Dioxygen affinities and catalytic oxidation activities of cobalt complexes with crown ether-containing Schiff bases (2023)


Complexes of transition metals with Schiff bases have been widely studied in the field of bioinorganic, bioorganic and catalytic chemistry [1], [2], [3], [4], [5], [6]. In the biomimetic oxygen transport field, the ability of cobalt-Schiff base complexes to reversibly bind oxygen has been extensively investigated since 1938. Tsumaki discovered that Co(Salen) can reversibly transport oxygen, and its oxygenation properties have been studied in thermodynamics and chemical kinetics [8], [9], [10], [11], [12], [13], [14]. However, at ambient temperature and pressure, some simple models with oxygen are easily handled.m-oxo-dimers after binding oxygen and lose the reversible ability to absorb oxygen [15]. In order to maintain the reversible ability of the biomimetic oxygen carrier to bind dioxygen, some groups, which can increase the capacity of the ligand, such as π-donating property, hydrophobic property and steric hindrance, were introduced into the ligand [15] . The crown ether ring has a hydrophobic outer ethylene shell and an ordered arrangement of internal oxygen atoms, and it is also a bulky group, so if the crown ether ring is introduced into the cobalt-based Schiff complex, it can improve the oxygen binding capacity of the Co(II) complex [16] , [17], [18]. As part of our continuing interest in the crowned Schiff base, we report here the oxygen affinities and catalytic performance in cyclohexene oxidation of six Schiff base complexes with cobalt.1a,1b,1c,2a,2b,2c. The influence of the crown ether ring on the dioxygen affinity of the cobalt complexes at different temperatures and catalytic activities compared to the analogous uncrowned complexes is discussed.

The structures of the cobalt-based Schiff crown complexes are listed in Scheme 1.

paragraphs of sections

Materials and physical measurements

Pyridine was purified by distillation after refluxing with KOH for 6 hours. Crown Schiff complexes based on cobalt (1a,1b,1c,2a,2b,2c) sintetizirani su literaturnom method [18], [19]. Kobaltni kompleksi sa,N,N′-′bis-(5-chlorosalicilideno)-4,5-dimethoxy-1,2-phenylenediamine (3a),N,N′-bis-(salicilideno)-4,5-dimethoxy-1,2-phenylenediamine (3b), eN,N-bis-(5-methoxysalicylideno)-4,5-dimethoxy-1,2-phenylenediamine (3c) were prepared using the literature method [16].

Gas chromatograph HP 5890 II

Oxygenation of cobalt complexes

The oxygen introduction process was carried out in a pyridine solution (axial base). This ensured that the tetradentate Schiff base complex (CoL) was completely converted to a pentacoordinate complex (CoLB) containing an axial base adduct [9], [11], [22] and then a dioxygen-bound pentacoordinate complex to reach equilibrium. Within the measured temperature range and in an atmosphere of pure oxygen, the maximum stoichiometry of oxygen absorption of cobalt complexes [n(O2)/n(komplex kobalta)] bili su


    they are leaving



    flame ionization detector

Quoted by (18)

  • Degradation of organic pollutants in the presence of new Mn(II) complexes under ambient light or dark conditions

    2023, Journal of Photochemistry and Photobiology A: Chemistry

    Mn(II) complexes prepared from Schiff bases, as salophene-type ligands, were complexed via N & O donors by solvothermal method. These Mn(II) complexes were initially validated using elemental data, confirmed by mass spectra. At the same time, various spectroscopic practices such as XPS, p-XRD, FT-IR, Raman, FESEM and thermal stability of Mn2+complexes were investigated from TGA. Band gap energies and oxidation potentials of Mn(II) complexes were evaluated by UV-visible DRS and CV studies. The emission spectra clearly show that the electron-hole pair recombination rate is lower for complex M-2 compared to complex M-1. The prepared Mn(II) complexes were used for the mineralization of cationic and anionic dyes such as rhodamine 6G (Rh6G λmax=553n) and Congo red (CR λmax=498nm) in dark environmental conditions. Complex M-2 is more active than M-1 due to low band gap energy, low hole-electron pair recombination rate, and in situ generation of superoxide radicals during catalytic mineralization in a dark environment. Active species are identified by ESR studies, which are supported by scavenger data, and then the mechanism of rapid mineralization of organic dye contaminants is determined.

