Covalent Metal Research Articles

Ni-Metalized Covalent Organic Cage as a Photocatalyst for Selective Photoreduction of CO2 to CO.

Metal complex-based photocatalysts are promising for CO2 reduction. Their catalytic performances greatly rely on the synergy of ligands and metal ions. Here, we demonstrate an assembly of covalent organic cage (COC) and metal ions for photocatalytic CO2 reduction. The coordinated metal serves as catalytically active site for CO2 reduction, while the cage not only chelates the metal site, but also enhances the local concentration of CO2 around metal site, and decreases the key intermediate reaction energy barrier, thereby promoting the CO2 reduction reaction kinetically and thermodynamically. Accordingly, a Ni metalized COC exhibited outstanding photocatalytic performance in CO2-to-CO conversion under visible light irradiation. This study highlights the feasibility and advantage of organic cages for the construction of photocatalysts for artificial photosynthesis.

Metallicious: Automated Force-Field Parameterization of Covalently Bound Metals for Supramolecular Structures.

Metal ions play a central, functional, and structural role in many molecular structures, from small catalysts to metal-organic frameworks (MOFs) and proteins. Computational studies of these systems typically employ classical or quantum mechanical approaches or a combination of both. Among classical models, only the covalent metal model reproduces both geometries and charge transfer effects but requires time-consuming parameterization, especially for supramolecular systems containing repetitive units. To streamline this process, we introduce metallicious, a Python tool designed for efficient force-field parameterization of supramolecular structures. Metallicious has been tested on diverse systems including supramolecular cages, knots, and MOFs. Our benchmarks demonstrate that parameters accurately reproduce the reference properties obtained from quantum calculations and crystal structures. Molecular dynamics simulations of the generated structures consistently yield stable simulations in explicit solvent, in contrast to similar simulations performed with nonbonded and cationic dummy models. Overall, metallicious facilitates the atomistic modeling of supramolecular systems, key for understanding their dynamic properties and host-guest interactions. The tool is freely available on GitHub (https://github.com/duartegroup/metallicious).

Recent progress in solar-driven CO2 reduction to multicarbon products.

Currently, most catalysts used for photoconverting carbon dioxide (CO2) typically produce C1 products. Achieving multicarbon (C2+) products, which are highly desirable due to their greater energy density and economic potential, still remains a significant challenge. This difficulty is primarily due to the kinetic hurdles associated with the C-C coupling step in the process. Given this, devising diverse strategies to accelerate C-C coupling for generating multicarbon products is requisite. Herein, we first give a classification of catalysts involved in the photoconversion of CO2 to C2+ fuels. We summarize metallic oxides, metallic sulfides, MXenes, and metal-organic frameworks as catalysts for CO2 photoreduction to C2+ products, attributing their efficacy to the inherent dual active sites facilitating C-C coupling. In addition, we survey covalent organic frameworks, carbon nitrides, metal phosphides, and graphene as cocatalysts for CO2 photoreduction to C2+ products, owing to the incorporated dual active sites that induce C-C coupling. In the end, we provide a brief conclusion and an outlook on designing new photocatalysts, understanding the catalytic mechanisms, and considering the practical application requirements for photoconverting CO2 into multicarbon products.

Metal-Based Drug-DNA Interactions and Analytical Determination Methods.

DNA structure has many potential places where endogenous compounds and xenobiotics can bind. Therefore, xenobiotics bind along the sites of the nucleic acid with the aim of changing its structure, its genetic message, and, implicitly, its functions. Currently, there are several mechanisms known to be involved in DNA binding. These mechanisms are covalent and non-covalent interactions. The covalent interaction or metal base coordination is an irreversible binding and it is represented by an intra-/interstrand cross-link. The non-covalent interaction is generally a reversible binding and it is represented by intercalation between DNA base pairs, insertion, major and/or minor groove binding, and electrostatic interactions with the sugar phosphate DNA backbone. In the present review, we focus on the types of DNA-metal complex interactions (including some representative examples) and on presenting the methods currently used to study them.

