Recent advances in the construction and applications of heterometallic macrocycles and cages

Chiral Truxene-Based Self-Assembled Cages: Triple Interlocking and Supramolecular Chirogenesis

Incorporating chiral elements in host-guest systems currently attracts much attention because of the major impact such structures may have in a wide range of applications, from pharmaceuticals to materials science and beyond. Moreover, the development of multi-responsive and -functional systems is highly desirable since they offer numerous benefits. In this context, we describe herein the construction of a metal-driven self-assembled cage that associates a chiral truxene-based ligand and a bis-ruthenium complex. The maximum separation between both facing chiral units in the assembly is fixed by the intermetallic distance within the lateral bis-ruthenium complex (8.4 Å). The resulting chiral cavity was shown to encapsulate polyaromatic guest molecules, but also to afford a chiral triply interlocked [2]catenane structure. The formation of the latter occurs at high concentration, while its disassembly could be achieved by the addition of a planar achiral molecule. Interestingly the planar achiral molecule exhibits induced circular dichroism signature when trapped within the chiral cavity, thus demonstrating the ability of the cage to induce supramolecular chirogenesis.

Recent advances in combatting bacterial infections via well-designed metallacycles/metallacages

Bacterial infections can lead to the development of large-scale outbreaks of diseases that pose a serious threat to human life and health. Also, conventional antibiotics are prone to producing resistance and allergic reactions, and their therapeutic effect is dramatically diminished when bacterial communities form biofilms. Fortunately, well-designed supramolecular coordination complexes (SCCs) have been used as antibacterials or anti-biofilms in recent years. SCCs can kill bacteria by directly engaging with the bacterial surface through electrostatic interactions or by penetrating the bacterial membrane through the auxiliary effect of cell-penetrating peptides. Furthermore, scientists have engineered fluorescent SCCs that can produce reactive oxygen species (ROS) to eliminate bacteria when exposed to laser irradiation, and they also demonstrate outstanding performance in in vivo imaging, enabling integrated diagnosis and treatment. In this review, we summarize the design strategy and applications of SCCs in antibacterials or anti-biofilms and provide an outlook on future research.

Heterometallic cages: synthesis and applications

High symmetry metallosupramolecular architectures (MSAs) have been exploited for a range of applications including molecular recognition, catalysis and drug delivery. Recently there have been increasing efforts to enhance those applications by generating reduced symmetry MSAs. While there are several emerging methods for generating lower symmetry MSAs, this tutorial review examines the general methods used for synthesizing heterometallic MSAs with a particular focus on heterometallic cages. Additionally, the intrinsic properties of the cages and their potential emerging applications as host-guest systems and reaction catalysts are described.

Applications of Supramolecular Polymers Generated from Pillar[n]arene-Based Molecules

Supramolecular chemistry enables the manipulation of functional components on a molecular scale, facilitating a "bottom-up" approach to govern the sizes and structures of supramolecular materials. Using dynamic non-covalent interactions, supramolecular polymers can create materials with reversible and degradable characteristics and the abilities to self-heal and respond to external stimuli. Pillar[n]arene represents a novel class of macrocyclic hosts, emerging after cyclodextrins, crown ethers, calixarenes, and cucurbiturils. Its significance lies in its distinctive structure, comparing an electron-rich cavity and two finely adjustable rims, which has sparked considerable interest. Furthermore, the straightforward synthesis, uncomplicated functionalization, and remarkable properties of pillar[n]arene based on supramolecular interactions make it an excellent candidate for material construction, particularly in generating interpenetrating supramolecular polymers. Polymers resulting from supramolecular interactions involving pillar[n]arene find potential in various applications, including fluorescence sensors, substance adsorption and separation, catalysis, light-harvesting systems, artificial nanochannels, and drug delivery. In this context, we provide an overview of these recent frontier research fields in the use of pillar[n]arene-based supramolecular polymers, which serves as a source of inspiration for the creation of innovative functional polymer materials derived from pillar[n]arene derivatives.

