Stability of Complexes of NH4 + with 18-Crown-6, Dicyclohexyl-18-Crown-6, Dibenzo-18-Crown-6 and Dibenzo-24-Crown-8 in Water Saturated Nitrobenzene

From extraction experiments with ²²Na tracer, the exchange extraction constants corresponding to the NH₄ ⁺(aq) + NaL⁺ (nb)NH₄L⁺(nb) + Na⁺ (aq) equilibrium taking place in the two-phase water-nitrobenzene system (L = 18-crown-6, dicyclohexyl-18-crown-6, dibenzo-18-crown-6 and dibenzo-24-crown-8; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the stability constants of the NH₄L⁺ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the order dibenzo-24-crown-8 (DB24C8) < dibenzo-18-crown-6 (DB18C6) < dicyclohexyl-18-crown-6 (DCH18C6) < 18-crown-6 (18C6).     

Extraction of microamounts of calcium into nitrobenzene using hydrogen dicarbollylcobaltate in the presence of dibenzo-21-crown-7 and dibenzo-24-crown-8

Extraction of microamounts of calcium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H⁺B⁻) in the presence of dibenzo-21-crown-7 (DB21C7) and dibenzo-24-crown-8 (DB24C8) has been investigated. The equilibrium data have been explained assuming that the complexes HL⁺, CaL²⁺, CaL₂²⁺ and CaHL₂³⁺ (L = DB21C7, DB24C8) are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined.     

Crown ether molecular complexes with urea and thiourea

Crystalline complexes of urea and thiourea with crown ethers, have been prepared, viz., 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6 (DC 18C6) and dibenzo-24-crown-8 (DB24C8). While the complexes of the large ring size crown ether, DB24C8, have high ether to (thio)urea ratios, the stoichiometry of the others lies between one molecule of crown ether and from one to six molecules of (thio)urea. An IR spectral study of the urea and thiourea complexes showed that the behavior of thiourea in these complexes is clearly different from that of urea, indicating the role of sulphur in the interaction of thiourea with crown ethers. The urea and thiourea complexes were classified according to their stoichiometries and their IR spectral behavior into three classes for which credible structures were proposed.     

Lithium-7 NMR Study of Several Li+-Crown Ether Complexes in Binary Acetone-Nitrobenzene Mixtures

⁷Li NMR measurements were employed to monitor the stoichiometry andstability of Li⁺ ion complexes with 12-crown-4 (12C4), 15-crown-5 (15C5), benzo-15-crown-5 (B15C5) l8-crown-6 (18C6), dicyclohexano-18-crown-6 (DC18C6) and dibenzo-18-crown-6 (DB18C6) in binary acetone-nitrobenzene mixtures of varying composition. In all cases studied, the variation of ⁷Li chemical shift with the crown/Li⁺ mole ratio indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant. In all solvent mixtures used, the stabilities of the resulting 1:1 complexes varied in the order15C5 > B15C5 > DC18C6 > 18C6 > 12C4 >DB18C6. It was found that,in the case of all complexes, an increase in the percentage of acetone in thesolvent mixtures significantly decreased the stability of the complexes.     

Synergistic extraction of americium(III) with 2-thenoyltrifluoroacetone and crown ethers

Extracton, of Am³⁺ in benzene with 2-thenoyltrifluoroacetone (HTTA) and crown ethers (CEs) such as 15-crown-5, 18-crown-6, dicyclohexano-18-crown-6, dibenzo-18-crown-6, dicyclohexano-24-crown-8, and dibenzo-24-crown-8 was investigated. Synergistic effect by CE was observed regardless of the kind of CE examined. The extracted species was found to be Am(TTA)₃(CE), and adduct formation constants between Am(TTA)₃ and CE in the organic phase were determined. The sequence of constant could not be explained only by basicity of CE and the steric effect of CE should be taken into account to elucidate the adduct complex formation.     

