Metal-organic Polyhedra Research Articles

Edge-2-transitive trinodal polyhedra and 2-periodic tilings.

All trinodal, edge-2-transitive polyhedra and 2-periodic tilings are enumerated and described. These are of special interest for the design and synthesis of materials such as metal-organic polyhedra and frameworks.

Unusually Flexible Indium(III) Metal-Organic Polyhedra Materials for Detecting Trace Amounts of Water in Organic Solvents and High Proton Conductivity.

Humidity-induced single-crystal transformation was observed in the indium metal-organic polyhedra [In2(TCPB)2]·2H2O (In1), where H3TCPB is 1,3,5-tri(4-carboxyphenoxy)benzene. When the humidity is above 58% relative humidity (RH) at room temperature, the neutral compound In1 could be successfully converted into the positively charged compound In1-H along with the color change from yellow to deep red, which also undergoes a reversible transformation into In1 driven by thermal dehydration. Notably, the color of In1 takes only 5 min to change under 58% RH at room temperature, which is much quicker than common desiccant bluestone. As the water content is increased from 0.0% to 0.2% in acetonitrile solvent, compound In1 exhibits rapid detection of trace amounts of water through turn-off luminescence sensing mechanism with a low detection limit of 2.95 × 10-4%. Because of the formation of extensive hydrogen-bonding network between the metal-organic polyhedra (MOPs) and surrounding guest OH- ions, compound In1-H, along with isostructural Ga1-H, displays excellent proton conductivity up to 2.84 × 10-4 and 2.26 × 10-4 S cm-1 at 298 K and 98% RH, respectively. Furthermore, the activation energies are found to be 0.28 eV for In1-H and 0.34 eV for Ga1-H. This method of incorporation of OH- ions to obtain high proton conductivity MOPs with low activation energy demonstrates the advantage of OH- ion conduction in the solid-state materials.

Evolution of form in metal\u2013organic frameworks

Self-assembly has proven to be a widely successful synthetic strategy for functional materials, especially for metal–organic materials (MOMs), an emerging class of porous materials consisting of metal–organic frameworks (MOFs) and metal–organic polyhedra (MOPs). However, there are areas in MOM synthesis in which such self-assembly has not been fully utilized, such as controlling the interior of MOM crystals. Here we demonstrate sequential self-assembly strategy for synthesizing various forms of MOM crystals, including double-shell hollow MOMs, based on single-crystal to single-crystal transformation from MOP to MOF. Moreover, this synthetic strategy also yields other forms, such as solid, core-shell, double and triple matryoshka, and single-shell hollow MOMs, thereby exhibiting form evolution in MOMs. We anticipate that this synthetic approach might open up a new direction for the development of diverse forms in MOMs, with highly advanced areas such as sequential drug delivery/release and heterogeneous cascade catalysis targeted in the foreseeable future.

Synthesis of vanillin via a catalytically active Cu(ii)-metal organic polyhedron

Crystalline Cu (ii)-MOP1was employed for the first time in the catalytic conversion oftrans-ferulic acid to vanillin.

Novel properties of 0D metal-organic polyhedra bonded to the surfaces of 2D graphene and 1D single-walled carbon nanotubes.

A strategy for the stabilization of metal-organic polyhedra (MOP) cages on graphene (Gr) and single-walled carbon nanotubes (NT) is reported. The surface area of the composites, MOPGr and MOPNT increases by an order of magnitude with a significant increase in pore volume in comparison to bulk MOP. The composites show an enhancement in the catalytic activity of up to ∼80% relative to bulk MOP in the conversion of propylene oxide into propylene carbonate. Depositing individual MOP cages on graphene or SWNT surfaces is beneficial in terms of gas adsorption and catalytic properties and provides a good example for useful effects of bonding materials of different dimensionalities.

Reversible photoreduction of Cu(ii)-coumarin metal-organic polyhedra.

We report a new approach for photoinduced reduction of Cu2+ that will enrich the structural diversity of coordination complexes and be a valuable contributor to the development of Cu+/Cu0-based catalysts. To realize controlled Cu2+ reduction, coumarin as a triplet quencher of excited benzophenone was tethered to Cu(ii)-metal-organic polyhedra (MOPs). The photoinduced catalytic activity of the coumarin-MOPs was also examined in a Cu(i)-catalyzed azide-alkyne cycloaddition (CuAAC).