  • Improved piezo-photocatalytic properties of new Ti(IV) complexes based on salophene

    2023, Inorganic Chemistry Communications

    Excerpt from the quote:

    Polydentate Schiff base ligands with N & O as donor atoms are known to complex with various metal ions and this has fascinated many researchers [7-10]. Metal(II) complexes of Schiff bases have been investigated for their interest in dioxygen [11] and oxidative catalysis [12]. Transition metal (II) complexes with 2-hydroxy-1-naphthaldehyde and aryl-1,2-diamine ligands have attracted considerable attention.

    Ti(IV) complexes formed from salophene-based ligands complexed with N & O donor atoms under solvothermal conditions are presented. These Ti(IV) complexes were initially confirmed by elemental analysis and supported by mass spectral data together with various spectroscopic techniques such as11 H NMR, FT-IR, Raman, p-XRD and FESEM. Band gap energies of Ti(IV) complexes were estimated by UV-visible DRS studies. The hole-electron pair recombination rate was confirmed using emission and photocurrent spectral studies. Synthesized Ti (IV) complexes were used for piezophotomineralization of cationic dyes such as methyl red (MR λmaximum.=467nm) i rodamin B (RhB λ).maximum.= 553 nm) under ultrasound visible light treatment. The [Ti(FPAMN)O] complex is more active than [Ti(CPAMN)O] and [Ti(MPAMN)O] because it has a low electron-hole pair recombination rate, low band gap energy, and enhanced luminosity. nature induced for the formation of hydroxyl radicals during the catalytic process of piezophotomineralization. In the presence of multiple scavengers, mechanistic studies of rapid paint mineralization were also supported.

  • Cobalt(II) complexes with minor variations in the heterocyclic ligand, crystal structure and DFT calculations

    2021, Journal of Molecular Structure

    Excerpt from the quote:

    Interest in cobalt compounds has continued to the present and has led to research into their applied properties. Co(II) complexes have become important due to their ability to reversibly bind oxygen [2,3] and catalytic properties in redox reactions [4,5], especially for the oxidation of flavonoids, nitroalkanes, hydrazines, olefins, etc. [6,7]. In addition, cobalt biomaterials play an important role in the biological processes of the human body, such as methyltransferases and isomerases, which process vitamin B12 (cobalamin), as a cofactor of the mentioned enzymes [8].

    New mononuclear cobalt(II) complexes, [Co(mbipy)(H2Eye2- Yes3)(η-NO3)] (1), [Co(dmbipy)(H2Eye2- Yes3)(η-NO3)] (2) e [Co(dmphen)(H2Eye2- Yes3)(η-NO3)] (3) were synthesized by reactions of Co(NO3)2·6h2O with bipyridine and phenanthroline derivatives (mbipy=6-methyl-2,2-bipyridine; dmbipy=6,6-dimethyl-2,2-bipyridine and dmphen=2,9-dimethyl-1,10-phenanthroline). The complexes were identified by elemental analysis, IR, UV-vis spectroscopy and X-ray crystallography. In the molecular structure of the three complexes, the coordination geometry around Co(II) is octahedrally distorted in [CoN2O4] System. The crystal structure is stabilized with ODioxygen affinities and catalytic oxidation activities of cobalt complexes with crown ether-containing Schiff bases (1)H···E (CDioxygen affinities and catalytic oxidation activities of cobalt complexes with crown ether-containing Schiff bases (2)H···Classical hydrogen bonding interactions as well as π-π interactions between pyridine rings in2e3. In addition, density functional theory (DFT) calculations were performed. A good consistency was observed between the calculated results and the experimental structure, in the gaseous and aqueous phases. The DFT approach was used to interpret the optical characterization. The electronic properties of the complex were also calculated and compared. The origin of intermolecular ODioxygen affinities and catalytic oxidation activities of cobalt complexes with crown ether-containing Schiff bases (3)H···Hydrogen bonds in the 3D structure of the complex were investigated by MEP.