Polarographic Study of Thallium(I) Complexes with Large Crown Ethers in Binary Acetonitrile-Water Mixtures

The complexation reactions between the Tl⁺ ion and large crown ethers dibenzo-30-crown-10 (DB30C10), dibenzo-27-crown-9 (DB27C9), dibenzo-24-crown-8 (DB24C8) and dibenzo-21-crown-7 (DB21C7) were studied in different acetonitrile-water mixtures at 25°C using an a.c. polarographic technique. The stoichiometry and stability of the complexes were determined by monitoring the shift in peak potential of the polarographic waves of the metal ion against the crown concentration. In all solvent mixtures used, the stability of the resulting 1:1 complexes was found to vary in the order DC24C8 » DB30C10 > DB21C7 > DB27C9 > DB24C8. There is an inverse relationship between the complex formation constants and the amount of water in the mixed solvent. In all cases, a linear relation was observed between log K_f and the mole fraction of acetonitrile in its mixtures with water.     

Synergism of crown ethers in the thenoyl trifluoroacetone extraction of americium(III) in benzene medium

The synergism of the crown ethers (CE) dicyclohexano-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6) and 18-crown-6 (18C6) has been investigated in the thenoyl trifluoroacetone (HTTA) extraction of americium(III) in benzene medium from an aqueous phase of ionic strength 0.5 and pH 3.50 at room temperature (23°C). The extracted synergistic species have the general formula Am(TTA)₃ · CE except for DC18C6 in which case the species Am(TTA)₃·2CE was also observed at high CE concentrations. The order of synergism was found to be DC18C6>DB18C6>18C6, which is the order of the basicity of CE as indicated by their ability to extract hydrogen ions from nitric acid solutions.     

<Superscript>133</Superscript>Cs NMR Study of Cs<Superscript>+</Superscript> Ion Complexes with Dibenzo-24-crown-8, Dicyclohexano-24-crown-8 and Dibenzo-30-crown-10 in Binary Acetonitrile-Nitromethane Mixtures

Complexation of the cesium ion with the macrocyclic ligands: dibenzo-24-crown-8 (DB24C8), dicyclohexano-24-crown-8 (DC24C8) and dibenzo-30-crown-10 (DB30C10) was studied in binary acetonitrile-nitromethane mixtures by ¹³³Cs NMR spectroscopy. The ¹³³Cs chemical shift data indicated that the cesium cation forms 1:1 cation:ligand complexes with DB24C8 and DB30C10 but forms 2:1, 1:1 and 1:2 cation:ligand complexes with DC24C8 in acetonitrile-nitromethane mixtures. The formation constants of the complexes were calculated from the computer fitting of the chemical shift mole ratio data. The results show that the complex formation constants with the Cs⁺ cation vary in the order DC24C8>DB24C8∼DB30C10. It was found that the stability of the resulting complexes increases with increasing nitromethane concentration in the solvent mixture.     

Conductance Study of the Thermodynamics of Binding of Some Macrocyclic Polyethers with Tl+ Ion in Dimethylformamide-Acetonitrile Mixtures

The complexation reactions between Tl⁺ ion and dibenzo-30-crown-10 (DB30C10), dibenzo-24-crown-8 (DB24C8), dibenzo-21-crown-7 (DB21C7), and aza-18-crown-6 (A18C6) were studied in different dimethylformamide-acetonitrile mixtures at various temperatures. The formation constants of the resulting 1 : 1 complexes were determined from the molar conductance-mole ratio data and found to vary in the order A18C6 > DB30C10 > DB21C7 > DB24C8. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants.     

Extraction of tetrafluoroborate with crown ethers and its application to silicate rock analysis

Summary The extraction behaviour of tetrafluoroborate with crown ethers was studied. A high distribution ratio of tetrafluoroborate is obtained by extraction with dicyclohexano-18-crown-6 (DC18C6) in an organic solvent of high dielectric constant from potassium fluoride solution. The molar ratios of crown ether to KBF₄ in the extracted species are probably 1:1 for DC18C6, dibenzo-18-crown-6 and 18-crown-6, and 2:1 for benzo-15-crown-5 and 15-crown-5. The flow-injection extraction-spectrophotometric determination of tetrafluoroborate with Brilliant Green was worked out. Many rock reference samples were analyzed for boron (1–150 ppm).     

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.     