Hetero-Diels-Alder Reaction between Singlet Oxygen and Anthracene Drives Integrative Cage Self-Sorting

A ZnII8L6 pseudocube containing anthracene-centered ligands, a ZnII4L'4 tetrahedron with a similar side length as the cube, and a trigonal prism ZnII6L3L'2 were formed in equilibrium from a common set of subcomponents. Hetero-Diels-Alder reaction with photogenerated singlet oxygen transformed the anthracene-containing "L" ligands into endoperoxide "LO" ones and ultimately drove the integrative self-sorting to form the trigonal prismatic cage ZnII6LO3L'2 exclusively. This ZnII6LO3L'2 structure lost dioxygen in a retro-Diels-Alder reaction after heating, which resulted in reversion to the initial ZnII8L6 + ZnII4L'4 ⇌ 2 × ZnII6L3L'2 equilibrating system. Whereas the ZnII8L6 pseudocube had a cavity too small for guest encapsulation, the ZnII6L3L'2 and ZnII6LO3L'2 trigonal prisms possessed peanut-shaped internal cavities with two isolated compartments divided by bulky anthracene panels. Guest binding was also observed to drive the equilibrating system toward exclusive formation of the ZnII6L3L'2 structure, even in the absence of reaction with singlet oxygen.

Stepwise assembly of heterometallic, heteroleptic "triblock Janus-type" metal-organic polyhedra

Increasing the chemical complexity of metal-organic cages (MOCs) or polyhedra (MOPs) demands control over the simultaneous organization of diverse organic linkers and metal ions into discrete caged structures. Herein, we show that a pre-assembled complex of the archetypical cuboctahedral MOP can be used as a template to replicate such caged structure, one having a "triblock Janus-type" configuration that is both heterometallic and heteroleptic.

Supramolecular Coordination Cages for Artificial Photosynthesis and Synthetic Photocatalysis

Because sunlight is the most abundant energy source on earth, it has huge potential for practical applications ranging from sustainable energy supply to light driven chemistry. From a chemical perspective, excited states generated by light make thermodynamically uphill reactions possible, which forms the basis for energy storage into fuels. In addition, with light, open-shell species can be generated which open up new reaction pathways in organic synthesis. Crucial are photosensitizers, which absorb light and transfer energy to substrates by various mechanisms, processes that highly depend on the distance between the molecules involved. Supramolecular coordination cages are well studied and synthetically accessible reaction vessels with single cavities for guest binding, ensuring close proximity of different components. Due to high modularity of their size, shape, and the nature of metal centers and ligands, cages are ideal platforms to exploit preorganization in photocatalysis. Herein we focus on the application of supramolecular cages for photocatalysis in artificial photosynthesis and in organic photo(redox) catalysis. Finally, a brief overview of immobilization strategies for supramolecular cages provides tools for implementing cages into devices. This review provides inspiration for future design of photocatalytic supramolecular host-guest systems and their application in producing solar fuels and complex organic molecules.

Spin Crossover Induced by Changing the Identity of the Secondary Metal Ion from PdII to NiII in a Face-Centered FeII 8 MII 6 Cubic Cage

Discrete spin crossover (SCO) heteronuclear cages are a rare class of materials which have potential use in next-generation molecular transport and catalysis. Previous investigations of cubic cage [Fe₈ Pd₆ L₈ ]²⁸⁺ constructed using semi-rigid metalloligands, found that Fe^II centers of the cage did not undergo spin transition. In this work, substitution of the secondary metal center at the face of the cage resulted in SCO behavior, evidenced by magnetic susceptibility, Mössbauer spectroscopy and single crystal X-ray diffraction. Structural comparisons of these two cages shed light on the possible interplay of inter- and intramolecular interactions associated with SCO in the Ni^II analogue, 1 ([Fe₈ Ni₆ L₈ (CH₃ CN)₁₂ ]²⁸⁺ ). The distorted octahedral coordination environment, as well as the occupation of the CH₃ CN in the Ni^II axial positions of 1, prevented close packing of cages observed in the Pd^II analogue. This led to offset, distant packing arrangements whereby important areas within the cage underwent dramatic structural changes with the exhibition of SCO.

Complementarity and Preorganisation in the Assembly of Heterometallic–Organic Cages via the Metalloligand Approach—Recent Advances

The design of new metallocage polyhedra towards pre-determined structures can offer both practical as well as intellectual challenges. In this mini-review we discuss a selection of recent examples in which the use of the metalloligand approach has been employed to overcome such challenges. An attractive feature of this approach is its stepwise nature that lends itself to the design and rational synthesis of heterometallic metal–organic cages, with the latter often associated with enhanced functionality.

Stereocontrolled Self-Assembly of Ln(III)-Pt(II) Heterometallic Cages with Temperature-Dependent Luminescence

Structurally well-defined discrete d/f heterometallic complexes show diverse application potential in electrooptic and magnetic materials. However, precise control of the component and topology of such heterometallic compounds with fine-tuned photophysical properties is still challenging. Herein, we report the stereocontrolled syntheses of a series of Ln^III-Pt^II heterometallic cages through coordination-driven self-assembly of enantiopure alkynylplatinum-based metalloligands (L₁^R/S, L₂^R/S) with lanthanide ions (Ln = Eu^III, Yb^III, Nd^III, Lu^III). Taking advantage of the metal-to-ligand charge transfer (MLCT) excited state on the designed alkynylplatinum ligands, the excitation window for the sensitized near-infrared (NIR) luminescence on the Yb^III- and Nd^III-containing cages can be extended to the visible region (up to 500 nm). Linear temperature-dependent red and NIR emissions observed on the Ln₄(L₂^R/S)₆ (Ln^III = Eu^III and Yb^III, respectively) complexes suggest their potential applications as luminescent temperature sensors, with sensitivities of -0.54% (Ln^III = Eu^III, 77-250 K) and -0.17% (Ln^III = Yb^III, 77-300 K) per K achieved. This work not only offers a good strategy to prepare new d/f heterometallic supramolecular cages but also paves the way for the design of stimuli-responsive luminescent materials.

Subcomponent self-assembly of circular helical Dy6(L)6 and bipyramid Dy12(L)8 architectures directed via second-order template effects

In situ metal-templated (hydrazone) condensation also called subcomponent self-assembly of 4,6-dihydrazino-pyrimidine, o-vanillin and dysprosium ions resulted in the formation of discrete hexa- or dodecanuclear metallosupramolecular Dy6(L)6 or Dy12(L)8 aggregates resulting from second-order template effects of the base and the lanthanide counterions used in these processes. XRD analysis revealed unique circular helical or tetragonal bipyramid architectures in which the bis(hydrazone) ligand L adopts different conformations and shows remarkable differences in its mode of metal coordination. While a molecule of trimethylamine acts as a secondary template that fills the void of the Dy6(L)6 assembly, sodium ions take on this role for the formation of heterobimetallic Dy12(L)8 by occupying vacant coordination sites, thus demonstrating that these processes can be steered in different directions upon subtle changes of reaction conditions. Furthermore, Dy6(L)6 shows an interesting spin-relaxation energy barrier of 435 K, which is amongst the largest values within multinuclear lanthanide single-molecular magnets.

