Metal Ligand Research Articles

Bimetallic zeolitic imidazolate frameworks Co/ZIF-8 crystals as carbonic anhydrase-mimicking nanozyme

Zeolitic imidazolate frameworks (ZIFs) materials are known for their excellent stability and their ability to provide an adjustable, controllable structure. The precise assembly of metal nodes and ligands in ZIFs enables them to possess active centers that closely resemble those found in natural enzymes. Building upon this, the objective of this study was to mimic the catalytic active center of natural carbonic anhydrase (CA) by employing defect coordination on the outer surface of bimetallic Co/ZIF-8 crystals. The synthesis process was meticulously controlled through the introduction of cobalt ions, resulting in the creation of a biomimetic CA with remarkable stability and catalytic prowess. The bimetallic Co/ZIF-8 nanozyme exhibited catalytic properties similar to those of natural enzymes. It efficiently facilitated the CO2 hydration reaction and demonstrated the ability to catalyze the reverse reaction. The esterase activity of all Co/ZIF-8 nanozymes was higher than that of the original ZIF-8 at room temperature. Notably, these nanozymes exhibited an impressive maximum esterase activity of 3.77 U/mg at 80 ℃, which surpassed the levels observed in natural CA. This enhancement can be attributed to the boosted catalytic activity of Co/ZIF-8, stemming from the introduction of metal ion doping, which increased the potential difference between bimetallic active centers and facilitated efficient charge transfer. Furthermore, thanks to the unique activation mechanism inherent in the structure of Co/ZIF-8, the esterase activity not only remained unaffected after 24 h of hydrothermal treatment, but also experienced a significant enhancement. This article represents a valuable breakthrough in the regulation and modification of ZIF-8, resulting in the fabrication of an efficient bimetallic Co/ZIF-8 nanozyme for CA-mimicking. These findings hold immense significance for further research and development in the realm of industrial CO2 capture catalysts.

Catalysis with Two-Dimensional Metal-Organic Frameworks: Synthesis, Characterization, and Modulation.

The demand for the exploration of highly active and durable electro/photocatalysts for renewable energy conversion has experienced a significant surge in recent years. Metal-organic frameworks (MOFs), by virtue of their high porosity, large surface area, and modifiable metal centers and ligands, have gained tremendous attention and demonstrated promising prospects in electro/photocatalytic energy conversion. However, the small pore sizes and limited active sites of 3D bulk MOFs hinder their wide applications. Developing 2D MOFs with tailored thickness and large aspect ratio has emerged as an effective approach to meet these challenges, offering a high density of exposed active sites, better mechanical stability, better assembly flexibility, and shorter charge and photoexcited state transfer distances compared to 3D bulk MOFs. In this review, synthesis methods for the most up-to-date 2D MOFs are first overviewed, highlighting their respective advantages and disadvantages. Subsequently, a systematic analysis is conducted on the identification and electronic structure modulation of catalytic active sites in 2D MOFs and their applications in renewable energy conversion, including electrocatalysis and photocatalysis (electro/photocatalysis). Lastly, the current challenges and future development of 2D MOFs toward highly efficient and practical electro/photocatalysis are proposed.

Metal–Ligand Cooperative Catalytic Coupling of Terminal Alkynes and Carboxylic Acids for the Stereoselective Synthesis of Dienyl Esters

Metal–Ligand Cooperative Catalytic Coupling of Terminal Alkynes and Carboxylic Acids for the Stereoselective Synthesis of Dienyl Esters

Synthesis of a novel triptycene-derived protected dithiolene ligand precursor for tri-nuclear mixed ligand metal dithiolene complexes

Abstract We synthesized a novel triptycene analogue, 3,3′,3″,3″′,3″″,3″″′-((triptycene-2,3,6,7,14,15-hexayl)hexakis(sulfanediyl))hexapropanenitrile (3), which served as a valuable precursor for the triptycene-derived tris-bidentate bridging dithiolene ligand, triptycene-2,3,6,7,14,15-hexakis(thiolate) (4), following the removal of the cyanoethyl moiety protection group. We determined the molecular and crystal structures of compound 3 and confirmed its capacity to yield compound 4. By reacting 3 with [NiCl2(BPY)] and [PtCl2(BPY)] (BPY: 2,2′-bipyridine) in methanol, we obtained crude samples of [Ni3(4)(BPY)3] and [Pt3(4)(BPY)3], respectively.