Cobalt and Nitrogen Co-Doped Nano-Porous Carbon: Synthesis and Application for Lithium-Sulfur Battery

S@C-Co-N nanoporous carbon co-doped with cobalt and nitrogen as the cathode of lithium-sulfur battery are prepared. The synthetic route is carried out via the carbonization of metal organic frameworks polyhedron ZIF-67, followed by the heat treatment with sulfur. The SEM images suggest that C-Co-N composite maintains almost the same size and polyhedron shape of ZIF-67. The XRD pattern confirms the existence of cobalt element. As cathode for lithium-sulfur battery, the S@C-Co-N composite delivers a reversible capacity of 916.6 mAh?g?1 at the initial cycle and 460.5 mAh?g?1 after 500 cycles at 0.5 C, with a capacity fading of 0.09% per cycle.

Metal–Organic Polyhedra-Coated Si Nanowires for the Sensitive Detection of Trace Explosives

Surface-modified silicon nanowire-based field-effect transistors (SiNW-FETs) have proven to be a promising platform for molecular recognition in miniature sensors. In this work, we present a novel nanoFET device for the sensitive and selective detection of explosives based on affinity layers of metal-organic polyhedra (MOPs). The judicious selection of the geometric and electronic characteristics of the assembly units (organic ligands and unsaturated metal site) embedded within the MOP cage allowed for the formation of multiple charge-transfer (CT) interactions to facilitate the selective explosive inclusion. Meanwhile, the host-stabilized CT complex inside the cage acted as an effective molecular gating element to strongly modulate the electrical conductance of the silicon nanowires. By grafting the MOP cages onto a SiNW-FET device, the resulting sensor showed a good electrical sensing capability to various explosives, especially 2,4,6-trinitrotoluene (TNT), with a detection limit below the nanomolar level. Importantly, coupling MOPs-which have tunable structures and properties-to SiNW-based devices may open up new avenues for a wide range of sensing applications, addressing various target analytes.

Metal-Organic Polyhedron Capped with Cucurbit[8]uril Delivers Doxorubicin to Cancer Cells.

Self-assembly of ligand 1 and Pd(NO3)2 delivers Fujita-type metal-organic polyhedron (MOP) 3 which bears 24 covalently attached methyl viologen units on its external surface, as evidenced by 1H NMR, diffusion-ordered spectroscopy NMR, electrospray mass spectrometry, transmission electron microscopy, and atomic force microscopy measurements. MOP 3 undergoes noncovalent complexation with cucurbit[n]urils to yield MOPs 4-6 with diameter ≈5-6 nm. MOP 5 can be fully loaded with doxorubicin (DOX) prodrug 2 via hetero-ternary complex formation to yield 7. The MOPs exhibit excellent stability toward neutral to slightly acidic pH in 10 mM sodium phosphate buffer, mitigating the concern of disassembly during circulation. The results of MTS assays show that MOP 7 is 10-fold more cytotoxic toward HeLa cells than equimolar quantities of DOX prodrug 2. The enhanced cytotoxicity can be traced to a combination of enhanced cellular uptake of 7 and DOX release as demonstrated by flow cytometry and confocal fluorescence microscopy. The confluence of properties imparted by the polycationic MOP architecture and plug-and-play CB[n] complexation provides a potent new platform for drug delivery application.

Poly(isophthalic acid)(ethylene oxide) as a Macromolecular Modulator for Metal-Organic Polyhedra.

A new strategy was developed by using a polymer ligand, poly(isophthalic acid)(ethylene oxide), to modulate the growth of metal-organic polyhedra (MOP) crystals. This macromolecular modulator can effectively control the crystal habit of several different Cu24L24 (L = isophthalic acid derivatives) MOPs. The polymer also directed the formation of MOP structures under reaction conditions that only produce metal-organic frameworks in the absence of modulator. Moreover, the polymer also enabled the deposition of MOP crystals on glass surfaces. This macromolecular modulator strategy provides an innovative approach to control the morphology and assembly of MOP particles.

