Conductance studies of salt solutions in the presence of poly(vinylbenzo crown ethers)

The conductance of acetone and methyl ethyl ketone solutions of tetraphenylborate salts in the presence of homopolymers and styrene copolymers of vinylbenzo-15-crown-5 and vinylbenzo-18-crown-6 was studied, and the results compared with data obtained for crown ethers. Polycations are formed on binding cations to the poly(crown ethers), and the conductance behavior of the polyelectrolytes depends on the nature of the cation-crown complex and the spacing between crown moieties which in turn determines the charge density on the polymer chain. The compositions of the crown-cation complexes were determined for crown ethers. The complex formation constants of sodium and potassium cations to poly(vinylbenzo-18-crown-6) were found to change as more cations bind to the chain. This is not the case for the copolymers where the crown ligands are spaced farther apart. A mixture of poly(vinylbenzo-15-crown-5) and 10^?3M potassium tetraphenylborate in methyl ethyl ketone or acetone has a minimum conductance at a crown to cation ratio of 3.0, but the conductance rapidly increases on addition of crown ether. This was used to qualitatively determine the binding efficiency of a series of crown ethers since the rate of increase in the conductance is a measure of the binding ability of the crown ether to the cation.     

Synthesis and Cation Recognition Study of Novel Benzo Crown Ether Functionalized Enamine Derivatives

A novel series of benzo crown ether (dibenzo 18-crown-6 ether, benzo 18-crown-6 ether, and benzo 15-crown-5 ether) functionalized enamines derivatives from amino benzo crown ether (4-amino dibenzo 18-crown-6 ether, 4-amino benzo 18-crown-6 ether, 4-amino benzo 15-crown-5 ether) and substituted 3-(dimethylamino)-1-phenylprop-2-en-1-one compounds have been synthesized. All the synthesized compounds were characterized by infrared, ¹H NMR, ¹³C NMR, distortionless enhancement polarization transfer, and mass and elemental analysis techniques. The cation recognition property for benzo crown ether enamine 8a was studied by absorption and fluorescence spectroscopy.     

Synthesis of new polysilane-crown ether

This paper presents the synthesis of new polysilane with pendant crown ether groups. The polymer was obtained through the addition reaction of 4^′-allylbenzo-15-crown-5 to poly[methyl(H)-co-methylphenylsilane] copolymer in anhydrous toluene solution using hexachloroplatinic acid as a catalyst. The allyl functionalization of the crown ether was achieved by the coupling of the crown ether bromide with allyl magnesium chloride. The availability of the crown ether sites in complexation reactions with Cu(II) cations was tested.The chemical structures of all products and intermediates were studied using spectral methods (IR, ¹H-NMR, ¹³C-NMR, UV), gel permeation chromatography (GPC) and thermogravimetric analysis (TGA).     

Cation-complexation-induced aggregation and specific ion conduction of lipophilic crowned azobenzenes

Lipophilic azobenzene derivatives incorporating a monoazacrown or oligooxyethylene moiety were employed as a component of ion-conducting composite films containing a polyester elastomer and an alkali metal (Li⁺, Na⁺, K^–) perchlorate. Composite films of monoaza-15-crown-5-containing azobenzene1 exhibited ionic conductivities following the order of Na > Li > K, reflecting the cation-binding selectivity of the 15-crown-5 ring. The ion-conducting behavior of composite films of1 is quite different from that of composite films containing a 1 : 1 mixture of an azobenzene derivative without any crown moiety andN-phenyl-monoaza-15-crown-5 (ionic conductivity order of Li > Na > K >). It was suggested that cation and anion migration is predominant in the LiClO₄ and NaClO₄ systems, respectively. The specific ion conduction can be attributed to ordered aggregation of1 induced by cation complex formation of its crown moiety. Azobenzene derivatives incorporating a monoaza-12-crown-4, monaza-18-crown-6, or oligooxyethylene moiety cannot afford such aggregate formation and specific ion-conduction as is seen in the1 system.     

Molecular clips based on diphenylglycoluril and benzocrown ethers: promising complexing agents for the alkali metal cations

The interaction of new molecular clips containing diphenylglycoluril and benzocrown ethers moieties with alkali metals ions was studied. Stability constants were determined by spectrophotometric titrations with chloride salts in methanol. Complex stability and cation binding selectivity were shown to be dependent on the size of the crown ether moiety. The “sandwich-type” 1:1 (clip to cation) complexes and the “classical” 1:2 complexes were found. Their ratio varies depending on the molecular clips nature and on the cation type. It was found an unexpected selectivity of the molecular clip with benzo-15-crown-5 moieties toward K⁺ and Rb⁺ cations. The molecular structure of the clip complex with benzo-15-crown-5 fragments and sodium picrate was determined by X-ray crystallography. The crystal structure and solution-state structure were proven to be similar.     

