Template Control over Dimerization and Guest Selectivity of Interpenetrated Coordination Cages

Enhancing Effect of Fullerene Guest and Counterion on the Structural Stability and Electrical Conductivity of Octahedral Metallo-Supramolecular Cages

Metallo-supramolecular cages have garnered tremendous attention for their diverse yet molecular-level precision structures. However, the physical properties of these supramolecular ensembles, which are of potential significance in molecular electronics, remain largely unexplored. We herein constructed a series of octahedral metallo-cages and cage-fullerene complexes with notably enhanced structural stability. As such, we could systematically evaluate the electrical conductivity of these ensembles at both the single-molecule level and aggregated bulk state (as well-defined films). Our findings reveal that counteranions and fullerene guests play a pivotal role in determining the electrical conductivity of the aggregated state, while such effects are less significant for single-molecule conductance. Both the counteranions and fullerenes effectively tune the electronic structures and packing density of metallo-supramolecular assemblies, and facilitate efficient charge transfer between the cage hosts and fullerenes, resulting in a notable one order of magnitude increase in the electrical conductivity of the aggregated state.

Multicomponent, Multicavity Metallacages That Contain Different Binding Sites for Allosteric Recognition

The encapsulation of different guest molecules by their different recognition domains of proteins leads to selective binding, catalysis, and transportation. Synthetic hosts capable of selectively binding different guests in their different cavities to mimic the function of proteins are highly desirable but challenging. Here, we report three ladder-shaped, triple-cavity metallacages prepared by multicomponent coordination-driven self-assembly. Interestingly, the porphyrin-based metallacage is capable of heteroleptic encapsulation of fullerenes (C60 or C70) and coronene using its different cavities, allowing distinct allosteric recognition of coronene upon the addition of C60 or C70. Owing to the different binding affinities of the cavities, the metallacage hosts one C60 molecule in the central cavity and two coronene units in the side cavities, while encapsulating two C70 molecules in the side cavities and one coronene molecule in the central cavity. The rational design of multicavity assemblies that enable heteroleptic encapsulation and allosteric recognition will guide the further design of advanced supramolecular constructs with tunable recognition properties.

Self-Assembly of Cluster-Mediated 3D Catenanes with Size-Specific Recognition Behavior

Although interlocked three-dimensional molecules display unique properties associated with their spatial structures, their synthesis and study of their host-guest properties remain challenging. We report the formation of a novel [2]catenane, [Et4N]@[(Tp*WS3Cu3Cl)2(cis-bpype)3]2(OTf)5 ([Et4N][1](OTf)5), by self-assembly of the cluster node [Tp*WS3Cu3Cl]+ and the organic linker (Z)-1,2-diphenyl-1,2-bis(4-(pyridin-4-yl)phenyl)ethene (cis-bpype). Single-crystal X-ray and NMR analyses established that [1]4+ is formed by the interpenetration of two cluster-organic cages. Unique cation-in-cation host-guest complexes were observed with this catenane. The crystalline, empty catenane was formed by taking advantage of the electrostatic repulsion-induced weak binding of the host. Encapsulation experiments also reveal that the empty catenane can adaptively encapsulate cations such as [Et4N]+ and [Pr4N]+ in the cross cavity but is unable to encapsulate [Bu4N]+ and [Me4N]+, although the size of the latter is compatible with that of the cavity. Theoretical calculations and volume analysis allow to unravel the ingenious role of catenane structures and the interplay between electrostatic repulsion and attractive noncovalent interactions for size-specific recognition behavior in host-guest systems involving species with similar electric charges.

Construction of metallo-helicoids with high antimicrobial activity via intermolecular coordination

Metallo-helicoids are constructed by intermolecular coordination interactions between covalent linear polymer and tritopic/hexatopic molecular templates. These metallo-polymers with helicoidal conformation exhibit high antimicrobial activities against both Gram-positive and Gram-negative pathogens.

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.

