Metal-organic Networks Research Articles

Uniform deposition of metal-organic coordination networks on BiVO4 through chemical bonding for efficient solar water splitting

Uniform deposition of metal-organic coordination networks on BiVO4 through chemical bonding for efficient solar water splitting

Assembly of Photochromic Molecules into Multiple Stimuli‐Responsive Hollow Microparticles via Templating Coordination

AbstractSupramolecular multifunctional metal–organic networks offer immense potential in drug delivery, bioimaging, catalysis, and therapeutics. However, the creation of multiple stimuli‐responsive fluorescent hollow nano/microparticles is a formidable challenge in this field. In this study, a novel strategy is reported for synthesizing photochromic hollow microparticles that exhibit responsiveness to light, pH, and glutathione (GSH). With the assistance of templating coordination from zeolitic imidazolate framework‐8 microparticles, bisphosphonate‐merocyanine ligands are successfully assembled to create hollow bisphosphonate‐spiropyran (BPSP)‐Zn2+ microparticles. The photochromic and pH responses stem from the reversible conversion between spiropyran and zwitterionic merocyanine components and between merocyanine and protonated merocyanine, respectively. The GSH response is attributed to the stronger affinity of Zn2+ to thiol groups than to phosphonate groups. These remarkable features render the hollow BPSP‐Zn2+ microparticles highly suitable for applications in stimulus‐triggered drug delivery, and these findings provide a platform for developing innovative materials that have the potential to transform the biomedical field.

Dicarboxylic Acids Induced Tandem Transformation of Silver Nanocluster.

Structural transformation of metal nanoclusters (NCs) is of great ongoing interest regarding their synthesis, stability, and reactivity. Although sporadic examples of cluster transformations have been reported, neither the underlying transformation mechanism nor the intermediates are unambiguous. Herein, we have synthesized a flexible 54-nuclei silver cluster (Ag54) by combining soft (tBuC≡C-) and hard (nPrCOO-) ligands. The existence of weakly coordinated nPrCOO- enhances the reactivity of Ag54, thus facilitating the dicarboxylic acid to induce structural transformation. X-ray structural analyses reveal that Ag54 transforms to Ag28 cluster-based 2D networks (Ag28a and Ag28b) induced by H2suc (succinic acid) and H2glu (glutaric acid), whereas with H2pda (2,2'-(1,2-phenylene)diacetic acid), a discrete Ag28 cluster (Ag28c) is isolated. The key intermediate Ag17 that emerges during the self-dissociation of Ag54 was isolated by using cryogenic recrystallization and characterized by X-ray crystallography. The "tandem transformation" mechanism for the structure evolution from Ag54 to Ag28a is established by time-dependent electrospray ionization mass spectrometry (ESI-MS) and UV-vis spectroscopy. In addition, the catalytic activity in the 4-nitrophenol reduction follows the sequence Ag28c > Ag28b > Ag28a > Ag54 due to more bare silver sites on the surface of the Ag28 cluster unit. Our findings not only open new avenues to the synthesis of silver NCs but also shed light on a better understanding of the structural transformation mechanism from one cluster to another or cluster-based metal-organic networks induced by dicarboxylates.