Designed metal–organic framework based on metal–organic polyhedron: Drug delivery

A new metal–organic framework having formula {[NH2(CH3)][Cu6(L)3(OAc)(H2O)4]·xsolvent} (H4L=3,5-bis(isophthalic acid)-1H-1,2,4-triazole) (1) was synthesized, in which two types of polyhedral cages and one-dimensional channels coexist. The incorporation of the drug 5-fluorouracil (5-FU) into the desolvated 1 was around 24.9wt% per gram of dehydrated 1. 5-FU is released in a controlled and progressive fashion with 98% of the drug released after 120h at PBS. The result from this work provides a new avenue for MOF to be used as potential drug delivery.

Refined Sulfur Nanoparticles Immobilized in Metal-Organic Polyhedron as Stable Cathodes for Li-S Battery.

The lithium-sulfur (Li-S) battery presents a promising rechargeable energy storage technology for the increasing energy demand in a worldwide range. However, current main challenges in Li-S battery are structural degradation and instability of the solid-electrolyte interphase caused by the dissolution of polysulfides during cycling, resulting in the corrosion and loss of active materials. Herein, we developed novel hybrids by employing metal-organic polyhedron (MOP) encapsulated PVP-functionalized sulfur nanoparticles (S@MOP), where the active sulfur component was efficiently encapsulated within the core of MOP and PVP as a surfactant was helpful to stabilize the sulfur nanoparticles and control the size and shape of corresponding hybrids during their syntheses. The amount of sulfur embedded into MOP could be controlled according to requirements. By using the S@MOP hybrids as cathodes, an obvious enhancement in the performance of Li-S battery was achieved, including high specific capacity with good cycling stability. The MOP encapsulation could enhance the utilization efficiency of sulfur. Importantly, the structure of the S@MOP hybrids was very stable, and they could last for almost 1000 cycles as cathodes in Li-S battery. Such high performance has rarely been obtained using metal-organic framework systems. The present approach opens up a promising route for further applications of MOP as host materials in electrochemical and energy storage fields.

A metal-organic polyhedron based on dibenzothiophene ligand: Gas adsorption and reductive properties

A new metal–organic polyhedron Cu-MOP with octahedral geometry was constructed by 2,8-dibenzothiophenedicarboxylic acid and dicopper paddlewheel. Cu-MOP exhibited H2 and CO2 sorption behavior. Furthermore, Cu-MOP revealed reductive properties towards TCNQ, DDQ, CR and MB due to the electron-donating nature of DBT ligand.

Remarkable Vapochromic Behavior of Pure Organic Octahedron Embedded in Porous Frameworks.

Vapochromic behavior is employed to selectively monitor the vapor changes in surrounding environment, particularly for toxic gas leaking and floating detection. Thus, sensitive trapping and accurate response to different toxic vapors are critical factors in vapochromic sensing. In this work, a self-assembled hybrid that consists of fluorescent organic octahedron encapsulated by metal-organic polyhedron (MOP) is reported. The fluorescent octahedron is used as a responsive sensor to probe various solvent vapors, while the MOP is employed as a protector to prevent the corrosion of solvents to the organic octahedron. The hybrid exhibits remarkable vapochromic behavior to different solvents, and shows the highest selectivity and sensitivity specifically to acetone. In addition, acetone vapor under different conditions is utilized for further studying the response mechanism of the hybrid. This work presents a promising vapochromic sensor with good stability, selectivity, and sensitivity. The study is expected to open up the applicability of MOP-based hybrids for specific molecular capture, interim storage, controlled release, and advanced sensing.

Metal-Organic Polyhedral Core as a Versatile Scaffold for Divergent and Convergent Star Polymer Synthesis.

