共查询到20条相似文献,搜索用时 15 毫秒
1.
Khalid M. Tawarah Fuad A. Ababneh 《Journal of inclusion phenomena and macrocyclic chemistry》1997,29(1):15-22
The binding of K+ by dibenzo-pyridino-18-crown-6 (B2-py-18-C-6) and1,10-N,N-didecyl-diaza-18-crown-6 (22-DD) has been studiedconductometrically at 10, 15, 20 and 25 °C in acetonitrile. Thecomplexes formed were assumed to have 1 : 1 stoichiometry. The complexes ofK+ with 18-crown-6 (18-C-6) and dibenzo-18-crown-6 (B2-18-C-6) were alsostudied for comparison purposes. The stability constant, K, of a givencomplex and its molar conductance, c, were obtained by subjectingthe conductance data to a non-linear least-squares curve fitting procedure.The values of the enthalpy change, H, the entropy change, Sand the Gibbs free energy, G, associated with the formation of the 1: 1 complexes were derived and compared with relevant literature data. Thevalues of G at 25 °C indicate that the binding capacity of thefour macrocycles follows the order 18-C-6 > 22-DD > B2-18-C-6 >B2-py-18-C-6. The difference between the molar ionic conductance of the freeK+ cation and that of the bound cation, KL+, was estimated and the trend insuch differences correlates with the molecular size of the macrocycle, L. 相似文献
2.
Mojtaba Shamsipur Mohammad Hossein Mashhadizadeh 《Journal of inclusion phenomena and macrocyclic chemistry》2000,38(1-4):277-286
Formation of the charge-transfer complexes betweenhexathia-18-crown-6, pentathia-15-crown-5,tetrathia-12-crown-4 and iodine in chloroform solution wasinvestigated spectrophotometrically. The molar absorptivities and formation constants of the resulting 1 : 1 molecularcomplexes were determined. The stability of the iodine complexes increased with the increasing number of donating sulfur atoms in thecrown ether ring. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. All molecular complexes formed were enthalpy stabilized, but entropy destabilized. From the thermodynamic data obtained, theT S° - H° plot shows a fairly good linear correlation, which indicates enthalpy-entropycompensation in the reactions. 相似文献
3.
The complexation reactions between Ag+ andTl+ ions with 15-crown-5 (15C5) and phenyl-aza-15-crown-5(PhA15C5) have been studied conductometrically in 90%acetonitrile-water and 50% acetonitrile - water mixed solvents attemperatures of 293, 298, 303 and 308 K. The stability constants of theresulting 1 : 1 complexes were determined, indicating that theTl+ complexes are more stable than the Ag+complexes. The enthalpy and entropy of crown complexation reactions were determined from the temperature dependence of the complexation constants.The enthalpy and entropy changes depend on solvent composition and the T S0
o–H0 plotshows a good linear correlation, indicating the existence of entropy –enthalpy compensation in the crown complexation reactions. 相似文献
4.
Mojtaba Shamsipur Gholamhossein Rounaghi Alexander I. Popov 《Journal of solution chemistry》1980,9(9):701-714
Formation constants for complexes of dibenzo-21-crown-7, dibenzo-24-crown-8 and dibenzo-27-crown-9 with the Na+, Cs+ and Tl+ ions have been determined by multinuclear NMR measurements in several nonaqueous solvents. The measurements of the cesium complexes were carried out at different temperatures and the enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants.The stabilities of these complexes in solvents of low to medium donicity, —nitromethane, acetonitrile, acetone, methanol, and propylene carbonate, vary in the order Tl+>Cs+>Na+. Depending on the relative sizes of the cation and of the ligand cavity, either a three-dimensional wrap-around complex or a two-dimensional crown complex are formed. For the cesium complexes, the values of H
c
o
and S
c
o
are definitely solvent-dependent and in all cases the complexes are enthalpy stabilized but entropy destabilized. A compensating effect is observed in the variation of the enthalpy and entropy of complexation so that the overall influence of the above solvents on the stability of the complexes is rather limited. 相似文献
5.
