Volume and compressibility changes of complex formation between 18-Crown-6 and NaCl,KCl, and CsCl in water

The apparent molal volumes and compressibilities of NaCl, KCl, and CsCl in mixtures of 18-Crown-6 and water have been calculated from density and speed-of-sound measurements at 25°C. The partial molal volumes and compressibilities of the salts when all cations have formed complexes with 18-Crown-6 molecules have been evaluated. The sign and magnitude of the volume and compressibility changes of complex formation strongly suggest that the charge of the cation becomes very effectively screened by the crown ether.     

Thermodynamics of Complex Formation and Solvation in the System NaCl-18-crown-6-Water-Dioxane

Stability constants of Na⁺ complexes with 18-crown-6-ether and thermodynamic characteristics of the complex formation in water and mixed water-dioxane solvents (0.2, 0.4, 0.6, and 0.8 wt. fraction of dioxane, 283-318 K) were determined by the method of EMF of galvanic circuits without transfer. Comparative thermodynamic analysis of the complex 18-crown-6Na⁺ formation reactions in water-dioxane, water-acetonitrile, water-acetone, water-methanol, and water-2-propanol mixtures was carried out. Contributions of the Gibbs energies of transfer (G _t) of 18-crown-6Na⁺, Na⁺, and the ligand to the increase in the stability of the complexes on replacement of water by mixed water-dioxane solvents were estimated. It was shown that the increase in the stability of sodium crown ether complexes primarily depends on solvation of the complex cation and desolvation of the central cation. Changes in the conformational Gibbs energy of the ligand and quantitative parameters of selective solvation of the reagents were estimated.     

Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali Cations

A series of double-armed benzo-15-crown-5 lariats (3–8) have been synthesized by the reaction of 4′, 5′-bis(bromomethyl)-benzo-15-crown-5 (2) with 4-hydroxybenzaldehyde, phenol, 4-chlorophenol, 4-methoxyphenol, 2-hydroxybenzaldehyde, and 4-acetamidophenol in 43 ~ 82% yields, respectively. The complex stability constants (K _S) and thermodynamic parameters for the stoichiometric 1:1 and/or 1:2 complexes of benzo-15-crown-5 1 and double-armed crown ethers 3–8 with alkali cations (Na⁺, K⁺, Rb⁺) have been determined in methanol–water (V/V=8:2) at 25 °C by means of microcalorimetric titrations. As compared with the parent benzo-15-crown-5 1, double-armed crown ethers 3–8 show unremarkable changes in the complex stability constants upon complexation with Na⁺, but present significantly enhanced binding ability toward cations larger than the crown cavity by the secondly sandwich complexation. Thermodynamically, the sandwich complexations of crown ethers 3-8 with cations are mostly enthalpy-driven processes accompanied with a moderate entropy loss. The binding ability and selectivity of cations by the double-armed crown ethers are discussed from the viewpoints of the electron density, additional binding site, softness, spatial arrangement, and especially the cooperative binding of two crown ether molecules toward one metal ion.     

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.     

Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali Cations

A series of double-armed benzo-15-crown-5 lariats (3–8) have been synthesized by the reaction of 4′, 5′-bis(bromomethyl)-benzo-15-crown-5 (2) with 4-hydroxybenzaldehyde, phenol, 4-chlorophenol, 4-methoxyphenol, 2-hydroxybenzaldehyde, and 4-acetamidophenol in 43 ~ 82% yields, respectively. The complex stability constants (K _S) and thermodynamic parameters for the stoichiometric 1:1 and/or 1:2 complexes of benzo-15-crown-5 1 and double-armed crown ethers 3–8 with alkali cations (Na⁺, K⁺, Rb⁺) have been determined in methanol–water (V/V=8:2) at 25 °C by means of microcalorimetric titrations. As compared with the parent benzo-15-crown-5 1, double-armed crown ethers 3–8 show unremarkable changes in the complex stability constants upon complexation with Na⁺, but present significantly enhanced binding ability toward cations larger than the crown cavity by the secondly sandwich complexation. Thermodynamically, the sandwich complexations of crown ethers 3-8 with cations are mostly enthalpy-driven processes accompanied with a moderate entropy loss. The binding ability and selectivity of cations by the double-armed crown ethers are discussed from the viewpoints of the electron density, additional binding site, softness, spatial arrangement, and especially the cooperative binding of two crown ether molecules toward one metal ion.Graphical Abstract Synthesis of Double-Armed Benzo-15-crown-5 and Their Complexation Thermodynamics with Alkali CationsYU LIU*, JIAN-RONG HAN, ZHONG-YU DUAN and HENG-YI ZHANG This revised version was published online in July 2005 with a corrected issue number.     

