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Introduction
Published in Jubaraj Bikash Baruah, Principles and Advances in Supramolecular Catalysis, 2019
Crown ether combined with a ligating part modulates the reactivity of metal complexes. For example, the pincer-crown-ether ligand complex of iridium complex 1.21a adopts different coordination modes (Figure 1.21). Depending on the number of coordinated acetonitrile molecules attached to the central iridium ion, the ability of the crown ether to coordinate iridium ion changes. Accordingly, the ligand adopts tri-dentate, tetra-dentate or penta-dentate binding to adopt different structures as shown through different equilibriums between structures 1.21b–e. Reaction of the complex with an excess amount of acetonitrile forms a bis-acetonitrile complex, but this process is more easily achieved when the reaction is carried out in the presence of alkali metal cations. The alkali metal cations bind to the crown, facilitating the incorporation of acetonitrile as ligand. This happens as the ligating atoms on the crown are engaged to bind to the alkali metal cations. This generates vacant coordination sites on the iridium ion making coordination unsaturation. Such effects lower the activation energy of a reaction and help to create a suitable coordination environment at the iridium centre for catalysis.
Nanoscale electrokinetic phenomena
Published in Zhigang Li, Nanofluidics, 2018
Allowing or screening the transport of ions can also be achieved by modifying channels with ion-responsive molecules. Figure 8.35a and b illustrates conical polyimide (PI) nanochannels modified with crown ether molecules to realize selective transport of ions, which are inspired by biological Na+ and K+ channels (Figure 8.35c) (Liu et al., 2015a). Crown ethers have a ring-shape structure and can bind with cations having a size similar to that of the cavity of crown ethers. To discriminate Na+ and K+, whose radii are about 0.98 and 1.38 Å, respectively, two types of crown ethers, 4′-aminobenzo-15-crown-5 (4-AB15C5) and 4′-aminobenzo-18-crown-6 (4-AB18C6), are used to modify PI nanochannels. The radius of 4-AB15C5 cavity is about 0.86–1.1 Å, which fits Na+ well. The cavity radius of 4-AB18C6 is in the range of 1.3–1.6 Å, similar to the size of K+. Therefore, these two crown ether molecules can selectively bind with Na+ or K+ and form stable complexes. If they are immobilized on a PI channel surface, the channel can be converted to a Na+-activated or K+-activated ionic gate.
Other Separation Processes — Alternative Separation Technologies for Treating Sodium-Containing Acidic Wastes
Published in Thomas E. Carleson, Nathan A. Chipman, Chien M. Wai, Separation Techniques in Nuclear Waste Management, 2017
Crown ethers have unique properties that allow them to selectively capture cations from multicomponent solutions. The selectivity is attributed to the high binding potential, which is a function of the crown ether cavity size and functional group(s), as well as synergistic effects of the diluent and additives(s) in the system. A crown ether system may exhibit the ability to perform any of the following reactions: (1) selective cation extraction of Na+, (2) ion-pair extraction (NaNO3), and (3) liquid-liquid ion exchange. These reactions are written as follows for sodium:13
An electrospray ionization mass spectrometric study of beryllium chloride solutions and complexes with crown ether and cryptand macrocyclic ligands
Published in Journal of Coordination Chemistry, 2020
Onyekachi Raymond, William Henderson, Joseph R. Lane, Penelope J. Brothers, Paul G. Plieger
A well-known feature of the crown ethers is their distinct cavity sizes and the corresponding ability to form more stable complexes with the proper matching cation size. Therefore, starting from stoichiometric compositions derived from the ESI MS ion assignment (Table 2), selected beryllium complexes with crown ethers were investigated computationally by density functional theory (DFT) to examine the question of size match between the crown ether cavities and the beryllium cation, as suggested from ESI MS data. The structural parameters of the optimized structures of the [BeL]2+ and [LBeX]+ complexes for L = 12-crown-4, 15-crown-5 and 18-crown-6 and X = Cl, OH are shown in Table 3. In principle, the Be2+ cation can be coordinated to crown ether ligands in a variety of modes that will result in several conformers on the potential energy surface. However, no search for the lowest lying conformation was made, rather initial structural conformers were adopted from the known X-ray structures, where available. Nevertheless, correlation of the bond distances of optimized structure with the corresponding X-ray structures revealed acceptable agreement, suggesting this computational method worked sufficiently well for structural evaluation of these complexes (see Table 3). From these data, the relative energetics for the formation of the various [BeL]2+, [LBeOH]+ and [LBeCl]+ complexes were explored.
Optimization of lithium separation conditions from Caspian seawater using fuzzy logic combined with dispersive liquid–liquid extraction
Published in Geosystem Engineering, 2019
Romina Pourhassan Motlagh Sharemi, Abbas Rashidi, Mohammad Hassan Mallah, Jaber Safdari
Since the volume of extraction solvent and dispersive solvent used in process of DLLE is higher than other methods, the separation phase is not necessarily dependent on centrifuging the samples. Furthermore, the separation of the two phases is possible based on differences in density (Hadadian, Mallah, Moosavian, Safdari, & Davoudi, 2016; Heumann & Schiefer, 1980). In order to form a lithium-ligand complex from the family of crown ether, benzo15-crown-5 property is it’s toward lithium ion has been used. Because of using this ligand, noticeable ability it’s to be solved in many organic solvents and not to be solved in water. Crown ethers are able to solve metal salts in organic solvents. The admixture which is oriented by electrostatic effects on polyether circles is also able to form admixture by cations (Gokel & Korzeniowski, 1983; Sadrzadeh, Ghadimi, & Mohammadi, 2009).
Synthesis, complexation and biological effects studies of new thiacrown ethers derived quinoline: part I
Published in Journal of Sulfur Chemistry, 2019
Muhammad Ashram, Ghassab M. Al-Mazaideh, Wael Al-Zereini, Ahmed Al-Mustafa, Shehadeh Mizyed
The first synthetic approach investigated towards crown ethers derived quinolone 7–9 is shown in Scheme 1 for 8 as an example. The dimer 21 was envisioned as being suitable precursor to condense with bis(2-mercaptoethyl)sulfide in presence of anhydrous potassium carbonate and anhydrous DMF at 85 oC. It was found that after heating for 24 h, most of staring material was recovered unchanged. Thus an alternative method for preparation of crown ethers 7–9 was successful as shown in Schemes 2 and 3. Reaction of two equivalents of 2-chloroquinoline-3-carbaldehyde 10 with one equivalent of ethane1,2-dithiol, bis(2-mercaptoethyl)sulfide or 2-mercaptoethylether in presence of anhydrous potassium carbonate in refluxing anhydrous acetonitrile for 24 h afforded the dimers of aldehydes 11, 14 and 15, respectively, in high yield. Reduction of dialdehydes with NaBH4 in tetrahydrofuran followed by chlorination with freshly distilled thionyl chloride in dry dichlorometane at room temperature produced dichlorides 13, 18 and 19 as key precursors in very good yield. The syntheses of crown ethers 7, 8 and 9 were accomplished by reaction of dichlorides 13, 18 and 19 with corresponding aliphatic thiols using anhydrous acetonitrile as solvent in presence of potassium carbonate at reflux temperature afforded the desired macrocycles 7, 8 and 9 in good yield.