Variety Of Organic Ligands Research Articles

Review on the Catalytic Significance of Zr‐Based Metal‐Organic Frameworks as Potential Catalyst for Various Organic Transformations

AbstractWithin the extensive array of metal‐organic frameworks (MOFs), Zr‐based MOFs stand out as particularly promising materials due to their diverse structures, exceptional stability, and intriguing properties. These MOFs are currently in the early stages of development, but noteworthy strides have been achieved in recent years. This overview focuses on the progress in Zr‐MOFs since 2012, covering design, synthesis, and applications in various reactions such as C−H activation, oxidation, C−C, and C−N coupling approaches. Different Zr‐MOF structural variants are explained in terms of Zr‐based secondary building units and a variety of organic ligands. The review highlights the roles that Zr‐MOFs play in catalysis by highlighting their uses as porous carriers, molecule adsorption, and separation. It is anticipated that this kind of concentrated review on Zr‐MOFs would offer important direction for next studies investigating MOFs for catalytic applications.

Improving curcumin bactericidal potential against multi-drug resistant bacteria via its loading in polydopamine coated zinc-based metal–organic frameworks

Multi-drug resistant (MDR) bactearial strains have posed serious health issues, thus leading to a significant increase in mortality, morbidity, and the expensive treatment of infections. Metal-organic frameworks (MOFs), comprising metal ions and a variety of organic ligands, have been employed as an effective drug deliveryy vehicle due to their low toxicity, biodegradability, higher structural integrity and diverse surface functionalities. Polydopamine (PDA) is a versatile biocompatible polymer with several interesting properties, including the ability to adhere to biological surfaces. As a result, modifying drug delivery vehicles with PDA has the potential to improve their antimicrobial properties. This work describes the preparation of PDA-coated Zn-MOFs for improving curcumin’s antibacterial properties against S. aureus and E. coli. Powder X-ray diffraction (P-XRD), FT-IR, scanning electron microscopy (SEM), and DLS were utilized to characterize PDA-coated Zn-MOFs. The curcumin loading and in vitro release of the prepared MOFs were also examined. Finally, the MOFs were tested for bactericidal ability against E. coli and S. aureus using an anti-bacterial assay and surface morphological analysis. Smaller size MOFs were capable of loading and releasing curcumin. The findings showed that as curcumin was encapsulated into PDA-coated MOFs, its bactericidal potential was significantly enhanced, and the findings were further supported by SEM which indicated the complete morphological distortion of the bacteria after treatment with PDA-Cur-Zn-MOFs. These studies clearly indicate that the PDA-Cur-Zn-MOFs developed in this study are extremely promising for long-term release of drugs to treat a wide range of microbial infections.

138 Analytical Methods for Organometallic Chelation Testing

Abstract Chelated minerals have increasingly captured the attention of scientists, manufacturers, and consumers in nutritional markets during the past five decades, due to their enhanced bioavailability compared to traditional ionic metal compounds. A wide variety of organic ligands bind to metal ions to form complexes that are generally referred to as chelates, including amino acids, peptides, proteins and carboxylic acids. Chemical reactions used to synthesize mineral chelates are affected by a number of factors that can alter the extent of chelation in manufactured products, such as pH, temperature, concentration, solvation, competing ions and ligands, and other variables. Qualitative and quantitative determination of chelation can be a daunting challenge, especially for dilute micronutrient minerals in complex matrices. Measuring chelation between metals and their ligands specifically focuses on the attractive forces between them. Analytical methods to determine the extent of chelation rely on a wide array of spectroscopic and electrochemical techniques. Very few standard methods of analysis exist to quantitatively measure the extent of chelation in nutritional products. A variety of these methods will be reviewed and compared for their potential use as standard methods of analysis.

Miscible-Solvent-Assisted Two-Phase Synthesis of Monolayer-Ligand-Protected Metal Nanoclusters with Various Sizes.

