Metal-organic Rotaxane Frameworks Research Articles

Mechanical bonding of rigid MORFs using a tetratopic rotaxane.

The preparation of highly rigid cobalt(II)- and copper(II)-organic frameworks incorporating a tetralactam [2]rotaxane as a ligand is described. The interlocked ligand is functionalized with two pairs of carboxylate groups placed at each counterpart, thus limiting its dynamics within the crystal. The solid structure of the metal-organic rotaxane frameworks showed different, unprecedented polycatenation modes of grids, depending on the employed metal, providing great rigidity to the structures. This rigidity has been evaluated by using single crystal X-ray diffraction analyses of the cobalt(II)-organic frameworks embedded in different solvents, observing that the lattices remain unchanged. Thus, this research demonstrates that rigid and robust materials with permanent porosity can be achieved using dynamic ligands.

A new metal–organic rotaxane framework for enhanced ion conductivity of solid-state electrolyte in lithium-metal batteries

The composite polymer electrolyte has been obtained via incorporating LiCUST-701 (a new metal–organic rotaxane framework modified by Li+) into poly(ethylene oxide) (PEO) matrix and give a high ionic conductivity of 4.02 × 10−4 S/cm at 60 °C. DFT calculations were used to visualize the possible diffusion pathway of Li+. The all-solid-state cell assembled with LiFePO4, composite polymer electrolyte and lithium metal foil delivered with excellent cycling capability and stability even under high current densities.

Metal-organic rotaxane frameworks constructed from a cucurbit[8]uril-based ternary complex for the selective detection of antibiotics.

Herein we report two 2D layered metal-organic rotaxane frameworks (MORFs), WUST-1 and WUST-2, constituted by a ternary host-guest complex based on cucurbit[8]uril (CB[8]) and an (E)-1-methyl-4-[4-(pyridin-4-yl)styryl] pyridinium (G1) ligand, and different metal ions and auxiliary linkers. Both MORFs are stable in water and highly fluorescence emissive, and can selectively sense nitrofurazone with low detection limits.

Three layered cucurbit[6]uril-based metal-organic rotaxane networks functionalized by sulfonic groups for proton conduction.

Three new cucurbit[6]uril (CB[6])-based metal-organic rotaxane networks (MORNs) (named CUST-711, CUST-712, and CUST-713) functionalized by a sulfonic group (-SO3H) have been designed and synthesized via a hydrothermal method. All three compounds exhibited similar two-dimensional (2D) wave layer structures. Their stability under different temperature and relative humidity conditions has been investigated and all the compounds showed excellent stability. Furthermore, their proton conduction properties were also discussed in detail. Due to different structures and sulfonic group sites, the three compounds exhibited different proton conduction abilities of which CUST-712 exhibited an intrinsic relatively high proton conductivity (1.75 × 10-4 S cm-1 at 85 °C and 97% relative humidity). These results provide ideas for the design and synthesis of functional CB[6]-based metal-organic rotaxane frameworks (MORFs) as proton conducting materials.

Pb2+-Containing Metal-Organic Rotaxane Frameworks (MORFs).

The metal-organic rotaxane framework (MORF) structures with the advantage of mechanically interlocking molecules (MIMs) have attracted intense interest from the chemical community. In this study, a set of MORFs (i.e., MORF-Pb-1 and MORF-Pb-2) are constructed using Pb2+, a tetraimidazolium macrocycle (Texas-sized molecular box; 14+), and aromatic dicarboxylate (p-phthalate dianions (PTADAs; 2) or 2,6-naphthalene dicarboxylate dianions (3)) via a one-pot three-layer diffusion protocol. In particular, an unusual Pb…Pb weak interaction was shown in MORF-Pb-1 (charactered with distance of 3.656 Å).

