Constructions of two polycatenanes and one polypseudo-rotaxane by discrete tetrahedral cages and stool-like building units

Polycatenanes Formed of Self-Assembled Metal-Organic Cages

Poly-[n]-catenanes (PCs) self-assembled of three-dimensional (3D) metal organic cages (MOCs) (hereafter referred to as PCs-MOCs) are a relatively new class of mechanically interlocked molecules (MIMs) that combine the properties of MOCs and polymers. The synthesis of PCs-MOCs is challenging because of the difficulties associated with interlocking MOCs, the occurrence of multiple weak supramolecular electrostatic interactions between cages, and the importance of solvent templating effects. The high density of mechanical bonds interlocking the MOCs endows the MOCs with mechanical and physical properties such as enhanced stability, responsive dynamic behavior and low solubility, which can unlock new functional properties. In this Minireview, we highlight the benefit of interlocking MOCs in the formation of PCs-MOCs structures as well as the synthetic approaches exploited in their preparation, from thermodynamic to kinetic methods, both in the solution and solid-states. Examples of PCs-MOCs self-assembled from various types of nanosized cages (i.e., tetrahedral, trigonal prismatic, octahedral and icosahedral) are described in this article, providing an overview of the research carried out in this area. The focus is on the structure-property relationship with examples of functional applications such as electron conductivity, X-ray attenuation, gas adsorption and molecular sensing. We believe that the structural and functional aspects of the reviewed PCs-MOCs will attract chemists in this research field with great potential as new functional materials in nanotechnological disciplines such as gas adsorption, sensing and photophysical properties such as X-ray attenuation or electron conductivity.

Mechanically Interlocked Water-Soluble Pd6 Host for the Selective Separation of Coal Tar-Based Planar Aromatic Molecules

Research on the synthesis of catenated cages has been a growing field of interest in the past few years. While multiple types of catenated cages with different structures have been synthesized, the application of such systems has been much less explored. Specifically, the use of catenated cages in the separation of industrially relevant molecules that are present in coal tar has not been explored before. Herein, we demonstrate the use of a newly synthesized interlocked cage 1 [C184H240N76O48Pd6] (M6L4), formed through the self-assembly of ligand L.HNO3 (tris(4-(1H-imidazole-1-yl)benzylidene)hydrazine-1-carbohydrazonhydrazide) with acceptor cis-[(tmchda)Pd(NO3)2] [tmchda = ±N,N,N',N'-tetramethylcyclohexane-1,2-diamine] (M). The interlocked cage 1 was able to separate the isomers (anthracene and phenanthrene) using a simple solvent extraction technique. Using the same technique, the much more difficult separation of structurally and physiochemically similar compounds acenaphthene and acenaphthylene was performed for the first time with 1 as the host. Other noninterlocked hexanuclear Pd6 cages having a wider cavity proved inefficient for such separation, demonstrating the uniqueness of the interlocked cage 1 for such challenging separation.

Paracetamol Inclusion in Mechanically Interlocked Nanocages

The solid-state synthesis and fast crystallization under kinetic control of poly-[n]-catenanes self-assembled of mechanically interlocked metal organic cages (MOCs) is virtually unexplored. This is in part, due to the lack of suitable crystals for single crystal X-ray diffraction (SC-XRD) analysis which limits their progress as advanced functional materials. Here we report the unprecedented inclusion of paracetamol in the cavities of amorphous materials constituted of M12L8, interlocked MOCs synthesized by mechanochemistry under kinetic control. Full structure determination of a low-crystallinity and low-resolution powders of the M12L8 poly-[n]-catenane including paracetamol has been carried out combining XRD data and Density Functional Theory (DFT) calculations using a multi-step approach. Each M12L8 cage contains six paracetamol guests which is confirmed by thermal analysis and NMR spectroscopy. The paracetamol loading has been also carried out by the instant synthesis method using a saturated paracetamol solution in which TPB and ZnI2 self-assemble immediately (i. e., 1-5 seconds) encapsulating ~7 paracetamol molecules in the M12L8 nanocages under kinetic control also giving a good selectivity. Benzaldehyde has been included in the M12L8 cages using amorphous M12L8 polycatenanes showing that the icosahedral cages can serve as potential nanoreactors for instance to study Henry reactions in the solid-state.