Solute-solvent interactions in water-tert-butyl alcohol mixtures. X. Partial molal volumes of alkali and halide lons

Ultrasonic vibration potentials for five alkali metal chlorides and five bromides in water-tert-butanol (t-BuOH) mixtures (t-BuOH mole percent X=2.5; 5.0; 7.5; 10.0 and 13.1%) have been measured as a function of concentration. From these data it has been possible to obtain for the first time the partial molal volumes of the individual ions in solvent mixtures. The partial molal volumes of Cl^– and Br^– ions go through a shallow minimum while those for alkali ions first incease or level off and then decrease as X is increased. A rapid decrease in the partial molal volumes occurs for H⁺ and Li⁺ in a narrow range of composition and these two ions appear to be essentially solvated by t-BuOH at X=13%. The modified Hepler's plots yield a single straight line for anions and cations up to X=5.0%, whereas two distinct lines are found at X7.5%. This change of behavior appears to be related to the maximum structuring effect of water upon addition of t-BuOH, which occurs in the same range.     

Synthesis and crystal structure of hexakis(isothiocyanato)erbium(III) thiocyanate bis(18-crown-6)dipotassium bis[(18-crown-6)ethanolpotassium]

A new complex compound, [K₂(18-crown-6)₂[K(18-crown-6)(EtOH)]₂[Er(NCS)₆](SCN) (I), was synthesized and its crystal structure was studied by X-ray diffraction. In this work, the synthes and X-ray difraction stady of the crystals of a new complex, hexakis (isothiocyanato) erbiu(III) thiocyanate bis(18-crown-6) dipotassium bis(18-crown-6) ethanolpotassium], [K₂(18-crown-6)₂][K(18-crown-6)(ETON)]₂[Er(NCS)₆(SCN)(I)] are described. In crystal I, the alternating [Er(NCS)₆]^3? anions and binuclear complex cation [K(18-crown-6)₂]²⁺ from infinite chains via the F-S bonds, while two complex cations [K(18-crown-6)(ETON)]⁺ and the statistically disordered SCN^? anion between them are linked by the hydragen bonds O-H…S and O-H…N. Complex I contains the host-guest complex cations [K₂(18-crown-6)₂)]²⁺ and [K(18-crown-6)(ETON)]⁺ [1]. The alternating octabedral [Er(NCS)₆]^3? anions and binuclear complex cations [K₂(18-crown-6)₂]²⁺of crystal I form infinite chains via the K-S bonds, while two complex cations [K(18-crown-6)(EtOH)]⁺ and the statistically disordered SCN^? anion lying between them are linked by interionic hydrogen bonds O-H…S and O-H…N. Complex I contains the host-guest complex cations [K₂(18-crown-6)₂]²⁺ and [K(18-crown-6)(EtOH)]⁺ [1].     

Nitro derivatives of <Emphasis Type="Italic">N</Emphasis>-alkylbenzoaza-15-crown-5: synthesis,structures, and complexation with metal and ammonium cations

A number of N-alkylnitrobenzoaza-15-crown-5 with the macrocycle N atom conjugated with the benzene ring were obtained. The structural and complexing properties of these compounds were compared with those of model nitrobenzo- and N-(4-nitrophenyl)aza-15-crown-5 using X-ray diffraction, ¹H NMR spectroscopy, and DFT calculations. The macrocyclic N atom of benzoazacrown ethers are characterized by a considerable contribution of the sp3-hybridized state and a pronounced pyramidal geometry; the crownlike conformation of the macrocycle is preorganized for cation binding, which facilitates complexation. The stability constants of the complexes of crown ethers with the NH₄ ⁺, EtNH₃ ⁺, Na⁺, K⁺, Ca²⁺, and Ba²⁺ ions were determined by 1H NMR titration in MeCN-d₃. The most stable complexes were obtained with alkaline-earth metal cations, which is due to the higher charge density at these cations. The characteristics of the complexing ability of N-alkylnitrobenzoaza-15-crown-5 toward alkaline earth metal cations are comparable with analogous characteristics of nitrobenzo-15-crown-5 and are much better than those of N-(4-nitrophenyl)aza-15-crown-5.     

