Cation- and Anion-Exchanges Induce Multiple Distinct Rearrangements within Metallosupramolecular Architectures

The Topological Transformation of 41 Knot to 412 Link through Supramolecular Fusion

Realizing topological transformation through supramolecular fusion is particularly challenging, as the self-assembly of disparate components often results in the orthogonal assembly of building blocks into distinct structures rather than the formation of a heteroleptic architecture. This study introduces a topological transformation, transitioning from a figure-eight knot (41 knot) to a Solomon link (412 link) through a supramolecular fusion process. By employing two structurally similar amino acid ligands (L1 and L3) of varying lengths as bridge ligands, we obtained figure-eight knot 1 and a molecular tweezer-like compound 3 when individually complexed with binuclear Cp*Rh acceptor B1. Our results revealed that subtle modifications to bridge ligands can lead to dramatic changes in their structures and recognition properties. Moreover, we successfully achieved the targeted formation of a heteroleptic Solomon link 4 by blending figure-eight knot 1 and compound 3 in a 1:1 ratio without the need for templates. This procedure effortlessly converted the 41 knot into a 412 link, thus marking a significant advancement in the topological transformation. This work not only marks the construction of the first heteroleptic Solomon link comprising two distinct metallamacrocycles but also demonstrates a process of supramolecular fusion-based topological transformation involving three distinct topological structures.

Enantiopure trigonal bipyramidal coordination cages templated by in situ self-organized D2h-symmetric anions

The control of a molecule's geometry, chirality, and physical properties has long been a challenging pursuit. Our study introduces a dependable method for assembling D3-symmetric trigonal bipyramidal coordination cages. Specifically, D2h-symmetric anions, like oxalate and chloranilic anions, self-organize around a metal ion to form chiral-at-metal anionic complexes, which template the formation of D3-symmetric trigonal bipyramidal coordination cages. The chirality of the trigonal bipyramid is determined by the point chirality of chiral amines used in forming the ligands. Additionally, these cages exhibit chiral selectivity for the included chiral-at-metal anionic template. Our method is broadly applicable to various ligand systems, enabling the construction of larger cages when larger D2h-symmetric anions, like chloranilic anions, are employed. Furthermore, we successfully produce enantiopure trigonal bipyramidal cages with anthracene-containing backbones using this approach, which would be otherwise infeasible. These cages exhibit circularly polarized luminescence, which is modulable through the reversible photo-oxygenation of the anthracenes.

A ring of rotaxanes: studies of a large paramagnetic assembly in solution

Here we report the synthesis and structural characterization of four [7]rotaxanes formed by coordinating hybrid inorganic-organic [2]rotaxanes to a central {Ni12} core. X-ray single crystal diffraction demonstrate that [7]rotaxanes are formed, with a range of conformations in the crystal. Small angle X-ray scattering supported by molecular dynamic simulations demonstrates that the large molecules are stable in solution and also show that the conformers present in solution are not those found in the crystal. Pulsed EPR spectroscopy show that phase memory times for the {Cr7Ni} rings, which have been proposed as qubits, are reduced but not dramatically by the presence of the {Ni12} cage.

Sterics and metal-ion radius control the self-assembly of [M2L3] helicates

The interplay of many factors influences the outcomes of self-assembly reactions. Using an acetylene-appended quaterpyridine ligand we show that both the size of the metal ion and the presence of steric repulsion between the acetylene groups result in the exclusive formation of [M₂L₃] helicates rather than a helicate/tetrahedron equilibrium.

Transformation networks of metal-organic cages controlled by chemical stimuli

The flexibility of biomolecules enables them to adapt and transform as a result of signals received from the external environment, expressing different functions in different contexts. In similar fashion, coordination cages can undergo stimuli-triggered transformations owing to the dynamic nature of the metal-ligand bonds that hold them together. Different types of stimuli can trigger dynamic reconfiguration of these metal-organic assemblies, to switch on or off desired functionalities. Such adaptable systems are of interest for applications in switchable catalysis, selective molecular recognition or as transformable materials. This review highlights recent advances in the transformation of cages using chemical stimuli, providing a catalogue of reported strategies to transform cages and thus allow the creation of new architectures. Firstly we focus on strategies for transformation through the introduction of new cage components, which trigger reconstitution of the initial set of components. Secondly we summarize conversions triggered by external stimuli such as guests, concentration, solvent or pH, highlighting the adaptation processes that coordination cages can undergo. Finally, systems capable of responding to multiple stimuli are described. Such systems constitute composite chemical networks with the potential for more complex behaviour. We aim to offer new perspectives on how to design transformation networks, in order to shed light on signal-driven transformation processes that lead to the preparation of new functional metal-organic architectures.