Ahmad Rouhollahi Mohammad Reza Ganjali Abolghasem Moghimi Gerald W. Buchanan Mojtaba Shamsipur 《Journal of inclusion phenomena and macrocyclic chemistry》1999,33(4):361-376
A synthetic procedure has been developed for the preparation of 4-carboxy-benzo-30-crown-10. The formation of Na+, K+, Rb+, Cs+ and Tl+ complexes with the large crown ether was investigated conductometrically in acetonitrile solution at various temperatures. The formation constants of the resulting 1:1 complexes were determined from the molar conductance-mole ratio data. It was found that the stability of the complexes vary in the order Tl+ > K+ > Rb+ > Cs+ > Na+. The data obtained in this study support the existence of a wrap around structure for the above complexes in solution. The enthalpy and entropy of complexation reactions were determined from the temperature dependence of the formation constants. In all cases, the complexes were enthalpy stabilized but entropy destabilized. The resulting TS° vs. H°plot showed a fairly good linear correlation, indicating the existence of an entropy-enthalpy compensation in the large crown complexation reactions. 相似文献
6.
Reed M. Izatt Tingmin Wang Jon K. Hathaway Xian X. Zhang Janet C. Curtis Jerald S. Bradshaw Cheng Y. Zhu Peter Huszthy 《Journal of inclusion phenomena and macrocyclic chemistry》1994,17(2):157-175
Equilibrium constant (K), enthalpy change (H), and entropy change (S) values were determined for the interactions of a series of chiral pyridino-18-crown-6 type ligands with enantiomers of several primary alkylammonium salts in various solvents. Good enantiomeric recognition in terms of logK was observed in many systems with logK values greater than 0.4. The extent of enantiomeric recognition and the stabilities of the chiral crown ether-ammonium salt complexes were found to depend on the rigidity of the macrocyclic frame of the ligand, the type and arrangement of the donor atoms on the ligand, the bulkiness of the substituents on the ligand's chiral centers, the location of the chiral centers on the ligand, and the solvent. The effects of these factors on the extent of enantiomeric recognition and on the stabilities of the complexes were examined for the systems studied. 相似文献
7.
Xian He Bu Dao Li An Yun Ti Chen Mitsuhiko Shionoya Eiichi Kimura 《Journal of inclusion phenomena and macrocyclic chemistry》1997,28(3):245-258
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. 相似文献
8.
First order solvolysis rates of the trans-dichlorobis (N-methylethylenediamine) cobalt(III) ion have been measured over a wide range of solvent compositions and temperatures in water–propan-2-ol and water–acetonitrile mixtures. The rate of solvolysis is faster in the former mixtures rather than the latter. Plots of log(rate constant) versus the reciprocal of the dielectric constant of the co-solvent, and also versus the Grunwald–Winstein Y-values are non-linear for both co-solvents; this non-linearity is derived from a large differential effect of solvent structure between the initial and transition states. However, extrema in the variation of enthalpy H and entropy S of activation correlate well with the extrema in physical properties of the mixtures which are related to changes in solvent structure. Linear plots of H versus S were obtained and the isokinetic temperature indicates that the reaction is entropy controlled. The application of a free-energy cycle shows that changes in solvent structure affect the pentacoordinated cobalt(III) ion in the transition state more than the hexacoordinated cobalt(III) ion in the initial state. In addition, the stabilizing influence of changes in solvent structure is greater in propan-2-ol–water mixtures than in acetonitrile–water mixtures, and the difference becomes greater as the mole fraction, x2 of the organic co-solvent increases. 相似文献
9.
Yoshikane Kawasaki Takuya Matsumoto 《Journal of inclusion phenomena and macrocyclic chemistry》1984,2(1-2):171-178
The rate constants k1 and activation enthalpies H of complex formation of dialkylthallium(III) perchlorates with some thia-18-crown-6 ethers were determined in acetonitrile. The equilibrium constants K were also obtained. More symmertrical thiacrown-ethers give smaller k1 and K values, which are mainly regulated by the entropy term rather than the enthalpy term. Diethylthallium(III) ion gives smaller rate constants than those of dimethylthallium(III) ion. The K values of these complexes decrease as oxygen of the 18-crown-6 was replaced by sulfur. 相似文献
10.
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. 相似文献
11.
Fatma M. Elzawawy 《Monatshefte für Chemie / Chemical Monthly》1991,122(11):921-925
Summary The stoichiometric stability constants for La(III) and Y(III)L-serine complexes were determined by potentiometric methods at different ionic strengths adjusted with NaClO4 and at different temperatures. The overall changes in free energy (G
o), enthalpy (H
o), and entropy (S
o) during the protonation ofL-serine and that accompanying the complex formation with the metal ions have been evaluated.