(18-Crown-6)sodium tribromide and (18-crown-6)potassium triiodide (with an admixture of bromodiiodide): Synthesis and crystal structure

Two crystalline host-guest complexes are synthesized and studied using X-ray diffraction analysis: (18-crown-6)sodium tribromide [Na(18-crown-6)]⁺ · Br ₃ ^? (I) and (18-crown-6)potassium tribromide (with an admixture of bromodiiodide) [K(18-crown-6)]⁺ · (Br_0.25I_2.75)^? (II). The structures of compound I (space group P2₁/_{n, a} = 8.957 Å, b = 8.288 Å, c = 14.054 Å, β = 104.80°, Z = 2) and compound II (space group Cc, a = 8.417 Å, b = 15.147 Å, c = 17.445 Å, β = 99.01°, Z = 4) are solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.098 (I) and 0.036 (II) for all 2311 (I) and 2678 (II) independent measured reflections on a CAD-4 automated diffractometer (λMoK _α). Similar crystalline complexes I and II exist as infinite chains of alternating complex cations and trihalide anions linked to each other through weak Na-Br or K-I coordination bonds. In [Na(18-crown-6)]⁺ and [K(18-crown-6)]⁺ complex cations, the Na⁺ or K⁺ cation (coordination number is eight) is located in the center of the cavity of the 18-crown-6 ligand and coordinated by the six O atoms and two terminal Br or I atoms of two trihalide anions lying on opposite sides of the rms plane of the crown ligand.     

Synthesis and crystal structure of aqua(dibenzo-18-crown-6)potassium (dibenzo-18-crown-6)-(tetrachlorocuprato(II)-Cl)potassium

New mixed complex compound aqua(dibenzo-18-crown-6)potassium (dibenzo-18-crown-6)(tetrachlorocuprato(II)-Cl)potassium, [K(CuCl₄)(Db18C6)]^? · [K(Db18C6)(H₂O)]⁺, is synthesized and its crystal structure is studied by the method of x-ray structural analysis. The structure includes two independent complex ions, both of guest-host type: two cations K⁺ are located in the respective cavities of the Db18C6 crown-ligand (one in each) and each is coordinated by all its six O atoms and one Cl atom of the anion-ligand [CuCl₄]^2? or O atom of the ligand water molecule. Coordination of these two K⁺ cations is completed to hexagonal pyramidal one by formation by each of unusually weak coordination bond K⁺ → π(\(C\dddot - C\)) with two C atoms of respective benzene ring in the neighboring Db18C6 ligand. In this crystal structure the complex anions and cations form dual infinite chains via these coordination bonds and interionic O-H?Cl hydrogen bonds.     

Separation of common monovalent and divalent cations by ion chromatography on calcined silica gel cation-exchange stationary phases, with tyramine-oxalic acid-containing crown ether mobile phases and indirect photometric detection

Summary Pure silica gels (Pia Seed 5S-60-SIL) calcined at 200, 400, 600, 800 and 1000°C for 5 h have been used as cation-exchange stationary phases in ion chromatography with indirect photometric detection for common monovalent and divalent cations (Li⁺, Na⁺, NH₄ ⁺, K⁺, Mg²⁺ and Ca²⁺); 0.75mm tyramine (4-(2-aminoethyl)phenol)-0.25mm oxalic acid, pH 5.0, containing crown ethers (18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane) or 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)) was used as mobile phase. With increasing calcination temperature, the amounts of the crown ethers adsorbed on the calcined silica gel column increased and, consequently, the effect of the crown ethers as retention modifiers for these cations increased. Excellent simultaneous separation and highly sensitive detection of these cations at 275 nm were achieved in 17 min by use of a 150 mm×4.6 mm i.d. column packed with silica gel calcined at 1000°C and use of 0.75mm tyramine-0.25mm oxalic acid, pH 5.0, containing either 0.5mm 18-crown-6 or 5.0mm 15-crown-5 as mobile phase.     

