Complexes of crown ethers with perfluorocarboxylic acids and their thermal decarboxylation

Crown ethers form strong proton-acceptor complexes with CF₃COOH or C₄F₉COOH that undergo thermal decarboxylation at 200–260 °C which results in 60–80% of CF₃H or C₄F₉H (including up to 20 % of a mixture of C₄F₈). Critical parameters of the process were determined in relation to the temperature and amount of crown ether. The relative activities of different crown ethers in decarboxylation were also established. A scheme is proposed that explains the effect of the structure of crown ethers on this reaction. The data obtained substantiate the view that the topological correspondence concept is insufficient to explain the ability of crown ethers to form complexes with cations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1098–1101, June, 1993.     

Structural and Chemical Features of Extraction with Crown Ethers

Unlike linear extracting agents, in the extraction of metal salts from aqueous solutions of inorganic acids with crown ethers, the inclusion compounds, whose composition depends on several external and internal factors, go to the organic phase. The study of the molecular structure of the formed complexes by X-ray diffraction analysis showed that adducts of crown ethers with inorganic acids are host–guest complexes in which the hydroxonium ion is in the polyether macrocycle cavity. When the aqueous phase contains metal ions capable of displacing the hydroxonium ions from the macrocycle (K⁺, Pb²⁺, Hg²⁺, Sr²⁺, NH₄ ⁺), complexes containing metal cations as the guest in the macrocycle cavity, according to X-ray diffraction data, go to the organic phase. In addition, metals forming ionic associates (AuCl₄ ^-, FeCl₄ ^-, GaCl₄ ^-) in an aqueous solution are extracted with crown ethers in accordance with the anion-exchange mechanism. A system in which traces of metals in the 2 M HNO₃ +5 M HCl mixture serve as the aqueous phase was proposed for estimation of the general extraction ability of crown ethers. Such a system can be used for metal extraction via any possible mechanism. The stereochemical peculiarities of the extraction ability of crown ethers (compared to linear molecules) can be used for selective extraction and separation of metals.     

N2O4 Chemisorbed onto n‐Propylsilica Kryptofix 21 and Kriptofix 22 as Two New Functional Polymers for the Fast Oxidation of Urazoles and 1,4‐Dihydropyridines

3‐Chloropropylsilica was reacted with Kriptofix 21 or 22 in the presence of triethylamine to form N‐propylsilica Kryptofix 21 and Kriptofix 22. Then N₂O₄ was added to each of these polymers to chemisorb onto cavity of aza‐crown ethers. These functionalized polymers were applied for the fast and simple oxidation of urazoles and 1,4‐dihydropyridines, respectively.     

Hemolytic activity of polyoxyethylene cholesteryl ethers

Hemolytic activity of nonionic surfactants, polyoxyethylene cholesteryl ethers, C₂₇H₄₅O(CH₂CH₂O) _n H (Chol-E _n ,n=, 25, 30, 50) and polyoxyethylene dihydrocholeseryl ethers, C₂₇H₄₇O(CH₂CH₂O) _n H (DHChol-E _n ,n=15, 30 50) were measured, changing the concentration of surfactant and erythrocyte at 37 °C. Maximum hemolytic activity was observed in these cholesteryl derivatives with 25–30 oxyethylene units. The time course of hemolysis was also measured as a function of the concentrations of surfactant and erythrocyte. Hemolysis started after a certain induction period,, and then apparently proceeded as a first-order reaction with respect to the erythrocyte concentration. The surfactant inducing 50% hemolysis at low concentration had a small value and large rate constant. The maximum amount of adsorption without inducing hemolysis,a ₀, decreased with increasing polyoxyethylene chain length. Chol-E₂₅ has the maximum activity for the solubilization of egg yolk lecithin at 37 °C. Based on these results, the mechanism of hemolysis by these surfactants was quantitatively discussed.     