Komplexbildungskonstanten und thermodynamische Parameter für La(III)- und Y(III)-L-Serin-Komplexe
Zusammenfassung Die stöchiometrischen Komplexbildungskonstanten für La(III)- und Y(III)-L-Serin-Komplexe wurden mittels potentiometrischer Methoden bei verschiedenen Ionenstärken (mit NaClO4 adjustiert) und bei verschiedenen Temperaturen bestimmt. Die Änderungen in der freien Energie (G o), Enthalpie (H o) und Entropie (S o) während der Protonierung und der Komplexbildung mit den Metallionen wurden ermittelt.相似文献
12.
Hans-Jürgen Buschmann E. Schollmeyer Lucia Mutihac 《Journal of inclusion phenomena and macrocyclic chemistry》1998,30(1):21-28
Complex formation between several crown ethers and the cryptand (222) and -amino acids in methanol was studied by calorimetric titration. The ligand structure and the donor atoms of the ligands play an important role in determining the measured values of the reaction enthalpies and entropies. However, with the exception of the diaza crown ether (22) all stability constants are of the same order of magnitude. The enthalpic and entropic contributions to the stabilities of the complexes formed compensate each other. In methanolic solution the amino acids exist in their zwitterionic form. This equilibrium can be influenced. Under acidic, neutral or basic conditions different values of the reaction enthalpies are measured for the complexation of some amino acids with 18-crown-6. These results demonstrate that the concentration of the zwitterionic form of the -amino acids can be influenced. Thus the reaction between macrocyclic and macrobicyclic ligands and amino acids should be described by at least two different reaction schemes. 相似文献
13.
The interaction between Cd2+ and Pb2+ ions and 18-crown-6 (18C6), 1,10-diaza-18-crown-6 (C22) and 1,7-diaza-15-crown-5 (C21) were studied in water solvent at 25, 35, 45 and 55° using square wave voltammetric technique. The stoichiometry and stability of the complexes were determined by monitoring the shift in half-wave or peak potential of the polarographic waves of metal against the ligand concentration. Thermodynamic parameters such as G, H and S were obtained by using a polarographic double wall cell in which the temperature could be fixed to ±0.1°C. The results of all experiments show 1 : 1 complexes, but in addition to 1 : 1 ratio, a 2 : 1 ratio of ligand to cation is also obtained for C22–Pb2+ complex. The selectivity order for 18C6 and C22 is Pb2+ > Cd2+. The thermodynamic data G, H and S values show that the complexes are stabilized by both the enthalpy and entropy terms, but C22–Pb2+ complex is stabilized by only enthalpy term. 相似文献
14.
The relative thermodynamic stabilities of a number of isomeric allyl vinyl and propenyl vinyl ethers were determined by chemical equilibration in DMSO solution with KOBu-t as catalyst. From the temperature dependence of the values of the equilibrium constant the parameters G
m
, H
m
and S
m
of isomerization at 298.15 K were evaluated. Propenyl vinyl ethers, owing to their low enthalpy contents, are much more stable than the isomeric allyl vinyl ethers. It appears that in the parent propenyl vinyl ether, the Me group attached to C- of the divinyl ether skeleton has a strong stabilizing effect, comparable to that of alkyl groups in ordinary olefins, on the unsaturated system. In more heavily alkyl-substituted divinyl ethers, however, the stabilizing effects of alkyl groups are less prominent, being comparable to the low stabilization energies of alkyl groups in vinyl ethers, and depend moreover, on the pattern of substitution. 相似文献
15.
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. 相似文献
16.
The thermodynamic and thermal properties of [Cu(L)2·Cl2], [Ni(L)2]·Cl2, [Co(L)2·Cl2]; L=1,2-bis(o-aminophenoxy)ethane (BAFE), complexes have been investigated. The thermal decomposition of the complexes took place in two distinct steps in endothermic reaction up to 700°C. The activation energy E, the entropy change S
#, enthalpy H change and Gibbs free energy change G
# were calculated from the results of thermogravimetry analysis (TG) and heat capacity from the results of differential scanning calorimetry (DSC). It was found that the thermal stabilities and activation energies of the complexes follow the order Ni(II)>Cu(II)>Co(II) and E
Co<E
Ni<E
Cu, respectively.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
17.