Molecular Recognition of Aromatics in Spherical Nanocages

In general, due to the lack of efficient specific molecular interactions, achieving host-guest molecular recognition inside large and neutral metal-organic cages (MOCs) is challenging. Preferential molecular recognition of aromatics using the internal binding sites of interlocked icosahedral (i. e., spherical) M12 L8 MOCs within poly-[n]-catenane (1) is reported. The guest absorption was monitored directly in the solid-state by consecutive single-crystal-to-single-crystal (SCSC) reactions in a gas-solid environment, in single-crystal X-ray diffraction (SC-XRD) experiments. The preferential guest uptake was corroborated by density functional theory (DFT) calculations by determining the host-guest interaction energy (Ehost-guest ) with a nitrobenzene (NB)≫p-xylene (p-xy)≫o-dichlorobenzene (o-DCB) trend (i. e., from 44 to 25 kcal mol-1 ), assessing the XRD outcomes. Combining SC-XRD, DFT and solid-state 13 C NMR, the exceptional stability of the M12 L8 cages, together with the guest exchange/release properties were rationalized by considering the presence of mechanical bonds (efficient π-π interactions) and by the pyridine's rotor-like behaviour (with 3 kcal mol-1 rotational energy barrier). The structure-function properties of M12 L8 makes 1 a potential candidate in the field of molecular sensors.

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.

Anion-Driven Programmable Chiral Self-Sorting in Metal-Organic Cages and Structural Transformations between Heterochiral and Homochiral Cages

When a racemic mixture of chiral building blocks self-assembles to form discrete molecular or supramolecular cages, the system can adopt either social or narcissistic chiral self-sorting. However, control over such chiral self-sorting is hard to achieve with a desired choice of outcome. Herein, we report anion templated high-fidelity chiral self-sorting during the coordination-driven self-assembly of [Pd₂ L₄ ] metal-organic cages, with a racemic mixture of an axially chiral ligand. Upon varying the counter-anions, the outcome of the choice of chiral self-sorting, whether social or narcissistic, leading to kinetically favored heterochiral or thermodynamically favored homochiral cages, can be controlled through specific anion encapsulation. Non-encapsulating anion afforded a mixture of all possible diastereomers. Anion exchange enabled structural transformations between the diastereomers and the conversion of the mixture of diastereomers into homochiral diastereomers.

Orientational self-sorting in cuboctahedral Pd cages

Cuboctahedral coordination cages of the general formula [Pd12L24]24+ (L = low-symmetry ligand) were analyzed theoretically and experimentally. With 350 696 potential isomers, the structural space of these assemblies is vast. Orientational self-sorting refers to the preferential formation of particular isomers within the pool of potential structures. Geometric and computational analyses predict the preferred formation of cages with a cis arrangement at the metal centers. This prediction was corroborated experimentally by synthesizing a [Pd12L24]24+ cage with a bridging 3-(4-(pyridin-4-yl)phenyl)pyridine ligand. A crystallographic analysis of this assembly showed exclusive cis coordination of the 3- and the 4-pyridyl donor groups at the Pd2+ ions.

Highly Stable Europium(III) Tetrahedral (Eu4L4)(phen)4 Cage: Structure, Luminescence Properties, and Cellular Imaging

Luminescent lanthanide cages have many potential applications in guest recognition, sensing, magnetic resonance imaging (MRI), and bioimaging. However, these polynuclear lanthanide assemblies' poor stability, dispersity, and luminescence properties have significantly constrained their practical applications. Furthermore, it is still a huge challenge to simultaneously synthesize and design lanthanide organic polyhedra with high stability and quantum yield. Herein, we demonstrate a simple and robust strategy to improve the rigidity, chemical stability, and luminescence of an Eu(III) tetrahedral cage by introducing the conjugated planar auxiliary phen ligand. The self-assembled tetrahedral cage, (Eu₄L₄)(phen)₄ [L = (4,4',4″-tris(4,4,4-trifluoro-1,3-dioxobutyl)-triphenylamine), phen = 1,10-phenanthroline], exhibited characteristic luminescence of Eu³⁺ ions with high quantum yield (41%) and long lifetime (131 μs) in toluene (1.0 × 10^-6 M). Moreover, the Eu(III) cage was stable in water and even in an aqueous solution with a pH range of 1-14. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cellular imaging revealed that the Pluronic F127-coated hybrid material, (Eu₄L₄)(phen)₄@F127, exhibited low cytotoxicity, good biocompatibility, and cellular imaging ability, which may inspire more insights into the development of lanthanide organic polyhedra (LOPs) for potential biomedical applications.