DFT Exploration of Metal Ion-Ligand Binding: Toward Rational Design of Chelating Agent in Semiconductor Manufacturing.

Chelating agents are commonly employed in microelectronic processes to prevent metal ion contamination. The ligand fragments of a chelating agent largely determine its binding strength to metal ions. Identification of ligands with suitable characteristics will facilitate the design of chelating agents to enhance the capture and removal of metal ions from the substrate in microelectronic processes. This study employed quantum chemical calculations to simulate the binding process between eleven ligands and the hydrated forms of Ni2+, Cu2+, Al3+, and Fe3+ ions. The binding strength between the metal ions and ligands was quantified using binding energy and binding enthalpy. Additionally, we explored the binding interaction mechanisms and explained the differences in binding abilities of the eleven ligands using frontier molecular orbitals, nucleophilic indexes, electrostatic potentials, and energy decomposition calculations based on molecular force fields. Based on our computational results, promising chelating agent structures are proposed, aiming to guide the design of new chelating agents to address metal ion contamination issues in integrated circuit processes.

A novel µ-carbido hetero-binuclear iron-ruthenium heteroleptic complex on macrocyclic platforms with efficient oxidative activity

Bimetallic µ-bridged complexes supported by macrocycles are worth addressing due to their excellent stability, rich redox chemistry and suitability in catalysis. This paper for the first-time reports on the synthesis and redox properties of an unexplored heterometallic μ-carbido-dimer derivative bearing iron-porphyrin and ruthenium-phthalocyanine parts and a FeIV = C = RuIV unit. The compound is identified by UV–visible, IR, EPR, MALDI TOF, electrochemistry techniques and DFT calculations. The redox activity of the compound toward H2O2, tBuOOH is examined. The results indicate that under oxidation conditions in dichloromethane, benzene and acetonitrile, the initial complex evolves rapidly via oxidation steps forming intermediates which are competent in β-carotene and methylene blue oxidation at room temperature. The site oxidation accessibility of the initial compound and the nature of high-charged intermediate species are established to depend on the solvent polarity and axial ligands. The findings contribute to a deeper understanding of the significant role of reaction conditions as well as the mixed macrocyclic ligand environment and metal nature in controlling the oxidizing capability and thus can aid the development of new more active and durable catalysts.

Reinforced, self-healing, recyclable rubber materials based on multiple dynamic bond constructs crosslinked with chemical groups

Enhancing the mechanical attributes of traditional rubber, while simultaneously imparting superior self-healing and recyclability, remains a formidable task within the realm of polymer science. In this study, we introduce, for the inaugural time, the utilization of metal–ligand interactions to amalgamate chemical cross-linking sites within a styrene-butadiene rubber matrix. This approach facilitates the creation of a fortified, self-healing, and recyclable rubber composite, interconnected by an array of dynamic bonds within a singular chemical entity. This chemical assembly engenders a microphase-separated architecture that exhibits reinforcement and resistance to creep. In addition, the presence of reversible oxime-carbamate and metal–ligand bonds bestow the rubber composites with remarkable self-healing and recyclability. Notably, the self-healing efficiency reached an impressive 87%, while the recyclability retention hovered between 85 and 91% (in terms of tensile strength) post multiple reprocesses. This research paves a novel avenue for the fabrication of rubber composites that are robust, self-healing, and recyclable.

In-situ interfacial synthesis of metal-organic framework/polyamide thin-film nanocomposite membranes with elevated nanofiltration performances