Effective yet versatile synthetic strategies for size-tunable metal nanoclusters (NCs) are scarce. This has hampered the development of this unique class of nanomaterials. Here, a general protocol is reported for the synthesis of high-quality metal NCs protected by a variety of organic ligands (e.g., selenolate, thiolate, and phosphine) based on a miscible-solvent-assisted phase transfer between water and organic solution. This method is demonstrated to be facile, rapid (≤3 h), scalable (gram-scale), and versatile. The size of the selenolated and thiolated Au NCs can be tuned from Au10 to Au61 by simply varying the miscible solvent in proportions and types. The advantages of this method, such as quick phase separation and no need for purification treatment, enable real-time monitoring of metal NC growth within the NaBH4 reduction system. The results show that the size of Au NCs gradually increases with increasing valence electron count by a stepwise 2x e- hopping mechanism (x = 0-5), i.e., 0 e- → 2 e- → 4 e- → 8 e- → 18 e- → 22 e- → 32 e- .

Probing the DOM-mediated photodegradation of methylmercury by using organic ligands with different molecular structures as the DOM model

Photodegradation is the main depletion pathway for methylmercury (MeHg) in surface water. The formation of MeHg-dissolved organic matter (DOM) complexes has been found to be a key step in MeHg photodegradation. However, the major functional groups involved in the DOM-mediated process have yet to be clearly resolved. In this work, we systematically investigated the effects of DOM molecular structures on MeHg photodegradation by using a variety of organic ligands with different functional groups (e.g., thiosalicylate, thiophenol, and thioaniline). The results showed that thiol and phenyl groups may be the major functional groups governing DOM-mediated MeHg photodegradation, with photodegradation rates also dependent on the type (carboxyl, hydroxyl, and amino group) and position (ortho-, meta-, and para-) of other chemical substituents. The addition of “non-photochemically active” thiol ligands (e.g., mercaptoethanol and dithiothreitol) and high concentrations of Cl− can significantly inhibit the o-thiosalicylate-induced MeHg photodegradation, indicating that complexation of MeHg with these ligands is necessary for MeHg photodegradation. Sparging with O2 had a negligible effect on MeHg photodegradation, while sparging with N2 significantly enhanced MeHg photodegradation. This finding suggests that MeHg photodegradation may be a reductive process, which was further supported by identification of the degradation products of MeHg. A possible protonolysis mechanism of MeHg photodegradation in the presence of o-thiosalicylate was then proposed based on the findings of this study.

Manganese and Iron Catalysts in Alkyd Paints and Coatings

Many paint, ink and coating formulations contain alkyd-based resins which cure via autoxidation mechanisms. Whilst cobalt-soaps have been used for many decades, there is a continuing and accelerating desire by paint companies to develop alternatives for the cobalt soaps, due to likely classification as carcinogens under the REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) legislation. Alternative driers, for example manganese and iron soaps, have been applied for this purpose. However, relatively poor curing capabilities make it necessary to increase the level of metal salts to such a level that often coloring of the paint formulation occurs. More recent developments include the application of manganese and iron complexes with a variety of organic ligands. This review will discuss the chemistry of alkyd resin curing, the applications and reactions of cobalt-soaps as curing agents, and, subsequently, the paint drying aspects and mechanisms of (model) alkyd curing using manganese and iron catalysts.

The preparation of metal-organic frameworks and their biomedical application.

The development of a safe and targetable drug carrier is a major challenge. An efficient delivery system should protect cargo from degradation and cleanup, and control of drug release in the target site. Metal–organic frameworks (MOFs), consisting of metal ions and a variety of organic ligands, have been applied for drug delivery due to their distinct structure. In this review, we summarized the synthesis strategies of MOFs, especially emphasizing the methods of pore creation in frameworks, which were based on recent literatures. Subsequently, the controlled size, biocompatibility, drug releasing performances, and imaging of MOFs were discussed, which would pave the road for the application in drug-delivery systems.