Rhenium(I)-Based Heteroleptic Pentagonal Toroid-Shaped Metallocavitands: Self-Assembly and Molecular Recognition Studies

A family of neutral, heteroleptic, dinuclear M₂LL'-type pentagonal toroid-shaped metallomacrocycles (1-8) were synthesized using flexible ditopic N donors (Lⁿ = L¹-L²), rigid bis-chelating ligands (H₂-L' = H₂-E), and Re₂(CO)₁₀ in a one-pot solvothermal self-assembly approach. The ligands and the metallomacrocycles were characterized using ATR-IR, electrospray ionization mass spectrometry, nuclear magnetic resonance, ultraviolet-visible, and emission spectroscopy methods. The molecular structures of 1, 2, 4, 6, and 7 were confirmed by an X-ray diffraction study and are similar to those of calix[5]arene. The cyclic inner cavities of the metallomacrocycles accommodate toluene/mesitylene/acetone/chlorobenzene as guest molecules that are stabilized by cumulative C-H···π and π···π interactions with the cyclic framework of metallomacrocycle. The photophysical properties of the ligands and the metallomacrocycles were studied. The host-guest recognition properties of metallocavitands 1, 2, 7, and 8 as a model host with phenol and nitrobenzene derivatives as guest molecules were studied by emission spectroscopy methods.

Self-Assembly of a Rare High Spin FeII/PdII Tetradecanuclear Cubic Cage Constructed via the Metalloligand Approach

Polynuclear heterobimetallic coordination cages in which different metal cations are connected within a ligand scaffold are known to adopt a variety of polyhedral architectures, many of which display interesting functions. Within the extensive array of coordination cages incorporating Fe(II) centres reported so far, the majority contain low-spin (LS) Fe(II), with high-spin (HS) Fe(II) being less common. Herein, we present the synthesis and characterisation of a new tetradecanuclear heterobimetallic [Fe8Pd6L8](BF4]28 (1) cubic cage utilising the metalloligand approach. Use of the tripodal tris-imidazolimine derivative (2) permitted the formation of the tripodal HS Fe(II) metalloligand [FeL](BF4)2·CH3OH (3) that was subsequently used to form the coordination cage 1. Magnetic and structural analyses gave insight into the manner in which the HS environment of the metalloligand was transferred into the cage architecture along with the structural changes that accompanied its occupancy of the eight corners of the discrete cubic structure.

Metal–Organic Cages: Applications in Organic Reactions

Supramolecular metal–organic cages, a class of molecular containers formed via coordination-driven self-assembly, have attracted sustained attention for their applications in catalysis, due to their structural aesthetics and unique properties. Their inherent confined cavity is considered to be analogous to the binding pocket of enzymes, and the facile tunability of building blocks offers a diverse platform for enzyme mimics to promote organic reactions. This minireview covers the recent progress of supramolecular metal–organic coordination cages for boosting organic reactions as reaction vessels or catalysts. The developments in the utilizations of the metal–organic cages for accelerating the organic reactions, improving the selectivity of the reactions are summarized. In addition, recent developments and successes in tandem or cascade reactions promoted by supramolecular metal–organic cages are discussed.

Metallosupramolecular cages: from design principles and characterisation techniques to applications

Although metallosupramolecular cages are self-assembled from seemingly simple building blocks, metal ions and organic ligands, architectures of increasingly large size and complexity are accessible and exploited in applications from catalysis to the stabilisation of reactive species. This Tutorial Review gives an introduction to the principles for designing metallosupramolecular cages and highlights advances in the design of large and lower symmetry cages. The characterisation and identification of cages relies on a number of complementary techniques with NMR spectroscopy, mass spectrometry, X-ray crystallography and computational methods being the focus of this review. Finally, examples of cages are discussed where these design principles and characterisation techniques are put into practice for an application or function of the cage.

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.

Mononuclear Transition Metal Cymantrenecarboxylates as Precursors for Spinel-Type Manganites

Novel mononuclear cymantrenecarboxylate complexes of transition metals, [Co(H₂O)₆](CymCO₂)₂·4H₂O (Cym = (η⁵-C₅H₄)Mn(CO)₃) (1), [Ni(H₂O)₆](CymCO₂)₂·4H₂O (2), [Zn(H₂O)₆](CymCO₂)₂·4H₂O (3), [Co(CymCO₂)₂(imz)₂] (imz = imidazole, 4), [Co(CymCO₂)₂(bpy)₂]·2PhMe (bpy = 2,2′-bipyridyl, 5), [Ni(CymCO₂)(bpy)₂(H₂O)][CymCO₂]·0.5MePh·2H₂O (6), [Cu(CymCO₂)₂(imz)₂] (7), and [Cu(CymCO₂)₂(bpy)(H₂O)] (8), were obtained and characterized by single-crystal X-ray analysis. Complexes 1–3 are isostructural. Magnetism of the Co complexes 1, 4, and 5 was studied; it was shown that they exhibit the properties of field-induced single-molecule magnets with magnetization reversal barriers (ΔE/k_B) of 44, 13, and 10 K, respectively. Thermal decomposition of complexes 1–8 was studied by means of DSC and TGA methods. The final products of thermolysis of 1–6 in air, according to powder XRD data, are the pure spinel phases MMn₂O₄; for the cases of copper complexes, the mixtures of CuMn₂O₄ and CuO were found in the products.

Impact of flexible succinate connectors on the formation of tetrasulfonylcalix[4]arene based nano-sized polynuclear cages: structural diversity and induced chirality study

The formation of three types of supramolecular coordination cages is described. Tetrasulfonylcalixarene, combined with metallic salts (Ni, Co and Zn) and the flexible succinate ligand, led to cages. H bonded induced chirality was observed for both isomorphous cages.

Phosphorus guiding palladium: [4+4] metallomacrocyclic PdII complex and self-assembly of heterometallic PdII/ZnII grid-type complex

The reaction of heteroditopic ligand 1 featuring a hard pyridine-hydrazone-pyrimidine (N,N,N) site and a softer pyrimidine-hydrazone-phosphane (N,N,P) pocket with [Pd(CH3CN4)](OTf)2 in different metal-to-ligand ratios (M:L) gave the homobimetallic PdII complex...

Supramolecular catalysis: the role of H-bonding interactions in substrate orientation and activation

Hydrogen bonding plays significant roles in various biological processes during substrate orientation and binding and therefore assists in assorted organic transformations. However, replicating the intricate selection of hydrogen bonds, as observed in nature, in synthetic complexes has met with only limited success. Despite this fact, recent times have seen the emergence of several notable examples where hydrogen bonds have been introduced in synthetic complexes. A few such examples have also illustrated the substantial role played by the hydrogen bonds in influencing and often controlling the catalytic outcome. This perspective presents selected examples illustrating the significance of hydrogen bonds offered by the coordination and the organometallic complexes that aid in providing the desired orientation to a substrate adjacent to a catalytic metal center and remarkably assisting in the catalysis.

Designing narcissistic self-sorting terpyridine moieties with high coordination selectivity for complex metallo-supramolecules

Coordination-driven self-assembly is a powerful approach for the construction of metallosupramolecules, but designing coordination moieties that can drive the self-assembly with high selectivity and specificity remains a challenge. Here we report two ortho-modified terpyridine ligands that form head-to-tail coordination complexes with Zn(II). Both complexes show narcissistic self-sorting behaviour. In addition, starting from these ligands, we obtain two sterically congested multitopic ligands and use them to construct more complex metallo-supramolecules hexagons. Because of the non-coaxial structural restrictions in the rotation of terpyridine moieties, these hexagonal macrocycles can hierarchically self-assemble into giant cyclic nanostructures via edge-to-edge stacking, rather than face-to-face stacking. Our design of dissymmetrical coordination moieties from congested coordination pairs show remarkable self-assembly selectivity and specificity.

High-component reactions (HCRs): An overview of MCRs containing seven or more components as versatile tools in organic synthesis

Recently, multi-component reactions (MCRs) have gained special attention due to their versatility for the synthesis of polycyclic heterocycles. Moreover, their applicability can become more widespread as they can be combined together as a union of MCRs. In this overview, the authors have tried to collect the MCRs containing more than seven components that can lead to effectual heterocycles in organic and/or pharmaceutical chemistry. The review contains papers published up to the end of 2020. The subject is classified based on the number of substrates, such as seven-, eight-, nine-, ten-, and more components. The authors expect their report to be helpful for researchers to clarify their route to significant MCRs.

A "Pretender" Croconate-Bridged Macrocyclic Tetraruthenium Complex: Sizable Redox Potential Splittings despite Electronically Insulated Divinylphenylene Diruthenium Entities

Careful optimization of the reaction conditions provided access to the particularly small tetraruthenium macrocycle ²Ru₂Ph-Croc, which is composed out of two redox-active divinylphenylene-bridged diruthenium entities {Ru}-1,4-CH=CH-C₆H₄-CH=CH-{Ru} (Ru₂Ph; {Ru} = Ru(CO)Cl(PⁱPr₃)₂) and two likewise redox-active and potentially non-innocent croconate linkers. According to single X-ray diffraction analysis, the central cavity of ²Ru₂Ph-Croc is shielded by the bulky PⁱPr₃ ligands, which come into close contact. Cyclic voltammetry revealed two pairs of split anodic waves in the weakly ion pairing CH₂Cl₂/NBu₄BAr^F₂₄ (BAr^F₂₄ = [B{C₆H₃(CF₃)₂-3,5}₄]⁻ electrolyte, while the third and fourth waves fall together in CH₂Cl₂/NBu₄PF₆. The various oxidized forms were electrogenerated and scrutinized by IR and UV/Vis/NIR spectroscopy. This allowed us to assign the individual oxidations to the metal-organic Ru₂Ph entities within ²Ru₂Ph-Croc, while the croconate ligands remain largely uninvolved. The lack of specific NIR bands that could be assigned to intervalence charge transfer (IVCT) in the mono- and trications indicates that these mixed-valent species are strictly charge-localized. ²Ru₂Ph-Croc is hence an exemplary case, where stepwise IR band shifts and quite sizable redox splittings between consecutive one-electron oxidations would, on first sight, point to electronic coupling, but are exclusively due to electrostatic and inductive effects. This makes ²Ru₂Ph-Croc a true “pretender”.

Coordination-Driven Selective Formation of D2 Symmetric Octanuclear Organometallic Cages

The coordination-driven self-assembly of organometallic half-sandwich iridium(III)- and rhodium(III)-based building blocks with asymmetric ambidentate pyridyl-carboxylate ligands is described. Despite the potential for obtaining a statistical mixture of multiple products, D₂ symmetric octanuclear cages were formed selectively by taking advantage of the electronic effects emanating from the two types of chelating sites - (O,O') and (N,N') - on the tetranuclear building blocks. The metal sources and the lengths of bridging ligands influence the selectivity of the self-assembly. Experimental observations, supported by computational studies, suggest that the D₂ symmetric cages are the thermodynamically favored products. Overall, the results underline the importance of electronic effects on the selectivity of coordination-driven self-assembly, and demonstrate that asymmetric ambidentate ligands can be used to control the design of discrete supramolecular coordination complexes.

Increasing structural and functional complexity in self-assembled coordination cages

Progress in metallo-supramolecular chemistry creates potential to synthesize functional nano systems and intelligent materials of increasing complexity. In the past four decades, metal-mediated self-assembly has produced a wide range of structural motifs such as helicates, grids, links, knots, spheres and cages, with particularly the latter ones catching growing attention, owing to their nano-scale cavities. Assemblies serving as hosts allow application as selective receptors, confined reaction environments and more. Recently, the field has made big steps forward by implementing dedicated functionality, e.g. catalytic centres or photoswitches to allow stimuli control. Besides incorporation in homoleptic systems, composed of one type of ligand, desire arose to include more than one function within the same assembly. Inspiration comes from natural enzymes that congregate, for example, a substrate recognition site, an allosteric regulator element and a reaction centre. Combining several functionalities without creating statistical mixtures, however, requires a toolbox of sophisticated assembly strategies. This review showcases the implementation of function into self-assembled cages and devises strategies to selectively form heteroleptic structures. We discuss first examples resulting from a combination of both principles, namely multicomponent multifunctional host-guest complexes, and their potential in application in areas such as sensing, catalysis, and photo-redox systems.