Effect of structural variation within sym-(R)dibenzo-16-crown-5-oxyacetic acid resins upon the selectivity and efficiency of alkali-metal cation sorption

Five new crown ether carboxyhc acid resins have been prepared by condensation polymerization of sym-(R)dibenzo-16-crown-5-oxyacetic acids with formaldehyde. Competitive alkali-metal cation sorption by these novel resins, which contain both ion-exchange and crown ether binding sites for metal ions, has been investigated. As the R-group was varied (methyl, ethyl, propyl, butyl, hexyl and decyl) both the alkali-metal cation sorption selectivity and efficiency were affected. The highest efficiency (loading) and Na⁺ sorption selectivity were obtained when R = methyl, ethyl and propyl. The longer alkyl groups were found to be detrimental to both sorption efficiency and selectivity.     

Synthesis and structure of an indium(I) “crown sandwich”

The treatment of the soluble reagent indium(I) trifluoromethanesulfonate, InOTf, with the crown ether 15-crown-5 generates the salt [In(15-crown-5)₂][OTf] regardless of the stoichiometry employed. The toluene-soluble salt has been characterized by single-crystal X-ray diffraction and features a cation that may be described as containing an In^I center that is “sandwiched” by the two crown ethers.     

Cation-crown ether complex formation in water. II. Alkali and alkaline earth cations and 12-crown-4, 15-crown-5, and 18-crown-6

The stability constants and the partial molal volume and isentropic partial molal compressibility changes of complex formation between cations and crown ethers in water at 25°C are presented. The cations involved are Na⁺, K⁺, Rb⁺, Cs⁺, Ca²⁺, and Ba²⁺, and the crown ethers are 12-crown-4, 15-crown-5, and 18-crown-6. Values of V of complex formation have been discussed in terms of two simple models, one based on the scaled particle theory, and the others on the Drude-Nernst continuum model. The results indicate that the charge of the potassium cation in 18-crown-6 is especially well screened from the water. On this basis hydration numbers of complexed cations have been calculated. This shows that the size of the cation compared to the crown ether hole is important for the contacts between complexed cations and water.     

Side arm participation in lariat ether carboxylate-alkali metal cation complexes in solution

Lariat ether carboxylic acids of structure CECH₂OCH₂C₆H₄-2-CO₂H with crown ether (CE) ring sizes of 12-crown-4, 15-crown-5 and 18-crown-6 are prepared and converted into alkali metal-lariat ether carboxylate complexes. Absorptions for the diastereotopic benzylic protons in the ¹H NMR spectra of the complexes in CDCl₃ are utilized to probe the extent of side arm interaction with the crown ether-complexed metal ion as a function of the crown ether ring size and identity of the alkali metal cation.     

Sodium Ion Selective Electrodes Based on Lipophilic 16-Crown-5 Derivatives

Abstract

Six kinds of lipopholic 16-crown-5 derivatives possessing double side-chains were synthesized. The Na⁺-selectivities were examined with poly(vinyl chloride) (PVC) matrix-membrane electrodes using these crown compounds. It is an effective way for obtaining high Na⁺-selectivity by introducing a bulky side-chain such as a benzyloxymethyl group into the 16-crown-5. The electrodes based on 16-crown-5 derivatives having both a methyl or ethyl group and a benzyloxymethyl group at the pivot carbon (C-15) (3 or 4, see Figure 1) exhibited excellent Na⁺-selectivity over K⁺ (log k _Na.x = -2.65 and -2.75 for 3 and 4, respectively).     

Complexation of cobalt(II) perchlorate with crown ethers. Synthesis,properties and structure of complexes of cobalt(II) perchlorate with 16-crown-5 and its lariat derivatives

Complexes of cobalt(II) perchlorate with 16-crown-5 (L¹) and its two lariat derivatives, 15,15-dimethyl-16-crown-5 (L²) and 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (L³), have been prepared and characterized. The crystal structure of [Co(L³)H₂O)](ClO₄)_{_2} has been determined by X-ray crystallography. The cobalt(II) ion is heptacoordinated with five crown ether oxygen atoms at the equatorial plane, a side arm oxygen atom and a water molecule at the apical position. The coordination polyhedron of cobalt is a distorted pentagonal bipyramid with the average Co-O(crown) distance of 2.20(2)Å.     