The extraction behavior of some dicarbollylcobaltate crown extraction systems

The extraction of cesium, strontium and barium by a nitrobenzene solution of dicarbollylcobaltate in the presence of various crown ethers has been investigated and the influence of the substituent of crown to the extraction possibility has been observed. It has been found, that the addition of DB15C5, DB18C6 and DB21C7 (but not DB24C8 and DCH24C8) increases the distribution ratio of Cs by one order of magnitude. The fivemembered crowns are usually more efficient extractants for strontium than DCH18C6, which is widely used for strontium separation. The distribution ratio of strontium D_Sr decreases in the order 15-crown-5>benzo-15-crown-5>2-hydroxymethyl-15-crown-5>cyclohexyl-15-crown-5 >dibenzo-15-crown-5> nitrobenzo-15-crown-5. The selectivity α(Sr/Ca) decreases in the order 15C5>B15C5>DB15C5>2HM15C5>CH15C5. A selectivity factor α(Sr/Ca)≥1000 can be reached in the presence of 15C5 and B15C5. Six-membered and four-membered crowns extract strontium worse than most of the five-membered crowns. The selectivity factors α(Sr/Ca)≈100 have been reached for six-membered crowns and α(Sr/Ca)<1 has been found for 12C4. The extraction of barium by a nitrobenzene solution of dicarbollylcobaltate in the presence of 15C5 is even more efficient as the extraction of strontium. In that system D_Sr>10⁴ and D_Ba>10⁴ have been found for the extraction of Sr and Ba by a 0.01M nitrobenzene solution of dicarbollylcobaltate (c_B=0.01 mol/l) from 0.1M HNO₃. Maximal values of separation factor α(Ba/Sr) have been found in the system containing DB21C7.     

Extraction of cesium into nitrobenzene using hydrogen dicarbollylcobaitate in the presence of dibenzo-24-crown-8

Extraction of microamounts of cesium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H⁺B⁻) in the presence of dibenzo-24-crown-8 (DB24C8,L) has been investigated. The equilibrium data have been explained assuming that the complexes HL⁺ and CsL⁺ are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined.     

Fencing of Photoinduced Electron Transfer in Nonconjugated Bichromophoric System by β-cyclodextrin Nanocavity

²³Na NMR measurements were employed to monitor the stability of Na⁺ ion complexes with 18-crown-6 (18C6), dicycloxyl-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6), 15-crown-5 (15C5) and benzo-15-crown-5 (B15C5) in binary acetonitrile–dimethylformamide mixtures of varying composition. In all cases, the variation of ²³Na chemical shift with [crown]/[Na⁺] mole ratios indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation which relates the observed chemical shifts to the formation constants. It was found that, in pure acetonitrile, the stabilities of the resulting 1:1 complexes vary in the order 15C5>DC18C6>B15C5>18C6>DB18C6, while in pure dimethylformamide the stability order is DC18C6>18C6>15C5>B15C5>DB18C6. The observed changes in the stability order could be related to the specific interactions between some crown ethers and acetonitrile. It was found that, in the case of all complexes, an increase in the percentage of dimethylformamide in the solvent mixtures would significantly decrease the stability of the complexes.     

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.     

Electrochemical behaviour of pyridoxine hydrochloride (vitamin B6) at carbon paste electrode modified with crown ethers

The electrochemical behaviour of pyridoxine hydrochloride (pyridoxine HCl) at the plain carbon paste electrode and the electrode modified with oxa crown ether has been studied using voltammetric and impedance measurements. The macrocycles used as modifiers were 18-crown-6, dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6 and dibenzo-24-crown-8, out of which DB18C6 gave better response for pyridoxine HCl. Tris buffer (pH 10.3) was chosen as an appropriate medium among the several supporting electrolytes of varying pH studied. The characterization of the DB18C6-modified electrode (CME-DB18C6) using kinetic parameters such as number of electrons (n) and electron transfer coefficient (α) is studied by cyclic voltammetry. Electrochemical impedance spectroscopic measurements obtained confirm the current enhancement over the modified electrode. Analytical applications of this electrode have been studied for the determination of pyridoxine HCl. A sensitive linear working range of 0.6 to 100 μg cm⁻³ with a detection limit of 0.4 μg cm⁻³ by differential pulse voltammetry was observed for pyridoxine HCl on CME-DB18C6. However, on decreasing the scan rate to 5 mV s⁻¹, the detection limit lowered to 0.2 μg cm⁻³. Interference from some vitamins like thiamine hydrochloride, riboflavin, nicotinamide, para-aminobenzoic acid, cyanocobalamin, folic acid and d-biotin and amino acid l-tryptophan was studied, and simultaneously, riboflavin, thiamine hydrochloride and pyridoxine HCl were determined over the modified electrode, CME-DB18C6. The modified electrode is successfully used for the determination of pyridoxine HCl in multivitamin pharmaceutical preparations.     