Heterotrimetallic Double Cavity Cages: Syntheses and Selective Guest Binding

A strategy for the generation of heterotrimetallic double cavity (DC) cages [Pdn Ptm L4 ]6+ (DC1: n=1, m=2; and DC2: n=2, m=1) is reported. The DC cages were generated by combining an inert platinum(II) tetrapyridylaldehyde complex with a suitably substituted pyridylamine and PdII ions. 1 H and DOSY nuclear magnetic resonance spectroscopy (NMR) and electrospray ionization mass spectrometry (ESIMS) data were consistent with the formation of the DC architectures. DC1 and DC2 were shown to interact with several different guest molecules. The structure of DC1, which features two identical cavities, binding two 2,6-diaminoanthraquinone (DAQ) guest molecules was determined by single-crystal X-ray crystallography. In addition, DC1 was shown to bind two molecules of 5-fluorouracil (5-FU) in a statistical (non-cooperative) manner. In contrast, DC2, which features two different cage cavities, was found to interact with two different guests, 5-FU and cisplatin, selectively.

Uptake, Trapping, and Release of Organometallic Cations by Redox-Active Cationic Hosts

The host-guest chemistry of metal-organic nanocages is typically driven by thermodynamically favorable interactions with their guests such that uptake and release of guests can be controlled by switching this affinity on or off. Herein, we achieve this effect by reducing porphyrin-walled cationic nanoprisms 1a¹²⁺ and 1b¹²⁺ to zwitterionic states that rapidly uptake organometallic cations Cp*₂Co⁺ and Cp₂Co⁺, respectively. Cp*₂Co⁺ binds strongly (K_a = 1.3 × 10³ M^-1) in the neutral state 1a⁰ of host 1a¹²⁺, which has its three porphyrin walls doubly reduced and its six (bipy)Pt²⁺ linkers singly reduced (bipy = 2,2'-bipyridine). The less-reduced states of the host 1a³⁺ and 1a⁹⁺ also bind Cp*₂Co⁺, though with lower affinities. The smaller Cp₂Co⁺ cation binds strongly (K_a = 1.7 × 10³ M^-1) in the 3e^- reduced state 1b⁹⁺ of the (tmeda)Pt²⁺-linked host 1b¹²⁺ (tmeda = N,N,N',N'-tetramethylethylenediamine). Upon reoxidation of the hosts with Ag⁺, the guests become trapped to provide unprecedented metastable cation-in-cation complexes Cp*₂Co⁺@1a¹²⁺ and Cp₂Co⁺@1b¹²⁺ that persist for >1 month. Thus, dramatic kinetic effects reveal a way to confine the guests in thermodynamically unfavorable environments. Experimental and DFT studies indicate that PF₆^- anions kinetically stabilize Cp*₂Co⁺@1a¹²⁺ through electrostatic interactions and by influencing conformational changes of the host that open and close its apertures. However, when Cp*₂Co⁺@1a¹²⁺ was prepared using ferrocenium (Fc⁺) instead of Ag⁺ to reoxidize the host, dissociation was accelerated >200× even though neither Fc⁺ nor Fc have any observable affinity for 1a¹²⁺. This finding shows that metastable host-guest complexes can respond to subtler stimuli than those required to induce guest release from thermodynamically favorable complexes.

