Solute–solvent interactions in the association of hexacyanoferrate(III) with group II A cations. A calorimetric study

1982 ◽  
Vol 60 (14) ◽  
pp. 1828-1831 ◽  
Author(s):  
Roberto Aruga
Keyword(s):  
Equilibrium Constants ◽  
Ion Pairs ◽  
Ion Pair ◽  
Pair Formation ◽  
Calorimetric Study ◽  
Thermodynamic Quantities ◽  
Gibbs Function ◽  
Direct Calorimetry ◽  
Solvent Interactions ◽  
Enthalpy Of Association

Enthalpy of association of hexacyanoferrate(III) ion with Mg(II), Ca(II), Sr(II), and Ba(II) cations has been determined by direct calorimetry. Using the equilibrium constants, Gibbs function and entropy were also obtained. Measurements were carried out in aqueous medium at 25 °C and ionic strength I = 0.1 mol L−1. Examination of the thermodynamic quantities obtained and calculation of the distance of closest approach between cation and anion show the presence of different desolvation processes for the metals studied. More particularly, solvent-separated ion pairs in the case of magnesium and contact pairs in the case of barium seem to be present. The presence of desolvation processes is uncertain for calcium and strontium. The ΔH0 and ΔS0 values show also an important influence from solvent-destructuring processes on ion pair formation.

Coordinating properties of pyrrolic and pyridinic nitrogen with metals in aqueous solution. A calorimetric study

1981 ◽  
Vol 34 (3) ◽  
pp. 501 ◽  
Author(s):  
R Aruga
Keyword(s):  
Equilibrium Constants ◽  
Carboxylate Ligand ◽  
Calorimetric Study ◽  
Thermodynamic Quantities ◽  
Gibbs Function ◽  
Direct Calorimetry ◽  
Enthalpy Of Complex Formation ◽  
Pyridinic Nitrogen ◽  
Enthalpy Data ◽  
Nitrogen Bond

Enthalpy of complex formation of pyrrole-2-carboxylate ligand with calcium(II), cobalt(II), nickel(II) and copper(II) cations has been determined by direct calorimetry. By means of the equilibrium constants, Gibbs function and entropy were also obtained. The measurements were carried out in aqueous medium at 25�C and an ionic strength of 1 (NaNO3). The thermodynamic quantities for pyrrole-2-carboxylate, compared with those for pyridine-2-carboxylate obtained previously, lead to the following conclusions. (A) The enthalpy factors which make the metal-pyridinic ligand complexes rather stable are absent in the case of pyrrolic ligand. The absence is probably due to the electronic structure of the pyrrole aromatic ring. (B) The enthalpy data seem to indicate, for the metal complexes of pyrazole and imidazole, a metal-pyridinic nitrogen bond rather than a metal-pyrrolic nitrogen bond.

Electrical conductivities of quaternary ammonium salts in acetone.: Part III. Ion-pair formation

1968 ◽  
Vol 46 (12) ◽  
pp. 2005-2011 ◽  
Author(s):  
W. A. Adams ◽  
K. J. Laidler
Keyword(s):  
Dissociation Constants ◽  
Ion Pairs ◽  
Ion Pair ◽  
Pair Formation ◽  
Quaternary Ammonium Salts ◽  
Acetone Solution ◽  
Ammonium Salts ◽  
Electrical Conductivities ◽  
Tetraethylammonium Iodide ◽  
Kbar Pressure

The ion-pair dissociation constants determined from a Shedlovsky analysis of conductivity (see Part I) were used to calculate the enthalpy, the internal energy at constant volume, the entropy, and the volume of dissociation of tetramethylammonium iodide, tetraethylammonium iodide, and tetra-n-propylammonium iodide ion pairs in acetone solution. The sign and magnitude of these parameters over the range of conditions investigated, temperature 25 to 55 °C and atmospheric to 1.1 kbar pressure, indicated that the free ions in acetone solution are extensively solvated and that, depending on the conditions, solvent-shared or solvent-separated ion pairs are formed.