Electrocatalytic Activity of Organically Functionalized Silver Nanoparticles in Oxygen Reduction

Silver nanoparticles capped by a variety of organic ligands (i.e., 1-hexanethiol, 1-octyne, and 4-trifluoromethylphenyl fragments) were synthesized by a chemical reduction route, with the resulting nanoparticles denoted as AgSC6, AgHC8, and AgPhCF3, respectively. The nanoparticle structures were characterized by using a variety of techniques including NMR, UV-vis, infrared, thermogravimetric analysis, and X-ray photoelectron spectroscopies, high-resolution transmission electron microscopy, and electrochemical methods; and their electrocatalytic activities in oxygen reduction in alkaline media were evaluated and compared within the context of metal-ligand interfacial bonding interactions by using “bare” Ag nanoparticles supported on carbon black (Ag/C) as the benchmark materials. The results demonstrated that the electrocatalytic activity increased in the order of AgSC6 < Ag/C < AgHC8 < AgPhCF3. Of these, the activity of the AgSC6 nanoparticles was even lower than that of Ag/C, whereas the AgPhCF3 nanoparticles exhibited a specific activity that was about 13 times that of Ag/C and an onset potential that was ca. 200 mV more positive than that of Ag/C. The observed discrepancy of the nanoparticle electrocatalytic performance was accounted for by the deliberate manipulation of the nanoparticle electronic energy by the metal-ligand interfacial bonding interactions that dictated the adsorption of oxygen and reaction intermediates and hence the electron-transfer dynamics of oxygen reduction.

Comprehensive study of the luminescent properties and lifetimes of Eu3+ and Tb3+ chelated with various ligands in aqueous solutions: influence of the synergic agent, the surfactant and the energy level of the ligand triplet

The formation and the properties of luminescent complexes of europium and terbium with a variety of organic ligands have been investigated in aqueous solutions. The ligands used include model compounds such as thenoyltrifluoroacetone and pyridine-2,6-dicarboxylic acid and organic analytes of biological or pharmaceutical interest. It is shown that the formation and the luminescent properties of these complexes depend at first on several parameters including the pH and the buffer, the synergic agent and the surfactant. In neutral solutions, trioctylphosphine oxide in the presence of Triton X-100 may act as a co-ligand to promote complex formation and protect the complex from radiationless deactivation processes. Working in slightly alkaline solutions in the presence of EDTA and hexadecyltrimethylammonium chloride may induce the deprotonation of a second coordinating group and favour the formation of a new complex with stronger luminescent properties. In both cases, the luminescence lifetimes are then ultimately related to the energy gap between the ligand triplet and the resonance level of the ion and to the number of water molecules coordinated to the lanthanide ion.

Inorganic-organic hybrids derived from oxovanadium sulfate motifs: synthesis and characterization of [VIVO(mu 3-SO4)(2,2'-bpy)]infinity.

The hydrothermal reaction of V2O5, V2O3, 2,2'-bpy and Na2SO4 in dilute sulfuric acid yields a novel hybrid, [VIVO(mu 3-SO4)(2,2'-bpy)]infinity, which demonstrates the potential of constructing a new class of robust composite solids composed of a (V/O/SO4)-based framework decorated with organic functionalities by combining appropriate vanadyl sulfate motifs with a variety of organic ligands.

Synthetic and structural developments in hetero-s-block-metal chemistry: new ring-laddering, ring-stacking and other architectures

Hetero-alkali metal organic compounds are of interest because they can exhibit superior reactivity to conventional organolithium reagents. Structurally well-defined mixed lithium–sodium and mixed lithium–sodium–potassium compositions, based on a variety of organic ligands, are surveyed here. A complicated assortment of architectures with lithium-rich, sodium-rich, or equimolar metal stoichiometries is revealed. These structures are analysed with respect to the ‘ring-laddering’ and ‘ring-stacking’ concepts used previously in the rationalisation of organolithium structures. Important homometallic structures, which have appeared since these concepts were reviewed, are also included. Finally, an intriguing new class of mixed lithium–magnesium amide, based around an oxo or peroxo core, is described.