Stabilities in Water of Alkali Metal Ion Complexes with Dibenzo-24-crown-8 and Dibenzo-18-crown-6 and Their Transfer Activity Coefficients from Water to Nonaqueous Solvents

Stability constants K _ML for the 1:1 complexes of Na⁺, K⁺, Rb⁺, and Cs⁺ with dibenzo-24-crown-8 (DB24C8) and dibenzo-18-crown-6 (DB18C6) in water have been determined by a capillary electrophoretic technique at 25°C. The K _ML sequence is Na⁺ < K⁺ < Rb⁺ < Cs⁺ for DB24C8 and Na⁺ < K⁺ > Rb⁺ > Cs⁺ for DB18C6. Compared with DB18C6, DB24C8 exhibits higher selectivity for K⁺ over Na⁺, but lower selectivity for K⁺, Rb⁺, and Cs⁺. To evaluate the solvation of the complexes in water, their transfer activity coefficients sH₂O between polar nonaqueous solvents and water have been calculated. The sH₂O values provide the following information: interactions with water of the metal ions and of the crown-ether oxygens are greatly reduced upon complexation and the complexes undergo hydrophobic hydration in water; the character of each alkali metal ion in solvation is more effectively masked by DB24C8 than by DB18C6, because of the larger and more flexible ring structure of DB24C8. Solvent effects on the complex stabilities are discussed on the basis of the sH₂O values.     

Extraction of barium into nitrobenzene using hydrogen dicarbollylcobaltate in the presence of dibenzo-18-crown-6

Summary Extraction of microamounts of barium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H⁺B^-) in the presence of dibenzo-18-crown-6 (DB18C6, L) has been investigated. The equilibrium data have been explained assuming that the complexes HL⁺, BaL²⁺, BaL, BaHL³⁺and BaHL are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined.     

Potentiometric study of complexation of phenylaza-15-crown-5, 4-nitrobenzo-15-crown-5 and dibenzopyridino-18-crown-6 and other derivative of 18-crowns-6 with Na+ ion in methanol

The complexation reaction of phenylaza-15-crown-5, and 4-nitrobenzo-15-crown-5, benzo-15-crown-5 and dibenzopyrdino-18-crwon-6, dibenzo-18-crown-6,dicyclohexyl-18-crown-6(cis and trans), and 18-crown-6 with Na⁺ ion in methanol have been studied by potentiometric method. The Na⁺ ion-selective electrode has been used both as indicator and reference electrode. The stoichiometry and stability constants of complexes of these crown ethers with sodium ion were evaluated by MINIQUAD program. The major trend of stability of resulting complexes of these macrocycle with Na⁺ ion varied in the order DCY18C6 > DB18C6 > 18C6 > DBPY18C6 > phenylaza-15C5 > benzo-15C5 > 4-nitrobenzo-15C5. The obtained results in particular stability constant of complexes of DBPY18C6, phenylaza-15C5 and 4-nitrobenzo-15C5 with sodium ion in comparison with other crowns ether are novel, and interesting.     

Extraction of microamounts of calcium,strontium and barium into nitrobenzene by using hydrogen dicarbollylcobaltate in the presence of dibenzo-18-crown-6

Extraction of microamounts of calcium, strontium and barium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H⁺B⁻) in the presence of dibenzo-18-crown-6 (DB18C6, L) has been investigated. The equilibrium data have been explained assuming that the complexes HL⁺, ML²⁺, ML₂²⁺ and MHL₂³⁺ (M²⁺ = Ca²⁺, Sr²⁺, Ba²⁺) are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined.