Free energy of transfer of cobalt(III) complexes from water into water—t-butyl alcohol mixtures

The solubility of trans-(Coen₂Cl₂)₂ReCl₆ has been determined in water and in water +t-butyl alcohol mixtures. By comparzng these values with the solubility of Cs₂ReCl₆ in similar mixtures, values for the difference in free energy of transfer, G _t ^o (i) between water and water + t-butyl alcohol can be calculated for i =[Coen₂Cl₂]⁺ and Cs⁺. The introduction of G _t ^o (Cs⁺) then produces values for G _t ^o (Coen₂Cl₂ ⁺). The difference in G _t ^o (i) for i=[Coon₂Cl]²⁺ in the transition state and i=[Coen₂Cl₂]⁺ in the initiad' tate for the solvolysis of the trans-[Coen₂Cl₂]⁺ ion in water + t-butyl alcohol can be derived from the application of a free energy cycle: using G _t ^o (Coen₂Cl₂ ⁺) determined from the solubility measurements allows the calculation of values for G _t ^o (Coen₂Cl²⁺). G _t ^o (i) in water + t-butyl alcohol for bis (1,2-diamino) cobalt (III) ions are compared with G _t ^o (i) for tetrapyridinecobalt (III) ions.     

Solubility of dichlorotetraalkylpyridinecobalt III hexachlororhenate(IV) in water + methanol mixtures: Free energies of transfer of the complex cation from water into the mixtures

The solubility of salts [Co(3Rpy)₄Cl₂]₂]ReCl₆] has been determined in water + methanol mixtures. By comparing these with the solubilities of the salt Cs₂ReCl₆ and using calculated activity coefficients for the ions in the water+methanol mixtures, values for {G _t ^o (Co(3Rpy)₄Cl ₂ ⁺ )–G _t ^o (Cs⁺)} can be determined where G _t ^o is the standard Gibbs free energy of transfer from water to an aqueous mixture. G _t ^o (Cs⁺) from the solvent sorting scale and from the TPTB scale are then used to calculate G _t ^o (Co(3Rpy)₄Cl ₂ ⁺ ). These two sets of values for G _t ^o (Co(3Rpy)₄Cl ₂ ⁺ ) on the differing scales are then inserted into a free energy cycle applied to the bond extension Co(3Rpy)₄Cl ₂ ⁺ (initial state)Co(3Rpy)₄Cl²⁺+Cl^– (transition state) for the solvolysis in water and in water + methanol mixtures to produce values for G _t ^o (Co(3Rpy)₄Cl²⁺) using both scales. Data for the solubilites of [Copy₄Cl₂]₂[ReCl₆] and [Co(4Rpy)₄Cl₂]₂[ReCl₆] have been re-calculated to compare free energies of transfer for these complex cations with those specified above.     

Rates of Dissociative Ionic Reactions in Aqueous Mixtures Correlated with Opposing Gibbs Energies of Transfer of Single Ions: Solvolysis of Chloropentacyanocobaltate(III) Anions in Water + Ethanol and Water + Urea

The kinetics of the solvolysis of Co(CN)₅Cl^3– have been investigated in water with an added structure former, ethanol, and with added urea, which has only a weak effect on the solvent structure. As this solvolysis involves a rate-determining dissociative step corresponding closely to a 100%; separation, Co³⁺ Cl^-, in the transition state, a Gibbs energy cycle relating Gibbs energies of activation in water and in the mixtures to Gibbs energies of transfer of individual ionic species between water and the mixtures, G _t ^o (i), can be applied. The acceleration of the reaction found with both these cosolvents results from the compensation of the retarding positive G _t ^o (Cl^- by the negative term [G _t ^o [Co(CN) ₅ ^2- ]-G _t ^o [Co(CN)₅Cl^3- arising from G _t ^o [Co(CN)₅Cl^3-]> G _t ^o [Co(CN) ₅ ^2- ]. Moreover, only a small tendency to extrema in the enthalpies and entropies of activation is found with both these cosolvents, as was also found with added methanol or ethane-1,2-diol, but unlike the extrema found when hydrophobic alcohols are added to water. With the latter, much greater negative values for G _t ^o [Co(CN) ₅ ^2- ]- _t ^o [Co(CN)₅Cl^3-] are found. When G G _t ^o [Co(CN) ₅ ^2- ]-G G _t ^o [CO(CN)₅Cl^3-] becomes low enough not to compensate for the positive G _t ^o (Cl^-), as with added hydrophilic glucose, the reaction is retarded. Compensating contributions of the various G _t ^o (i) involved in the Gibbs energy cycle with added methanol or ethane-1, 2-diol allow log (rate constant) to vary linearly with the reciprocal of the relative permittivity of the medium.     