Reactivity of an Arene Cobalt Triple Decker Complex Towards Various Ligands. Facile Arene Displacement in [Bis{( η5-pentamethylcyclopentadienyl)cobalt}-μ-{η4: η4-toluene}

The triple decker complex [{(η5-Cp*)Co}2-μ-{η4: η4-toluene}] 1b exhibits an unusual reactivity towards a variety of organic ligands, 1b reacts with CO, ethene, butadiene, H2, Al2O3, hexafluorobenzene, 1.5 Cod, 2-butyne, phenanthrene, naphthalene and the dinuclear Ni cluster [{(η5-Cp)NiP(C2H5)3}2] to form mainly mononuclear organocobalt complexes. Reaction of 1b with NO and the diazoalkanes di-t-butyl-diazomethane and 2-diazo-1,1′,3,3′-tetramethylcyclohexane results in the formation of the dinuclear complexes [{(η5-Cp*)CoNO}2], [{(η5-Cp*)(di-t-butyl-diazomethane)Co}2] and [{(η5-Cp*)(2-diazo-1,1′,3,3′-tetramethylcyclohexane) Co}2], respectively. In the reaction of 1b with elemental sulfur the formation of a tetranuclear Co-sulfide cluster is observed. In the majority of the reactions studied, l b looses its toluene ligand already at room temperature indicating an unusual high and hitherto unprecedented reactivity of an arene triple decker complex.

Rare earth element complexation by PO 43− ions in aqueous solution

Complexation of trivalent rare earths by PO 4 3− ions has been assessed at t = 25° C by examining the influence of aqueous phosphate concentrations on the distributions of 144Ce and 153Gd between 0.68 molar NaClO 4 and tributyl phosphate (TBP). Estimated Ce 3+ and Gd 3+ phosphate complexation constants appropriate to zero ionic strength are Ce 3+ + PO 4 3− ↔ CePO 4 0; log L β 1 0 ≤ 11.7 Gd 3+ + PO 4 3− ↔ GdPO 4 0; log L β 1 o = 12.2. Our estimates of these formation constants at zero ionic strength are approximately seven to eight orders of magnitude lower than previously reported estimates for lanthanide and actinide PO 4 3− complexation. Linear free energy relationships relating the complexation of Ca 2+ and lanthanides (Ln 3+) by a variety of organic ligands, in conjunction with previous direct observations of CaPO 4 − formation, are consistent with the experimentally derived CePO 4 0 and GdPO 4 0 formation constants reported in this work. Gadolinium speciation calculations indicate that the PO 4 3− ion can effectively compete with the CO 3 2− ion for free Gd 3+ in model groundwater at pH 7–9. Rare earth element phosphate complexation is a significant process in natural freshwater systems which are neutral to mildly basic when the concentration ratio [HPO 4 2−] [HCO 3 −] is greater than approximately 1 × 10 −3.

Model organo-cupric ion complexes in seawater.

Copper chelation in seawater by a variety of organic ligands is shown to be dependent upon the stability of the model complex and the pH of the medium. Amino acids, citric acid and citric acid-like compounds are potentially the most important contributors to the speciation of copper in the soluble organic realm of seawater.

A molecular-orbital study of some di-µ-phosphido-bis(tricarbonyliron) complexes. The importance of metal–bridging ligand interactions in determining molecular geometry

Extended Huckel molecular orbital (m.o.) calculations are used to examine the structures of [Fe2(CO)6(µ-AX2)2] systems (A = N, P, or As: X = a variety of organic ligands). The experimentally observed dramatic structural change, with a startling increase in metal–metal distance in the phosphido-bridged dimers when CF3 replaces Me, H, or Ph as a bridging substituent (for A = P), is found to be due to the nature of the energetically highest-occupied m.o. (HOMO). This orbital, whilst metal–metal bonding, is metal–phosphorus antibonding, and the balance between these two forces controls the equilibrium geometry to a large extent. Replacement of X by CF3leads to stronger Fe-P repulsions in the HOMO and a longer Fe–Fe distance. The importance of Fe–P interactions stands out clearly in the calculations and these should be considered together with Fe–Fe interactions when viewing the structures of this and similar molecules. The geometry of these dimeric ‘metal–metal-bonded’ systems is thus not determined purely by metal–metal interactions, as most previous studies have emphasised.