Hetero- and Homointerlocked Metal-Organic Cages

Interlocked molecular assemblies constitute a captivating ensemble of chemical topologies, comprising two or more separate components that exhibit remarkably intricate structures. The interlocked molecular assemblies are typically identical, and heterointerlocked systems that comprise structurally distinct assemblies remain unexplored. Here, we demonstrate that metal-templated synthesis can be exploited to afford not only a homointerlocked cage but also a heterointerlocked cage. Treatment of a carboxylated 2,9-dimethyl-1,10-phenanthroline (dmp) or Cu(I) bis-dmp linker with a Ni4-p-tert-butylsulfonylcalix[4]arene cluster affords noninterlocked octahedron and quadruply interlocked double cages consisting of two identical tetragonal pyramids, respectively. In contrast, when a mixture of dmp and Cu(I) bis-dmp linkers is used, a quadruply heterointerlocked cage is produced, consisting of a tetragonal pyramid and an octahedron. With photoredox-active [Cu(dmp)2]+ in the structures, both interlocked cages exhibit remarkable performance as photocatalysts for atom transfer radical addition (ATRA) reactions of trifluoromethanesulfonyl chloride with alkenes or oxo-azidations of vinyl arenes. These interlocked structures serve the dual purpose of stabilizing photocatalytically active components against deactivation and encapsulating substrates within the cavity, resulting in yields comparable to or even surpassing those of their molecular counterparts. This work thus provides a new strategy that combines metal templating and nontemplating approaches to design new types of interlocked assemblies with intriguing architectures and properties.

Piecewise-linear embeddings of decussate extended θ graphs and tetrahedra

An nθ graph is an n-valent graph with two vertices. From symmetry considerations, it has vertex–edge transitivity 1 1. Here, they are considered extended with divalent vertices added to the edges to explore the simplest piecewise-linear tangled embeddings with straight, non-intersecting edges (sticks). The simplest tangles found are those with 3n sticks, transitivity 2 2, and with 2⌊(n − 1)/2⌋ ambient-anisotopic tangles. The simplest finite and 1-, 2- and 3-periodic decussate structures (links and tangles) are described. These include finite cubic and icosahedral and 1- and 3-periodic links, all with minimal transitivity. The paper also presents the simplest tangles of extended tetrahedra and their linkages to form periodic polycatenanes. A vertex- and edge-transitive embedding of a tangled srs net with tangled and polycatenated θ graphs and vertex-transitive tangled diamond (dia) nets are described.

Synthesis and crystal structure of trans-diaqua(1,4,8,11-tetraazaundecane)copper(II) isophthalate monohydrate

The complex cation of the title compound contains a tetra­gonally distorted trans-CuN₄O₂ octa­hedron. In the crystal, the components are linked by numerous N—H⋯O and O—H⋯O hydrogen bonds, forming electroneutral sheets oriented parallel to the ac plane, which are further consolidated into bilayers due to hydrogen-bonding with the participation of the water mol­ecule of crystallization.

In the title hydrated mol­ecular salt, [Cu(C₇H₂₀N₄)(H₂O)₂](C₈H₄O₄)·H₂O, the metal ion is coordinated by the two primary and two secondary N atoms of the amine ligand and the mutually trans O atoms of the water mol­ecules in a tetra­gonally distorted octa­hedral geometry. The average equatorial Cu—N bond lengths (2.013 and 2.026 Å for Cu—N_prim and Cu—N_sec, respectively) are substanti­ally shorter than the average axial Cu—O bond length (2.518 Å). The tetra­amine ligand adopts its energetically favored conformation with its five- and six-membered chelate rings in gauche and chair conformations, respectively. In the crystal, the N—H donor groups of the tetra­amine, the acceptor carboxyl­ate groups of the isophthalate dianion and both the coordinated water mol­ecules and the water mol­ecule of crystallization are involved in numerous N—H⋯O and O—H⋯O hydrogen bonds, resulting in the formation of electroneutral layers oriented parallel to the ac plane.

Different Topologies of Hg(II)‐Bispidine 1D Coordination Polymers: Dynamic Behavior in Solvent Adsorption and Exchange Processes

One‐dimensional (1D) coordination polymers (CPs) featuring three different topologies, comprising zig‐zag, ribbon‐like and poly‐[n]‐catenane structures, were obtained by reaction of Hg(II) ions with a novel bispidine ligand L3, and structurally characterized by SC‐ and P‐XRD methods. The CPs obtained in the form of microcrystalline powders were tested for their ability to undergo solvent adsorption and exchange by P‐XRD and ¹H NMR spectroscopy. The extent of their dynamic behavior was then correlated to their structural features, highlighting the role of interchain interactions established among their constituting linear arrays. Zig‐zag CPs proved to be resilient to external chemical stimuli, while they differently respond to thermal treatments, depending on the solvent originally included within the CP. In the case of polycatenated structures, we observed transformations where the original topology was maintained upon guest exchange, but also cases where it changed to zig‐zag, even under solid/vapor conditions (i. e., no complete dissolution of the CP). Given the presence of linear interconnected 1D channels, 3  ⋅  ClBz‐polycatenane^Pwd is also able to trap volatile guests such as n‐hexane when exposed to its vapors.

