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.     

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.     

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.     

Conductance Study of Binding of Some Rb+ and Cs+ Ions by Macrocyclic Polyethers in Acetonitrile Solution

A conductance study of the interaction between Rb+ and Cs+ ions and18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6),dibenzo-24-crown-8 (DB24C8), and dibenzo-30-crown-10 (DB30C10) inacetonitrile solution has been carried out at various temperatures. The formationconstants of the resulting 1:1 complexes were determined from the molarconductance-mole ratio data and found to vary in the orderDC18C6 > 18C6 > DB30C10 > DB18C6 DB24C8for Rb+ ion andDC18C6 > 18C6 > DB30C10 DB24C8 > DB18C6for Cs+ ion. The enthalpy and entropy of complexation were determined fromthe temperature dependence of the formation constants. The complexes with the18-crowns are both enthalpy and entropy stabilized while, in the case of largecrown ethers, the corresponding complexes are enthalpy stabilized but entropydestabilized.     

Conductance Study of the Thermodynamics of Tl+ ion Complexes with Different 18-Membered Crown Ethers in Binary Dimethylformamide-Acetonitrile Mixtures

A conductance study of the interactionbetween Tl⁺ ion and 18-crown-6 (18C6),dicyclohexano-18-crown-6 (DC18C6), benzo-18-crown-6(B18C6), diaza-18-crown-6 (DA18C6),dibenzyldiaza-18-crown-6 (DBzDA18C6) andhexaaza-18-crown-6 (HA18C6) indimethylformamide-acetonitrile mixtures was carriedout at various temperatures. The formation constantsof the resulting 1 : 1 complexes were determined fromthe molar conductance-mole ratio data and found tovary in the order HA18C6 > DA18C6 > DBzDA18C6 >18C6 > DC18C6 > B18C6. The enthalpy and entropy ofthe complexation reactions were determined from thetemperature dependence of the formation constants.     

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.     

Combination of size selective binding ability of 18-crown-6 dissolved in aqueous phase and extractive properties of an amic acid; toward enhancement of rare earths separation

The separation of La(III), Eu(III) and Er(III) ions by an amic acid, N,N-dioctyldiglycolamic acid (HL), dissolved in carbon tetrachloride has been improved in the presence of 18-crown-6 (18C6) in aqueous phase as a selective masking agent. The interaction between the studied metal ions and 18C6 resulted a shift in the extraction curve of the studied metal ions versus pH toward higher pH region. The displacement of the extraction curves was more pronounced for lanthanum ions and was varied as La(III) > Eu(III) > Er(III). This order of complexing ability of 18C6 toward the studied ions was attributed to the size adaptation of the ions and that of the crown ether cavity. The stability constants of the lanthanide–crown ether complexes in aqueous phase were evaluated. The influence of temperature on the extraction of studied metal ions from aqueous phase in the absence and the presence of 18C6 was tested in the range 298–308 K. This investigation allowed evaluating the thermodynamic parameters associated with the extraction process and those of the complexation of cations by 18C6 in the aqueous phase.     

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.     

Synthesis and rare earth metal ion-sensing properties of aza-crown derivative incorporating with diaryl-1,3,4-oxadiazole

A new fluorescent chemosensor (A18C6-Ox) in which a monoaza-18-crown-6 is linked to a diaryl-1,3,4-oxadiazole fluorophore by a methylene spacer has been synthesized to evaluate binding interaction with the rare earth ions by means of absorption and emission spectrophotometry. Absorption spectra of A18C6-Ox showed a broad band at 289nm and there was no significant change in the presence of Sc3+, La3+, Pr3+, Sm3+, Gd3+, Tb3+, Yb3+ and Lu3+ except for Ce3+ and Eu3+. From the emission spectral change of A18C6-Ox, interaction of the rare earth ions with A18C6-Ox is very strong. The formation of A18C6-Ox complexing with Sc3+, La3+, Pr3+, Sm3+, Gd3+, Tb3+, Yb3+ and Lu3+ leads to an increase in fluorescence intensity of A18C6-Ox, while Ce3+ and Eu3+ ions interact strongly causing fluorescence quenching of A18C6-Ox. In addition, the optimal complexation stoichiometry of the rare earth ions with A18C6-Ox was investigated by the fluorescent titration.     

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.     