Vasil'ev V. P. Orlova T. D. Balashova T. V. 《Russian Journal of Coordination Chemistry》2002,28(10):706-708
Heats and constants of 15-crown-5 (R) complexation with silver and lead ions at 298, 308, and 318 K are determined using direct calorimetry. Thermodynamic parameters (G°, H°, S°, and C
p°) of formation of AgR+ and PbR2+ complexes at various temperatures are calculated. The effects of the properties of the cations and crown ethers on the thermodynamic parameters of complexation are discussed. 相似文献
18.
Susan Sadeghi Naader Alizadeh Mojtaba Shamsipur 《Journal of inclusion phenomena and macrocyclic chemistry》1999,34(4):431-443
The formation of molecular complexes with 1 : 1 stoichiometry between 2,4,6-trinitrophenol and aza-12-crown-4, aza-15-crown-5 and aza-18-crown-6 in chloroform solution was investigated spectrophotometrically. The resulting complexes were isolated and characterized by microchemical analysis, IR and NMR spectroscopy. The equilibrium constants of the 1 : 1 adducts were evaluated from the non-linear least-squares fitting of the absorbance-mole ratio data. The overall stability of the 2,4,6-trinitrophenol complexes was found to vary in the order aza-15-crown-5 > aza-18-crown-6 aza-12-crown-4. The kinetics of complex formation between 2,4,6-trinitrophenol and the aza-substituted crown ethers used were investigated and in all cases the results showed the occurrence of an oscillating chemical reaction in solution. 相似文献
19.
The kinetics of the solvolysis of [Co(CN)5Cl]3– have been investigated in water +2-methoxyethanol and water + diethylene glycol mixtures. Although the addition of these linear hydrophilic cosolvent molecules to water produces curvature in the variation of log(rate constant) with the reciprocal of the dielectric constant, their effect on the enthalpy and entropy of activation is minimal, unlike the effect of hydrophobic cosolvents. The application of a Gibbs energy cycle to the solvolysis in water and in the mixtures using either solvent-sorting or TATB values for the Gibbs energy of transfer of the chloride ion between water and the mixture shows that the relative stability of the emergent solvated Co(III) ion in the transition state compared to that of Co(CN)5Cl3– in the initial state increases with increasing content of cosolvent in the mixture. By comparing the effects of other cosolvents on the solvolysis, this differential increase in the relative stabilities of the two species increases with the degree of hydrophobicity of the cosolvent.List of Symbols v2
partial molar volume of the cosolvent in water + cosolvent mixtures
-
V
2
o
molar volume of the pure cosolvent
- H
mix
E
excess enthalpy of mixing water and cosolvent
- S
mix
E
excess entropy of mixing water and cosolvent
- G
t
o
(i)n
the Gibbs energy of transfer of speciesi from water into the water + cosolvent mixture excluding electrostatic contributions
-
k
s
first order rate constant for the solvolysis in water + cosolvent mixtures
-
D
s
dielectric constant of the water + cosolvent mixture
- H
*
the enthalpy of activation for the solvolysis
- S
*
the entropy of activation for the solvolysis
- G
*
the Gibbs energy of activation for the solvolysis
- V
*
the volume of activation for the solvolysis
-
i
*
speciesi in the transition state for the solvolysis
-
H
o
Hammett Acidity Function
- TATB
method for estimating the Gibbs energy of transfer for single ions assuming those for Ph4As+ and BPh
4
–
are equal 相似文献
20.
Al-Subu Mohammad M. Jondi Waheed J. Dado Saida A. Hilal Hikmat S. 《Transition Metal Chemistry》2002,27(2):223-227
The kinetics of oxidation of 1-octene and heptanal by 18-crown-6-ether-solubilized KMnO4 in benzene and CH2Cl2 have been investigated. In benzene, the oxidation of 1-octene is first order with respect to the oxidant and zero order with respect to the substrate, whereas in CH2Cl2 the reaction is first order with respect to both substrate and oxidant. The reaction of heptanal followed different kinetics being first order with respect to both substrate and oxidant, regardless of whether benzene or CH2Cl2 was employed as the solvent. The values of activation energy E
a, standard enthalpy H
*, standard entropy change S
*, and standard free energy G
*, for the reaction, are reported. Mechanistic pathways for the studied reactions are also proposed. 相似文献