Effective Encapsulation of C60 by Metal–Organic Frameworks with Polyamide Macrocyclic Linkers

AbstractA flexible benzylic amide macrocycle, functionalized with two carboxylic acid groups, was employed as the organic ligand for the preparation of robust copper(II)‐ and zinc(II)‐based metal–organic frameworks. These polymers crystallized in the C2/m space group of the monoclinic crystal system, creating non‐interpenetrated channels in one direction with an extraordinary solvent‐accessible volume of 46 %. Unlike metal–organic rotaxane frameworks having benzylic amide macrocycles as linkers, the absence of the thread in these novel reticular materials causes a decrease of dimensionality and an improvement of pore size and dynamic guest adaptability. We studied the incorporation of fullerene C60 inside the adjustable pocket generated between two macrocycles connected to the same dinuclear clusters, occupying a remarkable 98 % of the cavities inside the network. The use of these materials as hosts for the selective recognition of different fullerenes was evaluated, mainly encapsulating the smaller size fullerene derivative in several mixtures of C60 and C70.

Effective Encapsulation of C60 by Metal-Organic Frameworks with Polyamide Macrocyclic Linkers.

A flexible benzylic amide macrocycle, functionalized with two carboxylic acid groups, was employed as the organic ligand for the preparation of robust copper(II)- and zinc(II)-based metal-organic frameworks. These polymers crystallized in the C2/m space group of the monoclinic crystal system, creating non-interpenetrated channels in one direction with an extraordinary solvent-accessible volume of 46 %. Unlike metal-organic rotaxane frameworks having benzylic amide macrocycles as linkers, the absence of the thread in these novel reticular materials causes a decrease of dimensionality and an improvement of pore size and dynamic guest adaptability. We studied the incorporation of fullerene C60 inside the adjustable pocket generated between two macrocycles connected to the same dinuclear clusters, occupying a remarkable 98 % of the cavities inside the network. The use of these materials as hosts for the selective recognition of different fullerenes was evaluated, mainly encapsulating the smaller size fullerene derivative in several mixtures of C60 and C70 .

Coupling the Individual Motions of the Machine-like Components of Zirconium(IV) Organic Frameworks

Controlling the internal molecular dynamics in reticular materials is a major challenge for the development of nanotechnological applications. In this issue of Chem, Schurko, Loeb, and co-workers show how the ring motion of the [2]rotaxane-based linker and that of the surrounding triphenylene-based struts influence each other within a series of robust zirconium(IV) organic frameworks.

Cucurbit[7]uril-Based Metal-Organic Rotaxane Framework for Dual-Capture of Molecular Iodine and Cationic Potassium Ion.

Metal-organic rotaxane frameworks (MORFs) attracted much attention in the past years for construction of intelligent functional materials. Herein, a one-pot synthesis is reported of a three-dimensional (3D) cucurbit[7]uril (Q[7])-based MORF under hydrothermal conditions, namely Q[7]-MORF-1, formed by encapsulating the anionic benzoate moieties of the tricarboxylate ligand into the cavity of Q[7]. Furthermore, Q[7]-MORF-1 shows dual-capture capacity for iodine and K+ selectively among the alkali metal ions. The captured molecular iodine is included in the cavity of Q[7] through halogen-bonding interactions and the K+ cations are positioned at the carbonyl port of the Q[7] through K-O coordination interactions.

Mechanically interlocked materials. Rotaxanes and catenanes beyond the small molecule.

A mechanical bond presents a combination of the best features of covalent and supramolecular chemistries (stability and structural integrity), plus a unique dynamic nature, that makes it a very interesting tool for materials chemistry. Here, we overview the chemistry of the mechanical bond applied to polymers, metal-organic frameworks (MOFs) and carbon nanotubes. We first describe synthetic strategies towards polycatenanes and polyrotaxanes, and highlight their potential impact in polymer chemistry, exemplified by their use to make stimuli-responsive gels and as binders in battery electrodes. We continue by showing how to include mechanically interlocked components in MOFs, and analyse the distinctive dynamic properties of the final constructs. Finally, we describe the strategies towards mechanically interlocked derivatives of single-walled carbon nanotubes (SWNTs), and discuss the potential of the mechanical bond to tackle some of the classic problems of SWNT chemistry.

Syntheses and magnetic properties of high-dimensional cucurbit[6]uril-based metal-organic rotaxane frameworks.