  • Thermodynamics of complex formation in dimethylsulfoxide: the case of Co(II) complexes with nitrogen donor ligands and their O adducts2

    2019, Minute of inorganic chemistry

    Excerpt from the quote:

    Therefore, in principle, the choice of media can modulate the stability and type of Co2+ species created, as well as the stability and kinetics of oxygenated adduct formation [4,26]. In aprotic solvents such as DMF, pyridine, toluene, acetonitrile, CH2Cl2, it has been proven that Co(II) chelated with other N-donor ligands (Schiff bases, porphyrins, amines...) is active in catalyzing the oxidation of alkanes, phenols, olefins, benzyl alcohols at room temperature and atmospheric pressure [8,15-17,27-29]. Knowing the speciation and stability of Co2+ complexes in a certain medium is crucial for promoting oxygen binding, especially the correlation between the structural and donor properties of the used ligands and the thermodynamic parameters of complex formation.

    Data for the formation of complexes of Co(II) withN-donors in dimethylsulfoxide were reviewed and rationalized based on solvation effects and structural and electronic characteristics of the ligands. For polyamine ligands, the number and stability of the species formed decreases with increasing noN-methyl groups, due to increased spatial agglomeration and relatively low basicity of nitrogen donors. However, stabilization by forming hydrogen bonds with other sphere solvent molecules is also an important factor. The same factor causes a greater electron donation from the ligand to the metal ion, stabilizing the complex as shown by thermodynamic and structural data. Comparing the thermodynamic parameters with those available in water, it is shown that the stability constants are higher than in water, despite the stronger solvation of the metal ion in DMSO. This is attributed to ligand solubilization playing an important role, especially for primary and secondary amines. When considering ligands that can only be H-bond acceptors (tertiary amines and pyridines), the expected complex stability based on metal ion solvation is observed. When the oxygen affinity of Co(II) complexes in DMSO is taken into account, it turns out that complexes with primary and secondary amines are able to bind O2. how2Absorption is a redox process that largely depends on ligand-metal charge transfer and solvation of the resulting complex. Thus, the same factors that affect the stability of Co(II) complex sN-The considered donor ligands also affect their affinity for oxygen. Correlation between enthalpy and electrochemical data in DMSO supports this hypothesis.

  • Characterization and catalytic activity of a new Fe nanocatalyst as an effective heterogeneous catalyst for the selective oxidation of ethylbenzene, cyclohexene and benzyl alcohol

    2013, Journal of Molecular Catalysis A: Chemistry

    Excerpt from the quote:

    In the past, many chemists paid much attention to the production of benzylic and allylic ketones by oxidizing agents such as the oxidation of ethylbenzene (EB) to acetophenone (AP) using KMnO4 [16], H2O2 [17-25], TBHP [17,26 – 31], CrO3–SiO2 [32], SeO2 [33] and O2 [34–39]. Furthermore, the use of a heterogeneous catalyst enabled good to excellent conversion with good selectivity for 2-cyclohexen-1-one [40-48]. In order to gain an insight into the catalytic activity of a simple heterogeneous nanocatalyst for the oxidation of inert hydrocarbon bonds with tert-butyl hydroperoxide (TBHP) as an oxygen donor under mild conditions and without any additives, a study was made for the first time showing the systematic and step-by-step synthesis of an ecological heterogeneous catalyst based on ferrocenecarboxaldehyde (FCA) as a commercially available molecule.

    In this study, a heterogeneous Fe-nanocatalyst was covalently anchored on a modified SiO nanoscale2/Al2O3. The synthesized materials were characterized by FT-IR, DS UV-vis spectroscopy, CHN, BET, EDS, SEM, TEM, TGA and XPS elemental analysis. The catalytic activity of Fe nanocatalysts (FNC) on the oxidation of ethylbenzene, cyclohexene and benzyl alcohol was studied usingtert-butyl hydroperoxide as a source of oxygen, without the need for any solvent. (FNC)-catalyzed oxidation of ethylbenzene, cyclohexene, and benzyl alcohol gave acetophenone, 2-cyclohexen-1-one, and benzaldehyde as major products, respectively. Suitable reaction conditions were optimized for the Fe-nano-catalyst by considering the effect of various parameters such as reaction time and amount of oxidant, different solvents, substrate concentration for maximum substrate conversion and high selectivity. This catalyst can be easily prepared from inexpensive commercially available reagents and is stable and reusable for the oxidation of ethylbenzene, cyclohexene, and benzyl alcohol.