Recent Progress on Covalent Organic Frameworks Supporting Metal Nanoparticles as Promising Materials for Nitrophenol Reduction

With the utilization of nitrophenols in manufacturing various materials and the expansion of industry, nitrophenols have emerged as water pollutants that pose significant risks to both humans and the environment. Therefore, it is imperative to convert nitrophenols into aminophenols, which are less toxic. This conversion process is achieved through the use of noble metal nanoparticles, such as gold, silver, copper, and palladium. The primary challenge with noble metal nanoparticles lies in their accumulation and deactivation, leading to a decrease in catalyst activity. Covalent organic frameworks (COFs) are materials characterized by a crystalline structure, good stability, and high porosity with active sites. These properties make them ideal substrates for noble metal nanoparticles, enhancing catalytic activity. This overview explores various articles that focus on the synthesis of catalysts containing noble metal nanoparticles attached to COFs as substrates to reduce nitrophenols to aminophenols.

Investigating coherent and semi-coherent interfacial structures and energetics in [formula omitted] interfaces: Theoretical insights into aluminum matrix composites bonding

Understanding the intricate interfacial structures and energetics between ceramics and aluminum is crucial for elucidating the mechanical properties of aluminum matrix composites (AMCs). However, previous theoretical simulations primarily focused on coherent interfaces, neglecting lattice constant variations on heterogeneous interfaces, which has led to discrepancies with experimentally observed semi-coherent interfaces. Here, using recently synthesized Al/Al3BC AMCs as a case study to systematically construct six semi-coherent interfacial models containing 383 to 588 atoms. These models are used to investigate the Al(11¯1)/Al3BC(0001) and Al(3¯11¯)/Al3BC(0001) structures and their associated energetics. Additionally, we examine 39 coherent interfaces for comparison. Work of adhesion and interfacial energy results reveal that the stable termination for semi-coherent interfaces is Al(B), which contrasts with AlC termination observed in coherent interfaces. Both Al(11¯1)/Al3BC(0001) and Al(3¯11¯)/Al3BC(0001) semi-coherent interfaces demonstrate higher stability but lower bonding strength compared to coherent interfaces. Bonding strength and stability of Al(B)-terminated semi-coherent interface in Al(3¯11¯)/Al3BC(0001) are lower than those in Al(11¯1)/Al3BC(0001). Electronic structure analysis indicates that AlC-terminated coherent interface exhibits greater charge transfer and stronger covalent metal bonds, while the Al(B)-terminated semi-coherent interface shows less charge transfer and more pronounced metallic bond characteristics. These computational insights provide valuable theoretical understanding of interfacial bonding mechanisms inherent in ceramic-reinforced AMCs.

Covalent organic frameworks and metal–organic frameworks for sustainable adsorptive removal/extraction of dirty dozen chemicals: A review

AbstractDirty dozen chemicals (DDCs) are a group of 12 extremely toxic chemicals that were recognized at the Stockholm convention in 2001 for their severe impact on the ecosystem and human health. Despite the embargo and restraint placed on DDCs usage, these chemicals continue to find their way into the ecosystem because they are still secretly or openly applied by many nations, especially in African regions. Moreover, DDCs can still be perceived where they have been employed previously before the Stockholm convention treaty due to their persistent profile. This study aimed to critically review original works directed toward the removal of various dirty dozen chemicals using covalent and metal–organic frameworks (COFs and MOFs). Specifically, in this study, various COFs/MOFs and their composites with remarkably tailored adsorptive profiles are evaluated for their adsorption efficiency for different DDCs. In addition, the effect of various operating parameters that are of importance to environmentalists and various stakeholders for optimization purposes was empirically discussed. This review also fills knowledge vacuums about the COF/MOF‐DDCs adsorption process, offers insights into their reusability potential, fundamental mechanism, isotherm, and kinetic modeling, and offers a framework for future studies. Findings from this study revealed that COF and MOF have high DDC removal capacity and reusability potential attributed to their admirable porosity and the existence of a plethora of oxygen‐rich functional groups that allow for better interactions with DDCs through chelation, halogen bonding, H‐bonding, and π‐π interactions and stacking. This points to the upscaling potential of this remediation technique. Future researchers need to direct more efforts to the use of density functional theory for mechanism interpretation, exploration of hybrid technology, cost analysis, scalability, isotherm, thermodynamics, adsorption, and desorption kinetic modeling.