Steric effects as a basis for improved monovalent cation extraction selectivity in crown ethers

Incorporation into a 20-crown-6 of a bulky substituent capable of impeding cation/anion access to one face of the crown ether cavity is shown to afford compounds exhibiting good extraction selectivity for potassium ion over both alkaline earth cations (Ca²⁺, Sr²⁺) and other alkali metal ions (Na⁺, Cs⁺), an apparent result of diminished flexibility of the crown ether cavity, inhibition of the formation of extractable sandwich complexes with large cations, and the destabilizing effect of forcing charge-neutralizing counter anions to approach from one face of the crown cavity.     

Synthesis and crystal structure of 18-crown-6 <Emphasis Type="Italic">E</Emphasis>-2-phenylethenylphosphonic acid diaqua(18-crown-6)sodium <Emphasis Type="Italic">E</Emphasis>-2-phenylethenylphosphonate

New complex compound, diaqua(18-crown-6)sodium E-2-phenylethenylphosphonate 18-crown-6 E-2-phenylethenylphosphonic acid, [Na(18-crown-6)(H₂O)₂]⁺·HO ₃ ^? PCH=CHPh·18-crown-6·H₂O₃PCH=CHPh, was obtained and its crystal and molecular structures were studied by the X-ray structural analysis. In this structure the complex cation [Na(18-crown-6)(H₂O)₂]⁺ is of guest-host type. The coordination polyhedron of its Na⁺ cation is a slightly screwed hexagonal bipyramid with the base consisting of all 6 O atoms of 18-crown-6 ligand and with two opposite apexes at two O atoms of two ligand water molecules. In the studied crystal structure the alternating complex cations and 18-crown-6 molecules as well as the molecules of acid and its anion HO ₃ ^? PCH=CHPh form by means of hydrogen bonds the infinite chains of two different types.     

Synthesis and complexing properties of bis-crown ethers incorporating benzo-15-crown-5 and metallocene

Bis-crown ethers in which the benzo-15-crown-5 units were linked to 1,1′-positions of metallocene (M = Fe or Ru) with amide, ester, or ? C? C? bonds were synthesized. Complexing ability of the compounds with alkali, alkali earth, and transition metal cations were measured by the solvent extraction method. The results showed that these crown ethers had high affinity toward alkali metal cations (Li⁺, Na⁺, K⁺, and Rb⁺) and heavy-metal cations (Ag⁺ and Tl⁺). The difference of complexing ability for metal cations between ferrocene and ruthenocene derivatives could not be detected significantly. The extractability of metallocene-bis-crown ethers for metal cations was more larger than that of the corresponding mono-crown ethers, and irregular increments of extractability were explained by assuming the existence of a mixture of 1:1 and 2:1 complexes.     

Densities and compressibilities of aqueous HCl and NaOH from 0 to 45°C. The effect of pressure on the ionization of water

The densities and sound speeds of aqueous HCl and NaOH solutions were measured from 0.1 to 1.0m and from 0 to 45°C. These data were combined with literature data and fitted to functions of molality and temperature. The apparent molal volumes V and compressibilities K of these solutions were fitted to functions of molality and temperature. The partial molal volumes and compressibilities of HCl and NaOH solutions were used to calculate the partial molal volume V and compressibility changes for the ionization of water. Combined with literature data these values of V adn were used to calculated the effect of pressure on the ionization constant of water K _w from 0 to 200°C. The effect of pressure on K _w calculated from partial molal quantities are in reasonable agreement with that determined directly from high pressure measurements taken from the literature up to 1000 bar. It is necessary to use the pressure dependence of K ⁰ to extend the calculated pressure dependence of K _w up to 6000 bar.     

Benzoaza-15-crown-5 ethers: synthesis,structure, and complex formation with metal and ethylammonium ions