  • Dinuclear Cobalt(II) Complexes of Compartmental Schiff Base Ligands: Synthesis, Crystal Structure, and Biorelevant Catalytic Activities

    2013, Polidar

    Excerpt from the quote:

    Cobalt (II) Schiff base complexes are interesting compounds due to their ability to reversibly bind oxygen [1-3] and their catalytic activity in oxidation reactions [4-7], especially the oxidation of phenols, alcohols, flavonoids, nitroalkanes, hydrazine or olefins [8- 10].

    Tri complexa dicobalt(II), tj. [Co2(EU1H)(H2O)2(OAc)2](OAc)2 (1), [Co2(EU2)(H2O)2(OAc)2](OAc) (2) and society2(EU3)(H2O)2(OAc)2](OAc) (3) p-cresol 2,6-bis(R-iminomethyl)-4-methyl-phenolate end compartment binders, where R=N-ethylpiperazine para L1, 2-ethylpyridine for L2eN-ethylpiperidin for L3, were synthesized and characterized by common physicochemical techniques and, in the case of complexes1also by X-ray diffraction analysis of single crystals. All complexes show excellent catecholase-like activity, followed not only by 3,5-di-tert-butylcatechol, but also with tetrachlorocatechol, a substrate that is reluctant to oxidize. As far as we know, no cobalt complex has been found in the literature that would show such an effect. It was observed that the complexes effectively interact with CT-DNA and upon incubation (using plasmid pTZ57/R/T DNA) show concentration-dependent DNA cleavage activity. Mechanisms related to DNA cleavage and catecholase-like activities were investigated. The cytotoxicity of the complex was also examined using the MTT assay.

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What do the crown ethers have the property of forming complexes with? ›

Crown Ethers

They are macrocyclic polyethers, soluble in both aqueous and organic solvents, which form stable complexes with enantiomers, which have a primary amine or alkylamine functionality.

What is the role of crown ether in organic synthesis? ›

The application of crown ethers in organic synthesis is related to their ability to solubilize ionic reagents in nonpolar media and thereby increase the activity of the ionic species.

What is the role of crown ethers in nucleophilic substitution reaction? ›

Crown Ethers act as good complexing agents. The cations are trapped in the rings with oxygens forming dative bonds with the metal ion. With the trapping of metal ions, the nucleophile becomes more powerful and thus the rate of reaction increases.

Do crown ethers selectively bind to metal cations? ›

The availability of crown ethers with cavities of different sizes allows specific cations to be solvated with a high degree of selectivity. Crown ethers prefer to bind alkali metal cations with sizes that match that of their binding cavity.

What is the role of crown ethers as a phase transfer catalyst? ›

The oxygen atoms are well situated to coordinate with a cation located at the interior of the ring, whereas the exterior of the ring is hydrophobic. The resulting cations often form salts that are soluble in nonpolar solvents, and for this reason crown ethers are useful in phase transfer catalysis.

What is the structure and properties of crown ethers? ›

Crown-ethers are macrocyclic polyethers discovered by Pedersen in the late 1960s. Due to their strong ability to complex with cations and to solvate salts in aprotic solvents, crown-ethers have been used in phase-transfer catalysis, sensors, solvent extraction, analytical chemistry, biochemistry, and electrochemistry.

Can a crown ether be used as a phase transfer catalyst? ›

Crown ethers having aliphatic chains in the molecule, e.g. dicyclohexyl-18-crown-6, can be used as phase-transfer catalysts in anion promoted two-phase reactions.

What are the functions of crown ethers? ›

Use of Crown Ether Functions as Secondary Coordination Spheres for the Manipulation of Ligand–Metal Intramolecular Electron Transfer in Copper–Guanidine Complexes - PMC. The .

How do crown ethers increase solubility? ›

Crown ethers enhanced riboflavin's aqueous solubility and its penetration into in vitro bovine corneas; the smaller sized crown ethers gave greatest enhancement. They were shown to sequester Ca2+ ions from corneal epithelia; doing so loosens cellular membrane tight junctions thus enhancing riboflavin penetration.

