Properties of cis- and trans-bis(crown ether)s for complexation and extraction of alkali metal picrates

The properties of cis- and trans-bis(crown ether)s containing benzo-15-crown-5 or benzo-18-crown-6 units as complexants and extractants for alkali metal picrates have been studied. The optical spectra suggest that the cis-bis(crown ether)s can form intramolecular 2:1 crown ether unit/cation complexes with particular metal cations easily, while the trans-bis(crown ether)s can form only 1:1 crown ether unit/cation complexes because of the unfavourable trans configuration for the formation of the 2:1 complexes. It was found that the cis isomer possesses much higher extractive power than the trans isomer for the metal cations, which also reflects their complexing properties. The extraction equilibrium constants and thermodynamic quantities have been also evaluated, and the effect of the stereochemical structure of the bis(crown ether) on the complexing and extractive properties is discussed.     

Supramolecular diaryliodonium salt‐crown ether complexes as cationic photoinitiators

Diaryliodonium salts spontaneously form crystalline 1:1 supramolecular complexes at room temperature in good to excellent yields with 18‐crown‐6 ether and its cyclohexano‐ and benzo‐substituted analogs. The complexes were characterized using IR, UV, MS, ¹H, and ¹³C‐NMR spectroscopy and by single crystal X‐ray crystallography. The analytical data obtained were consistent with a structure in which the positively charged iodine atom of diaryliodonium cation is positioned above and over the center of the crown ether ring with the positively charged iodine atom coordinated to the crown ether oxygen atoms. The diaryliodonium salt‐crown ether complexes are photosensitive and were used to carry out the photoinitiated cationic polymerizations of a number of mono‐ and difunctional monomers. During irradiation with UV light, the supramolecular complexes undergo photolysis with the generation of a Brønsted acid and with the concomitant release of the crown ether. When used as photoinitiators, the crown ether that is released markedly influences the kinetics of the subsequent cationic polymerization of the monomer. Further studies demonstrated that the photolysis of diaryliodonium salt‐crown ether supramolecular complexes can be photosensitized using typical‐electron transfer photosensitizers. Free radical‐promoted photosensitization using typical unimolecular free radical photoinitiators such as 2,2‐dimethoxy‐2‐phenylacetophenone also takes place readily. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Recoordination of a metal ion in the cavity of a crown compound: a theoretical study. 1. Conformers of arylazacrown ethers and their complexes with Ca2+ cation

Photoinduced recoordination of Ca²⁺ complexes of the photochromic azacrown ethers is studied by the density functional method. The study included model arylazacrown ethers containing various acceptor groups in the aromatic ring in the para position to the azacrown ether moiety and a real azacrown-containing styryl dye. It is found that both free azacrown ethers and their complexes can adopt two types of conformations: (1) axial conformations, in which the aromatic ring axis passing through the crown ether nitrogen N_cr and the opposite atom of the aromatic ring is perpendicular to the root-mean-square (RMS) plane of the crown ether (least-squares fitted plane for all the crown ether atoms), and (2) equatorial conformations, in which the aromatic ring axis only slightly deflects from the RMS plane of the crown ether. In the equatorial conformers, the metal cation is coordinated only to the O atoms of the azacrown ether cycle, the metal—nitrogen bond is broken, and N_cr is conjugated with the aromatic ring. In the axial conformers, the metal cation is additionally coordinated to N_cr. It is found that the presence of an acceptor group bearing a formal positive charge decreases the relative energy of the equatorial conformer and favors metal—nitrogen bond dissociation, which results in the recoordination of the metal cation. However, a long distance between the charged group and N_cr has the reverse effect. The photoinduced recoordination observed in the alkaline-earth metal complexes of the photochromic azacrown ethers is explained by the transitions between the axial and equatorial conformers facilitated by the charge transfer in the excited state of the complex.     

Modeling the effect of crosslinking in methyl-pendant poly(p-phenylene benzobisthiazole)

Molecular mechanics and dynamics simulations have been performed on methyl-pendant PBZT to study the effects of intermolecular crosslinking. Several possible crosslinked structures were investigated. The effect of crosslinking was found to be strongly dependent upon crosslink type and, in some instances, crosslink density. A significant axial stress is predicted to occur upon the formation of phenyl-to-phenyl type crosslinks. This provides a reasonable explanation for the experimental observation of transverse cracks in the skin of crosslinked, MePBZT fiber. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3057–3064, 1998     

Novel synthesis of polyphosphonates by the polyaddition of bis(epoxide) with diaryl phosphonates