Multi-functional, Low Symmetry Pd2 L4 Nanocage Libraries*

Although many impressive metallo-supramolecular architectures have been reported, they tend towards high symmetry structures and avoid extraneous functionality to ensure high fidelity in the self-assembly process. This minimalist approach, however, limits the range of accessible structures and thus their potential applications. Herein is described the synthesis of a family of ditopic ligands wherein the ligand scaffolds are both low symmetry and incorporate exohedral functional moieties. Key to this design is the use of CuI -catalysed azide-alkyne cycloaddition (CuAAC) chemistry, as the triazole is capable of acting as both a coordinating heterocycle and a tether between the ligand framework and functional unit simultaneously. A common precursor was used to generate ligands with various functionalities, allowing control of electronic properties whilst maintaining the core structure of the resultant cis-Pd2 L4 nanocage assemblies. The isostructural nature of the scaffold frameworks enabled formation of combinatorial libraries from the self-assembly of ligand mixtures, generating a statistical mixture of multi-functional, low symmetry architectures.

[CrIII8NiII6]n+ Heterometallic Coordination Cubes

Three new heterometallic [Cr^III₈Ni^II₆] coordination cubes of formulae [Cr^III₈Ni^II₆L₂₄(H₂O)₁₂](NO₃)₁₂ (1), [Cr^III₈Ni^II₆L₂₄(MeCN)₇(H₂O)₅](ClO₄)₁₂ (2), and [Cr^III₈Ni^II₆L₂₄Cl₁₂] (3) (where HL = 1-(4-pyridyl)butane-1,3-dione), were synthesised using the paramagnetic metalloligand [Cr^IIIL₃] and the corresponding Ni^II salt. The magnetic skeleton of each capsule describes a face-centred cube in which the eight Cr^III and six Ni^II ions occupy the eight vertices and six faces of the structure, respectively. Direct current magnetic susceptibility measurements on (1) reveal weak ferromagnetic interactions between the Cr^III and Ni^II ions, with J_Cr-Ni = + 0.045 cm^-1. EPR spectra are consistent with weak exchange, being dominated by the zero-field splitting of the Cr^III ions. Excluding wheel-like structures, examples of large heterometallic clusters containing both Cr^III and Ni^II ions are rather rare, and we demonstrate that the use of metalloligands with predictable bonding modes allows for a modular approach to building families of related polymetallic complexes. Compounds (1)-(3) join the previously published, structurally related family of [M^III₈M^II₆] cubes, where M^III = Cr, Fe and M^II = Cu, Co, Mn, Pd.

Self-Assembly of a Redox Active, Metallosupramolecular [Pd3 L6 ]6+ Complex Using a Rotationally Flexible Ferrocene Ligand

A new ferrocene-containing [Pd₃ (L_4EFc )₆ ]⁶⁺ (X^- )₆ (C ⋅ BF₄ and C ⋅ SbF₆ where X=BF₄ ^- or SbF₆ ^- ) self-assembled double-walled triangle has been synthesized from the known, rotationally flexible, 1,1'-bis(4-pyridylethynyl)ferrocene ligand (L_4EFc ), and characterized by ¹ H, ¹³ C and diffusion ordered (DOSY) NMR spectroscopies, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), X-ray crystallography and cyclic voltammetry (CV). The molecular structures confirmed that double-walled triangle cage systems (C ⋅ BF₄ and C ⋅ SbF₆ ) were generated. C ⋅ BF₄ was shown to interact with the anionic guest, p-toluenesulfonate. CV experiments revealed that the triangles were redox active, however addition of the guest did not influence the redox potentials.