Three new high-dimensional cucurbit[6]-based metal-organic rotaxane frameworks [Co2(PR43)(BDC)2Cl2]·4H2O (1), [Co2(PR43)(BTC)2]·6H2O (2) and [Co2(PR43)(BPT)2]·20H2O (3) were obtained via the hydrothermal synthesis method. Compound 1 comprised a two-dimensional layered structure, while compounds 2 and 3 exhibited three-dimensional pillared structures. All the compounds showed good thermal stabilities. Furthermore, the magnetic properties of compounds 1-3 were also investigated in detail.

A channel rotaxane coordination polymer (RCP) based on the assembly of p-sulfonatocalix[8]arene and 4,4′-bipyridine-N,N′-dioxide ligand

In this paper, we report the first rotaxane structure of p-sulfonatocalix[8]arene as part of a supramolecular 3D co-ordination polymer. In this structure, 4, 4′-bipyridine-N, N’-dioxide (bpdo) as the linear axle and p-sulfonatocalix[8]arene as the wheel have been reported. The structure provides new opportunities for large calixarenes as wheels to be applied in the field of metal–organic rotaxane frameworks.

Releasing Metal-Coordination Capacity of Cucurbit[6]uril Macrocycle in Pseudorotaxane Ligands for the Construction of Interwoven Uranyl-Rotaxane Coordination Polymers.

As an emerging type of actinide hybrid material, uranyl-rotaxane coordination polymers (URCPs) with new coordination patterns and topological structures are still desired. In this work, we propose a new strategy to construct URCPs by promoting the simultaneous coordination of both the wheel and axle moieties in pseudorotaxane linkers with metal nodes. Starting from a series of cucurbit[6]uril (CB[6])-based pseudorotaxane ligands, C nBPCA@CB[6] [C nBPCA = 1,1-(α,ω-diyl)bis[4-(ethoxycarbonyl)pyridin-1-ium] bromides, where n = 5-8] with slightly deformed CB[6], four new URCPs (URCP1, URCP3, URCP4, and URCP5) with interwoven network structures, as well as another noninterwoven polymer(URCP2), have been successfully prepared. According to single-crystal structure analysis, we attribute the interwoven structures of the URCPs to the distortion of CB[6] in pseudorotaxane ligands with shorter or longer spacers (C5, C7, and C8). This indicates that the deformation could effectively diminish the steric hindrance around the portals, thus endowing the "inert" CB[6] host with coordination ability like the string molecule. Besides, the participation of water molecules and sulfate anions in the uranyl coordination sphere is also found to have a great influence on the final structures of the obtained URCPs. The successful preparation of interwoven URCPs in this work gives some new insights into the metal coordination of supramolecular entities and could facilitate other new applications of CB[6]-based pseudorotaxane ligands. Most importantly, the strategy proposed in this work provides some hints in the controllable design of metal-organic rotaxane frameworks with unique topologies.

Guest exchange in a porous cucurbit[6]uril-based metal-organic rotaxane framework probed by NMR and X-ray crystallography.

The first CB[6]-based 3D porous metal-organic rotaxane framework is constructed by the reaction of CuCl2, terephthalic (H2BDC) and CB[6]-based [2]pseudorotaxanes ([PR44]2+·2[PF6]-) under solvothermal conditions. The structure of MORF-1 is a pillared-layer structure with 5-connected sqp topology, in which the effective free volume is 45.4% of the crystal volume. The guest molecules exchange in a single-crystal-to-single-crystal fashion, which was investigated using NMR spectroscopy and X-ray crystallography.

Metal–Organic Rotaxane Frameworks Assembly by Cucurbit[6]uril-Based Pseudorotaxanes and Mixed Ligands

Four novel high-dimensional metal–organic rotaxane frameworks (MORFs) were successfully fabricated by cucurbit[6]uril-based pseudorotaxanes ([PR43]) and rigid carboxylate ligands by adjusting the synthesis temperature and the length of ligands. Compound 1 represents a three periodic 2-fold interpenetrating dia network based on a binuclear {Cd2Cl4O4} second building unit (SBU). 2 and 3 are isostructural pcu networks constructed by binuclear and trinuclear cadmium clusters, respectively, while compound 4 is a two-dimensional layered network with a large grid 44.3 × 19.8 A2. Furthermore, their fluorescent properties in different solvents are investigated.