Beyond Platonic: How to Build Metal-Organic Polyhedra Capable of Binding Low-Symmetry, Information-Rich Molecular Cargoes

The field of metallosupramolecular chemistry has advanced rapidly in recent years. Much work in this area has focused on the formation of hollow self-assembled metal-organic architectures and exploration of the applications of their confined nanospaces. These discrete, soluble structures incorporate metal ions as 'glue' to link organic ligands together into polyhedra.Most of the architectures employed thus far have been highly symmetrical, as these have been the easiest to prepare. Such high-symmetry structures contain pseudospherical cavities, and so typically bind roughly spherical guests. Biomolecules and high-value synthetic compounds are rarely isotropic, highly-symmetrical species. To bind, sense, separate, and transform such substrates, new, lower-symmetry, metal-organic cages are needed. Herein we summarize recent approaches, which taken together form the first draft of a handbook for the design of higher-complexity, lower-symmetry, self-assembled metal-organic architectures.

Flexible Vertex Engineers the Controlled Assembly of Distorted Supramolecular Tetrahedral and Octahedral Cages

Designing and building unique cage assemblies attract increasing interest from supramolecular chemists but remain synthetically challenging. Herein, we propose the use of a flexible vertex with adjustable angles to selectively form highly distorted tetrahedral and octahedral cages, for the first time, in which the flexible vertex forms from the synergistic effect of coordination and covalent interactions. The inherent interligand angle of the vertex can be modulated by guest anions present, which allows for the fine-tuning of different cage geometries. Furthermore, the reversible structural transformation between tetrahedral and octahedral cages was achieved by anion exchange monitored by mass spectrometric technique, the smaller anions favoring tetrahedral cages, while the larger anions supporting octahedral cages. Additionally, the KBr-based cage thin films exhibited prominent enhancement of their third-order NLO responses in two or three orders of magnitude compared to those obtained for their corresponding solutions. This work not only provides a new methodology to build irregular polyhedral structures in a controlled and tunable way but also provides access to new kinds of promising functional optical materials.

Templation and Concentration Drive Conversion Between a FeII12L12 Pseudoicosahedron, a FeII4L4 Tetrahedron, and a FeII2L3 Helicate

We report the construction of three structurally distinct self-assembled architectures: FeII12L12 pseudoicosahedron 1, FeII2L3 helicate 2, and FeII4L4 tetrahedron 3, formed from a single triazatriangulenium subcomponent A under different reaction conditions. Pseudoicosahedral capsule 1 is the largest formed through subcomponent self-assembly to date, with an outer-sphere diameter of 5.4 nm and a cavity volume of 15 nm3. The outcome of self-assembly depended upon concentration, where the formation of pseudoicosahedron 1 was favored at higher concentrations, while helicate 2 exclusively formed at lower concentrations. The conversion of pseudoicosahedron 1 or helicate 2 into tetrahedron 3 occurred following the addition of a CB11H12- or B12F122- template.

Metal Ions Determined Self-Assembly Using Terpyridine Building Blocks

Due to the dynamic reversibility of coordination-driven force, the structures of metallo-cages are sensitive to many stimulus, including ligand geometry, temperature, concentration, anions, pH, light, and so on. Among them,...

Self-Assembly of a Purely Covalent Cage with Homochirality by Imine Formation in Water

Self-assembly of host molecules in aqueous media via metal-ligand coordination is well developed. However, the preparation of purely covalent counterparts in water has remained a formidable task. An anionic tetrahedron cage was successfully self-assembled in a [4+4] manner by condensing a trisamine and a trisformyl in water. Even although each individual imine bond is rather labile and apt to hydrolyze in water, the tetrahedron is remarkably stable or inert due to multivalence. The tetrahedral cages, as well as its neutral counterparts dissolved in organic solvent, have homochirality, namely that their four propeller-shaped trisformyl residues adopt the same rotational conformation. The cage is able to take advantage of hydrophobic effect to accommodate a variety of guest molecules in water. When a chiral guest was recognized, the formation of one enantiomer of the cage became more favored relative to the other. As a consequence, the cage could be produced in an enantioselective manner. The tetrahedron is able to maintain its chirality after removal of the chiral guest-probably on account of the cooperative occurrence of intramolecular forces that restrict the intramolecular flipping of phenyl units in the cage framework.