Hierarchical communication of chirality for aromatic oligoamide sequences

The communication of chirality at a molecular and supramolecular level is the fundamental feature capable of transmitting and amplifying chirality information. Yet, the limitation of one-step communication mode in many artificial systems has precluded the ability of further processing the chirality information. Here, we report the chirality communication of aromatic oligoamide sequences within the interpenetrated helicate architecture in a hierarchical manner, specifically, the communication is manipulated by three sequential steps: (i) coordination, (ii) concentration, and (iii) ion stimulus. Such approach enables the information to be implemented progressively and reversibly to different levels. Furthermore, the chiral information on the side chains can be accumulated and transferred to the helical backbones of the sequences, resulting in that one of ten possible diastereoisomers of the interpenetrated helicate is finally selected. The circular dichroism experiments with a mixture of chiral and achiral ligands demonstrate a cooperative behavior of these communications, leading to amplification of chiral information.

Communication of chirality at a molecular level is the fundamental for transmitting chirality information but one-step communication modes in many artificial systems limits further processing the chirality information. Here, the authors report chirality communication of aromatic oligoamide sequences within interpenetrated helicate architecture in a hierarchical manner.

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 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.

An S10-Symmetric 5-Fold Interlocked [2]Catenane

The reaction of sym-pentakis(4-aminothiophenyl)corannulene with 2-formyl-6-methylpyridine and Cu^I or 2-formyl-1,10-phenanthroline and M^II (M = Co, Zn) yields an S₁₀-symmetric 5-fold interlocked [2]catenane of two interpenetrating [Cu^I₅L₂]⁵⁺ cages or D₅-symmetric [M^II₅L₂]¹⁰⁺ cages, respectively. The new structures were characterized by X-ray crystallography, NMR spectroscopy, and mass spectrometry. Density functional theory computations point to dispersive energies on par with traditional covalent bond energies. Subcomponent exchange reactions favored formation of the [Co^II₅L₂]¹⁰⁺ cage over the [Cu^I₁₀L₄]¹⁰⁺ catenane. The single cage and catenane each cocrystallized with a corannulene guest to form a bowl-in-bowl substructure.

Effecting structural diversity in a series of Co(II)-organic frameworks by the interplay between rigidity of a dicarboxylate and flexibility of bis(tridentate) spanning ligands

In a one-pot self-assembly reaction of Co(OAc)2·4H2O, thiophene-2,5-dicarboxylic acid (H2tdc) and four different bis(tridentate) polypyridyl spanning ligands under ambient conditions, a series of structurally diverse metal-organic frameworks has been synthesised and characterized by single crystal X-ray diffraction: {[Co2(tdc)2(tpbn)(H2O)2]·solvent}n (solvent = 2H2O, 1; solvent = 2CH3OH, 2H2O, 1a), {[Co2(tdc)2(tphn)]·solvent}n (solvent = H2O, 2; solvent = CH3OH, 2.5H2O, 2a), {[Co2(tdc)2(tpchn)(H2O)2]·solvent}n (solvent = 5H2O, 3; solvent = C2H5OH, 2H2O, 3a), and {[Co2(tdc)2(tpxn)]·solvent}n (solvent = 6H2O, 4; when no solvent, 4a), where tpbn (N,N',N'',N'''-tetrakis(2-pyridylmethyl)-1,4-diaminobutane), tphn = N,N',N'',N'''-tetrakis(2-pyridylmethyl)-1,6-diaminohexane, tpchn = N,N'-(cyclohexane-1,4-diylbis(methylene))bis(1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine) and tpxn = N,N'-(1,4-phenylenebis(methylene))bis(1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine). There is a profound effect of the nature of spacer between the alkyl nitrogens in the spanning ligands (flexible vs. semiflexible) on the molecular structures of 1a-4a. The notable differences are (a) the binding mode of the tridentate part of polypyridyl ligands to the Co(ii) center is facial in 1a, 3a and 4a but meridional in 2a, (b) the Co(ii) centers in 1a-3a are hexacoordinated (with a coordinated water in 1a and 3a) but are pentacoordinated in 4a, and (c) the binding mode of tdc linker is bis(monodentate) in 1a, 3a and 4a but chelated in one end and monodentate in the other end in 2a. Thus, the overall framework structure of 1a, 2a, 3a and 4a is cis-decalin type 2D polymer, ladder-shaped 1D polymer, hexagonal 2D net and cis-decalin type 2D polymer, respectively. Their thermal stabilities have been established by thermogravimetric analysis (TGA). The presence of an unsaturated metal center in 4 has provided us an opportunity for its use as an efficient Lewis acid catalyst for the Knoevenagel condensation reaction of malononitrile with various aldehydes (100% conversion in 60 minutes with 2 mol% catalyst in methanol).