Ring-Closing Reactions of Porphyrins on Noble Metal Surfaces

On-surface chemistry protocols provide elegant routes to individual molecular complexes, oligomers, and hybrid structures at confining interfaces, yielding distinct chemical, physical, and structural properties [1]. In this context, porphyrins and other tetrapyrroles represent versatile precursors that can undergo metalation, ring-opening, and ring-closing reactions. Furthermore, they are often used as functional tectons for self-assembled molecular films, metal-organic coordination networks, and covalent architectures at interfaces [2].We will report on temperature-induced ring-closing reactions of porphyrins on single crystalline Ag and Au surfaces in an ultrahigh vacuum environment. Examples covered include dehydrogenative homocoupling as well as intramolecular ring-closing. Specifically, distinct oligomers including square-type porphyrin tetramers featuring a planar, central antiaromatic cyclooctatetraene (COT) moiety were achieved on a Ag(100) support by employing unsubstituted Zn- and free-base porphines (see Figure) as precursors [3]. Low-temperature scanning tunnelling microscopy (STM), spectroscopy (STS), and bond-resolved atomic force microscopy (AFM) supported by complementary theoretical modelling were used to comprehensively characterize chemical structure and electronic properties of the square-type tetramers with sub-molecular resolution. Furthermore, the synthesis of π-extended oxygen-embedded porphyrins via O-annulation on Au(111) will be discussed. This surface chemical approach yields high selectivity and yield for planar porphyrin products with distinct symmetries and oxygen content that is not achieved by solution chemistry. The bond-resolved AFM characterization is complemented by X-ray photoelectron spectroscopy measurements. These studies thus give access, and insights, to novel porphyrinoids with distinct properties on noble metal supports.

Indicator films based on anthocyanins loaded on Metal-Organic Framework carriers and BP neural network for monitoring meat freshness

This study presented a novel indicator film for monitoring chicken freshness based on polyvinyl alcohol (PVA) and chitosan (CS) incorporated with a natural dye of anthocyanin loaded on MOFs (UiO-66 and UiO-66-Br) carriers. The characterization results of UiO-66/A and UiO-66-Br/A dyes showed that most anthocyanins bind to MOFs by intermolecular forces without disrupting the MOFs structure. Different dyes (anthocyanin, UiO-66/A, UiO-66-Br/A) with the same effective dye content were added into PVA/CS matrices to form PVA/CS/A (PCA) film, PVA/CS/UiO-66/A (PCUA) film and PVA/CS/UiO-66-Br/A (PCBA) film. With the addition of UiO-66/A and UiO-66-Br/A, the tensile strength and elongation at break of indicator films decreased. Small amounts of dye migration were observed in acidic and neutral food simulants for PCUA and PCBA films, while no dye migration was observed in alcoholic food simulants. PCUA and PCBA films exhibited higher sensitivity for detecting ammonia vapor, with a detection limit of 24.39 ppm for PCBA films. When all films were used to monitor changes in chicken breast freshness, PCBA films presented more accurate color changes than other films. The BP neural network-based prediction model utilizing the color change of PCBA film effectively predicted the freshness of chicken breast.

Inhalable capsular polysaccharide-camouflaged gallium-polyphenol nanoparticles enhance lung cancer chemotherapy by depleting local lung microbiota.

Local lung microbiota is closely associated with lung tumorigenesis and therapeutic response. It is found that lung commensal microbes induce chemoresistance in lung cancer by directly inactivating therapeutic drugs via biotransformation. Accordingly, an inhalable microbial capsular polysaccharide (CP)-camouflaged gallium-polyphenol metal-organic network (MON) is designed to eliminate lung microbiota and thereby abrogate microbe-induced chemoresistance. As a substitute for iron uptake, Ga3+ released from MON acts as a "Trojan horse" to disrupt bacterial iron respiration, effectively inactivating multiple microbes. Moreover, CP cloaks endow MON with reduced immune clearance by masquerading as normal host-tissue molecules, significantly increasing residence time in lung tissue for enhanced antimicrobial efficacy. In multiple lung cancer mice models, microbe-induced drug degradation is remarkably inhibited when drugs are delivered by antimicrobial MON. Tumor growth is sufficiently suppressed and mouse survival is prolonged. Ourwork develops a novel microbiota-depleted nano-strategy to overcome chemoresistance in lung cancer by inhibiting local microbial inactivation of therapeutic drugs. This article is protected by copyright. All rights reserved.

Removal of disperse blue textile dye 56 from water using a metal-organic framework of erbium

The disperse blue dye 56 (AD56) is of the anthraquinone type and is considered an important source of water pollution due to the discharges generated by the textile industry. An efficient way to eliminate it is using porous materials, for example, metal-organic networks (MOF). In this work, the adsorption of AD56 with an Er MOF was studied and synthesized by microwave-assisted method and using 1,4-benzene dicarboxylic acid (BDC) as an organic ligand. Physicochemical analysis of the Er2BDC3 was carried out by XRD, FTIR, SEM, and UV-Vis spectroscopy to determine the dye concentration. Due to its high porosity, the results show that the MOF can be reused for up to seven adsorption cycles for the AD56 dye. The adsorption process changed the structure of the MOF, obtaining a more pure and stable material in an aqueous medium. The maximum AD56 adsorption capacity obtained was 33.97 mg/g after seven cycles. This material can be used in consecutive adsorption processes and for other anthraquinone dyes.

Nigella sativa extract phytochemicals: Effective green/bio-active anti-corrosion agent for steel protection in saline media

This research aims to develop a low-VOC silane (sol-gel) coating functionally protected by novel non-toxic metal-organic networks (MONs) based on extracted Nigella sativa bio-molecules/Zinc nitrate. The effectiveness of the silane coating containing the MONs pigment was investigated via electrochemical (i.e., EIS) and accelerated (i.e., salt spray) corrosion experiments. Based on the electrochemical tests' results in the solution phase, an efficiency of 67.8% and a mixed-type corrosion mitigation mechanism were obtained for the hybrid pigment to protect the mild steel against the NaCl media. Moreover, adding the synthesized MONs into the silane coating matrix dramatically increased its protection performance. Fourier-transform infrared spectroscopy (FT-IR) results revealed that the coating’s curing index is affected after the MONs pigment’s inclusion in the silane matrix. The change in the coating curing index increases the silane film crosslinking density, improving coating adhesion to the metallic substrate and then enhancing its anti-corrosion protection performance. The electrochemical tests were employed in the presence of artificial defects to study the active protection performance of the silane layer. Results indicated that the active anti-corrosion protection performance of the silane coating was significantly improved after employing the synthesized MONs in its structure. Adsorbing the inhibitive species in the scratched region of the silane coating and fabricating the inhibitive film at this region is the main protection mechanism, which was illustrated via SEM/EDS analysis.

Construction of 2D metal-organic precursor networks with tunable porosity: A Monte Carlo simulation approach

Two-dimensional network structures comprising functional organic building blocks have been recently recognized as promising platforms for various physio-chemical processes running in confined spaces. In this study, we present theoretical results of the self-assembly of metal-organic precursor networks on a crystalline surface and provide quantitative characteristics of these planar architectures. To that end, a coarse-grained model of the adsorbed overlayer comprising halogenated polyaromatic aromatic hydrocarbon (PAH) molecules and bivalent metal atoms was used in combination with the equilibrium Monte Carlo (MC) simulation method. Our calculations focused on the effect of molecular features, such as size, shape and distribution of halogen substituents in the PAH monomer, on the quality and morphology of the networks formed on a model (111) crystalline surface. For the simulated porous assemblies, representing the precursor stage of the surface-assisted Ullmann coupling reaction, such descriptors as the unit cell parameters, radial distribution functions, pore size distributions and structure factors were determined. The obtained results demonstrated that fine-tuning of the monomeric PAH units enables the creation of periodic and aperiodic networks having diverse porous properties, ranging from monoporous to heteroporous with bi- and multimodal pore-size distributions. The findings of our theoretical investigations, apart from the potential application in the optimization of 2D polymeric networks, can also be helpful in designing real confined nanoenvironments for selective capture and immobilization/transformation of guest species.

Tuning Chirality of Self-Assembled PTCDA Molecules on a Au(111) Surface by Na Coordination.

Chiral nanostructures are much desired in many applications, such as chiral sensing, chiroptics, chiral electronics, and asymmetric catalysis. In building chiral nanostructures, the on-surface metal-organic self-assembly is naturally suitable in obtaining atomically precise structures, but that is under the premise that there are enantioselective assembly strategies to create large-scale homochiral networks. Here, we report an approach to build chiral metal-organic networks using 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) molecules and low-cost sodium chloride (NaCl) in a controllable manner on Au(111). The chirality induction and transfer processes during network evolution with increased Na ion ratios were captured by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) methodologies. Our findings show that Na ion incorporation into achiral PTCDA molecules partially breaks intermolecular hydrogen bonds and coordinates with carboxyl oxygen atoms, which initiates a collective sliding motion of PTCDA molecules along specific directions. Consequently, "molecular columns" linked by hydrogen bonds were formed in the rearranged Na-PTCDA networks. Notably, the direction of Na ion incorporation determines the chiral characteristic by guiding the sliding direction of the molecular columns, and chirality can be transferred from Na0.5PTCDA to Na1PTCDA networks. Furthermore, our results indicate that the chirality transferring process is disrupted when intermolecular hydrogen bonds are entirely replaced by Na ions at a high Na dopant concentration. Our study provides fundamental insights into the mechanism of coordination-induced chirality in metal-organic self-assemblies and offers potential strategies for synthesizing large homochiral metal-organic networks.

Stoichiometry-Directed Two-Level Hierarchical Growth of Lanthanide-Based Supramolecular Nanoarchitectures.

The design of a well-ordered arrangement of atoms on a solid surface has long been sought due to the envisioned applications in many different fields. On-surface synthesis of metal-organic networks is one of the most promising fabrication techniques. Hierarchical growth, which involves coordinative schemes with weaker interactions, favours the formation of extended areas with the desired complex structure. However, the control of such hierarchical growth is in its infancy, particularly for lanthanide-based architectures. Here the hierarchical growth of a Dy-based supramolecular nanoarchitecture on Au(111) is described. Such an assembly is based on a first hierarchical level of metallo-supramolecular motifs, which in a second level of hierarchy self-assemble through directional hydrogen bonds, giving rise to a periodic two-dimensional supramolecular porous network. Notably, the size of the metal-organic based tecton of the first level of hierarchy can be tailored by modifying the metal-ligand stoichiometric ratio.

Mathematical analysis and molecular descriptors of two novel metal–organic models with chemical applications

Metal–Organic Networks (MONs) are made by chemical molecules that contain metal ions and organic ligands. A crystalline porous solid called Metal–Organic Networks (MONs) is made up of a 3D metal network of ions held in place by a multidentate ligand. (MONs) can be used for gas storage, purification drug delivery, gas separation, catalysis, and sensing applications. There is enormous potential for effective integration and research of MONs in diverse applications. Molecular descriptors are arithmetic measures that reveal a chemical substance's physical and chemical characteristics in its foundational network in a natural relationship. They demonstrate an important role in theoretical and ecological chemistry, and in the field of medicine. In this research, we calculated various recently discovered molecular descriptors viz. the modified version of second zagreb index, harmonic index, reciprocal randic index, modified version of forgotten topological index, redefined first zagreb topological index, redefined second zagreb topological index and redefined third zagreb topological index for two separate metal–organic networks. The numerical and graphical comparative analysis of these considered molecular descriptors are also performed.

Engineering Flexible Metal-Phenolic Networks with Guest Responsiveness via Intermolecular Interactions.

Flexible metal-organic materials are of growing interest owing to their ability to undergo reversible structural transformations under external stimuli. Here, we report flexible metal-phenolic networks (MPNs) featuring stimuli-responsive behavior to diverse solute guests. The competitive coordination of metal ions to phenolic ligands of multiple coordination sites and solute guests (e.g., glucose) primarily determines the responsive behavior of the MPNs, as revealed experimentally and computationally. Glucose molecules can be embedded into the dynamic MPNs upon mixing, leading to the reconfiguration of the metal-organic networks and thus changes in their physicochemical properties for targeting applications. This study expands the library of stimuli-responsive flexible metal-organic materials and the understanding of intermolecular interactions between metal-organic materials and solute guests, which is essential for the rational design of responsive materials for various applications.

Topological indices of line graph of transition metal tetra cyano benzene organic network

The molecular graph theory is one of the essential tools for developing and constructing molecular structure. In particular, using topological invariant, which is a numerical descriptor of molecular graph, has become widespread in predicting physical properties. Topological indices provide knowledge about the overall form of molecular graphs, particularly various degree-based topological indices. This research paper focuses on the first and second Zagreb index and their coindices for the line graph of a transition metal-organic network. The network, denoted by , comprises the transition metals Ti, V, Cr, Fe, Co, Ni, Cu or Zn, and the TCNB ligand. The line graph of a network is a graph that represents the connections between the edges of the original network. The Zagreb indices are widely used to describe the molecular graph's shape and structure. The paper highlights the importance of these indices in modelling the chemical properties of the transition metal-organic network. The study results show that the Zagreb indices and their coindices strongly correlate with several physical characteristics, for instance the boiling points, melting points, and density of the network.

Partial selenium surface modulation of metal organic framework assisted cobalt sulfide hollow spheres for high performance bifunctional oxygen electrocatalysis and rechargeable zinc-air batteries

There is still a significant technological barrier in the development of high-performance electrocatalysts with synergistic unreliable functions and morphological integrity that improves reversible electrochemical activity, electrical conductivity, and mass transport properties. Metal-organic compound networks are envisioned as a defect-rich porous framework that provides mesoporous hollow carbon nanostructures composed primarily of an in situ-grown N-doped graphitic carbon matrix and embedded selenium-doped CoS2 hollow spheres as efficient, highly reactive, and long-lasting chemical energy conversion functions of the system. This method enables hitherto inaccessible synthesis approaches to produce a highly porous conductive network at the microscopic level while exposing rich unsaturated reactive sites at the atomic level without losing electrical or structural integrity. Because of their inherent increased electrochemical surface area, and electron transfer, the porous framework, doping motifs, and tailored structural defects provide outstanding bifunctional oxygen electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reactions (OER). Moreover, using this selenium-doped MOF CoS2 hollow spheres electrode as an air-cathode, a rechargeable zinc-air battery with excellent discharge-charge performance and mechanical stability is successfully constructed. This study provides a feasible and universal technique for constructing diverse functional interconnected metal-organic coordinated compounds that may be employed for a wide variety of energy storage, conversion (e.g., fuel cells and metal-air batteries), and environmental applications.

Computational screening of chemically active metal center in coordinated dipyridyl tetrazine network

Creation, stabilization, characterization, and control of single transition metal (TM) atoms may lead to significant advancement of the next-generation catalyst. Metal organic network (MON) in which single TM atoms are coordinated and separated by organic ligands is a promising class of material that may serve as a single atom catalyst. Our density functional theory-based calculations of MONs in which dipyridyl tetrazine (DPTZ) ligands coordinate with a TM atom to form linear chains leads to two types of geometries of the chains. Those with V, Cr, Mo, Fe, Co, Pt, or Pd atoms at the coordination center are planar while those with Au, Ag, Cu, or Ni are non-planar. The formation energies of the chains are high (∼2.0–7.9 eV), suggesting that these MON can be stabilized. Moreover, the calculated adsorption energies of CO and O2 on the metal atom at center of the chains with the planar configuration lie in the range 1.0–3.0 eV for V, Cr, Mo, Fe, and Co at the coordination center, paving the way for future studies of CO oxidation on TM-DPTZ chains with the above five atoms at the coordination center.