Coordinating Properties of Aromatic and Aliphatic Sulfur with Bivalent Metals in Aqueous Solution. A Calorimetric Study

1979 ◽  
Vol 32 (4) ◽  
pp. 709 ◽  
Author(s):  
R Aruga
Keyword(s):  
Aqueous Solution ◽  
Ionic Strength ◽  
Complex Formation ◽  
Aqueous Medium ◽  
Formation Constants ◽  
Calorimetric Study ◽  
Thermodynamic Quantities ◽  
Direct Calorimetry ◽  
Bivalent Metals

Heats and entropies of complex formation of the thiophen-2-carboxylate ion with Ni2+, Cu2+, Zn2+ and Cd2+ have been determined by direct calorimetry, the formation constants being known from the literature. The measurements were carried out in aqueous medium at 25�C and an ionic strength of 1. The values of the thermodynamic quantities for thiophen-2-carboxylate, compared with those for (ethylthio)acetate and (phenylthio)acetate obtained previously, indicate a greater tendency for aromatic sulfur to form bonds with the above metals than for aliphatic sulfur. The causes of this behaviour are discussed.

ION PAIR EFFECTS IN THE REACTION BETWEEN POTASSIUM FERROCYANIDE AND POTASSIUM PERSULFATE

1966 ◽  
Vol 44 (4) ◽  
pp. 437-445 ◽  
Author(s):  
R. W. Chlebek ◽  
M. W. Lister
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Ion Pairs ◽  
Ion Pair ◽  
Glass Electrode ◽  
Potassium Ferrocyanide ◽  
Potassium Persulfate ◽  
Ion Concentration ◽  
True Rate

The rate of the reaction between potassium ferrocyanide and potassium persulfate has been measured over a range of conditions. The rate is dependent on the potassium ion concentration, and it is shown that this is explained if it is assumed that KFe(CN)63− and KS2O8− are the reacting species. The equilibrium constants governing the formation of these ion pairs were measured with a cation-sensitive glass electrode. Similar constants for the products KFeCCN6)2− and KSO4−, and also for KNO3, were measured. From these equilibrium constants, the true rate constants of the reaction can be obtained, and it is shown that these vary with ionic strength in the manner predicted by Brönsted's equation.

Thermodynamics and mechanism of hydrophobic interaction

1977 ◽  
Vol 30 (4) ◽  
pp. 741 ◽  
Author(s):  
DG Oakenfull ◽  
DE Fenwick
Keyword(s):  
Free Energy ◽  
Volume Change ◽  
Hydrophobic Interaction ◽  
Ion Pairs ◽  
Hydrophobic Hydration ◽  
Partial Molar Volumes ◽  
Hydrocarbon Chain ◽  
Ion Pair ◽  
Pair Formation ◽  
Ion Pair Formation

.In the mixed solvent, 0.1 mole fraction ethanol-water, long-chain decyltrimethylammonium carboxylates form ion pairs. Ion-pair association constants (and hence the free energy of ion-pair formation) can be measured conductometrically. It is possible to separate the hydrophobic from the electrostatic contribution to the free energy of ion-pair formation by systematically varying the hydrocarbon chain length. We report measurements of the free energy of hydrophobic interaction (ΔG°HI) over the temperature range 278-328 K. The value of ΔG°HI becomes more negative (stronger hydrophobic interaction) with increasing temperature. The temperature coefficient of ΔG°HI was used to calculate the enthalpy (ΔH°HI) and entropy (ΔS°HI) of hydrophobic interaction. At low temperature the entropic contribution to the free energy is the larger but ΔH°HI, dominates at temperatures above c. 324 K. The volume change of hydrophobic interaction was similarly estimated from the volume change of ion-pair formation. We obtained values of apparent molar volume of the decyltrimethylammonium carboxylates (over a range of concentrations) from very precise density measurements. These could then be combined with the appropriate ion-pair association constant (from the conductance measurements) to give the partial molar volumes of the free ions and the ion pair. Hydrophobic interaction was found to be accompanied by a substantial increase in volume amounting to 10.2 ± 0.3 ml mol-1 for each pair of interacting methylene groups. Our results support the view that hydrophobic interaction occurs with a further ordering of water molecules over and above that which exists in the hydrophobic hydration layer surrounding an isolated hydrophobic molecule.

