that aligns and locks the two complementary wood components. This strategy is expected to open the door to sophisticated designer supramolecules and nonbiological materials. The multivalent connections within the mutual ligands give rise to the formation of stable assemblies, which are unambiguously characterized by NMR, ESI-MS, TWIM-MS, and TEM analyses.

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.

Multiple Pathways in the Self-Assembly Process of a Pd4L8 Coordination Tetrahedron

The self-assembly of a Pd₄1₈ coordination tetrahedron (Tet) from a ditopic ligand, 1, and palladium(II) ions, [PdPy*₄]²⁺ (Py* = 3-chloropyridine), was investigated by a ¹H NMR-based quantitative approach (quantitative analysis of self-assembly process, QASAP), which allows one to monitor the average composition of the intermediates not observed by NMR spectroscopy. The self-assembly of Tet takes place mainly through three pathways and about half of the Tet structures were produced through the reaction of a kinetically produced Pd₃L₆ double-walled triangle (DWT) and 200-nm-sized large intermediates (Int^L). In two of the three pathways, the leaving ligand (Py*), which is not a component of Tet, catalytically assisted the self-assembly. Such a multiplicity of the self-assembly process of Tet suggests that molecular self-assembly takes place on an energy landscape like a protein-folding funnel.

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

Comprehensive summary of the recent developments in the growing field of terpyridine-based, discrete metallosupramolecular architectures.

Mapping the Assembly of Metal-Organic Cages into Complex Coordination Networks

Structural transformations of supramolecular assemblies play an important role in the synthesis of complex metal-organic materials. Nonetheless, often little is known of the assembly pathways that lead to the final product. This work describes the conversion of cubic metal-organic polyhedra to connected-cage networks of varying topologies. The neutral cubic cage assembly of formula {Pd₃ [PO(NiPr)₃ ]}₈ (PZDC)₁₂ has been synthesized from {Pd₃ [(NiPr)₃ PO](OAc)₂ (OH)}₂ ⋅2 (CH₃ )₂ SO and 2,5-pyrazenedicarboxilic acid (PZDC-2H). This 42-component self-assembly is the largest known among the neutral cages with Pd^II ions. The cage contains twenty-four vacant carboxylate O-sites at the PZDC ligands that are available for further coordination. Post-assembly reactions of the cubic cage with Fe^II and Zn^II ions produced cage-connected networks of dia and qtz topologies, respectively. During these reactions, the discrete cubic cage transforms into a network of tetrahedral cages that are bridged by the 3D metal ions. The robustness of the [Pd₃ {[PO(NiPr)₃ }]³⁺ molecular building units made it possible to map the post-assembly reactions in detail, which revealed a variety of intermediate 1D and 2D cage networks. Such step-by-step mapping of the transformation of discrete cages to cage-connected frameworks is unprecedented in the chemistry of coordination driven assemblies.

Supersnowflakes: Stepwise Self-Assembly and Dynamic Exchange of Rhombus Star-Shaped Supramolecules

With the goal of increasing the complexity of metallo-supramolecules, two rhombus star-shaped supramolecular architectures, namely, supersnowflakes, were designed and assembled using multiple 2,2':6',2″-terpyridine (tpy) ligands in a stepwise manner. In the design of multicomponent self-assembly, ditopic and tritopic ligands were bridged through Ru(II) with strong coordination to form metal-organic ligands for the subsequent self-assembly with a hexatopic ligand and Zn(II). The combination of Ru(II)-organic ligands with high stability and Zn(II) ions with weak coordination played a key role in the self-assembly of giant heteroleptic supersnowflakes, which encompassed three types of tpy-based organic ligands and two metal ions. With such a stepwise strategy, the self-sorting of individual building blocks was prevented from forming the undesired assemblies, e.g., small macrocycles and coordination polymers. Furthermore, the intra- and intermolecular dynamic exchange study of two supersnowflakes by NMR and mass spectrometry revealed the remarkable stability of these giant supramolecular complexes.

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.

Star motifs are ubiquitous throughout nature and in man-made architectures, but their molecular level design remains challenging. Here the authors present a stepwise approach to self-assemble pentagonal and hexagonal star-shaped metallo-architectures through the careful design of metallo-organic ligands.

Direct Self-Assembly of a 2D and 3D Star of David

Two- and three-dimensional metallosupramolecules shaped like a Star of David were synthesized by the self-assembly of a tetratopic pyridyl ligand with a 180° diplatinum(II) motif and Pd^II ions, respectively. In contrast to other strategies, such as template-directed synthesis and stepwise self-assembly, this design enables the formation of 2D and 3D structures in one step and high yield. The structures were characterized by both one-dimensional (¹ H, ¹³ C, ³¹ P) and two-dimensional (COSY, NOESY, DOSY) NMR spectroscopy, ESI-MS, ion-mobility mass spectrometry (IM-MS), AFM, and TEM. The stabilities of the 2D and 3D structures were measured and compared by gradient tandem mass spectrometry (gMS² ). The high stability of the 3D Star of David was correlated to its high density of coordination sites (DOCS).

Transition-Metal-Free Oxidative C(sp2 )-H Hydroxylation of Terpyridines: A HOMO-Raising Strategy for the Construction of a New Super-Stable Terpyridine Chromophores

Direct functionalization of terpyridines is an increasingly important topic in the field of dyes and catalysis as well as supramolecular chemistry, but its synthesis and transformation is usually challenging. Herein, a HOMO-raising strategy is reported for the construction of a super-stable novel terpyridine chromophores, in which the selective oxidation of terpyridines at its 3-position was determined successfully to the synthesis of phenol-functionalization of terpyridines (TPyOHs) bearing a hydrogen bonding group. The corresponding TPyOHs displayed strong aggregation-induced emission and exhibited highly selective and visual detection of Zn^II cation with a record green terpyridine-based luminophore with nanomolar sensitivity (125 nm).