Coordination-driven self-assembly of discrete supramolecular double-metallacycles

This review comprehensively summarizes the recent advances in the coordination-driven self-assembly of discrete supramolecular double-metallacycles.

A new supramolecular catalytic system: the self-assembly of Rh8 cage host anthracene molecules for [4 + 4] cycloaddition induced by UV irradiation

The supramolecular assembly is significant in host–guest chemistry. In this work, a new supramolecular system assembled through a distorted cuboid was introduced. Moreover, the [4 + 4] cycloaddition reaction of the guest molecules was further studied under UV light.

Cavity-based applications of metallo-supramolecular coordination cages (MSCCs)

This review describes cavity-based applications of cage-like SCCs such as molecular recognition and separation, stabilization of reactive species by encapsulation, as drug delivery systems and as molecular flasks.

A discrete Cu2(Pd-bpy)2L2 heterometallic compound with superoxide dismutase enzyme like activity

An aqueous soluble discrete heterometallic compound consisting of Cu(ii) and Pd(ii) units with SOD mimicking activity has been demonstrated.

Dynamic Open Coordination Cage from Nonsymmetrical Imidazole-Pyridine Ditopic Ligands for Turn-On/Off Anion Binding

This work demonstrates a new nonconventional ligand design, imidazole/pyridine-based nonsymmetrical ditopic ligands (1 and 1^S ), to construct a dynamic open coordination cage from nonsymmetrical building blocks. Upon complex formation with Pd²⁺ at a 1:4 molar ratio, 1 and 1^S initially form mononuclear PdL₄ complexes (Pd²⁺ (1)₄ and Pd²⁺ (1^S )₄ ) without formation of a cage. The PdL₄ complexes undergo a stoichiometrically controlled structural transition to Pd₂ L₄ open cages ((Pd²⁺ )₂ (1)₄ and (Pd²⁺ )₂ (1^S )₄ ) capable of anion binding, leading to turn-on anion binding. The structural transitions between the Pd₂ L₄ open cage and the PdL₄ complex are reversible. Thus, stoichiometric addition (2 equiv) of free 1^S to the (Pd²⁺ )₂ (1^S )₄ open cage holding a guest anion ((Pd²⁺ )₂ (1^S )₄ ⋅G^- ) enables the structural transition to the Pd²⁺ (1^S )₄ complex, which does not have a cage and thus causes the release of the guest anion (Pd²⁺ (1^S )₄ +G^- ).

Self-Assembled Fluorescent Pt(II) Metallacycles as Artificial Light-Harvesting Systems

Light-harvesting is one of the key steps in photosynthesis, but developing artificial light-harvesting systems (LHSs) with high energy transfer efficiencies has been a challenging task. Here we report fluorescent hexagonal Pt(II) metallacycles as a new platform to fabricate artificial LHSs. The metallacycles (4 and 5) are easily accessible by coordination-driven self-assembly of a triphenylamine-based ditopic ligand 1 with di-platinum acceptors 2 and 3, respectively. They possess good fluorescence properties both in solution and in the solid state. Notably, the metallacycles show aggregation-induced emission enhancement (AIEE) characteristics in a DMSO-H₂O solvent system. In the presence of the fluorescent dye Eosin Y (ESY), the emission intensities of the metallacycles decrease but the emission intensity of ESY increases. The absorption spectrum of ESY and the emission spectra of the metallacycles show a considerable overlap, suggesting the possibility of energy transfer from the metallacycles to ESY, with an energy transfer efficiency as high as 65% in the 4^a+ESY system.