Stability of ion pairs from gypsum solubility degree of ion pair formation between the major constituents of seawater

1975 ◽  
Vol 3 (3) ◽  
pp. 215-225 ◽  
Author(s):  
Bengt Elgquist ◽  
Margareta Wedborg
Keyword(s):  
Ion Pairs ◽  
Ion Pair ◽  
Pair Formation ◽  
Ion Pair Formation

Elektronentransfer und Kontaktionen-Bildung, 42 [1,2] Cyclovoltammetrische und ESR / ENDOR-Untersuchungen der Einelektronen-Reduktion von Diphenochinonen / Electron Transfer and Contact Ion Pair Formation, 42 [1,2] Cyclovoltammetric and ESR / ENDOR Investigations of the One-Electron Reduction of Diphenoquinones

1995 ◽  
Vol 50 (11) ◽  
pp. 1699-1716
Author(s):  
Andreas John ◽  
Hans Bock
Keyword(s):  
Radical Anion ◽  
Ion Pairs ◽  
Ion Pair ◽  
Pair Formation ◽  
Coupling Constants ◽  
Semiquinone Radical ◽  
Additional Information ◽  
Ion Pair Formation ◽  
Contact Ion Pair ◽  
The Difference

Semiquinone radical anions are prototype compounds for contact ion pair formation with metal counter cations. In order to investigate the still open question whether bulky alkyl groups can sterically interfere, diphenoquinone derivatives O=C(RC=CH)2C=C(HC=CR)2C=O with R = C(CH3)3, CH(CH3)2 and CH3 have been selected and the following ESR/ENDOR results are obtained for the alkaline metal cations: The tetrakis(tert-butyl)-substituted radical anion only adds Li⊕ and Na⊕, while K⊕ forms no ion pair. The 3,3ʹ,5,5ʹ-tetra(isopropyl)diphenoquinone radical anion is accessible to all cations Me⊕, although Rb⊕ and Cs⊕ seem to be present solvent-separated in solution. The tetramethyl-substituted radical anion unfortunately polymerizes rapidly. Additional information concerns the ESR/ENDOR proof for ion triple radical cation formation [Li⊕ M•⊖Li⊕]•⊕, or the difference in the coupling constants upon Me⊕ docking at one δ⊖O=C group, suggesting that about 87% of the spin density is located in the cation-free molecular half of the diphenoquinone radical anion. Based on the wealth of ESR/ENDOR information, crystallization of the contact ion pairs and their structural characterization should be attempted.

Ion-Pair Formation of Sodium Salts of Several Oxo Anions and Cadmium Halides in Water and the Distribution of Monovalent Sulfate Ion Pairs in Nitrobenzene

2010 ◽  
Vol 55 (7) ◽  
pp. 2463-2469 ◽  
Author(s):  
Yoshihiro Kudo ◽  
Daisuke Todoroki ◽  
Naoki Horiuchi ◽  
Shoichi Katsuta ◽  
Yasuyuki Takeda
Keyword(s):  
Ion Pairs ◽  
Ion Pair ◽  
Pair Formation ◽  
Sulfate Ion ◽  
Sodium Salts ◽  
Ion Pair Formation ◽  
Oxo Anions

MD Studies of Transport in Polymer-Salt Complexes: A Progress Report

1990 ◽  
Vol 210 ◽  
Author(s):  
M. Forsyth ◽  
V. A. Payne ◽  
M. A. Ratner ◽  
S. W. De Leeuw ◽  
D. F. Shriver
Keyword(s):  
Polymer Electrolytes ◽  
Ion Pairs ◽  
Solvent Molecule ◽  
Ion Pair ◽  
Pair Formation ◽  
Progress Report ◽  
Lennard Jones ◽  
Solvent Model ◽  
Solvent Systems ◽  
Dynamics Simulations

AbstractMolecular dynamics simulations performed on highly concentrated Coulomb/solvent systems are used to help interpret the transport mechanism in polymer ionics. Using simple Coulomb and Lennard-Jones forces among the ions and a solvent model of a fixed dipole contained in a spherical solvent particle, we investigated the nature of ion pair formation and stability. For a model NaI system, we find that ion pairs decrease with increase in solvent dipole moment or temperature. The latter observation is at variance with experimental results on polymer electrolytes, probably because of entropy terms that do not occur with our simple solvent molecule.

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