Controlled photophysical behaviors between dibenzo-24-crown-8 bearing terpyridine moiety and fullerene-containing ammonium salt

A novel [2]pseudorotaxane was successfully constructed by the complexation of dibenzo[24]-crown-8 (DB24C8) derivative bearing terpyridine moiety (1) with lanthanide ion (Tb(3+)) and fullerene-containing ammonium salt (2), exhibiting the controlled photophysical behaviors as a reversible luminescent lanthanide switch in the presence of K(+) or 18-crown-6 (18C6).     

Conductance Study of Complexation of Lead Ions by Several 18-Membered Crown Ethers in Acetonitrile-Dimethyl Sulfoxide Mixtures Between 25 and 55°C

A conductance study of the interaction between Pb²⁺ ion and 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dicyclohexyl-18-crown-6 (DC18C6), aza-18-crown-6 (A18C6), diaza-18-crown-6 (DAI8C6), dibenzopyridino-18-crown-6 (DBPy18C6), and dibenzyldiaza-18-crown-6 (DBzDA18C6) in acetonitrile–dimethyl sulfoxide mixtures was carried out 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 DA18C6 > A18C6 > DBzDA18C6 > DC18C6 > 18C6 > B18C6 > DBPy18C6. The enthalpy and entropy of complexation reactions were determined from the temperature dependence of the formation constants. In all cases, the resulting complexes are enthalpy stabilized, but entropy destabilized. A linear relationship is observed between log K _f of different complexes and mole fraction of acetonitrile in the solvent mixtures. The TS ⁰ vs. H ⁰ plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of an enthalpy–entropy compensation in the complexation reactions.     

Spectroscopic study of charge transfer complexes of some benzo crown ethers with π-acceptors DDQ and TCNE in dichloromethane solution

Formation of the charge transfer complexes between benzo-15-crown-5, dibenzo-18-crown-6, dibenzo-24-crown-8 and dibenzo-crown-10 and the π-acceptors DDQ and TCNE in dichloromethane solution was investigated spectrophotometrically. The molar absorptivities and formation constants of the resulting 1:1 molecular complexes were determined. The stabilities of the complexes of both π-acceptors vary in the order DB18C6 > DB3OC10 ⋍ DB24C8 > B15C5. All of the resulting complexes were isolated in crystalline form and characterized. The influences of potassium ion on the formation and stability of the TCNE molecular complexes were studied. Effects of the crown ether structure and the role of the K⁺ ion on the formation of charge transfer complexes are discussed.     

Charge Transfer Complexes of Crown Ethers with Π-Acceptors. The Influence of NaCl and KCl on Their Stability

A spectrophotometric study was conducted on solutions of benzo-15-crown-5, dibenzo-18-crown-6 and dibenzo-24-crown-8 with the -acceptors, DDQ, and CHL in dichloromethane at room temperature. The stabilities of the resulting charge transfer complexes with the -acceptors DDQ were found to decrease in the order DB18C6>DB15C5>DB24C8 and with CHL it follows the order DB18C6>DB24C8. The addition of either NaCl or KCl affects the values of formation constants (K_c) and the order of stabilities of the charge transfer complexes. The formation constants in the absence and presence of NaCl and KCl salts were calculated and discussed.     

Complex formation of hydronium ion with several crown ethers in 1,2-dichloroethane,acetonitrile, and nitrobenzene solutions

A conductance study concerning the interaction between hydronium ion and several crown ethers in acetonitrile, nitrobenzene and 1,2-dichloroethane solutions has been carried out at 25°C. The stability constants of the resulting 1:1 complexes in acetonitrile and nitrobenzene solutions were determined from the molar conductance-mole ratio data and found to vary in the order 18C6>DB30C10>DC18C6>DB18C6>DB21C7>DB24C8>B15C5. In 1,2-dichloroethane solution, the complexation process results in the dissociation of ion pairs. There is an inverse relationship between the stabilities of the complexes and the Gutmann donicity of the solvents. In nitrobenzene solution, some evidence for the formation of a 2:1 sandwich adduct between the smaller crowns (i.e., B15C5 and 18-crowns) are observed from the molar conductance-mole ratio data which is supported by the¹H NMR data.     

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.     

稀土(III)与不饱和冠醚配位作用的热力学性质

用量热滴定法测定了2，3－二苯基-烯-[2]-1，4，7，10，13-五氧杂环十五烷（以下称2，3-二苯基-烯-[2]-15-冠-5）与稀土（Ⅲ）硝酸盐（La，Ce，Pr，Nd，Sm，Eu）在无水乙腈溶液中，298.15 K时配位作用的热力学性质．化学计量法表明，所有的稀土硝酸盐均与不饱和冠醚形成了1:1的配合物．实验中，由联接的计算机直接算出了配位物的稳定常数和配合作用的焓，进而算出了吉布斯自由能和配位熵. 结果表明，2，3-二苯基-烯-[2]-15-冠-5与Pr(NO_3)_3形成的配位化合物，其稳定常数最高，并与15-冠-5的实验结果作了比较．从热力学的观点讨论了不饱和冠醚分子结构和阳离子的性质对配位稳定性的影响．     

双冠醚配位作用的热力学性质V. 双(苯并-15-冠-5)与稀土(III)硝酸盐在无水乙腈溶液中分子内夹心配位作用

本文用分光光度滴定法测定了双(苯并-15-冠-5)(1)与轻稀土(III)硝酸盐在无水乙腈溶液中, 20.0-35.0℃时分子内夹心配位作用的稳定常数, 进而计算了配位焓和配位熵, 并与母体苯并15-冠-5(2)的实验结果作了比较。化学计量法表明, 所有稀土硝酸盐均与双(苯并-15-冠-5)形成了1 : 1的配合物。从热力学的观点, 讨论了双冠醚分子结构、尺寸效应和空间构型等配位稳定性的影响。研究结果发现, 双冠醚(1)对于Eu^3^+具有较强的配位能力和配位选择性, Nd^3^+次之。配合物的稳定性主要来自于熵的贡献。     

Lanthanide paramagnetic probes for NMR spectroscopic studies of fast molecular conformational dynamics and temperature control. Effective six-site proton exchange in 18-crown-6 by exchange spectroscopy

(1)H and (13)C NMR measurements are reported for the CDCl(3) and CD(2)Cl(2) solutions of [La(18-crown-6)(NO(3))(3)] (I), [Pr(18-crown-6) (NO(3))(3)] (II), [Ce(18-crown-6)(NO(3))(3)] (III), and [Nd(18-crown-6)(NO(3))(3)] (IV) complexes. Temperature dependencies of the (1)H NMR spectra of paramagnetic II-IV have been analyzed using the dynamic NMR (DNMR) methods for six-site exchange. Two types of conformational dynamic processes were identified (the first one is conditioned by interconversion of complex enantiomeric forms and pseudorotation of a macrocycle molecule upon the C(2) symmetry axis; the second one is conditioned by macrocycle molecule inversion). Application of exchange spectroscopy (2D-EXSY) of DNMR for investigation of this dynamic system (II-IV) simplifies the assignment of the NMR signals and represents the first experimental study of multisite exchange. In the present work, the methodology of paramagnetic 4f (Ce, Pr, and Nd) probe applications for the study of free-energy, enthalpy, and entropy changes in chemical exchange processes, as well as the advantages of this method in a comparison with DNMR studies of diamagnetic substances, is discussed. In particular, as a result of paramagnetic chemical shifts in 4f complexes, the range of measurable rate constants expands considerably compared to the analogous range in diamagnetic compounds. Coordination compounds investigated in the paper represent new types of thermometric NMR sensors and lanthanide paramagnetic probes for in situ temperature control in solution.     

Transport of silver ion through bulk liquid membrane using macrocyclic and acyclic ligands as carriers in organic solvents

The bulk liquid membrane transport of silver (I) ion was studied by dibenzopyridino-18-crown-6(DBPY18C6), 4-nitrobenzo-15-crown-5(NB15C5), 2-aminothiaphenol and a new synthesized ligand, 1,4-dioxa-7,10-dithiacyclododecane-2,3-dione as carriers in nitrobenzene (NB). The effects of pH on the source phase and receiving phase, the nature and concentration of stripping agents in the receiving phase and the picrate concentration as counter ion in source phase were investigated. The results show that the efficiency of transport of the Ag⁺ ion through membranes, changes with the nature of the ligand. The efficiency transport increases for the ligands with donating nitrogen and sulfur atoms with respect to oxygen donor atoms. Maximum transport efficiency was observed for silver (I) ion in the presence of thiosulfate ion ( ) as a suitable stripping agent. The results show that the sequence of transport efficiency for Ag⁺ ion using DBPY18C6, NB15C5, 2-aminothiaphenol and 1,4-dioxa-7,10-dithiacyclododecane-2,3-dione as carriers in organic solvents is: nitrobenzene > dichloromethane > 1,2- dichloroethane > chloroform.