Construction and two-dimensional assembly of double-shell Na@Sn6L6@Sn3L3 clusters through tetrahedral citrate ligands

Herein we report a double-shell Na@Sn6L6@Sn3L3 cluster and their further assembly into 2D layer, which belongs to rare Sn-oxo coordination cage based extended structure. Tetrahedral citrate ligands with multiple coordination...

A porous supramolecular ionic solid

We report a synthetic strategy to integrate discrete coordination cages into extended porous materials by decorating opposite charges on the singular cage, which offers multidirectional electrostatic forces among cages and leads to a porous supramolecular ionic solid. The resulting material is non-centrosymmetric and affords a piezoelectric coefficient of 8.19 pC N^-1, higher than that of the wurtzite ZnO.

A Zn(II) Metallocycle as Platform to Assemble a 1D + 1D → 1D Polyrotaxane via π···π Stacking of an Ancillary Ligand

A new [Zn2L2] metallocycle bearing two metal centers that can coordinate ancillary ligands and a pocket suitable to host guest molecules is reported. These two features are exploited by reacting the metallocycle with a pyridine ligand to self-assemble in the solid state an extended intertwined system with the rare 1D + 1D → 1D topology. This interpenetrated architecture is supported by π···π stacking between two pyridine units of two different metallocycles in the pocket of a third metallocycle.

A luminescent edge-interlocked prismatic heteroleptic metallocage assembled through a ligand replacement reaction

A luminescent edge-interlocked heteroleptic metallocages based on Cu₃(pyrazolate)₃ was prepared through a ligand replacement reaction from a homoleptic metallocage and a new ligand.

A Cu(ii) metallocycle for the reversible self-assembly of coordination-driven polyrotaxane-like architectures

We report the design and synthesis of a Cu(ii) metallocycle (1) and use the possibility to expand the Cu(ii) coordination sphere to self-assemble mechanically interlocked species via interpenetration. Metallocycle 1 can be used as a platform to reversibly assemble a 1D + 1D → 1D coordination-driven polyrotaxane (3), where 1 acts as the hosting ring as well as the stopper, and 4,4'-bipyridine is the guest-axle. A coordinating solvent can substitute the 4,4'-bipyridine axle to disassemble the polyrotaxane (3 → 2) that is easily restored by further adding 4,4'-bipyridine (2 → 3). Other polyrotaxanes can be isolated by reacting 1 with pyridine (4) and phenylpyridine (5). Interconversion among the presented species is demonstrated and ensured by the open position of each copper center in platform 1.

A flexible doubly interpenetrated metal–organic framework with gate opening effect for highly selective C2H2/C2H4 separation at room temperature

A flexible doubly interpenetrated MOF is realized at room temperature, whose pore spaces could accommodate a significant amount of C₂H₂ at room temperature via the gate-opening effect but exclude C₂H₄ and C₂H₆ outside.

I2-induced SC–SC transformation within two-dimensional Zn(ii)-triazole framework: an ideal detector of cyano-containing molecules

A SC–SC transformation process driven by I₂ has been shown to generate a 2D + 1D → 2D interpenetrated architecture from a 2D + 2D → 2D network. For the first time we demonstrate a selective sensor toward cyano-containing molecules.

Conformation driven in situ interlock: from discrete metallocycles to infinite polycatenanes

A novel conformation driven self-assembly system, where four metallocycles with different conformations have been in situ self-assembled, has been reported. Interestingly, only square metallocycles can further interlock into polycatenanes. However, rectangular and rhombus metallocycles fail to overcome such an entropically unfavourable process, which constitutes an obstacle to the formation of polycatenanes.

