Metal-organic Networks Research Articles

Structural evolution of ZIF-67-derived catalysts for furfural hydrogenation

Zeolitic imidazolate framework-67 (ZIF-67) can be converted to metallic Co nanoparticles supported on N-doped carbon (Co/NC) through reduction. However, its unique properties, including extremely high surface area, isoreticular pore structure, and regular metal–organic network, disappear after high-temperature (>500 °C) reduction. Aggregated CoOx particles reduce the number of surface-active sites, resulting in poor catalytic activity. If the original ZIF-67 structure is maintained after the high-temperature reduction, promoting the uniform distribution of active sites in the porous carbon, the catalytic performance can be further improved. Herein, the correlation between the catalytic furfural hydrogenation performance, Co/NC morphology, and oxidation state of Co was investigated as a function of the H2 reduction temperature and time. The reduction of ZIF-67 at 400 °C for 6 h yields a highly dispersed Co/NC catalyst, while preserving the overall morphology. The resulting Co/NC-400-6 catalyst exhibits the highest activity, promoting high selectivity toward 2-methylfuran. The product selectivity can be further altered by incorporating Cu into ZIF-67 to produce furfuryl alcohol. With proper H2 treatment to minimize the damage to the intrinsic surface area and pore structure, metal–organic frameworks can be utilized as high-performance heterogeneous catalysts by maximizing the distribution of active sites.

Atomic-Scale Visualization of Stepwise Growth Mechanism of Metal-Alkynyl Networks on Surfaces.

One of the most appealing topics in the study of metal-organic networks is the growth mechanism. However, its study is still considered a significant challenge. Herein, using scanning tunneling microscopy, the growth mechanisms of metal-alkynyl networks on Ag(111) and Au(111) surfaces were investigated at the atomic scale. During the reaction of 1,3,5-tris(chloroethynyl)benzene on Ag(111), honeycomb Ag-alkynyl networks formed at 393 K, and only short chain intermediates were observed. By contrast, the same precursor formed honeycomb Au-alkynyl networks on Au(111) at 503 K. Progression annealing led to a stepwise evolution process, in which the sequential activation of three Cl-alkynyl bonds led to the formation of dimers, zigzag chains, and novel chiral networks as the intermediates. Moreover, density functional theory calculations indicate that chlorine atoms are crucial in assisting the breakage of metal-alkynyl bonds to form Cl-metal-alkynyl, which guarantees the reversibility of the break/formation equilibration as the key to forming regular large-scale organometallic networks.

Fabrication of Nonmetal-Modulated Dual Metal-Organic Platform for Overall Water Splitting and Rechargeable Zinc-Air Batteries.

The fast development of portable water-splitting devices has led to a great deal of work on rechargeable metal-air batteries or solar cells; however, the lack of affordable multifunctional electrocatalysts still hampers their widespread applications. Herein, a well-aligned ternary metal (oxy)hydroxide nanostructure is a sacrificial pseudomorphic transformation template of an integrated metal-organic network on the carbon cloth (CC) surface, that is, the Fe-doped metal-organic framework (MOF) ZnNiCoSe@CC nanosheet network, exhibiting powerful and efficient multifunctional electrocatalysts such as the oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction in alkaline media combined with desirable electrode kinetics. As a proof-of-concept observational study, the nanostructured Fe-doped MOF ZnNiCoSe@CC could be used as air-cathode materials in the rechargeable metal-air battery. The fabricated device delivered higher open-circuit voltage, higher capacity, and peak power density, excellent discharge-charge performance, and long cycle life. Thus, our research creates a unique perspective on the development of highly portable air electrodes with a favorable electrocatalytic application of overall water-splitting reaction.

Sericin microparticles enveloped with metal-organic networks as a pulmonary targeting delivery system for intra-tracheally treating metastatic lung cancer