Combining Synthesis and Self-Assembly in One Pot To Construct Complex 2D Metallo-Supramolecules Using Terpyridine and Pyrylium Salts

Multicomponent self-assembly in one pot provides an efficient way for constructing complex architectures using multiple types of building blocks with different levels of interactions orthogonally. The preparation of multiple types of building blocks typically includes tedious synthesis. Here, we developed a multicomponent synthesis/self-assembly strategy, which combined covalent interaction (C-N bond, formed through condensation of pyrylium salt with primary amine) and metal-ligand interaction (N → Zn bond, formed through 2,2':6',2″-terpyridine-Zn coordination) in one pot. The high compatibility of this pair of interactions smoothly and efficiently converted three and four types of components into the desired complex structures, which are supramolecular Kandinsky Circles and spiderwebs, respectively.

Palladium(II)-Based Self-Assembled Heteroleptic Coordination Architectures: A Growing Family

Metal-driven self-assembly is one of the most effective approaches to lucidly design a large range of discrete 2D and 3D coordination architectures/complexes. Palladium(II)-based self-assembled coordination architectures are usually prepared by using suitable metal components, in either a partially protected form (PdL') or typical form (Pd; charges are not shown), and designed ligand components. The self-assembled molecules prepared by using a metal component and only one type of bi- or polydentate ligand (L) can be classified in the homoleptic series of complexes. On the other hand, the less explored heteroleptic series of complexes are obtained by using a metal component and at least two different types of non-chelating bi- or polydentate ligands (such as L^a and L^b ). Methods that allow the controlled generation of single, discrete heteroleptic complexes are less understood. A survey of palladium(II)-based self-assembled coordination cages that are heteroleptic has been made. This review article illustrates a systematic collection of such architectures and credible justification of their formation, along with reported functional aspects of the complexes. The collected heteroleptic assemblies are classified here into three sections: 1) [(PdL')_m (L^a )_x (L^b )_y ]-type complexes, in which the denticity of L^a and L^b is equal; 2) [(PdL')_m (L^a )_x (L^b )_y ]-type complexes, in which the denticity of L^a and L^b is different; and 3) [Pd_m (L^a )_x (L^b )_y ]-type complexes, in which the denticity of L^a and L^b is equal. Representative examples of some important homoleptic architectures are also provided, wherever possible, to set a background for a better understanding of the related heteroleptic versions. The purpose of this review is to pave the way for the construction of several unique heteroleptic coordination assemblies that might exhibit emergent supramolecular functions.

Anion Pairs Template a Trigonal Prism with Disilver Vertices

Here we describe the formation of a trigonal prismatic cage, utilizing 2-formyl-1,8-naphthyridine subcomponents to bind pairs of silver(I) ions in close proximity. This cage is the first example of a new class of subcomponent self-assembled polyhedral structures having bimetallic vertices, as opposed to the single metal centers that typically serve as structural elements within such cages. Our new cage self-assembles around a pair of anionic templates, which are shown by crystallographic and solution-phase data to bind within the central cavity of the structure. Many different anions serve as competent templates and guests. Elongated dianions, such as the strong oxidizing agent peroxysulfate, also serve to template and bind within the cavity of the prism. The principle of using subcomponents that have more than one spatially close, but nonchelating, binding site may thus allow access to other higher-order structures with multimetallic vertices.

Chiral Self-Discrimination and Guest Recognition in Helicene-Based Coordination Cages

Chiral nanosized confinements play a major role for enantioselective recognition and reaction control in biological systems. Supramolecular self-assembly gives access to artificial mimics with tunable sizes and properties. Herein, a new family of [Pd2 L4 ] coordination cages based on a chiral [6]helicene backbone is introduced. A racemic mixture of the bis-monodentate pyridyl ligand L1 selectively assembles with PdII cations under chiral self-discrimination to an achiral meso cage, cis-[Pd2 L1P2 L1M2 ]. Enantiopure L1 forms homochiral cages [Pd2 L1P/M4 ]. A longer derivative L2 forms chiral cages [Pd2 L2P/M4 ] with larger cavities, which bind optical isomers of chiral guests with different affinities. Owing to its distinct chiroptical properties, this cage can distinguish non-chiral guests of different lengths, as they were found to squeeze or elongate the cavity under modulation of the helical pitch of the helicenes. The CD spectroscopic results were supported by ion mobility mass spectrometry.