Incorporation of nanomaterials in the thin film polyamide (PA) is instrumental to overcome the intrinsic trade-off between permeability and selectivity of polymeric nanofiltration (NF) membranes. However, the universal method of preparing thin film nanocomposite (TFN) NF membranes by directly combining the synthesized nanofillers into PA faces a stubborn issue of poor compatibility for filler-PA, which is adverse to membrane separation. Herein, an in-situ interfacial synthetic strategy was induced in interfacial polymerization (IP) process to prepare TFN membranes with metal-organic framework (MOF) in the PA selective layer. The metal ions and ligands constituting the MOF were dissolved individually in the aqueous and organic phases. MOF particles and the PA layer were simultaneously formed at the liquid-liquid interface. The increment of cross-linking degree confirmed the good compatibility between MOF and PA. Compared with the thin film composite (TFC) membrane, the acquired TFN-1 membrane exhibited 100 % enhancement of pure water permeance (from 10.0 to 20.6 L m−2 h−1 bar−1) due to the markedly reduced thin film thickness. Meanwhile, the rejection of rhodamine B (99.9 %) and Na2SO4 (96.5 %) for TFN membrane were higher than those of TFC membrane (97.2 % and 95.6 %), respectively. The TFN membrane exhibited long-term stability without deterioration. The in-situ interfacial synthesis of the MOF/PA layer provides a new avenue in TFN membrane fabrications.

Fire‐retardant and high‐strength polymeric materials enabled by supramolecular aggregates

AbstractHigh‐performance polymers have proliferated in modern society across a variety of industries because of their low density, good chemical stability, and superior mechanical properties. However, while polymers are widely applied, frequent fire disasters induced by their intrinsic flammability have caused massive impacts on human beings, the economy, and the environment. Supramolecular chemistry has recently been intensively researched to provide fire retardancy for polymers via the physical barrier and char‐catalyzing effects of supramolecular aggregates. In parallel, the noncovalent interactions between supramolecular and polymer chains, such as hydrogen bonding, π–π interactions, metal–ligand coordination, and synergistic interactions, can endow the matrix with enhanced mechanical strength. This makes it possible to integrate physical–chemical properties and noncovalent interactions into one supramolecular aggregate‐based high‐performance polymeric system on demand. However, fulfilling these promises needs more research. Here, we provide an overview of the latest research advances of fire‐retardant and high‐strength polymer materials based on supramolecular structures and interactions of aggregates. This work reviews their conceptual design, characterization, modification principles, performances, applications, and mechanisms. Finally, development challenges and perspectives on future research are also discussed.

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.

Open-cage fullerenes as ligands for metals.

The remarkable structures of open-cage fullerenes with functionalization on the outer surface and an accessible inner void make them interesting ligands for reactions with metal complexes. The behaviors of open-cage fullerenes in reactions with various metal complexes are examined and compared to the corresponding reactions with intact fullerenes. The structural results from X-ray diffraction are emphasized. Open-cage fullerenes frequently undergo unanticipated structural changes such as carbon-carbon bond cleavage upon reactions with metal complexes. Much more remains to be learned about the possibility of inserting metal ions larger than Li+ into the interior void of these open-cage fullerenes and about the effects of redox reactions on metal complexes of open-cage fullerenes.

Pathway control in metallosupramolecular polymerization of a monoalkynylplatinum(ii) terpyridine complex through competitive complex formation.

Understanding the pathway complexity of supramolecular polymerization in biomimetic systems has been a challenging issue due to its importance in the development of rationally controlled materials and insight into self-assembly in nature. We herein report a kinetic trapping strategy as a new methodology on how to control the pathway of metallosupramolecular polymerization by employing secondary metal ions and/or ligands which form competitive complex species. For this, we proposed monoalkynylplatinum(ii) metalloligand (Pt-L1) derived from a bis(amideterpyridine) receptor with one unoccupied terpyridyl terminal as a coordination site for the secondary metal ion (Ag+ or Fe2+). The inherent pathway complexity intrinsic to the Pt-L1-anchored supramolecular polymerization has been modulated through the incorporation of Ag+ or Fe2+. During the supramolecular polymerization of Pt-L1 in the presence of Ag+ and Fe2+, the added secondary ligand bpy (4,4'-dimethyl-2,2'-bipyridine) or DA18C6 (1,14-diaza-18-crown-6) form complexes as kinetic species, thereby inhibiting spontaneous polymerizations. The supramolecular polymer (SP-I), with a spherical structure composed of Pt-L1 in the absence of metal ions as a kinetic product, did not transform into the thermodynamic product, namely supramolecular polymer (SP-III) with a left-handed fiber structure, due to a high energy barrier. However, the supramolecular polymer (SP-II) with a left-handed fiber structure, which was formed by Pt-L1 in the presence of AgNO3, converted to SP-III upon the addition of NaCl. Additionally, SP-II transformed into supramolecular polymer (SP-IV) upon the addition of Fe(BF4)2, through an on-pathway process. Both the morphological and emissive characteristics of the resulting supramolecular polymers can be fine-tuned via the Pt⋯Pt or Ag⋯Ag interactions as well as through the changes of the coordination geometry depending on the existing Ag+ or Fe2+ ions. The present results have important implications in expanding the scope of pathway complexity to produce a variety of products via kinetically controlled processes involving secondary metal ions and ligands.

All-in-one Rh(iii)-covalent organic framework for sustainable and regioselective C(sp2)–H bond functionalization

RhCOF-SYNU-1 serves as a transition-metal catalyst, photocatalyst, and metal ligand, enabling regioselective C(sp2)–H bond functionalization and offering a sustainable approach for Rh(iii) catalysis.

Modelling ligand exchange in metal complexes with machine learning potentials.

Metal ions are irreplaceable in many areas of chemistry, including (bio)catalysis, self-assembly and charge transfer processes. Yet, modelling their structural and dynamic properties in diverse chemical environments remains challenging for both force fields and ab initio methods. Here, we introduce a strategy to train machine learning potentials (MLPs) using MACE, an equivariant message-passing neural network, for metal-ligand complexes in explicit solvents. We explore the structure and ligand exchange dynamics of Mg2+ in water and Pd2+ in acetonitrile as two illustrative model systems. The trained potentials accurately reproduce equilibrium structures of the complexes in solution, including different coordination numbers and geometries. Furthermore, the MLPs can model structural changes between metal ions and ligands in the first coordination shell, and reproduce the free energy barriers for the corresponding ligand exchange. The strategy presented here provides a computationally efficient approach to model metal ions in solution, paving the way for modelling larger and more diverse metal complexes relevant to biomolecules and supramolecular assemblies.

Novel terephthalaldehyde bis(thiosemicarbazone) Schiff base ligand and its transition metal complexes as antibacterial Agents: Synthesis, characterization and biological investigations

The synthesis and structural characterization of mixed ligand metal complexes from terephthalaldehyde bis(thiosemicarbazone) (TPTSC) (L1) and alanine (L2) by using ultrasonication are reported. The ligand and their transition metal complexes were characterized on the basis of their elemental, FT-IR, magnetic moment, molar conductance, mass spectra, and SEM analysis. The mixed ligand complexes are in the ratio 2:1:2 [M:L1:L2] ratio as found from the elemental analyses and found to have the formulae [M2L1(L2)2].nH2O where M = Co(II), Ni(II), Cu(II), Cd(II) and Zn(II), L1 = TPTSC and L2 = alanine. The molar conductance data show that complexes are non-electrolytes. FT-IR spectra show that the Schiff base is coordinated to the metal ions in a bidentate manner with N and S donor sites of the terephthalaldehyde bis(thiosemicarbazone) and second ligand alanine coordinated to the metal ions via its N and O of amino acid. The geometrical structure of these complexes is found to be tetrahedral. The antimicrobial activity of the synthesized Schiff base ligand and mixed-ligand metal complexes have been screened against gram-positive and gram-negative bacteria and two fungi species were tested. Mixed ligand complexes exhibited significant antibacterial activity against Klebsiella Pneumoniae, Salmonella typhi, Enterococcus Faecalis, Staphylococcus aureus, Escherichia coli and the fungi Aspergillus flavus and Aspergillus niger. Further, these compounds have been screened for their anticancer activity using Human Breast Cancer Cell Line MDA-MB-231.

CHITOSAN-SUPPORTED MERCURY(II) ACETATE AS A CATALYST FOR TRANSVINYLATION REACTIONS OF AZOLES

The application of homogeneous catalysts - transition metal complexes - on organic polymers is of a great interest among researchers. Heterogeneous catalysts often have a long life span and are easy to separate from the reactants and reaction products, and they can also be reused. A homogeneous catalyst on a heterogeneous support acts as if it were in solution, but simultaneously it is a separate stationary phase. In this study we tried to use chitosan as a carrier for metal ions (particularly mercury(II), knowing in advance that chitosan is a good ligand for transition metals). Interest in chitosan is associated with their unique physiological and environmental properties, such as biocompatibility, biodegradation, and chelating ability. Here, an efficient and easy method of vinylation of azoles in the presence of chitosan-supported mercury(II) acetate heterogenous catalytic system is reported. As a result, several products were synthesized in high yields. The developed procedure is easy to perform, requires less amount of catalyst, shortens reaction time, excludes the formation of side products, and provides higher selective yields of vinylated products, reduces water contamination with mercury salts. Furthermore, it is possible to recover the catalyst from the reaction mixture and recycle this catalytic system more than four times.