Solvent-dependent fac/mer-isomerization and self-assembly of triply helical complexes bearing a pivot part

Tris-chelate metal complexes of unsymmetrical bidentate ligands can form two geometric stereoisomers, facial (fac) and meridional (mer) isomers. Due to the small difference in their properties, the highly-selective synthesis of one of the isomers is challenging. We now designed a series of tripodal ligands with a tris(3-(2-(methyleneoxy)ethoxy)phenyl)methane pivot. Surprisingly, the ratio of the fac/mer isomers of the triply helical Fe^II complexes significantly changed depending on the solvents. To the best of our knowledge, this is the first example of fac/mer isomerism of a labile tris(2,2'-bipyridine) Fe^II complex governed by the solvent. Furthermore, well-defined self-assemblies were quantitatively produced by imine bond formation with a suitable diamine. The supramolecular assemblies contained only the fac isomer even though a mixture of the two isomers existed in solution before the condensation reaction. Namely, the self-assembly formation effectively adjusted the geometries of the building unit that results in the suitable supramolecular structure.

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 Lanthanide-Covalent Organic Polyhedra: Chameleonic Luminescence and Efficient Catalysis

A series of multinuclear lanthanide-covalent organic polyhedra (LnCOPs), including pillar-typed triangular prisms 1-Ln₃ and tetrahedra 2-Ln₄ (Ln = La^III, Sm^III, Eu^III), have been constructed for the first time, through either one-pot subcomponent self-assembly or postassembly metalation. In contrast to the known tetrahedral cages based on transition metals, the pillar-typed polyhedra were favored from the same organic components in the presence of lanthanides. Besides this, facile transmetalations between the 1-Ln₃ polyhedra endow cascade chameleonic luminescence. Meanwhile, the open metal sites and pendent amine groups on 1-Ln₃ enable these polyhedra to catalyze the Henry reaction efficiently.

Oxidation triggers guest dissociation during reorganization of an FeII 4L6 twisted parallelogram

A three-dimensional FeII 4L6 parallelogram was prepared from ferrocene-containing ditopic ligands. The steric preference of the bulky ferrocene cores towards meridional vertex coordination brought about this new structure type, in which the ferrocene units adopt three distinct conformations. The structure possesses two distinct, bowl-like cavities that host anionic guests. Oxidation of the ferrocene FeII to ferrocenium FeIII causes rotation of the ferrocene hinges, converting the structure to an FeII 1L1 + species with release of anionic guests, even though the average charge per iron increases in a way that would ordinarily increase guest binding strength. The degrees of freedom exhibited by these new structures - derived from the different configurations of the three ligands surrounding a meridional FeII center and the rotation of ferrocene cores - thus underpin their ability to reconfigure and eject guests upon oxidation.

Triple Self-Sorting in Constitutional Dynamic Networks: Parallel Generation of Imine-Based CuI , FeII , and ZnII Complexes

Three imine-based metal complexes, having no overlap in terms of their compositions, have been simultaneously generated from the self-sorting of a constitutional dynamic library (CDL) containing three amines, three aldehydes, and three metal salts. The hierarchical ordering of the stability of the three metal complexes assembled and the leveraging of the antagonistic and agonistic relationships existing between the constituents within the constitutional dynamic network corresponding to the CDL were pivotal in achieving the sorting. Examination of the process by NMR spectroscopy showed that the self-sorting of the FeII and ZnII complexes depended on an interplay between the thermodynamic driving forces and a kinetic trap involved in their assembly. These results also exemplify the concept of "simplexity"-the fact that the output of a self-assembling system may be simplified by increasing its initial compositional complexity-as the two complexes could self-sort only in the presence of the third pair of organic components, those of the CuI complex.

Self-sorting of two imine-based metal complexes: balancing kinetics and thermodynamics in constitutional dynamic networks

A major hurdle in the development of complex constitutional dynamic networks (CDNs) is the lack of strategies to simultaneously control the output of two (or more) interconnected dynamic processes over several species, namely reversible covalent imine bond formation and dynamic metal-ligand coordination. We have studied in detail the self-sorting process of 11 constitutional dynamic libraries containing two different amines, aldehydes and metal salts into two imine-based metal complexes, having no overlap in terms of their compositions. This study allowed us to determine the factors influencing the fidelity of this process (concentration, electronic and steric parameters of the organic components, and nature of the metal cations). In all 11 systems, the outcome of the process was primarily determined by the ability of the octahedral metal ion to select its pair of components from the initial pool of components, with the composition of the weaker tetrahedral complex being imposed by the components rejected by the octahedral metal ions. Different octahedral metal ions required different levels of precision in the "assembling instructions" provided by the organic components of the CDN to guide it towards a sorted output. The concentration of the reaction mixture, and the electronic and steric properties of the initial components of the library were all found to influence the lifetime of unwanted metastable intermediates formed during the assembling of the two complexes.