Complex Formation of Crown Ethers with Cations in Water–Organic Solvent Mixtures. Part IV. Thermodynamics of Interaction of Na+ Ion with Benzo-15-crown-5 Ether in the Mixtures of Water with Acetonitrile at 298.15 K

The equilibrium constants of complex formation of benzo-15-crown-5 ether with sodium ion have been determined by molar conductance at various molar ratios of benzo- 15-crown-5 ether and sodium iodide in mixtures of water with acetonitrile at 298.15 K. The thermodynamic quantities of complex formation of benzo-15-crown-5 ether with sodium cation are calculated. The enthalpy of solvation of benzo-15-crown-5 ether and sodium ion complex is discussed together with solvation enthalpies of the cation and ligand. The contribution of the benzene ring to the thermodynamic properties of complex formation and to the enthalpy of solvation of the crown ether/ Na⁺ complex in the mixtures of water with acetonitrile are analyzed and discussed.     

Synthesis of poly(vinyl alcohol)-based poly(crown ether)s and permeability of their polymeric membranes

Polymers that contain crown ether moieties at the side chain and are capable of forming rather tough film were synthesized by the polymer reaction of poly(vinyl alcohol) with formyl derivatives of aliphatic crown ethers such as 12-crown-4, 15-crown-5, and 18-crown-6. In the passive transport of alkali metal picrates across the poly(crown ether) membranes the permeation, particularly of alkali metals which tend to form intramolecular sandwich-type complexes with the crown ether rings, was retarded, compared with a poly(vinyl alcohol) membrane. The cation selectivities in the permeation of poly(crown ether) membranes differed significantly from those of poly(vinyl alcohol).     

Study of complexation of phenylaza-15-crwon-5, 4-nitrobenzo- 15-crown-5, and benzo-15-crown-5 with Ag+, Tl+ and Pb2+ ions in methanol by competitive potentiometry

The complexation reaction of phenylaza-15-crwon-5, 4- nitrobenzo- 15-crown-5, and benzo-15-crown-5 with Ag⁺, Tl⁺ and Pb²⁺ ions in methanol solution have been studied by a competitive potentiometric method. The Ag⁺/Ag electrode used both as an indicator and reference electrode in a concentration cell. The emf of cell monitored as the crown ethers concentration varies through the titration. The stoichiometry and stability constants of resulting complexes have been evaluated by MINIQUAD. The stoichiometry for all resulting complexes was 1:1. The stability of these metal ions with derivatives of 15-crown-5 are in order phenylaza-15-crown-5 > Benzo-15-crown-5 > 4-nitrobenzo-15-crown-5, and for the each used crown ethers are as Pb²⁺ > Ag⁺ > Tl⁺. The effect of the substituted group on the stability of resulting complexes was considered. The obtained results are novel and interesting.     

Coprecipitation of 15-crown-5 ether complexes of lead and strontium with tungstosilicic acid

Lead as well as strontium form low solubility compounds of composition (ML₂)₂A·nH₂O, (M=Pb²⁺, Sr²⁺), in the presence of 15-crown-5 (L) and tungstosilicic acid (H₄A) in acid media as found by radiometric precipitation titration. “Sandwich” structure of crown-ether complexes of lead and strontium could be expected due to the small size of cavity of 15-crown-5. Coprecipitation of PbL_2/su2+ with crown complexes of strontium cation after adding tungstosilicic acid was studied in 0.01 mol·dm⁻³ HNO₃. A significant influence of H⁺ cation in 1 mol·dm⁻³ HNO₃ on coprecipitation of lead was observed. Formation of HL⁺ complexes by protonisation of 15-crown-5 competes to the formation of ML₂ ²⁺ complexes (approximately twenty percent of 15-crown-5 are used for creation of HL⁺ complexes). Formation of low solubility salts was utilised for separation of lead from strontium in 0.01 mol·dm⁻³ HNO₃. The ratio of constant stability of lead and strontium β‘ with 15-crown-5 in 0.01 mol·dm⁻³ HNO₃ was calculated. The separation factor S(Pb/Sr) depends on the ratio of stability constants β_PbL2/β_SrL2 The precipitation method can be used for separation of metals with high constant stability with crown ethers from solutions containing other metals in the case of gradual addition of crown.     