Metal-binding studies of linear rigid-axle [2]pseudorotaxanes with in situ generated anionic metal halide complexes

A systematic study of metal–pseudorotaxane binding, using the linear N,N′-bis(4-pyridyl)-4,4′-bipyridinium axle (PyBP2+) and aromatic crown ethers bis(1,5-naphtho)-32-crown-8 (BN32C8), bis(1,5-naphtho)-38-crown-10 (BN38C10) and bis-para-phenylene-34-crown-10 (BPP34C10), is presented. The three corresponding [2]pseudorotaxanes, including the novel, fully characterized (visible absorption and nuclear magnetic resonance spectra, association constant, electrochemistry, crystal structure) [PyBP/BPP34C10]2+ system, were each reacted with MX2 (M = Zn2+, Cd2+, Hg2+; X = Cl−, Br−, I−). Of the twenty-seven different pseudorotaxane/MX2 combinations explored, fifteen yielded single-crystals containing a pseudorotaxane unit, and were characterized by X-ray diffraction; in eight of those crystals metal–pseudorotaxane binding was observed. The results reflect the lower association constant of [PyBP/BPP34C10]2+ (170 M−1) than the corresponding ones of [PyBP/BN32C8]2+ (870 M−1) and [PyBP/BN38C10]2+ (420 M−1) in solution, where pseudorotaxanes are in equilibrium with the corresponding free axle and wheel components. In all cases, the isolated crystals contain anionic metal halide species, such as singly charged MX3− (M = Zn, Cd; X = Cl, Br, I) or doubly charged CdX42− (X = Br, I) and Hg2X62− (X = Cl, Br, I). Ordered 3D-arrays of perfectly aligned pseudorotaxane units are found in the dichroic mercury-based crystals. Our study demonstrates that although specific intermolecular interactions (collectively called crystal packing forces), may occasionally interfere with the crystallization of metal–pseudorotaxane complexes based on pseudorotaxanes with low association constants, the use of pseudorotaxanes instead of synthetically more challenging rotaxanes is a promising approach for the construction of metal–organic rotaxane frameworks (MORFs).

An Interwoven Metal‐Organic Framework Combining Mechanically Interlocked Linkers and Interpenetrated Networks

New dibenzo[24]crown-8 ether derivatives were prepared that contain appendages with thioether donors that can coordinate to a metal ion. These macrocycles were then combined with 1,2-bis(pyridinium) ethane axles to create two types of [2]rotaxane ligands; those with the four thioether donors on the crown ether and those with six donor groups, four from the crown ether and two more attached to the stoppering groups of the dumbbell. The crown ethers and both types of [2]rotaxane ligands were allowed to react with Ag(I) ions to form metal-organic rotaxane framework (MORF) style coordination polymers. The interlocked hexadentate ligand forms the first example of a new type of lattice containing interwoven frameworks resulting from both interpenetration of frameworks due to the presence of an interlocked ligand and more classical interpenetration of independent frameworks.

Rings and threads as linkers in metal–organic frameworks and poly-rotaxanes

Coordination polymers and metal-organic rotaxane frameworks are reported where the organic linker is replaced by functionalised inorganic clusters that act as bridging ligands.

Metal ion directed metal–organic rotaxane frameworks with intrinsic features of self-penetration and interpenetration

Three novel self-catenated 4-connected uninodal (6(5)·8)- metal-organic rotaxane frameworks (MORFs) containing cucurbit[6]uril were constructed from the in situ trans/cis-configuration (1 : 1) of rotaxanes by taking advantage of a d(10) metal ion directed synthesis. It was revealed that the effect of hydrogen bonds and π-π stacking interactions play significant roles in the self-assembly process.

Rare-earth cation effects on three-dimensional metal–organic rotaxane framework (MORF) self assembly

A set of metal-organic rotaxane frameworks (MORFs) are constructed with the use of a tetraimidazolium macrocycle, the terephthalate dianion, and the trivalent lanthanide metal cations Nd(III), Sm(III), Eu(III) or Tb(III) and are reported herein. The specific choice of the metal cation allows for control of the structure and luminescent properties of the resulting molecular frameworks.