The polyaddition of bisphenol A diglycidyl ether (BPGE) with bis(4‐chlorophenyl) phenylphosphonate was carried out using quaternary onium salts or crown ether complexes as catalysts. When the polyaddition was performed using tetrabutylammonium chloride, tetrabutylphosphonium chloride, or 18‐crown‐6/KCl in N‐ methyl‐2‐pyrrolidone at 110°C for 48 h, the corresponding polyphosphonate with moderated molecular weights was obtained in 88–96% yields. The structure of the resulting polyphosphonate was confirmed by IR and ¹H‐NMR spectra. The polyaddition of BPGE with various diaryl phosphonates also proceeded very smoothly to produce the corresponding polyphosphonates with moderate molecular weights. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 959–965, 1999     

Incorporating a flexible crown ether into neutral discrete self-assemblies driven by metal coordination

Driven by metal coordination, a flexible crown ether was self-assembled into neutral discrete complexes with two organoplatinum acceptors. Specifically, a [1 + 1]-assembled structure was separated from self-assemblies with different stoichiometries by vapor diffusion of acetone into their dichloromethane solution. The formation of these crown ether-incorporated self-assemblies was confirmed by NMR, elemental analysis, and X-ray single-crystal analysis.     

Lead‐sensitive PNIPAM microgels modified with crown ether groups

A series of lead‐sensitive poly(N‐isopropylacrylamide) microgels with pendant crown ether groups were prepared. Their cation‐sensitive behaviors were studied by dynamic light scattering. When ionic strength is not controlled, adding salts causes the microgel particles to deswell. However, when the salt effect is ruled out by keeping a constant ionic strength, adding Pb²⁺ results in much larger swelling. The Pb²⁺‐induced swelling was explained by the formation of host–guest complex between Pb²⁺ and the pendant crown ether groups, which increases the hydrophilicity of the polymer and accordingly the degree of swelling. The lead sensitivity of the microgels increases with increasing crown ether content. For the modified microgel with the highest crown ether content, it swells to ～430% of its original volume at [Pb²⁺] = 10 mM. Other cations also increase the swelling degree of the modified microgels. The extent of the cation‐induced swelling mainly depends on their affinity to the pendant crown ether groups. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4120–4127, 2010     

EXAFS investigations of strontium complexation by a polymer-supported crown ether

Extended X-ray absorption fine-structure (EXAFS) measurements have been used to probe the coordination environment of strontium ion sorbed from aqueous nitric acid solutions on an extraction chromatographic resin comprising a macrocyclic polyether dispersed on a polymeric support. The strontium EXAFS of the metal ions sorbed onto the resin are consistent with a 1:1:2 strontium:crown ether:nitrate stoichiometry in which the strontium is enveloped in the crown ether ring and both nitrate anions are coordinated to the strontium as bidentate ligands. This is the same structure and stoichiometry observed for complexes in liquid-liquid extraction when the macrocyclic polyether is dissolved in a diluent with low water miscibility like 1-octanol.     

Synthesis of helical polyisocyanides bearing aza‐crown ether groups as pendant

We, herein, present a novel synthesis of responsive helical poly(aryl isocyanide)s bearing aza‐crown ethers as pendant groups. Chiral aryl isocyanide monomers bearing an aza‐crown ether as a pendant were designed and synthesized, piror to polymerization using a Pd‐Pt µ‐ethynediyl complex as an initiator to give the corresponding polymers in good yield. The resulting polyisocyanides adopted a stable helical structure in solution, as confirmed by circular dichroism spectroscopic analysis. In addition, the polymers were soluble in various solvents. Furthemore, the addition of suitable alkali metal ions to the crown ether of the sidechain on the helical polyisocyanide to form host‐gest complexes resulted in deformation of the helix due to electrostatic repulsion, and these phenomena depended on the size of metal cations. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 496–504.     

Specific essential work of fracture of polyurethane thin films with different molecular structures

A series of polyurethane (PU) thin films with different hard-to-soft segment ratios were synthesized in our laboratory. The molecular and morphological structures of the PU films were characterized with Fourier transform infrared (FTIR), small-angle X-ray scattering (SAXS), wide-angle x-ray diffraction, dynamic mechanical analysis, and differential scanning calorimetry. The PU films showed a single glass transition when the hard-to-soft segment ratio varied from 1:2 to 1:8, suggesting no significant phase separation between the hard and soft segments. FTIR and SAXS results disclosed that the PU films had a network structure with the physical crosslinks formed via the intermolecular hydrogen bonds established between the hard segments. The fracture toughness of the ductile PU films was characterized with the essential work of fracture method under different conditions. It was found that the specific essential work of fracture was a function of the chain length between crosslinks and independent of the test temperature when fracture occurred at a temperature below the glass transition temperature. The physical meaning of this fracture parameter was proposed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1418–1424, 2007     