冠醚配合物热力学性质的研究(Ⅶ)-碱金属与2,3-苯并-6-甲基-15-冠-5配位反应的量热滴定研究

用自制跟踪绝热式滴定量热计研究了新合成的2,3-苯并-6-甲基-15-冠-5在无水甲醇介质中与碱金属的配位反应。     

A novel covalent functionalisation of poly (styrene-alt-maleic anhydride) with 4-amino benzo-9-crown-3 ether

The grafting of 4-amino benzo-9-crown-3 ether to poly (styrene-alt-maleic anhydride) has been described. The covalent grafting of crown ether has led to a considerable increase in the solubility of polymer in organic solvents such as dimethyl sulphoxide, dimethylformamide and tetrahydrofuran. The highest solubility was attained in DMF and DMSO. The covalently bonded 4-benzo-9-crown-3 ether allowed the hosting of Li⁺. The covalently grafted crown ether to polymer was identified by infrared spectroscopy and thermogravimetric analysis methods.     

Conductance study of the complexation of substituted and lariat 16-crown-5 derivatives with alkali metal ions in nonaqueous solvents

Formation constants (K _ML) of 1:1 complexes of 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (L16C5) and 15,15-dimethyl-16-crown-5 (DM16C5) with alkali metal ions were determined in acetonitrile (AN) and propylene carbonate (PC) by conductometry at 25°C. Except for the case of Li⁺-and K⁺-16C5 complexes in PC, the selectivity sequences of L16C5 and DM16C5 are identical with those of the parent crown ether 16-crown-5 (16C5) regardless of the solvent (AN, PC, methanol) (Na¹ > Li⁺ > K⁺ > Rb⁺ > Cs⁺), which show the size-fit correlation. The selectivities of L16C5 and DM16C5 for the alkali metal ions are governed not by the sidearms but by the cavity size. The stability of the crown ether complex is dependent not on the dielectric constant but largely on the donor number of the solvent. TheK _ML(M₁ ⁺)/K _ML(M₂ ⁺) ratio of L16C5 or 16C5 varies very much with the solvent in the cases of M₁=Na, M₂=K and M₁=Na, M₂=Li, but that of DM16C5 is almost constant regardless of the solvent.     

Cation-Coordinating Properties of Perfluoro-15-Crown-5

The coordinative properties of perfluoro-15-crown-5 with monocations were investigated using ¹⁹F NMR spectroscopy and ion-selective electrodes with perfluoro-15-crown-5 as the matrix of their sensor membranes and the fluorophilic tetrakis[3,5-bis(perfluorohexyl)phenyl]borate as ion exchanger site. The results show that perfluoro-15-crown-5 interacts weakly but significantly with Na⁺ and K⁺. Assuming 1:1 stoichiometry, the formal complexation constants were determined to be 5.5 and 1.7 M⁻¹, respectively. This weak binding is consistent with the strong electron withdrawing nature of the many fluorine atoms in the perfluorocrown ether. While perfluorinated crown ethers have been known to form host-guest complexes with the anions O₂⁻ and F⁻ in the gas-phase, this is the first study that quantitatively confirms cation binding to a perfluorocrown ether.     

Raman study of 12-crown-4, 15-crown-5, 18-crown-6 and their complexation with metal cations using Fourier deconvolution of CH stretching spectra

The Raman CH stretching spectra of 12-crown-4, 15-crown-5 and 18-crown-6 and their complexes with some metal cations— Li⁺, Na⁺, K⁺ and Cu⁺ in water solutions are studied. For the first time Fourier deconvolution is applied to resolve the overlapped components in the corresponding isotropic and anisotropic spectra. A model is introduced which explains the variety of components in the spectra by means of splitting of the unperturbed CH stretching frequency owing to intramolecular interactions and Fermi resonance. The coupling constants of these interactions, as well as all parameters according to the model, are calculated for studied crowns and their complexes. The differences in the number and intensity of the resolved components in the spectra of the various crowns are explained with the corresponding differences in the coupling constants and model parameters. It is established that complexation leads to some increase in the unperturbed stretching frequency, probably owing to the increase in strain of the crown molecule. It is concluded that 15-crown-5 forms 2:1 and 1:1 complexes with K⁺ and Na⁺ cations respectively and 12-crown-4 forms a 2:1 complex with the Na⁺ cation.