Controllable Coordination Self-Assembly Based on Flexible Tripodal Ligands: From Finite Metallocages to Infinite Polycatenanes Step by Step

This article describes the developments in coordination self-assembly based on flexible tripodal ligands with different metal species. Various finite metallocages such as M3 L2 , M6 L8 , M6 L4 , M4 L4 and different catenanes based on discrete metallocages constructed from flexible tripodal ligands with suitable metal species are presented here. Many M3 L2 metallocages based on ligands L(1) -L(12) and different two-coordinated metal species have been prepared, in which various Ag(I) salts and other metal species that have been protected by suitable groups, such as Zn(OAc)2 , ZnBr2 , and PdBr2 , have been used as effective acceptors. All of the M6 L8 -type metallocages are constructed from ligands L(2) or L(12) -L(20) and different four-coordinated metal species, such as various palladium(II) salts or NiCl2 , and have similar topological structures. Only a few discrete M6 L4 -type metallocages, based on ligands L(21) -L(24) , have been reported, using different strategies such as protecting groups and steric hindrance. All of the M4 L4 -type cages have similar topological structures and are constructed from ligands L(25) -L(29) with multiple donor sites. More intriguing interlocking ensembles constructed from discrete metallocages are also described here in detail, namely, three [2]catenanes based on ligands L(30) -L(32) and four polycatenanes based on ligands L(33) -L(34) .

Controllable coordination-driven self-assembly: from discrete metallocages to infinite cage-based frameworks

CONSPECTUS: Nanosized supramolecular metallocages have a unique self-assembly process that allows chemists to both understand and control it. In addition, well-defined cavities of such supramolecular aggregates have various attractive applications including storage, separation, catalysis, recognition, drug delivery, and many others. Coordination-driven self-assembly of nanosized supramolecular metallocages is a powerful methodology to construct supramolecular metallocages with considerable size and desirable shapes. In this Account, we summarize our recent research on controllable coordination-driven assembly of supramolecular metallocages and infinite cage-based frameworks. To this end, we have chosen flexible ligands that can adopt various conformations and metal ions with suitable coordination sites for the rational design and assembly of metal-organic supramolecular ensembles. This has resulted in various types of metallocages including M3L2, M6L8, M6L4, and M12L8 with different sizes and shapes. Because the kinds of metal geometries are limited, we have found that we can replace single metal ions with metal clusters to alternatively increase molecular diversity and complexity. There are two clear-cut merits of this strategy. First, metal clusters are much bigger than single metal ions, which helps in the construction and stabilization of large metallocages, especially nanosized cages. Second, metal clusters can generate diverse assembly modes that chemists could not synthesize with single metal ions. This allows us to obtain a series of unprecedented supramolecular metallocages. The large cavities and potential unsaturated coordination sites of these discrete supramolecular cages offer opportunities to construct infinite cage-based frameworks. This in turn can offer us a new avenue to understand self-assembly and realize certain various functionalities. We introduce two types of infinite cage-based frameworks here: cage-based coordination polymers and cage-based polycatenanes, which we can construct through coordination bonds and mechanical bonds, respectively. Through either directly linking the unsaturated coordination sites of metallocages or replacing the labile terminal ligands with bridging ligands, we can produce infinite cage-based frameworks based on coordination bonds. We introduce several interesting cage-based coordination polymers, including a single-crystal-to-single-crystal transformation from a M6L8 cage to an infinite cage-based chain. Compared with discrete metallocages, these kinds of materials can give us higher structural stability and complexity, favoring the applications of metallocages. In addition, we discuss how we can use mechanical bonds, such as interlocking and interpenetrating, to construct extended cage-based frameworks. So far, study in this field has focused on polycatenanes constructed from M6L4 and M12L8 cages, as well as a controllable and dynamic self-assembly based on M6L4 metallocages. We also discuss cage-based polycatenanes, which can give dynamic properties to discrete metallocages. We hope that our investigations will bring new insights to the world of the supramolecular metallocages by enlarging its breadth and encourage us to devote more effort to this blossoming field in the future.

Sterically controlled self-assembly of tetrahedral M6L4cages via cationic N-donor ligands

Inter-ligand steric effects dictate the self-assembly between tripodal cationic ligandLand M^II(M = Cu, Pd) generating an unusual tetrahedral M₆L₄cage instead of the expected M₆L₈species.

A rare (3,4,5)-connected metal–organic framework featuring an unprecedented 1D + 2D → 3D self-interpenetrated array and an O-atom lined pore surface: structure and controlled drug release

A rare (3,4,5)-connected metal–organic framework has been constructed, which features an unprecedented 1D + 2D → 3D self-interpenetrated array and an O-atom lined pore surface, and shows good controlled release of ibuprofen.