Assembling Pentatopic Terpyridine Ligands with Three Types of Coordination Moieties into a Giant Supramolecular Hexagonal Prism: Synthesis, Self-Assembly, Characterization, and Antimicrobial Study

Three dimensional (3D) supramolecules with giant cavities are attractive due to their wide range of applications. Herein, we used pentatopic terpyridine ligands with three types of coordination moieties to assemble two giant supramolecular hexagonal prisms with a molecular weight up to 42 608 and 43 569 Da, respectively. Within the prisms, two double-rimmed Kandinsky Circles serve as the base surfaces as well as the templates for assisting the self-sorting during the self-assembly. Additionally, hierarchical self-assembly of these supramolecular prisms into tubular-like nanostructures was fully studied by scanning tunneling microscopy (STM) and small-angle X-ray scattering (SAXS). Finally, these supramolecular prisms show good antimicrobial activities against Gram-positive pathogen methicillin-resistant Staphylococcus aureus (MRSA) and Bacillus subtilis (B. subtilis).

Coordination-driven self-assembly of M10L8 metal–organic bi-capped square antiprisms with adaptable cavities

A family of copper-imidazolate cages consisting of flexible ligands have been synthesized, featuring an unusual bicapped square antiprism structure with an adaptable cavity.

Synthesis and in vitro evaluation of diverse heterocyclic diphenolic compounds as inhibitors of DYRK1A

Dual-specificity tyrosine phosphorylation-related kinase 1A (DYRK1A) is a dual-specificity protein kinase that catalyses phosphorylation and autophosphorylation. Higher DYRK1A expression correlates with cancer, in particular glioblastoma present within the brain. We report here the synthesis and biological evaluation of new heterocyclic diphenolic derivatives designed as novel DYRK1A inhibitors. The generation of these heterocycles such as benzimidazole, imidazole, naphthyridine, pyrazole-pyridines, bipyridine, and triazolopyrazines was made based on the structural modification of the lead DANDY and tested for their ability to inhibit DYRK1A. None of these derivatives showed significant DYRK1A inhibition but provide valuable knowledge around the importance of the 7-azaindole moiety. These data will be of use for developing further structure-activity relationship studies to improve the selective inhibition of DYRK1A.

Discovering privileged topologies of molecular knots with self-assembling models

Despite the several available strategies to build complex supramolecular constructs, only a handful of different molecular knots have been synthesised so far. Here, in response to the quest for further designable topologies, we use Monte Carlo sampling and molecular dynamics simulations, informed by general principles of supramolecular assembly, as a discovery tool for thermodynamically and kinetically accessible knot types made of helical templates. By combining this approach with the exhaustive enumeration of molecular braiding patterns applicable to more general template geometries, we find that only few selected shapes have the closed, symmetric and quasi-planar character typical of synthetic knots. The corresponding collection of admissible topologies is extremely restricted. It covers all known molecular knots but it especially includes a limited set of novel complex ones that have not yet been obtained experimentally, such as 10124 and 15n41185, making them privileged targets for future self-assembling experiments.

Control over multiple molecular states with directional changes driven by molecular recognition

Recently, ligand-metal coordination, stimuli-responsive covalent bonds, and mechanically interlinked molecular constructs have been used to create systems with a large number of accessible structural states. However, accessing a multiplicity of states in sequence from more than one direction and doing so without the need for external energetic inputs remain as unmet challenges, as does the use of relatively weak noncovalent interactions to stabilize the underlying forms. Here we report a system based on a bispyridine-substituted calix[4]pyrrole that allows access to six different discrete states with directional control via the combined use of metal-based self-assembly and molecular recognition. Switching can be induced by the selective addition or removal of appropriately chosen ionic guests. No light or redox changes are required. The tunable nature of the system has been established through a combination of spectroscopic techniques and single crystal X-ray diffraction analyses. The findings illustrate a new approach to creating information-rich functional materials.