Chemotherapy is one of the major approaches for the treatment of metastatic lung cancer. However, systemic chemotherapy is limited by poor therapeutic efficiency and severe toxic side effects, due to the extremely low delivery efficacy and non-specificity of anticancer drugs. Herein, we report a sericin microparticles enveloped with metal-organic networks as a pulmonary delivery system for treating lung metastasis of breast cancer in an animal model. The sericin microparticles (SMPs) were prepared using water in oil (w/o) emulsification method. After doxorubicin (DOX) loading, tannic acid (TA)/ferric irons (Fe3+) based metal organic networks (MON) were coated on the particles to obtain DOX-loaded microparticles (DOX@SMPs-MON). The SMPs-MON with good biocompatibility could effectively encapsulate DOX and sustainably unload cargos in a pH-dependent manner. The DOX-loaded microparticles could be uptaken by 4T1 cells, and effectively kill the cancer cells. In vivo, DOX@SMPs-MON was deposited in the lungs and remained for over 5 days after pulmonary administration. In contrast to conventional DOX treatment that did not show significantly inhibitory effects on lung metastatic tumor, DOX@SMPs-MON markedly decreased the number and size of metastatic nodules in lungs, and the lung weight and appearance were similar to those of healthy mice. In summary, the sericin microparticles with MON wrapping might be a promising pulmonary delivery system for treating lung metastatic cancer.

Mn–Cu Transmetalation as a Strategy for the Assembly of Decoupled Metal–Organic Networks on Sn/Cu(001) Surface Alloys

Surface alloying of Cu(001) by Sn deposition is a finely controllable method of tuning the degree of copper reactivity in order to drive the on-surface assembly and synthesis of metal–organic coord...

Anisotropic Electron Conductance Driven by Reaction Byproducts on a Porous Network of Dibromobenzothiadiazole on Cu(110).

Efficiency in charge-transport is a fundamental but demanding prerequisite to allow better exploitation of molecular functionalities in organic electronics and energy-conversion systems. Here, we report on a mechanism that enables a one-dimensional conductance structure by connecting discrete molecular states at 2.1 eV through the pores of a metal-organic network on Cu(110). Two adjacent, periodic and isoenergetic contributions, namely a molecular resonance and the confined surface-state, add-up leading to anisotropic structures, as channels, observable in real-space conductance images. The adsorption configurations of Br atoms, inorganic byproduct of the redox-reacted 4,7-dibromobenzo[c]-1,2,5-thiadiazole (2Br-BTD) molecules on the copper surface, drive the confinement of the Cu surface state within the pores and critically control the channel continuity. Small displacements of the Br atoms change the local surface potential misaligning the energy levels. This work visualizes the effect of order-disorder transitions caused by the movement of single atoms in the electronic properties of two-dimensional organic networks.

Irregularity Measures for Metal-Organic Networks

Topological index plays an important role in predicting physicochemical properties of a molecular structure. With the help of the topological index, we can associate a single number with a molecular graph. Drugs and other chemical compounds are frequently demonstrated as different polygonal shapes, trees, graphs, etc. In this paper, we will compute irregularity indices for metal-organic networks.

Homologous Series of Flower Phases in Metal–Organic Networks on Au(111) Surface

Supramolecular coordination self-assembly on the solid surface offers great possibilities for creating nanostructures and thin films with unique physicochemical properties. In this work, we present...

Construction of Polymeric Metal-Organic Nanocapsule Networks via Supramolecular Coordination-Driven Self-Assembly.

Polymeric metal-organic nanocapsule networks (polyMONCs), where metal-organic nanocapsules (MONCs) are connected by functional polymers, could possess the properties of traditional polymers and also retain the structures of MONCs. In this work, we constructed novel polyMONCs based on Mg-seamed pyrogallol[4]arene-containing MONCs through supramolecular coordination-driven self-assembly. The MONCs can be successfully polymerized using poly(ethylene glycol) as the linker, and the prepared polyMONCs can be further made into gels with self-healing properties and stimuli responsiveness. Advantageously, single crystals of MONCs cross-linked by ethylene glycol/diethylene glycol were obtained, giving us direct perspectives to mimic and investigate the self-assembly process of polyMONCs.

Vertically Aligned Metal-Organic Framework Derived from Sacrificial Cobalt Nanowire Template Interconnected with Nickel Foam Supported Selenite Network as an Integrated 3D Electrode for Overall Water Splitting.

The development of bifunctional, highly active electrocatalysts for an overall water splitting reaction remains a major challenge. Here, the sacrificial template-assisted transformation of cobalt hydroxide nanowire (Co(OH)2 NW) into a metal-organic framework network (MOF) is conceived as a porous structure that provides extremely active and durable electrochemical energy conversion characteristics. After this, the 1D MOF modified Co NWs can be further transformed into a hybrid structure (MOF CoSeO3 NWs) by selenization. The self-template transformation strategy allows the interconnected porous conductive network to be exposed to abundant reactive sites and to improve electronic conductivity/structural integrity. Thus, the obtained catalyst established by electrocatalytic activity in the course of the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in 1 M KOH solution requires overpotentials (η) of 290 and 150 mV to achieve a current density of 50 and 10 mA cm-2 for both OER and HER. Interestingly, as a full cell water electrolyzer (MOF CoSeO3 NWs (+) // MOF CoSeO3 NWs (-)), the MOF CoSeO3 NW's modified electrode exhibits an affordable cell voltage of 1.675 V at a current density of 100 mA cm-2. This work involves a viable and systematic strategy to prepare many other functional integrated MOFs that can be used for energy storage and conversion in multiple applications.

Zinc-orotate coordination polymer: synthesis, thermogravimetric analysis and luminescence properties

Orotic acid formulated coordination network of formula [Zn(HOr)·3H2O]n (1) prepared by reactions of orotic acid potassium salt [K(H2Or)] accompanied by metal salts Zn(OAc)2·2H2O at room temperature. X-ray single-crystal investigation confirms that the carbonyl oxygen of the ring in 1 is structure factor for 1D Zn-orotate coordination chain. The hydrogen bonding among uncoordinated carboxylate oxygen of ligand and one of the aqua ligand assembles the nearby parallelly stacked 1D coordination chain into 2D hydrogen bonded architecture, further hydrogen bonding among coordinated water and carbonyl oxygen incorporating O‒H···O synthons yielding into 3D hydrogen bonded coordination network. O‒H···O synthons were the only concoction for hydrogen bonded metal–organic network of zinc coordination polymers. The emission spectra of Zn-orotate complex shows excitation wavelength at 270 nm which depicts that 1 has strengthened photoluminescence with peak recorded of 376 nm (3.2975 eV) and is the outcomes of n–π* and π–π* transitions of orotate ligand. Thermal decomposition predicts that at 120 °C, lattice water molecule entirely release out from the complex, moderately degradation starts and around 370 °C the entire disintegration has been inspected.

Amorphous-to-crystalline transition and photoluminescence switching in guest-absorbing metal-organic network thin films.

An amorphous metal-organic framework (aMOF) is an oxymoron as the porosity derived from the ordered network of the metal and organic moieties is the main characteristic of conventional crystalline MOFs. However, amorphous metal-organic materials can be synthesized from gaseous precursors through atomic/molecular layer deposition (ALD/MLD). We demonstrate an exciting interplay between luminescence properties and amorphous-to-crystalline transition realized upon water absorption in ALD/MLD aMOF films.

Electron Transmission through Coordinating Atoms Embedded in Metal-Organic Nanoporous Networks.

On-surface metal-organic nanoporous networks generally refer to adatom coordinated molecular arrays, which are characterized by the presence of well-defined and regular nanopores. These periodic structures constructed using two types of components confine the surface electrons of the substrate within their nanocavities. However, the confining (or scattering) strength that individual building units exhibit is apriori unknown. Here, we study the modification of the substrate's surface electrons by the interaction with a Cu-coordinated TPyB metal-organic network formed on Cu(111) and disentangle the scattering potentials and confinement properties. By means of STM and angle-resolved photoemission spectroscopy we find almost unperturbed free-electron-like states stemming from the rather weak electron confinement that yields significant coupling between adjacent pores. Electron plane wave expansion simulations match the superlattice induced experimental electronic structure, which features replicating bands and energy renormalization effects. Notably, the electrostatic potential landscape obtained from our abinitio calculations suggests that the molecules are the dominant scattering entities while the coordination metal atoms sandwiched between them act as leaky channels. These metal atom transmission conduits facilitate and enhance the coupling among quantum dots, which are prone to be exploited to engineer the electronic structure of surface electron gases.

Ordered Mesoporous Metal-Phenolic Network Particles.