What do you understand by crown ether complexes? ›

Crown ethers are cyclic compounds that have several ether linkages. A crown ether specifically binds certain metal ions or organic molecules, depending on the size of its cavity. In principle, co-polymerization of a 1,2-diol and a 1,2-dihalide might lead to a polyether.

What do oxygen atoms in crown ethers act as? ›

Ch16 : Crown Ethers. Oxygen atoms are capable of acting as Lewis bases due to the presence of the lone pairs (e.g. in hydrogen bonding between water molecules or hydration of a metal ion in aqueous solution, see below).

What are the methods of synthesis of crown ethers? ›

The synthesis of functionalised crown ethers is performed following two main approaches: templated macrocyclisation, using pre-functionalised starting materials, or direct functionalisation of previously formed CE.

What is the binding constant of crown ether? ›

Like other crown ethers, 18-crown-6 functions as a ligand for some metal cations with a particular affinity for potassium cations (binding constant in methanol: 106 M1).

Which mechanism is favored by the use of crown ethers in nonpolar solvents? ›

The free anion readily undergoes an S N 2 reaction mechanism. Thus, the use of crown ethers in non-polar solvents is favored by S N 2 mechanism.

What are the unique characteristics of crown ethers and cryptates? ›

The key difference between crown ethers and cryptands is that crown ethers are cyclic structures containing ether groups. But, cryptands are either cyclic or non-cyclic structures containing ether groups and nitrogen atoms. Crown ethers and cryptands are organic compounds.

What type of catalyst is a crown ether? ›

Uncomplexed crown ethers could also be used as asymmetric catalysts for addition reactions.

Can crown ethers bind to cations? ›

One of the earliest and most important classes of hosts is crown ethers. Their ability to bind metal cations and small neutral molecules makes them useful for medical applications, chiral recognition, extracting hazardous materials, and more.

What is the function of the catalysts in the potential energy level of the transition state? ›

The catalyst lowers the energy of the transition state for the reaction. Since the activation energy is the difference between the transition state energy and the reactant energy, lowering the transition state energy also lowers the activation energy.

What is the advantage of crown ether? ›

The advantage of aza-crown ethers over the “normal crowns,” containing only oxygen atoms, is their better complexing ability toward ammonium and transition-metal cations. They are also useful precursors of the lariat aza-crown ethers.

What are the types of crown ethers used in extraction of alkali and alkaline earth metals? ›

For what i know, 16-crown ether is the best for alkaline metal ions, especially for potassium.

What is the disadvantage of phase-transfer catalyst? ›

The disadvantages ofPTC are: sometimes difficult separation of the product from catalyst; • rapid decomposition of some of the most commonly used PTC catalysts at elevated temperatures; • toxicity of some catalysts, necessitating expensive catalysts; • recovery or waste treatment.

What are two examples of phase-transfer catalyst? ›

Common PTC catalysts are onium salts (ammonium and phosphonium salts), macrocyclic polyethers (crown ethers), aza-macrobicyclic ethers (cryptands), and open-chain polyethers (polyethylene glycols, PEGs, and their dimethyl ethers, glymes).

What is the difference between crown ether and lariat ether? ›

Lariat ethers are a variant of crown ethers that have pendant side arms. The original design for these molecules included donor groups in the side arms that were envisioned to enhance alkali metal cation binding without diminishing binding dynamics.

What are 3 uses of ethers? ›

Relative to alcohols, ethers are generally less dense, are less soluble in water, and have lower boiling points. They are relatively unreactive, and as a result they are useful as solvents for fats, oils, waxes, perfumes, resins, dyes, gums, and hydrocarbons.

How do alkali metals form complexes with crown ethers? ›

Electrostatic interactions also allow alkali metal ions to form complexes with certain cyclic polyethers and related compounds, such as crown ethers and cryptands.

Why is ether so often used as an extraction solvent? ›

Diethyl ether is a common laboratory solvent. It has limited solubility in water, thus it is commonly used for liquid-liquid extraction. Being less dense than water, the ether layer is usually on top.