Zintl Phase versus Covalent Metal: Chemical Bonding in Silicon Dumbbells of Ca5Si3 and CaSi3.

Silicon dumbbells constitute identifiable anionic molecular species in Zintl phases and so-called covalent metals holding units with homopolar bonding inside a metallic framework. Based on electron-precise Ca5Si3 and metallic CaSi3, the chemical bonding in Si2 units is investigated by computational quantum chemical methods considering the dual nature of the wave function. This concerted wave-vector and real space study substantiates that the Si2 dumbbells in Ca5Si3 can be referred to as molecular building units Si26- with additional metallic and ionic contributions in the solid. In the covalent metal CaSi3, however, the bonding within the dumbbells falls short of fulfilling the octet rule. As a result, antibonding states of the Si2 building units are depopulated and attend metallic interactions, simultaneously giving rise to stronger covalent Si-Si bonds.

Sn Nanoclusters Confined in COP‐Derived Carbon for Catalytic Oxygen Reduction Reaction

AbstractThe development of catalysts composed of single atoms is crucial for enhancing the performance of oxygen reduction reaction (ORR). However, the unsatisfactory intrinsic activity of these catalysts still poses a major challenge, limiting their overall effectiveness. One approach to addressing this challenge is the introduction of metal clusters, which can form a synergistic effect with the single atoms, ultimately improving their performance. In this study, core‐shell structured carbon polymer is constructed with Zn atoms and Sn nanoclusters by directly subjecting pyrolysis of the covalent organic polymer (COP) and metal organic framework (MOF) (COP@MOF). The thin COP shell serves a dual purpose: it prevents the collapse and aggregation of zeolitic imidazolate framework‐8 (ZIF‐8) and promotes the formation of mesopores, facilitating mass transport and enhancing the graphitization degree to improve conductivity. The resulting Sn‐COP@MOF800 exhibits promising catalytic performance in the ORR, demonstrating a half‐wave potential of 0.81 V and current density of 5.56 mA cm−2 in 0.1 m KOH, which is comparable to that of Pt/C. This study provides new ideas for exploring the application of metal single atoms and metal nanoclusters in ORR catalysis through synergistic effects.

Outstanding Lithium Storage Performance of a Copper‐Coordinated Metal‐Covalent Organic Framework as Anode Material for Lithium‐Ion Batteries

Metal‐covalent organic frameworks (MCOF) as a bridge between covalent organic framework (COF) and metal organic framework (MOF) possess the characteristics of open metal sites, structure stability, crystallinity, tunability as well as porosity, but still in its infancy. In this work, a covalent organic framework DT‐COF with a keto‐enamine structure synthesized from the condensation of 3,3′‐dihydroxybiphenyl diamine (DHBD) and triformylphloroglucinol (TFP) was coordinated with Cu2+ by a simple post‐modification method to a obtain a copper‐coordinated metal‐covalent organic framework of Cu‐DT COF. The isomerization from a keto‐enamine structure of DT‐COF to a enol‐imine structure of Cu‐DT COF is induced due to the coordination interaction of Cu2+. The structure change of Cu‐DT COF induces the change of the electron distribution in the Cu‐DT COF, which greatly promotes the activation and deep Li‐storage behavior of the COF skeleton. As anode material for lithium‐ion batteries (LIBs), Cu‐DT COF exhibits greatly improved electrochemical performance, retaining the specific capacities of 760 mAh g−1 after 200 cycles and 505 mAh g−1 after 500 cycles at a current density of 0.5 A g−1. The preliminary lithium storage mechanism studies indicate that Cu2+ is also involved in the lithium storage process. A possible mechanism for Cu‐DT COF was proposed on the basis of FT‐IR, XPS, EPR characterization and electrochemical analysis. This work enlightens a novel strategy to improve the energy storage performance of COF and promotes the application of COF and MCOF in LIBs.

Theoretical screening of corrole-based covalent organic framework metal single-atom catalysts for ORR and OER

Corrole-based covalent organic frameworks (COFs) are newly developing porous crystalline materials in the catalysis field due to their thermal stability, and ease of being functionalized by high-valent metal at the corrole center. In this work, based on the monolayer TPAPC-COF (m-TPAPC-COF), a series of stable metal corrole-based 2D monolayer SACs M1@TPAPC-COFs (M = Fe, Co, Ni, Cu, Ru, Rh, Os, Ir, Pt, Au) have been obtained by screening using density functional theory (DFT) calculations. As O2 can be adsorbed and activated on M1@TPAPC-COFs (M = Fe, Co, Ru, Rh, Os, Ir), we predicted two types of non-noble metal corrole-based COFs SACs, one is a bifunctional SAC Fe1@TPAPC-COF with high electrocatalytic activity for ORR/OER and the other is a Co1@TPAPC-COF with high electrocatalytic activity for OER, respectively. This work demonstrates that corrole-based COF is a promising 2D material for constructing high-performance SACs for the ORR and OER.

Core–shell MOF@COF composites for ultra-efficient selective recovery of Pd(II)

Developing efficient and selective recovery of Pd(II) adsorbents is crucial for addressing environmental pollution issues. Among them, covalent organic framework (COF) and metal organic framework (MOF) composites due to the multi-site functional groups are expected to exhibit excellent Pd(II) adsorption. However, the design and preparation of COF and MOF composite adsorbents for highly efficient adsorption of heavy metal Pd(II) still face many challenges. Herein, we constructed a series of novel core–shell structure UiO-66-NH2@TAP-COF (denoted as M@C) adsorbents (M@C-X, X = 1–5, representing different MOF doses) by Schiff base reaction and applied in the adsorption of Pd(II). The findings indicated that the M@C-3 exhibited ultra-high adsorption performance, reaching a capacity of 2134.1 mg/g, and displayed excellent selectivity, making it the best among similar materials. Experimental data and density functional theory (DFT) calculations revealed that the efficient and selective adsorption of Pd(II) is attributed to coordination interaction and strong electrostatic between Pd(II) and the abundant N and O groups in M@C. This work demonstrates the significant potential of the constructed core–shell M@C composites for the efficient and selective recovery of precious metal Pd(II).

Superhard and Superconducting Bilayer Borophene.

Two-dimensional superconductors, especially the covalent metals such as borophene, have received significant attention due to their new fundamental physics, as well as potential applications. Furthermore, the bilayer borophene has recently ignited interest due to its high stability and versatile properties. Here, the mechanical and superconducting properties of bilayer-δ6 borophene are explored by means of first-principles computations and anisotropic Migdal-Eliashberg analytics. We find that the coexistence of strong covalent bonds and delocalized metallic bonds endows this structure with remarkable mechanical properties (maximum 2D-Young's modulus of ~570 N/m) and superconductivity with a critical temperature of ~20 K. Moreover, the superconducting critical temperature of this structure can be further boosted to ~46 K by applied strain, which is the highest value known among all borophenes or two-dimensional elemental materials.

Time-series analysis of rhenium(I) organometallic covalent binding to a model protein for drug development.