Synthesis and crystal structure of ammonium (picrate) (dibenzo-18-crown-6)

NH₄(Pic)(DB18C6) (Pic=picrate and DB18C6=dibenzo-18-crown-6), (C₂₆H₃₀N₄O₁₃) FW 606.56, arthorhombic,Pmn2₁,a=26.045(5),b=12.055(3),c=8.982(3) Å,V=2820(1) ų,Z=4,D _c =1.429 g/cm³, CuK, =1.54184 Å, (CuK)=9.5 cm^–1,F(000)=1272,T=298 K. The structure has been refined toR=0.0475 for 2617 unique observed reflections. In the lattice the 1:1 complex exists as a 2:2 dimer in which the crown are coupled through the Pic anions and NH₄ ⁺ cations. The asymmetric unit consists of two independent half crown ethers of which two opposite O atoms are on the mirror plane, two half ammonium cations of which the N and two H atoms are also on the mirror plane while the Pic anion is in a general position. Relative to each other, the corwn ethers are shifted by about 7.3 Å alongb and 1 Å alongc. The 1:1 sandwich of NH₄ with DB18C6 and Pic on dimerisation becomes a club pseudo-sandwich with three phenyl rings on either side of the mirror plane, thus forming a nearly parallel stack with a 3.6 Å inter-ring distance. The NH₄ ions hold the structure; two H atoms on the mirror plane are hydrogen-bonded to the opposite oxygens of the crown located on the purely aliphatic part of the ring (2.10(1), 2.06(3) and 2.26(3), 2.05(1) Å) for the two independent crowns, respectively, while the other two H atoms form mirror-related bifurcated hydrogen bonds with the phenoxide oxygen (1.99(1) and 2.01(1) Å) and theo-nitrogen oxygen (2.44(2) and 2.34(1) Å) of the picrates. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82037 (29 pages)     

Synthesis and structures of oligothioarylenecyclophosphonites

A new representative of phospho(scIII)crown ethers was obtained based on 4,4-thiodiphenol and tetraethyldiamide of phenylphosphonous acid. Thiaphospho(III)crown ethers can be prepared by different methods depending on the ratio of the initial reactants and the reaction conditions. The structures of the compounds obtained were confirmed by spectroscopic data and X-ray structural analysis.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2313–2315, September, 1996.     

Hydroxyl radical,sulfate radical and nitrate radical reactivity towards crown ethers in aqueous solutions

Reaction rate constants of crown ethers (12-crown-4, 15-crown-5, 18-crown-6) and their analogs 1,4-dioxane (6C2) with some important oxidative radicals, hydroxyl radical (OH), sulfate radical (SO₄^?) and nitrate radical (NO₃), were determined in various aqueous solutions by pulse radiolysis and laser photolysis techniques. The reaction rate constants for 6C2 and crown ethers with OH and SO₄^? increase with the number of hydrogen atoms in the ethers, indicating that the hydrogen-atom abstraction is a dominant reaction between crown ethers and these two radicals. The presence of cations in solution has negligible effect on the rate constants of crown ether towards OH and SO₄^?. However, for the NO₃, the rate constants are not proportional to the number of hydrogen atoms in ethers, and 12-crown-4 (12C4) is the most reactive compared with other crown ethers. Except 12C4 and 6C2, the cations in the aqueous solution affect the reactivities of 15-crown-5 (15C5) and 18-crown-6 (18C6). The cations with high binding stability for crown ether would improve the reactivity of 15C5. For the studied crown ethers, the reaction rate constants of these oxidative radicals have the order OH>SO₄^?>NO₃. Furthermore, the formation of radicals after the reaction of crown ethers with sulfate radical could be observed in the range of 260–280 nm using laser photolysis and pulse radiolysis. This is the first report on the kinetic behavior of crown ethers with NO₃, and it would be helpful for the understanding of stability of crown ethers in the processing of spent nuclear fuel.     

Synthesis,spectroscopic, magnetic and biological activity studies of copper(II) complexes of an antipyrine Schiff base

The Schiff base, 4-(2-pyrrolylmethylideneamino)antipyrine (HPAP), (1), and its copper(II) complexes were synthesized and characterized by elemental analysis and by physical and spectral methods such as i.r., u.v.–vis., ¹H-n.m.r., ¹³C-n.m.r. and e.s.r. as well as by molar conductance and magnetic moment determinations. Both the bis-ligand, [(HPAP)₂Cu]X₂ (4, 5), [(PAP)₂Cu] (6), and the dimer, [(PAP)Cu]₂X₂ (2, 3), complexes were isolated. In these complexes, the Schiff base acts as a bidentate or tridentate neutral or monobasic ligand. Interaction of the isolated [(PAP)Cu]₂Cl₂ (2), with strong coordinating organic bases was studied and the resultant adducts, [(PAP)CuLs]Cl; Ls = pyridine (7), -picoline (8), -picoline (9), -picoline (10) or n-propylamine (11), were isolated and characterized. Biological activity screening was studied and an activity correlation coefficients matrix was constructed for HPAP and the copper(II) complexes against gram-positive, gram-negative and fungi species. The copper content, structure of the complex as well as the degree of exposure of the metal center control the biological activity of the isolated complexes.     