The sulfonation of crosslinked poly(ether ether ketone)—Diffusion‐controlled kinetics

The effect of crosslinks introduced by ion irradiation with 11.7 MeV proton and 30 MeV helium ions on the reactivity of poly(ether‐ether‐ketone) (PEEK) to sulfonation have been investigated following the kinetics of the reaction at room temperature. Concentrated sulfuric acid was used as a swelling and sulfonating agent and the reaction was followed by changes in the FTIR spectrum. The rate of reaction decreased with the degree of crosslinking and the progress with time was consistent with diffusion control of the sulfuric acid into the crosslinked matrix. The results were consistent with the efficiency of the ions in crosslinking PEEK and in particular with the differences in their linear energy transfer (LET). © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 775–783, 2009     

Calculation of lithium isotope effects in extraction systems with crown ethers

Complexes of lithium salts with benzo-15-crown-5 and its derivatives have been prepared. Their structure has been established by X-ray diffraction analysis. On the basis of obtained data, the dependence of partition function ratios for isotopic forms (β factors) of these compounds on the type of extracted salt anion and other factors has been analyzed. Taking into account previously calculated value of β factor for aqua complex of lithium ion, single isotope extraction separation factors (α) for Li⁶–Li⁷ pair have been determined. Quantum chemical calculations for vibrational frequencies of isotope forms of complexes with crown ethers have been performed with the aid of Firefly (PC GAMESS) software. Lithium cation complexes with crown ethers have been calculated using RHF/6-311++G** basis set. Isotope extraction separation factors have been shown to be independent of lithium ion concentration in aqueous phase and the type of extracted salt anion but depend only on the type and size of crown ether ring.     

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.     

Piezoelectric Crystal Liquid Flow Detection Systems Based on Alkyl (C18)‐Benzo‐15‐Crown 5 for Organic Compounds and Metal Ions

A water in soluble long‐chain crown ether alkyl (C18)‐benzo‐15‐crown‐5 was synthesized and applied as a coating material on quartz crystal membranes of a liquid flow piezo electric crystal sensor. The oscillating crown ether‐coated piezo electric (PZ) crystal with a home‐made computer inter face was prepared as a liquid chromato graphic (LC) detector for organic species and metal ions in aqueous solutions. The oscillating frequency of the quartz crystal decreased due to the adsorption of organic molecules or metal ions on crown ether molecules. Effects of functional group, molar mass, steric hindrance, and polarity of organic molecules on frequency responses of the crown ether coated PZ crystal detector were investigated. The frequency responses of the crown ether coated PZ crystal detector for various molecules were in the order: amines > carboxylic acids > alcohols > ketones. The crown ether PZ detector also exhibited good sensitivity for some heavy metal ions and the frequency shifts were in the order: Cr³⁺ » Pb²⁺ > Co²⁺ > Cd²⁺ > Ni²⁺ > Cu²⁺. The crown ether coated piezo electric crystal LC detector demonstrated low detection limits for various polar organic molecules, e.g., 6.0 × 10^?5 M for propylamine, and metal ions, e.g., 2.9 × 10^?5 M (1.8 ppm) for Cu²⁺; the crown ether PZ detector also gave good reproducibility when re used. A quite sensitive electrochemical quartz crystal microbalance (EQCM) detection system was also set‐up for detecting trace heavy metal ions in solutions. The variation in frequency of the PZ crystal and the diffusion current were observed simultaneously after the reduction in heavy metal ions such as Cu²⁺ and Ni²⁺. The EQCM detection system exhibited fairly good sensitivity, e.g., 112 Hz/ppm for Cu²⁺ and a good detection limit, e.g., 0.13 ppm for Cu²⁺ ions. Comparison between EQCM and PZ detection systems was made and discussed.     

Out-cage metal ion coordination by novel benzoazacrown bisamides with carboxyl,pyridyl and picolinate pendant arms

A new series of macrocyclic diamides with carboxyl, pyridyl and picolinate pendant arms have been synthesized and the stability constants of their complexes with Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺ in water were determined. Complexes with a stoichiometry of 1 : 1 (M: L) were found for all ligands with the exception of 15-membered crown ethers with one pendant carboxyl or pyridine group. The ligand containing two picolinate backbone groups exhibits the highest values of the stability constants for all studied cations (logβ_ML?=?12.5–15.7). X-ray study of free ligands showed that the introduction of benzene and amide fragments into the macrocyclic moiety provides a flatten open structure of the ligand. The crystallographic analysis of Cu²⁺ and Zn²⁺ complexes revealed the external coordination of the metal atom by amine N atoms of the macrocycle and heteroatoms of the pendant groups.     