Why is ether a good solvent for extraction? ›

Ethers as Solvents

Because diethyl ether has a dipole moment, polar substances readily dissolve in it. Polar compounds that can serve as hydrogen bond donors dissolve in diethyl ether because they can form hydrogen bonds to the nonbonding electron pairs of the ether oxygen atoms.

How do you identify ether in structure? ›

For a functional group to be called an ether, it must consist of an oxygen atom that is single-bonded to two non-carbonyl carbons. Carbonyl: A carbon atom is described as a "carbonyl" when it is double-bonded to an oxygen.

What does ether mean in organic chemistry? ›

Ethers are a class of organic compounds that contain an oxygen between two alkyl groups. They have the formula R-O-R', with R's being the alkyl groups. these compounds are used in dye, perfumes, oils, waxes and industrial use.

What are the two types of ether? ›

Ethers can again be classified into two varieties: if the alkyl or aryl groups are the same on both sides of the oxygen atom, then it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers.

Are crown ethers polar or nonpolar? ›

CCl4 is known as a non-polar solvent. If CCl4 and water are mixed, there is an attraction between the different molecules but although it is nothing to be scoffed at, it is far weaker than the forces between water molecules.

What happens when ether reacts with oxygen? ›

Ethers will slowly react with oxygen in the air in an oxidation reaction, forming peroxides. Peroxides are molecules that have a functional group with two oxygens attached to each other. This is a particularly dangerous reaction because the peroxides are so unstable, they tend to explode!

Can ethers be explosive when oxygenated? ›

Ethers form peroxides if exposed to oxygen or air during storage; the ether peroxides can detonate with friction, shock, or heat, releasing enough energy to start a secondary fire in the unperoxidized ether. Ethers tend to form unstable peroxides when exposed to oxygen.

Which method is best for ether synthesis? ›

The Williamson ether synthesis is the most widely used method to produce ethers. It occurs by an SN2 reaction in which a metal alkoxide displaces a halide ion from an alkyl halide. The alkoxide ion is prepared by the reaction of an alcohol with a strong base such as sodium hydride.

What are catalyst synthesis techniques? ›

Current metal oxide catalyst synthesis involves oxidizing metal powder or chips with nitric acid at elevated temperatures under agitation. The resulting metal nitrate solution is treated with a base to precipitate the metal salt, which is washed with water to remove salts and ions.

What affects binding constants? ›

Binding affinity is influenced by non-covalent intermolecular interactions such as hydrogen bonding, electrostatic interactions, hydrophobic and Van der Waals forces between the two molecules. In addition, binding affinity between a ligand and its target molecule may be affected by the presence of other molecules.

What are crown ethers able to form strong ion dipole interactions with? ›

Crown-ethers can incorporate protonated primary amine compounds by formation of ion-dipole bonds with the oxygen atoms of the chiral selector.

Is crown ether a phase transfer catalyst? ›

Crown ethers having aliphatic chains in the molecule, e.g. dicyclohexyl-18-crown-6, can be used as phase-transfer catalysts in anion promoted two-phase reactions.

What are crown ether complexes? ›

Crown ethers are specialized cyclic polyethers that surround specific metal ions to form crown-shaped cyclic complexes. They are named by using the parent name crown preceded by a number describing the size of the ring and followed by the number of oxygen atoms in the…

What are crown ethers and cryptates with example? ›

The crown ethers and cryptands have cavities that form tightly bound complexes with metal ions <CHEC-III(14.12. 2)668>. For example, 18-crown-6, which is an 18-membered ring with six oxygen atoms, forms a complex with potassium ions and will solubilize potassium permanganate in organic solvents.

Does crown ethers form complexes with alkali metals? ›

Macrocyclic compounds such as crown ethers and cryptands that are selective for particular alkali metal ions have been synthesized. They form cationic complexes that can be dissolved in organic solvents such as chloroform (CHCl3) with counterions such as picrate (C6H2[NO2]3O-).

What are the properties and characteristics of an ether? ›

Relative to alcohols, ethers are generally less dense, are less soluble in water, and have lower boiling points. They are relatively unreactive, and as a result they are useful as solvents for fats, oils, waxes, perfumes, resins, dyes, gums, and hydrocarbons.


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