Metal-based complexes with their unique chemical properties, including multiple oxidation states, radio-nuclear capabilities and various coordination geometries yield value as potential pharmaceuticals. Understanding the interactions between metals and biological systems will prove key for site-specific coordination of new metal-based lead compounds. This study merges the concepts of target coordination with fragment-based drug methodologies, supported by varying the anomalous scattering of rhenium along with infrared spectroscopy, and has identified rhenium metal sites bound covalently with two amino acid types within the model protein. A time-based series of lysozyme-rhenium-imidazole (HEWL-Re-Imi) crystals was analysed systematically over a span of 38 weeks. The main rhenium covalent coordination is observed at His15, Asp101 and Asp119. Weak (i.e. noncovalent) interactions are observed at other aspartic, asparagine, proline, tyrosine and tryptophan side chains. Detailed bond distance comparisons, including precision estimates, are reported, utilizing the diffraction precision index supplemented with small-molecule data from the Cambridge Structural Database. Key findings include changes in the protein structure induced at the rhenium metal binding site, not observed in similar metal-free structures. The binding sites are typically found along the solvent-channel-accessible protein surface. The three primary covalent metal binding sites are consistent throughout the time series, whereas binding to neighbouring amino acid residues changes through the time series. Co-crystallization was used, consistently yielding crystals four days after setup. After crystal formation, soaking of the compound into the crystal over 38 weeks is continued and explains these structural adjustments. It is the covalent bond stability at the three sites, their proximity to the solvent channel and the movement of residues to accommodate the metal that are important, and may prove useful for future radiopharmaceutical development including target modification.

Surging efficient PMS activation through a COF-MOF dual immobilized catalytic platform: Synergy of enhanced electron transfer and adsorption-PMS activation

In heterogeneous catalytic systems used for peroxymonosulfate (PMS) catalysis, the effectiveness of the catalyst and the leaching rate of metal ions have gained considerable attention. Taking inspiration from the advantages of combining covalent organic frameworks (COF) and metal–organic frameworks (MOF) to facilitate charge transfer and metal immobilization, this study proposes an alternative method through immobilizing the catalysts with MOF and COF coating. The synthesis of Co-Fe3O4@UiO-66@TpBD was carried out with a pre-synthesizing method, followed by COF coating through a Schiff-based reaction. The introduction of MOF has largely limited the metal leaching from 7.85 mg/L to 1.03 mg/L, and the subsequent introduction of COF has enhanced electron transfer and adsorption of PMS, as well as a further reduction in the metal leaching from 1.03 mg/L to 0.50 mg/L. Impressively, the dual immobilization strategy has guaranteed a more stable utility and the materials showed comparable performances even after 5 cycles. Moreover, singlet oxygen (1O2) is the dominant reactive oxygen species responsible for the degradation through electrophilic substitution of Acetaminophen (APAP).

A Covalent‐Metal Hybrid‐Link Organic Framework Spray for Portable and Instant Therapy of Deep‐Degree Burn

AbstractDeep burns lead to extensive damage to the dermal layer, necessitating a longer treatment duration than typical skin injuries. Such burn wounds become more susceptible to drug‐resistant bacterial infections, thereby complicating and prolonging the therapeutic process. In this study, a unique spray composed of covalent metal hybrid‐linked organic frameworks (HLOF) material is developed that effectively eradicates methicillin‐resistant Staphylococcus aureus (MRSA) within 20 min by disrupting MRSA's surface electrons, destroying its cell membrane structure, and ultimately causing its demise with an impressive antibacterial rate of 96.7%. This HLOF material exhibited exceptional biological activity and stability. During the wound recovery procedure, HLOF promoted the expression of Vascular endothelial growthfactor(VEGF) to stimulate angiogenesis while inhibiting the proinflammatory factor Tumor necrosis factor alpha (TNF‐α) expression to eliminate inflammation and further enhance wound repair. This study presents an innovative approach for achieving outstanding antibacterial properties and improved biocompatibility through modifications made to common metal organic frameworks (MOFs), thus expanding their potential applications.