Post-synthetic modifications of cadmium-based knots and links

Three topologically non-trivial cadmium(ii)-based complexes-Cd-[2]C, Cd-TK and Cd-SL-were simultaneously self-assembled in a dynamic library, individually isolated and fully characterized using solid-state, gas-phase and solution-phase techniques. Post-synthetic modifications, including reduction and transmetalation, were subsequently achieved. Imine bond reduction followed by demetallation led to the isolation of the corresponding organic molecules [2]C, TK and SL. Transmetalation of Cd-TK and Cd-SL with the zinc(ii) cation resulted in isolation of the corresponding zinc(ii)-containing complexes Zn-TK and Zn-SL.

Differential metal-binding properties of dynamic acylhydrazone polymers and their sensing applications

As one of common dynamic covalent bonds, acylhydrazone bond plays an important role in developing intelligent responsive materials. In this report, we present acylhydrazone-based dynamic polymers with multi-stimuli responsiveness, particularly metal recognition behaviours and their modulation. A series of polyacylhydrazones with different metal-binding sites were designed and prepared in a modular fashion. Titration of these receptors with a diverse set of metal ions, including Cu²⁺, Zn²⁺ and La³⁺, resulted in unique optical changes, and both the sensitivity and selectivity profiles can be regulated. Moreover, the metal-binding feature was facilely modulated by changing the solvent. The addition of weakly basic anions was employed to further fine-tune the responsiveness of the polymers by taking advantage of the cooperative effect with metal coordination. Finally, the sensitive detection of 6-mercaptopurine and pyrophosphate was achieved to demonstrate the application potential of these systems.

Adaptive self-assembly and induced-fit transformations of anion-binding metal-organic macrocycles

Container-molecules are attractive to chemists due to their unique structural characteristics comparable to enzymes and receptors in nature. We report here a family of artificial self-assembled macrocyclic containers that feature induced-fit transformations in response to different anionic guests. Five metal-organic macrocycles with empirical formula of M_nL_2n (M=Metal; L=Ligand; n=3, 4, 5, 6, 7) are selectively obtained starting from one simple benzimidazole-based ligand and square-planar palladium(II) ions, either by direct anion-adaptive self-assembly or induced-fit transformations. Hydrogen-bonding interactions between the inner surface of the macrocycles and the anionic guests dictate the shape and size of the product. A comprehensive induced-fit transformation map across all the M_nL_2n species is drawn, with a representative reconstitution process from Pd₇L₁₄ to Pd₃L₆ traced in detail, revealing a gradual ring-shrinking mechanism. We envisage that these macrocyclic molecules with adjustable well-defined hydrogen-bonding pockets will find wide applications in molecular sensing or catalysis.

Subcomponent Exchange Transforms an FeII4L4 Cage from High- to Low-Spin, Switching Guest Release in a Two-Cage System

Subcomponent exchange transformed new high-spin Fe^II₄L₄ cage 1 into previously-reported low-spin Fe^II₄L₄ cage 2: 2-formyl-6-methylpyridine was ejected in favor of the less sterically hindered 2-formylpyridine, with concomitant high- to low-spin transition of the cage’s Fe^II centers. High-spin 1 also reacted more readily with electron-rich anilines than 2, enabling the design of a system consisting of two cages that could release their guests in response to combinations of different stimuli. The addition of p-anisidine to a mixture of high-spin 1 and previously-reported low-spin Fe^II₄L₆ cage 3 resulted in the destruction of 1 and the release of its guest. However, initial addition of 2-formylpyridine to an identical mixture of 1 and 3 resulted in the transformation of 1 into 2; added p-anisidine then reacted preferentially with 3 releasing its guest. The addition of 2-formylpyridine thus modulated the system’s behavior, fundamentally altering its response to the subsequent signal p-anisidine.

Self-Assembly Can Direct Dynamic Covalent Bond Formation toward Diversity or Specificity

With the advent of reversible covalent chemistry the study of the interplay between covalent bond formation and noncovalent interactions has become increasingly relevant. Here we report that the interplay between reversible disulfide chemistry and self-assembly can give rise either to molecular diversity, i.e., the emergence of a unprecedentedly large range of macrocycles or to molecular specificity, i.e., the autocatalytic emergence of a single species. The two phenomena are the result of two different modes of self-assembly, demonstrating that control over self-assembly pathways can enable control over covalent bond formation.

Carboxylatopillar[n]arenes: a versatile class of water soluble synthetic receptors

Carboxylatopillar[n]arenes (CP[n]As, n = 5, 6, 7, 9, 10) constitute a family of water soluble synthetic receptors. These receptors are excellent hosts for a wide range of cationic organic molecules and have shown promising application in the fields of stimuli-responsive supramolecular assemblies, targeted drug delivery vehicles and sensors. Analogous metal-coordinated prismatic structures have shown excellent affinities for analytes.