We herein report the divergent and convergent synthesis of coordination star polymers (CSP) by using metal-organic polyhedrons (MOPs) as a multifunctional core. For the divergent route, copper-based great rhombicuboctahedral MOPs decorated with dithiobenzoate or trithioester chain transfer groups at the periphery were designed. Subsequent reversible addition-fragmentation chain transfer (RAFT) polymerization of monomers mediated by the MOPs gave star polymers, in which 24 polymeric arms were grafted from the MOP core. On the other hand, the convergent route provided identical CSP architectures by simple mixing of a macroligand and copper ions. Isophthalic acid-terminated polymers (so-called macroligands) immediately formed the corresponding CSPs through a coordination reaction with copper(II) ions. This convergent route enabled us to obtain miktoarm CSPs with tunable chain compositions through ligand mixing alone. This powerful method allows instant access to a wide variety of multicomponent star polymers that conventionally have required highly skilled and multistep syntheses. MOP-core CSPs are a new class of star polymer that can offer a design strategy for highly processable porous soft materials by using coordination nanocages as a building component.

Bis-Calix[4]arenes: From Ligand Design to the Directed Assembly of a Metal-Organic Trigonal Antiprism.

Calix[4]arenes (C[4]s) are versatile platforms for the construction of polymetallic clusters containing paramagnetic metal ions. Synthetic modification at the C[4] methylene bridge allows for the design of bis-C[4]s that, depending on the linker employed, can be used to either dictate which clusters can be formed or direct the assembly of a new metal-organic polyhedron (MOP). The assembly resulting from the latter approach displays thermal stability and uptake of N2 or H2 gas, confirming that this is a viable route to the synthesis of new, functional supramolecular architectures.

Functionalized metal‐organic polyhedra hybrid membranes for aromatic hydrocarbons recovery

Pervaporation membranes are potentially useful in the separation of aromatic/aliphatic mixtures. Wherein, the membrane material plays a key role. Herein, a series of functionalized metal‐organic polyhedra (MOPs)/hyperbranched polymer hybrid membranes are molecularly designed and fabricated for the recovery of aromatic hydrocarbons. The isostructural MOP molecules with different functional groups are uniform in shape/size and soluble in solvents, which enable them to disperse well and be compatible in/with the polymer. Pervaporation results demonstrated significant improvements of these membranes in separation performances. Particularly, the membrane with MOP‐SO3NanHm showed the separation factor of 8.03 and the permeation flux of 528 g/m2h for the recovery of toluene from its 50 wt % n‐heptane mixture, and those values are 8.4 and 540 g/m2h for benzene/cyclohexane mixture. We propose that the selectivity of these membranes is affected primarily by the polarity of functional groups in MOPs, which were further explained by the adsorption experiments and molecular simulations. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3706–3716, 2016

Fabrication of Isolated Metal–Organic Polyhedra in Confined Cavities: Adsorbents/Catalysts with Unusual Dispersity and Activity

Metal-organic polyhedra (MOPs) have attracted great attention due to their intriguing structure. However, the applications of MOPs are severely hindered by two shortcomings, namely low dispersity and poor stability. Here we report the introduction of four MOPs (constructed from dicopper and carboxylates) to cavity-structured mesoporous silica SBA-16 via a double-solvent strategy to overcome both shortcomings simultaneously. By judicious design, the dimension of MOPs is just between the size of cavities and entrances of SBA-16, MOP molecules are thus confined in the cavities. This leads to the formation of isolated MOPs with unusual dispersion, making the active sites highly accessible. Hence, the adsorption capacity on carbon dioxide and propene as well as catalytic performance on ring opening are much superior to bulk MOPs. More importantly, the structure and catalytic activity of MOPs in confined cavities are well preserved after exposure to humid atmosphere, whereas those of bulk MOPs are degraded seriously.

ChemInform Abstract: Self‐Assembled Metal‐Organic Polyhedra: An Overview of Various Applications

AbstractReview: 217 refs.

Multifunctional single-layered vesicles derived from Cu(ii)-metal-organic-polyhedra.

Cu(ii) metal-organic-polyhedra (MOP) derived from a tris-pyridyl ligand gave stable single-layered vesicles capable of encapsulating an anti-cancer drug (doxorubicin - DOX) and its pH responsive release. While encapsulation of DOX was further confirmed by MTT assay and cellular imaging, α-chymotrypsin inhibition assay corroborated well with the single crystal structures of the MOP. The MOP derived vesicles reported herein not only represent the rare examples of such hierarchical architectures derived from MOP but also provide the first example of multifunctional organic-inorganic synthetic bio-membranes.