Synthesis of enantiopure 1,2,3-triazolylidene-type mesoionic carbene (MIC) conjugate acids featuring a rigid bicyclic scaffold

Chiral NHCs have found numerous applications as ligands for transition metals and in their own right for asymmetric catalysis. We report a synthetic route from l-malic acid to enantiopure 1,2,3-triazoliums with the chiral center in a fused ring.

Mitochondria-targeted neutral and cationic iridium(III) anticancer complexes chelating simple hybrid sp2-N/sp3-N donor ligands.

Most platinum group-based cyclometalated neutral and cationic anticancer complexes with the general formula [(C^N)2Ir(XY)]0/+ (neutral complex: XY = bidentate anionic ligand; cationic complex: XY = bidentate neutral ligand) are notable owing to their intrinsic luminescence properties, good cell permeability, interaction with some biomolecular targets and unique mechanisms of action (MoAs). We herein synthesized a series of neutral and cationic amine-imine cyclometalated iridium(III) complexes using Schiff base ligands with sp2-N/sp3-N N^NH2 chelating donors. The cyclometalated iridium(III) complexes were identified by various techniques. They were stable in aqueous media, displayed moderate fluorescence and exhibited affinity toward bovine serum albumin (BSA). The complexes demonstrated promising cytotoxicity against lung cancer A549 cells, cisplatin-resistant lung cancer A549/DDP cells, cervical carcinoma HeLa cells and human liver carcinoma HepG2 cells, with IC50 values ranging from 9.98 to 19.63 μM. Unfortunately, these complexes had a low selectivity (selectivity index: 1.62-1.98) towards A549 cells and BEAS-2B normal cells. The charge pattern of the metal center (neutral or cationic) and ligand substituents showed little influence on the cytotoxicity and selectivity of these complexes. The study revealed that these complexes could target mitochondria, cause depolarization of the mitochondrial membrane, and trigger the production of intracellular ROS. Additionally, the complexes were observed to induce late apoptosis and perturb the cell cycle in the G2/M or S phase in A549 cells. Based on these results, it appears that the anticancer efficacy of these complexes was predominantly attributed to the redox mechanism.

Metal-organic framework (MOF)-based materials for pyroptosis-mediated cancer therapy.

Pyroptosis is regarded as a promising strategy to modulate tumor immune microenvironments for anticancer therapy. Although pyroptosis inducers have been extensively explored in the biomedical field, their drug resistance, off-targeting capacity, and adverse effects do not fulfill the growing demands of therapy. Nowadays, metal-organic frameworks (MOFs) with unique structures and facile synthesis/functionalization characteristics have shown great potential in anticancer therapy. The flexible choices of metal ions and ligands endow MOFs with inherent anti-cancer efficiency, whereas the porous structures in MOFs make them ideal vehicles for delivering various chemodrug-based pyroptosis inducers. In this review, we provide the latest advances in MOF-based materials to evoke pyroptosis and give a brief but comprehensive review of the different types of MOFs for pyroptosis-mediated cancer therapy. Finally, we also discuss the current challenges of MOF-based pyroptosis inducers and their future prospects in this field.

A new era of LMCT: leveraging ligand-to-metal charge transfer excited states for photochemical reactions.

Ligand-to-metal charge transfer (LMCT) excited states are capable of undergoing a wide array of photochemical reactions, yet receive minimal attention compared to other charge transfer excited states. This work provides general criteria for designing transition metal complexes that exhibit low energy LMCT excited states and routes to drive photochemistry from these excited states. General design principles regarding metal identity, oxidation state, geometry, and ligand sets are summarized. Fundamental photoreactions from these states including visible light-induced homolysis, excited state electron transfer, and other photoinduced chemical transformations are discussed and key design principles for enabling these photochemical reactions are further highlighted. Guided by these fundamentals, this review outlines critical considerations for the future design and application of coordination complexes with LMCT excited states.