A heterobimetallic tetrahedron from a linear platinum(II)-bis(acetylide) metalloligand

Employing 4-ethynylaniline as a simple organic ligand we were able to prepare the stable trans-bis(acetylide)platinum(II) complex [Pt(L1)2(PBu3)2] as a linear metalloligand. The reaction of this metalloligand with iron(II) cations and pyridine-2-carbaldehyde according to the subcomponent self-assembly approach yielded decanuclear heterobimetallic tetrahedron [Fe4Pt6(L2)12](OTf)8. Thus, combination of these two design concepts - the subcomponent self-assembly strategy and the complex-as-a-ligand approach - ensured a fast and easy synthesis of large heterobimetallic coordination cages of tetrahedral shape with a diameter of more than 3 nm as a mixture of all three possible T-, S 4- and C 3-symmetric diastereomers. The new complexes were characterized by NMR and UV-vis spectroscopy and ESI mass spectrometry. Using GFN2-xTB we generated energy-minimized models of the diastereomers of this cage that further corroborated the results from analytical findings.

Better Together: Functional Heterobimetallic Macrocyclic and Cage-like Assemblies

Metallosupramolecular chemistry has attracted the interest of generations of researches due to the versatile properties and functionalities of oligonuclear coordination complexes. Quite a number of different discrete cages were investigated, mostly consisting of only one type of ligand and one type of metal cation. Looking for ever more complex structures, heterobimetallic complexes became more and more attractive, as they give access to new structural motifs and functions. In the last years substantial success has been made in the design and synthesis of cages consisting of more than one type of metal cations, and a rapidly growing number of functional materials has appeared in the literature. This Minireview describes recent developments in the field of discrete heterometallic macrocycles and cages focusing on functional materials that have been used as host‐systems or as magnetic, photo‐active, redox‐active, and even catalytically active materials.

The Covalent and Coordination Co-Driven Assembly of Supramolecular Octahedral Cages with Controllable Degree of Distortion

Discovering and constructing novel and fancy structures is the goal of many supramolecular chemists. In this work, we propose an assembly strategy based on the synergistic effect of coordination and covalent interactions to construct a set of octahedral supramolecular cages and adjust their degree of distortion. Our strategy innovatively utilizes the addition of sulfur atoms of a metal sulfide synthon, [Et₄N][Tp*WS₃] (A), to an alkynyl group of a pyridine-containing linker, resulting in a novel vertex with low symmetry, and of Cu(I) ions. By adjusting the length of the linker and the position of the reactive alkynyl group, the control of the deformation degree of the octahedral cages can be realized. These supramolecular cages exhibit enhanced third-order nonlinear optical (NLO) responses. The results offer a powerful strategy to construct novel distorted cage structures as well as control the degree of distortion of supramolecular geometries.

Recent developments in the construction and applications of platinum-based metallacycles and metallacages via coordination

Coordination-driven suprastructures have attracted much interest due to their unique properties. Among these structures, platinum-based architectures have been broadly studied due to their facile preparation. The resultant two- or three-dimensional (2D or 3D) systems have many advantages over their precursors, such as improved emission tuning, sensitivity as sensors, and capture and release of guests, and they have been applied in biomedical diagnosis as well as in catalysis. Herein, we review the recent results related to platinum-based coordination-driven self-assembly (CDSA), and the text is organized to emphasizes both the synthesis of new metallacycles and metallacages and their various applications.

Discrete Supramolecular Stacks Based on Multinuclear Tweezer-Type Rhodium Complexes

By taking advantage of self-complementary π-π stacking and CH-π interactions, a series of discrete quadruple stacks were constructed through the self-aggregation of U-shaped dirhodium metallotweezer complexes featuring various planar polyaromatic ligands. By altering the conjugate stacking strength and bridging ligands, assemblies with a range of topologies were obtained, including a binuclear D-shaped macrocycle, tetranuclear open-ended cagelike frameworks, and duplex metallotweezer stacking structures. Furthermore, a rare stacking interaction resulting in selective C-H activation was observed during the self-assembly process of these elaborate architectures.