Synthesis of formyl derivatives of benzodiazacrown ethers and benzocryptands

A simple and convenient procedure was developed for the synthesis of formyl derivatives of benzodiazacrown ethers and benzocryptands by condensation of 3,4-bis(2-iodoethoxy)benzaldehyde with ,-oligooxaalkanediamines or diazacrown ethers in the presence of alkali metal carbonates under high-dilution conditions in various organic solvents and their mixtures with water. In the reactions giving rise to diazacrown ethers, alkali metal cations exhibit the negative template effect resulting in a decrease in the yield of the target product if the size of the cation matches well the size of the cavity of the crown ether formed. An N,N"-bis(carboxymethyl) derivative was prepared from the formyl derivative of benzodiaza-18-crown-6.     

Novel C1-symmetric chiral crown ethers bearing rosin acids groups: synthesis and enantiomeric recognition for ammonium salts

Four types of novel C₁-symmetric chiral crown ethers including 28-crown-8, 20-crown-6, 17-crown-5 and 14-crown-3 (9a–m) were synthesized and their enantiodiscriminating abilities with protonated primary amines (10–14) were examined by ¹H NMR spectroscopy. 20-crown-6 crown ethers exhibited good chiral recognition properties toward these guests and showed different complementarity to some chiral guests, indicating that 20-crown-6 crown ethers could be used as a chiral NMR solvating agent to determine the enantiopurity of these guests. In addition, the binding model and binding site between the hosts and guests were also studied by the computational modeling and experimental calculation.     

Coordination chemistry of alkali and alkaline earth cations. Barium-crown encapsulation studies: The synthesis and crystal structure of barium(picrate)2(benzo-15-crown-5) monohydrate

The interaction of barium with benzo-15-crown-5 (B15C5) has been followed under the competitive effect of various chelating organic anions (L), nitrophenolates and nitrobenzoates, in ethanol and ethanol-water (9:1). The rather heavily hydrated BaL₂ salts yield novel 1:1 stoichiometric products in monohydrated or anhydrous states. Use of excess crown does not under any condition lead to the formation of 1:2 charge separated complexes, expected in view of the cavity and the cation sizes. The 1:1 Ba–B15C5 interaction is counteracted by L in accordance with its nucleophilicity, i.e., the pK _a value of its parent acid, HL. The complex Ba(picrate)₂(B15C5)·H₂O (BaC₂₆H₂₆N₆O₂₀, FW=879.0), is monoclinic,P2₁/c,a=11.43(1),b=16.31(3),c=17.38(2) Å, =92.265(3)°,Z=4,D _c=1.77 g/cm³,D ₀=1.73 g/cm³, MoK, =0.71069 Å, 2 (4.0–50°), =13.5 cm^–1,F(000)=1752,T=–32°C. FinalR for the 5926 reflections was 0.049. The structure reveals barium to be 10-coordinated through all the five crown oxygens (Ba–O, 2.800 to 3.002 Å), the two bidentate picrates (Ba–O, 2.642 and 2.666 Å; Ba–ONO, 2.825 and 2.994 Å), and the water molecule (2.711 Å) so that the cation constitutes a pseudo-sandwich of the crown on one side and the anionic species on the other. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82007 (50 pages). To obtain copies, see page ii of this issue.     

Synthesis and electrochemical properties of amphiphilic crown ether langmuir-blodgett films [1]

4-Octadecanoylbenzo-15-crown-5 (I) and four 4-alkylbenzo-15-crown-5 ligands [4-XB15C5 where X =n-C₁₈H₃₇ (II), X =n-C₁₆H₃₃ (III), X =n-C₁₄H₂₉ (IV), and X =n-C₁₂H₂₅ (V)] have been synthesized. The -A isotherms ofI andII were systematically investigated. The results indicated that the Langmuir-Blodgett (LB) films have high stability where the ratios ofI/SA andII/SA were 1 : 1 and 1 : 10, respectively, with a 6.2 pH subphase. The LB films of the crown ethers were deposited onto graphite electrodes pretreated by immersing them in liquid wax. The peak current reached the maximum value when the electrode surface was modified with five layers of the amphiphilic crown ethers.     

Thermodynamics of 15-Crown-5 Complexation with Ag+ and Pb2+ Ions

Heats and constants of 15-crown-5 (R) complexation with silver and lead ions at 298, 308, and 318 K are determined using direct calorimetry. Thermodynamic parameters (G°, H°, S°, and C _p°) of formation of AgR⁺ and PbR²⁺ complexes at various temperatures are calculated. The effects of the properties of the cations and crown ethers on the thermodynamic parameters of complexation are discussed.     

Synthesis of new water-soluble phosphonate calixazacrowns and their use as drug solubilizing agents

This study presents the selective chloromethylation of calix[4](aza)crown ethers 2a–c, using chloromethyl n-octyl ether and SnCl₄ in chloroform at room temperature in good yield for the first time. Chloromethylated products 2a–c are used as key intermediates to synthesize new water-soluble p-phosphonato calix[4](aza)crown ethers 5a–c. Liquid–liquid phase extraction and phase solubility studies with poor water soluble drug molecules such as nifedipine, niclosamide and furosemide are performed to evaluate their binding properties. Among the studied drugs, furosemide was the most effectively dissolved drug by p-phosphonato calix[4](aza)crown ethers 5a–c in water.     

Crystal Structure and Properties of a New Copper(II) Complex of Dioxocyclam Appended with 8-Methylquinoline (Dioxocyclam = 1,4,8,11-tetraazacyclotetradecane-5,7-dione)

The IR spectra of the crystalline complexes of 3-and 4-nitrophenol with crown ethers were studied, viz.,18-crown-6 (18C6), benzo-18-crown-6 (B18C6),dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6 (DC18C6) and dibenzo-24-crown-8 (DB24C8). The spectra of uncomplexed crown ethers showed water absorption bands which indicate the presence of two types of bound water molecules, viz., cavitant water enclosed by the strong ether-cavity field and outer-layer hydrogen-bonded water molecules. Upon complexation with 3- and 4-nitrophenol, the bands attributed to cavitant water disappeared, leaving the outer layer water to act as a bridge between the host crown ether and the guest phenols. The results further showed that of the crown ethers and of the phenols, B18C6 and DC18C6 and 3-nitrophenol, have the strongest interaction. The behaviour of the phenols was explained by the increased contribution of the inductive-moment over the resonance -moment in thecomplexes.     

Cover Picture: Construction of Crown Ether‐Stoppering [3]Rotaxanes Based on N‐Hetero Crown Ether Host (Chin. J. Chem. 7/2017)

The cover picture shows shows the construction of crown etherstoppering [3]rotaxanes based on N ‐hetero crown ether host. Usually, crown ethers play the role of host macrocycles to combine with the guest molecules in the construction of rotaxanes. Based on the fact that crown ethers have large dimension, two [3]rotaxanes containing four crown ether units were designed and synthesized, of which, two N ‐hetero crown ether components were employed as the macrocyclic hosts to assemble the mechanically interlocked framework by using a template‐directed clipping reaction while bis (metaphenylene‐26‐crown‐8) located on two sides of template diammonium acting as the stoppering groups of [3]rotaxanes. More details are discussed in the article by Yin et al. on page 1050–1056.

     

ESR spectroscopy of copper(ii) complexes with aza- and thia-containing crown ethers

Six copper(ii) chloride complexes with crown ethers containing besides oxygen also nitrogen or sulfur atoms in 15- or 18-membered cycle were studied by ESR and electron absorption spectroscopies. Theg and HFI tensor components determined by spectral simulation indicate rhombic symmetry and localization of an unpaired electron on the d _xy orbital for all the complexes. The unpaired electron fractions on - and -type metal ion and ligand AO were estimated from ESR and absorption spectra using LCAO MO method. Both - and -type bond covalences were shown to be greater in these complexes compared to only oxygen-containing crown ether complexes. The temperature dependence of g and A components in some complexes may be due to conformational changes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1938–1944, November, 1994.The present work was carried out with financial support from the Russian Foundation for Basic Research (Project 93-03 04089).     

Twelve-membered crown ethers: Crystal structures of benzo-12-crown-4 and naphtho-12-crown-4

The crystal structures of two 12-membered crown ethers, benzo-12-crown-4 (1) and naphtho-12-crown-4 (2), have been determined by X-ray analysis. Both structures are molecular. Compound1 is monoclonic,P2₁/b,a=8.466(3),b=8.019(3),c=33.590(10) Å, =90.99(3)^o. The unit cell contains two crystallographically independent molecules of1 with similar conformations. Compound2 is also monoclinic,P2₁/a,a=24.148(8),b=14.535(4),c=7.987(5) Å, =102.87(2)^o. Two independent molecules in the unit cell have significantly different conformations. Supplementary data relating to this publication have been deposited with the British Library as Supplementary Publication No. SUP 82145 (19 pages).     

Spin exchange between transition metal complexes and nitroxyl radicals in nonaqueous media

New complexes of diaza- and tetraaza-containing crown ethers, viz., 1,10-diaza-18-crown-6 (1), 1,4,8,12-tetraazacyclopentadecane (2), 1,4,8,11-tetraazacyclotetradecane (3), and 1,4,8,11-tetraazacyclotetradecane 1,4,8,11-tetrachloride tetraacetic acid tetrahydrate (4), with the divalent copper and nickel ions and the Cl^–, Br^–, ClO₄ ^–, NO₃ ^–, and AcO^– counterions were synthesized. The exchange interactions of these compounds and paramagnetic copper and nickel salts with the TEMPO radical in MeOH—CHCl₃ binary mixtures of different compositions were studied. The plots of the linewidths of the hyperfine coupling components of TEMPO vs. concentration of the ions and temperature show that the frequency of diffusion collisions is the rate-limiting step for spin exchange (strong exchange regime). A strong dependence of the exchange rate constant (k _ex) on the crown ether and counterion structure was found. The isotropic hyperfine coupling constants (a _Cu) and g factors (g _i ) were measured for the Cu^II complexes with the crown ethers. In the case of the crown ether complexes 1—3 with CuCl₂, the a _Cu constant decreases linearly with an increase in g _i = g _i – 2.0023 in the series 3 < 2 < 1, whereas k _ex increases linearly in the same series with a decrease in the contact HFC on the Cu^II nucleus (K) and a decrease in covalence of bonding. For the complexes of 2 with Cu^II and different axial ligands (counterions), k _ex increases in the series Cl^– < ClO₄ ^– AcO^– Br^–; < NO₃ ^–. In the case of the complexes of 2 with NiCl₂, k _ex increases in the series 1 < 4 < 3 2. For the Cu^II and Ni^II salts with the Cl^–, ClO₄ ^–, and NO₃ ^– anions, the k _ex values are almost independent of the anion nature. The correlation of the k _ex values with the electron-spin parameters of the complexes is discussed.     

Neue Kronenether‐stabilisierte Oxoniumhalogenochalkogenate: [H3O(Dibromo‐benzo‐18‐Krone‐6)]2[Se3Br10] und [H5O2(Bis‐dibromo‐dibenzo‐24‐Krone‐8]2[Se3Br8]

Novel Oxonium Halogenochalcogenates Stabilized by Crown Ethers: [H₃O(Dibromo‐benzo‐18‐crown‐6)]₂[Se₃Br₁₀] and [H₅O₂(Bis‐dibromo‐dibenzo‐24‐crown‐8]₂[Se₃Br₈] Two novel complex oxonium bromoselenates(II,IV) and –(II) are reported containing [H₃O]⁺ and [H₅O₂]⁺ cations coordinated by crown ether ligands. [H₃O(dibromo‐benzo‐18‐crown‐6)]₂[Se₃Br₁₀] ( 1 ) and [H₅O₂(bis‐dibromo‐dibenzo‐24‐crown‐8]₂[Se₃Br₈] ( 2 ) were prepared as dark red crystals from dichloromethane or acetonitrile solutions of selenium tetrabromide, the corresponding unsubstituted crown ethers, and aqueous hydrogen bromide. The products were characterized by their crystal structures and by vibrational spectra. 1 is triclinic, space group (Nr. 2) with a = 8.609(2) Å, b = 13.391(3) Å, c = 13.928(3) Å, α = 64.60(2)°, β = 76.18(2)°, γ = 87.78(2)°, V = 1404.7(5) ų, Z = 1. 2 is also triclinic, space group with a = 10.499(2) Å, b = 13.033(3) Å, c = 14.756(3) Å, α = 113.77(3)°, β = 98.17(3)°, γ = 93.55(3)°. V = 1813.2(7) ų, Z = 1. In the reaction mixture complex redox reactions take place, resulting in (partial) reduction of selenium and bromination of the crown ether molecules. In 1 the centrosymmetric trinuclear [Se₃Br₁₀]^2? consists of a central Se^IVBr₆ octahedron sharing trans edges with two square planar Se^IIBr₄ groups. The novel [Se₃Br₈]^2? in 2 is composed of three planar trans‐edge sharing Se^IIBr₄ squares in a linear arrangement. The internal structure of the oxonium‐crown ether complexes is largely determined by the steric restrictions imposed by the aromatic rings in the crown ether molecules, as compared to complexes with more flexible unsubstituted crown ether ligands.