Mesoporous metal-organic networks have attracted widespread interest owing to their potential applications in diverse fields including gas storage, separations, catalysis, and drug delivery. Despite recent advances, the synthesis of metal-organic networks with large and ordered mesochannels (>20 nm), which are important for loading, separating, and releasing macromolecules, remains a challenge. Herein, we report a templating strategy using sacrificial double cubic network polymer cubosomes (Im3̅m) to synthesize ordered mesoporous metal-phenolic particles (meso-MPN particles) with a large-pore (∼40 nm) single cubic network (Pm3̅m). We demonstrate that the large-pore network and the phenolic groups in the meso-MPN particles enable high loadings of various proteins (e.g., horseradish peroxidase (HRP), bovine hemoglobin, immunoglobulin G, and glucose oxidase (GOx)), which have different shapes, charges, and sizes (i.e., molecular weights spanning 44-160 kDa). For example, GOx loading in the meso-MPN particles was 362 mg g-1, which is ∼6-fold higher than the amount loaded in commercially available SiO2 particles with an average pore size of 50 nm. Furthermore, we show that HRP, when loaded in the meso-MPN particles (486 mg g-1), retained ∼82% activity of free HRP in solution and can be recycled at least five times with a minimal (∼13%) decrease in HRP activity, which exceeds HRP performance in 50 nm pore SiO2 particles (∼36% retained activity and ∼30% activity loss when recycled five times). Considering the wide selection of naturally abundant polyphenols (>8000 species) and metal ions available, the present cubosome-enabled strategy is expected to provide new avenues for designing a range of meso-MPN particles for various applications.

Evaluation of materials for iodine and technetium immobilization through sorption and redox-driven processes.

Radioactive iodine-129 (129I) and technetium-99 (99Tc) pose a risk to groundwater due to their long half-lives, toxicity, and high environmental mobility. Based on literature reviewed in Moore et al. (2019) and Pearce et al. (2019), natural and engineered materials, including iron oxides, low-solubility sulfides, tin-based materials, bismuth-based materials, organoclays, and metal organic frameworks, were tested for potential use as a deployed technology for the treatment of 129I and 99Tc to reduce environmental mobility. Materials were evaluated with metrics including capacity for IO3- and TcO4- uptake, selectivity and long-term immobilization potential. Batch testing was used to determine IO3- and TcO4- sorption under aerobic conditions for each material in synthetic groundwater at different solution to solid ratios. Material association with IO3- and TcO4- was spatially resolved using scanning electron microscopy and X-ray microprobe mapping. The potential for redox reactions was assessed using X-ray absorption near edge structure spectroscopy. Of the materials tested, bismuth oxy(hydroxide) and ferrihydrite performed the best for IO3-. The commercial Purolite A530E anion-exchange resin outperformed all materials in its sorption capacity for TcO4-. Tin-based materials had high capacity for TcO4-, but immobilized TcO4- via reductive precipitation. Bismuth-based materials had high capacity for TcO4-, though slightly lower than the tin-based materials, but did not immobilize TcO4- by a redox-drive process, mitigating potential negative re-oxidation effects over longer time periods under oxic conditions. Cationic metal organic frameworks and polymer networks had high Tc removal capacity, with TcO4- trapped within the framework of the sorbent material. Although organoclays did not have the highest capacity for IO3- and TcO4- removal in batch experiments, they are available commercially in large quantities, are relatively low cost and have low environmental impact, so were investigated in column experiments, demonstrating scale-up and removal of IO3- and TcO4- via sorption, and reductive immobilization with iron- and sulfur-based species.

2D Cu-TCNQ Metal–Organic Networks Induced by Surface Alloying

We have studied the self-assembly of 7,7,8,8-tetracyanoquinodimethane molecules on the (3√2 × √2)R45° reconstruction of the SnCu(001) surface alloy by means of X-ray photoemission spectroscopy, sca...

Spectroscopic investigation of supramolecular organometallic compound L-threonine cadmium acetate monohydrate

Single crystal of L-Threonine cadmium acetate monohydrate, a supramolecular compounds crystallized by evaporation technique. The coordination network exhibit interesting structural property and have been investigated by Powder and single crystal X-ray diffraction. The functional group was identified using FTIR analysis. Dielectric property in a metal organic frame network plays an important role in the use of solid state as bioelectrical materials for various tissue engineering applications due to its relative permittivity. The UVVis studies suggested that UV absorption ability might be used as a corrosion resistant semiconductor material for optical device fabrication system. The non linear optical efficiency predicts that the material possesses good absorption coefficient.