Cation-π Interactions:Synthesis and Crystal Structure of Complex:[Na(DB18C6)]2[Pd(SCN)4]

The cation-π interactions have attracted much attention as an important noncovalent binding force. We have synthesized and characterized the first example[K(DB 18C6)]₂[Pd(SCN)₄] which exist K⁺-π interactions in crown ether compounds^[1]. However,the reported Na+ complexes structurally characterized by X-ray diffraction analysis have so far been limited to a few compounds. We now report the structure of complex:[Na(DB18C6)]₂[Pd(SCN)₄] which also exist Na⁺-n interactions.     

Crown ether styryl dyes

Regio- and stereoselectivity of [2+2]-photocycloaddition in complexes containing crown ether styryl dyes and alkaline-earth metal cations were studied using molecular mechanics. The main assumption is that the rate of the allowed concerted photocycloaddition correlates with the relative energies of the ground states of dimeric adducts, which are treated as pre-reaction complexes, and the resulting cyclobutanes. These energies are estimated by molecular mechanics within the MMX parameterization. The calculated characteristics of different dyes are studied as functions of the structure of the heterocyclic moiety, the structure and size of the N-substituent, the size of the crown ether cycle, and the nature of the metal cation. A comparison between the computational results and the experimental data showed that the observed quantum yield of the reaction is governed by the relative energies of the dimeric complexes and the resulting cyclobutanes as well as by the mutual arrangement of dye molecules in the dimeric complexes. Both factors are closely interrelated. The approach used in this work furnishes an explanation for the experimental data and provides a guideline for supramolecular control of regio- and stereochemistry of cation-dependent [2+2]-photocycloaddition. For Part 24, sec Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2185–2191, November, 1998.     

The interaction of alkali metal cations with aromatic molecules in complexes of the type M[AlMe3X]·aromatic,M[Al2Me6X]·aromatic,and related

The crystal structures of 13 compounds of the form M[Al₂Me₆X]·aromatic and related have been examined in order to learn about the M⁺...aromatic approach. Four types of interactions have been discerned: (1) metal...aromatic, (2) metal...aromatic...metal, (3) aromatic...metal...aromatic, and (4) no metal...aromatic contact. It was found that the closest K⁺...C(aromatic) and Cs⁺...C(aromatic) separations are essentially equal after a correction for the difference in metal radii. The strength of the K⁺...aromatic attraction was found to be sufficient to move the K⁺ ion 0.3 Å out of the plane of the crown ether in two complexes of dibenzo-18-crown-6.     

Crowned dendron: ion-responsive flexibility of macromolecules induced by integrated crown ether moieties

Polybenzyl ether type dendrons bearing the crown ether moieties at the periphery, namely, crowned dendrons were synthesized, and the effect of complex formation on their flexibility with metal-ion binding properties was examined. Upon addition of Na⁺, ¹H NMR spectra of the crowned dendrons in CD₃CN were significantly broadened, reflecting the flexibility restriction of the crowned dendrons by the complex formation with Na⁺. Such a significant flexibility restriction was observed only with Na⁺, although ESI-MS studies revealed that the crowned dendrons formed 1:2 complexes (a metal ion:the crown ether moiety) regardless of the kind of metal ions. The flexibility restriction became significant with increasing dendron generation on the basis of ¹H NMR spectra and spin-lattice relaxation time (T₁) measurements. Binding constants of the crowned dendrons with metal ions in CD₃CN decreased with the increase of the dendron generation, reflecting an influence of the charge repulsion as well as a dendrimer effect to cause the steric hindrance. The examination of UV-vis absorption spectra for complexes of the crowned dendron with metal picrates in THF displayed the formation of a loose ion-pair complex with Na⁺, namely, a typical sandwich type complex. However, in CH₃CN, all metal picrates were solvated to be in a loose ion-pair even without complex formation. These results suggested that the control of macromolecular flexibility with metal ions is feasible by the integration of crown ether moieties with a dendritic structure.     

A fast atom bombardment mass spectrometric analysis of crown ether complexes [1]

Analyses of crown ether complexes of alkali metal ions and characterization of the complexes formed inm-nitrobenzyl alcohol have been carried out by fast atom bombardment (FAB) mass spectrometry. By using m-nitrobenzyl alcohol as a matrix for measurements, the stoichiometry of the complexes was assessed on the basis of the observed FAB peaks. In addition, the formation of crown ether-alkali metal complexes at a 2 : 1 molar ratio was enhanced by increasing the ionic radius of the metal ion in agreement with previous observations. On these grounds, FAB mass spectrometry may provide a rapid means for investigation of the complexation behavior of crown ethers and the stoichiometry of the complexes.