Benzoaza-15-crown-5 ethers containing one or two nitrogen atoms in different positions of the macrocycle and bearing different substituents at these atoms were synthesized. The structures of azacrown ethers and their metal complexes were studied by X-ray diffraction. The stability constants of the complexes of azacrown ethers with Na⁺, Ca²⁺, Ba²⁺, Ag⁺, Pb²⁺, and EtNH₃ ⁺ ions were determined by ¹H NMR titration in MeCN-d₃. In free benzoazacrown ethers containing secondary nitrogen atoms bound to the benzene ring, as well as in N-acetyl derivatives, the N atoms are sp²-hybridized and have a planar geometry. The nitrogen lone pairs on the p orbitals are efficiently conjugated to the benzene ring or the carbonyl fragment of the acetyl group, which is unfavorable for the complex formation. In addition, the formation of complexes with benzoazacrown ethers containing secondary nitrogen atoms is hindered because the hydrogen atoms of the NH groups are directed to the center of the macrocyclic cavity. In benzoazacrown ethers bearing N-alkyl substituents or secondary nitrogen atoms distant from the benzene ring, the N atoms show a substantial contribution of the sp³-hybridized state and have a pronounced pyramidal configuration, which promotes the complex formation. The lead and calcium cations form the most stable complexes due to the high affinity of Pb²⁺ ions for O,N-containing ligands, a high charge density on these ions, and the better correspondence of the cavity size of the 15-membered macrocycles to the diameter of the Ca²⁺ ion. An increase in the stability of the complexes is observed mainly in going from monoazacrown ethers to diazacrown ethers containing identical substituents at the N atoms and in the following series of substituents: C(O)Me < H < Me < CH₂CO₂Et. In the case of the CH₂CO₂Et substituents, the carbonyl oxygen atom is also involved in the coordination to the cation. The characteristic features of the complexing ability of N-alkylbenzomonoaza-15-crown-5 ethers bearing the nitrogen atom conjugated to the benzene ring show that macro-cyclic ligands having this structure are promising as selective and efficient complexing agents for metal cations.     

Diaquabromo(18-crown-6)rubidium and triaqua(18-crown-6)barium dibromide monohydrate: Synthesis and crystal structures

Two complexes are synthesized: diaquabromo(18-crown-6)rubidium [RbBr(18-crown-6)(H₂O)₂] (I) and triaqua(18-crown-6)barium dibromide monohydrate [Ba(18-crown-6)(H₂O)₃]²⁺ 2Br^? · H₂O (II). The orthorhombic structure of compound I (space group Pnma, a = 10.124 Å, b = 15.205 Å, c = 12.544 Å, Z = 4) and the monoclinic structure of compound II (space group C 2/c, a = 17.910 Å, b = 10.315 Å, c = 14.879 Å, β = 123.23°, Z = 4) are determined by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.063 (I) and 0.042 (II) for all 2293 (I) and 3363 (II) independent measured reflections (CAD-4 automated diffractometer, λMoK _α). The complex molecule [RbBr(18-crown-6)(H₂O)₂] in compound I and the randomly disordered cation [Ba(18-crown-6)(H₂O)₃]²⁺ in compound II are of the host-guest type: their Rb⁺ or Ba²⁺ cation (its coordination number is nine) is located in the cavity of the 18-crown-6 ligand and coordinated by all six O atoms. In structure I, the coordination polyhedron of Rb⁺ is a distorted hexagonal pyramid with a triple apex at the Br^? ligand and two O atoms of the water molecules. In structure II, the Ba²⁺ polyhedron is a distorted hexagonal bipyramid with one apex at the O atom of the water molecule and the other split apex at two O atoms of water molecules.     

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.     

Competitive Potentiometric Study of a Series of 18-crown-6 with Some Alkali and Alkaline Earth Metal Ions in Methanol Using an Ag+/Ag Electrode

The complexation of some alkali and alkaline earth cations with18-crown-6(18C6), dibenzo-18-crown-6 (DB18C6), dicyclohexyl-18-crown-6 (DCY18C6), and dibenzopyridino-18-crown-6 (DBPY18C6) in a methanol solution has been studied by a competitive potentiometric titration using Ag⁺/Ag electrode as a probe. The stoichiometry and stability constants of the resulting complexes have been evaluated by the MINIQUAD program. The stoichiometry for all resulting complexes was 1:1. The order of stability of Ag⁺ complexes with desired crown ethers varied as DBPY18C6 > DCY18C6 > 18C6 > DB18C6.The stability of the resulting complexes for each of these crown ethers varies in the order ofK⁺ > Na⁺ and Ba²⁺ > Sr²⁺ > Ca²⁺ > Mg²⁺.For each of the used metal ions the major sequence of the stability constants of the resulting complexes varies as DCY18C6 > 18C6 > DB18C6 > DBPY18C6 with minor exceptions.     

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.