One-pot synthesis and construction of a high performance metal-organic structured nano pigment based on nanoceria decorated cerium (III)-imidazole network (NC/CIN) for effective epoxy composite coating anti-corrosion and thermo-mechanical properties improvement

For the first time, a novel metal-organic framework (MOF)-like nano-pigment was synthesized for fabrication of a high-performance epoxy composite material with excellent anti-corrosion and thermo-mechanical properties. The nanoceria-decorated cerium (III)-imidazole network (NC/CIN) as a new metal-organic network (MON) structure was produced by a one-pot co-precipitation route through covalent and/or coordinate networking of cerium (III) as metallic cation centers and 2-methylimidazole as organic linker in methanol medium. The NC/CIN structure was analyzed by UV–Visible spectroscopy (UV–Vis), Furrier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), Raman spectroscopy, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) examinations. The characterization results revealed that the thermal-stable CIN hybrid product decorated by ceria nanocrystals (with average particle sizes below 51 nm) was produced via chemical bonding/networking of the cerium and imidazole precursors, resulting in only 0.047 cm3 g−1 pore free volume of the final networked product. Thermo-mechanical and anti-corrosion performance of the NC/CIN-incorporated epoxy composite were examined by tensile, dynamic mechanical thermal analysis (DMTA), electrochemical impedance spectroscopy (EIS) and salt spray evaluations. The results exhibited that the NC/CIN-contained epoxy composite provided remarkable barrier-inhibitive protection for mild steel in the corrosive environment (log |Z|10 mHz = 9.91 Ω cm2 after 7 weeks exposure of the intact coating to saline solution) as well as self-repairing protective properties in the artificial defected nanocomposite. Moreover, the great reinforcement in the cross-linking density (~40.8 mol cm−3, more than 4 times efficiency), ductility and toughness (~246 J, 4 times efficiency) features of the epoxy composite was explored.

Alkali- and alkaline-earth metal–organic networks based on a tetra(4-carboxyphenyl)bimesitylene-linker

Four new 3D-metal–organic and supramolecular frameworks based on the 3,3′,5,5′-tetrakis(4-carboxyphenyl)-2,2′,4,4′,6,6′-hexamethyl-1,1′-biphenyl ligand (H4L) namely: [Na2(H4L)(H2L)(DMF)2(H2O)2]n (1), 2[Mg(H2O)6]·2H3L·H2L (2), [Mg2L(DMF)2(H2O)]·2.5DMF (3), and 2[Ca(H2L)(H2O)4.5(DMF)0.5]·[Ca(H2L)(H2O)5]n·2H2O (4) were obtained and fully characterized. The sodium ion in compound 1 is coordinated by six oxygen atoms in a distorted octahedral geometry, with the oxygen atoms provided by four monodentate carboxylate groups, one water and one DMF molecule. The polycarboxylate ligand acts as a bridge between four Na ions to form an extended 3D coordination network with (4,4) topology. In compound 2 two crystallographically independent [Mg(H2O)6]2+ complex cations and three non-coordinated mono- and doubly deprotonated tetracarboxylic acid molecules form a 3D supramolecular network consolidated by a multiple system of OH⋯O hydrogen bonds. Compound 3 consists of two Mg2+ cations, one L4− tetra-anion, two coordinated DMF molecules and one aqua ligand to form a 3D coordination polymer. The crystal structure of compound 4 includes three crystallographically independent and chemically non-equivalent molecular entities: two molecular complexes [Ca(H2L)(H2O)4.5(DMF)0.5] and a coordination-polymeric helical strand of repeating formula unit [Ca(H2L)(H2O)5]n. The crystal structure of compound 4 is described as a supramolecular architecture where 1D coordination polymers [Ca(H2L)(H2O)5]n and two molecular units [Ca(H2L)(H2O)4.5(DMF)0.5] are linked through numerous intermolecular H-bonds.

Stabilizing Metal-Organic Polyhedra (MOP): Issues and Strategies.

Metal-organic polyhedra (MOPs) are discrete, metal-organic molecular entities composed of edge-sharing molecular polygons or connected molecular vertices. Unlike the infinite metal-organic coordination networks popularized by metal-organic frameworks (MOFs), spherical MOPs, also known as nanocages, nanospheres, nanocapsules, or nanoballs, are obtained through the self-organization of metal-carboxylate or metal-pyridine/pyrimidine links to afford cage-like nanoarchitectures. MOPs offer much promise as porous materials owing to their well-defined structures and solution processability. However, these advantages become moot if their poor aqueous stability and/or guest-removal-induced aggregation handicaps remain unaddressed. The concise premise of this contribution limits our discussion to the design principles in action behind recent developments in stable carboxylate MOPs. To highlight the structure-property relationships between the structural and compositional features of these metal carboxylate polyhedra, related scientific challenges and state-of-the-art research directions for further exploration are presented in brief.