Retracted: Topological Aspects of Certain Covalent Organic Frameworks and Metal Organic Frameworks

Retracted: Topological Aspects of Certain Covalent Organic Frameworks and Metal Organic Frameworks

Solvent control of dimensionality in titanium aryloxide coordination polymers prepared from 4,4′-bis(hydroxyphenyl)sulfide

The crystal and molecular structures of three covalent metal–organic network (CMON) materials synthesized from titanium (IV) isopropoxide and the Bisphenol-A analog 4,4′-bis(hydroxyphenyl)sulfide in three different solvents have been determined. The structures of the one-dimensional chain coordination polymer [trans-Ti(μ-O:O’-OC6H4SC6H4O)2(C5H5N)2]n (1) obtained from pyridine and the two-dimensional sheet coordination polymer {[Ti2(μ-O:O’-OC6H4SC6H4O)2(μ2O:κO’-OC6H4SC6H4O)2(C4H8O)2]∙(C4H8O)y}n (2) from tetrahydrofuran both contain octahedral titanium (IV) coordination geometries, whereas the doubly interpenetrated three-dimensional coordination network [Ti2(μ-O:O’-OC6H4SC6H4O)2(μ2O:κO′-OC6H4SC6H4O)2]n (3) synthesized from benzene contains trigonal bipyramidal titanium (IV). Each material has been characterized by single crystal and powder X-ray diffraction, elemental analysis, and by 1H NMR quench when it contains more than one organic component.

Highly Flexible and Self‐Standing Covalent Organic Framework–Metal–Organic Framework (COF–MOF) Composite Crystalline Porous Material (CPM) Membrane for Molecular Separation

AbstractCrystalline porous materials (CPMs), including covalent organic frameworks (COFs) and metal–organic frameworks (MOFs), are promising materials for advanced separation technologies. However, the challenge of transforming nanoscale CPMs into large‐area functional membranes hinders their application in the membrane separation process. Herein, a self‐standing pure COF (TpPa‐1) nanofiber membrane with high crystallinity, good flexibility, excellent mechanical properties, and scalability is prepared using an electrospinning process and polymer sacrificial template strategy. Subsequently, the COF nanofiber membrane is innovatively used to replace traditional inorganic discs, metal meshes, and polymer membranes as porous supports, and the COF–MOF composite CPM membrane is prepared through the tailorable and confined growth of zeolite imidazolium salt frame‐8 (ZIF‐8) on the surface of the COF membrane and in the gaps of the COF nanofibers. The COF–MOF composite membrane exhibits excellent permeability and significantly enhances separation selectivity for organic dyes. Moreover, MOF and COF form an interpenetrating network structure, and their similar chemical properties improve the interfacial stability between the two phases, giving the COF–MOF composite membrane good long‐term separation performance. This is the first self‐standing composite CPM membrane with excellent molecular sieving performance, which provides new insights into the design of high‐performance and robust composite membranes.

Density functional theory investigations on the mechanisms of homogeneous Sm complex catalyzed CO[formula omitted] cycloaddition with epoxides

Converting excess CO2 into chemically valuable products is a promising routine for sustainable development. Catalyzing epoxides and CO2 cycloaddition reactions homogeneously with rare-earth compounds is an emerging approach. The reaction efficiency can be understood by mechanism study. In this work, we report a detailed density functional theory investigation on a well-designed experimental Sm catalyst. We calibrate the ωB97XD exchange–correlation functional as the best candidate functional for this specific catalytic system. The energetic span of catalytic cycle is approximately 25 kcal mol−1. The rate-determining transition state is the one for ring-closure to generate the product. Two competing paths are revealed. Through both ionic and covalent metal–ligand interactions, the lowering of the epoxide substrate ring-opening step barrier is significant compared with the Sm compound free case. This work demonstrate the values for utilizing modern density functional theory to complement the understandings on the homogeneous rare-earth catalytic processes.