Preparation and characterization of dense membrane based metal organic networks (MOF- 5) for separation :aromatic-aliphatic mixtures

ABSTRACT Polyvinyl chloride (PVC)-based mixed matrix membranes were prepared with metal organic-framework MOF-5 particles, and the hybrid membranes were studied for the separation of toluene-heptane mixtures. It was found that the PVC transport properties could be significantly modified by the amount of MOF-5 incorporated. The permeate flux of PVC-20% MOF-5 was 22.9 kg/h m2 with a separation factor of 10.4 when separating a 50 wt% toluene-n heptane mixture, and swelling tests were performed at 55°C and ambient temperature. Hybrid membranes were characterized by IR FT spectroscopy, TGA, an X-Ray diffractometer, and SEM microscopy.

Different Stepwise Growth Mechanism of AIE-Active Tetraphenylethylene-Functionalized Metal-Organic Frameworks on Au(111) and Cu(111) Surfaces.

Fabricating tetraphenylethylene (TPE)-functionalized metal-organic frameworks (MOFs) with aggregation- induced emission on surfaces and understanding the growth mechanism have not yet been pursued. Herein, MOFs constructed via the Ullmann-type reaction of a C2-symmetry TPE derivative (p-BrTBE) on Au(111) and Cu(111) surfaces were thoroughly investigated using scanning tunneling microscopy. On a Au(111) surface, p-BrTBE molecules formed the self-assembled pattern at 298 K. Stepwise annealing led to a progressive evolution process, in which the stepwise debromination reaction led to organometallic intermediates, and surface-stabilized radicals and metal-organic networks were formed. By contrast, the relatively ordered MOFs were obtained by replacing the underlying substrate with the more catalytically active Cu(111) at 298 K. Density functional theory calculations demonstrated that the formation of different networks on Au(111) and Cu(111) was determined by the different conformations of the TBE unit on the different substrates due to the different adsorption energy.

Lanthanide-directed metal-organic coordination networks.

The synthesis of two-dimensional metal-organic networks (2D-MOCNs) on solid substrates is a rapidly growing field of research due to their potential applications in gas sensing, catalysis, energy storage, spintronics, and quantum information. In addition, the possibility of using lanthanides as coordination nodes makes them a very straightforward alternative to create an ordered array of magnetic atoms on a surface, thus paving the way for their use in information storage at the single-atom level. This feature article reviews the strategies to design two-dimensional periodic nanoarchitectures comprising lanthanide atoms in ultra-high vacuum (UHV) environment, focusing on lanthanide-directed 2D-MOCNs on metal surfaces and decoupling substrates. The characterization of their structure, electronic, and magnetic properties is also discussed, including the use of state-of-the-art scanning probe microscopies and photoelectron spectroscopies, complemented by density functional theory calculations and multiplet simulations.

Reactive oxygen nanobiocatalysts: activity-mechanism disclosures, catalytic center evolutions, and changing states.

Benefiting from low costs, structural diversities, tunable catalytic activities, feasible modifications, and high stability compared to the natural enzymes, reactive oxygen nanobiocatalysts (RONBCs) have become dominant materials in catalyzing and mediating reactive oxygen species (ROS) for diverse biomedical and biological applications. Decoding the catalytic mechanism and structure-reactivity relationship of RONBCs is critical to guide their future developments. Here, this timely review comprehensively summarizes the recent breakthroughs and future trends in creating and decoding RONBCs. First, the fundamental classification, activity, detection method, and reaction mechanism for biocatalytic ROS generation and elimination have been systematically disclosed. Then, the merits, modulation strategies, structure evolutions, and state-of-art characterisation techniques for designing RONBCs have been briefly outlined. Thereafter, we thoroughly discuss different RONBCs based on the reported major material species, including metal compounds, carbon nanostructures, and organic networks. In particular, we offer particular insights into the coordination microenvironments, bond interactions, reaction pathways, and performance comparisons to disclose the structure-reactivity relationships and mechanisms. In the end, the future challenge and perspectives for RONBCs are also carefully summarised. We envision that this review will provide a comprehensive understanding and guidance for designing ROS-catalytic materials and stimulate the wide utilisation of RONBCs in diverse biomedical and biological applications.