Model calculations of changes of thermodynamic variables for the transfer of nonpolar solutes from water to water-d2

A recently introduced modified hydration shell hydrogen bond model for rationalizing the thermodynamic consequences of hydrophobic hydration is adapted for use with heavy water. The required adjustment of parameters employs the assumption that breaking hydrogen bonds in water-d₂ involves a greater enthalpy change and a larger entropy increase than bond breaking in ordinary water. It also makes some use of information derived from studies of gas solubilities in the two solvents, although a review of the data leads to serious questions about the reliability of results obtained in this way. The model permits calculations of hydrogen bonding contributions to the changes, G _t ^o , H _t ^o , S _t ^o , and C _p,t ^o , for transfer of nonpolar solutes from water to water-d₂ and implies that such data should show regular trends. Although some of the numerical results depend strongly on the values chosen for the parameters, the pattern defined by these trends is nearly independent of parameters. Predicted values of C _p,t ^o are large and positive for all nonpolar solutes, while S _t ^o is expected to be negative near 0°C, becoming progressively less negative on warming and eventually positive. Both of these quantities should be proportional to the molecular surface area of the solute. Analogous predictions regarding G _t ^o and H _t ^o can also be made, but only if it is permissible to neglect possible contributions to these quantities from van der Waals interactions.     

Heats of solution of 1:1 electrolytes in 1,2- and 1,1-dichloroethane and derived enthalpies and entropies of transfer of electrolytes from water to these solvents

Heats of solution of nine electrolytes in 1,2-dichloroethane and of three electrolytes in 1,1-dichloroethane have been determined calorimetrically at various electrolyte concentrations and extrapolated to zero concentration to yield H _s ^o values for these electrolytes. It is shown that values of H _t ^o for transfer from water to the dichloroethanes of 11 electrolytes are often negative, so that these electrolytes can be more stable enthalpically in the less polar solvents. Combinations of the H _t ^o values with previously determined G _t ^o values yield values of S _t ^o for transfer of 11 electrolytes from water to the dichloroethanes. These S _t ^o values are mostly very negative; they can be correlated very well by the method of Abraham, and in this way S _t ^o values for transfer of numerous other anions and cations have been predicted. The Ph₄As⁺/Ph₄B^– convention yields single-ion entropies of transfer from water to the dichloroethanes in reasonable agreement with values calculated by the correspondence-plot method.     

Kinetics of the solvolysis oftrans-dichlorotetra-(4-t-butylpyridine)-cobalt(III) ions in water +t-butyl alcohol mixtures

Rates of solvolysis of the complex cation [Co(4tBupy)₄Cl₂]⁺ have been determined in mixtures of water with the hydrophobic solvent, t-butyl alcohol. The solvent composition at which the extremum is found in the variation of the enthalpy H^* and the entropy S^* of activation correlates well with the extremum in the variation of the relative partial molar volume of t-butyl alcohol in the mixture and the straight line found for the variation of H^* with S^* is coincident with the same plot for water + 2-propanol mixtures. A free energy cycle is applied to the process initial state (C ⁿ⁺) going to the transition state [M⁽ⁿ⁺¹⁾⁺...Cl^–] in water and in the mixture using free energies of transfer of the individual ionic species, G _t ^o (i), from water into the mixture. Values for G _t ^o (i) are derived from the solvent sorting method and from the TATB/TPTB method: using data from either method, changes in solvent structure on going from water into the mixture are found to stabilize the cation in the transition state, M⁽ⁿ⁺¹⁾⁺, more than in the initial state, C ⁿ⁺. This is compared with the application of the free energy cycle to the solvolysis of complexes [Co(Rpy)₄Cl₂]⁺ and [Coen₂LCl]⁺ in mixtures of water with methanol, 2-propanol or t-butyl alcohol: the above conclusion regarding the relative stabilization of the cations holds for all these complexes in their solvolyses in water+alcohol mixtures using values of G _t ^o (Cl^–) from either source.     

The influence of solvent structure on the solvolysis oftrans-dichlorotetra (4-ethylpyridine) cobalt(III) perchlorate

Summary The solvolysis oftrans-[Co(4-Etpy)₄Cl₂]ClO₄, was followed spectrophotometrically in water/isopropanol at different temperatures. The activation energy varied nonlinearly with the mole fraction of the co-solvent, ₂. The plot of logk versus D _s ^–1 was also non-linear. These features were attributed to the differential solvation of the initial and transition states. On plotting H versus S, the points fall very close to straight line. The isokinetic temperature was found to be 334K, indicating that the solvolysis reaction is controlled by S and not H. The change in H and S with the mole fraction of the cosolvent shows extrema at the composition range where changes in solvent structure occur. The influence of the solvent structure on the complex ion in the transition state dominates over that in the initial state, where –G _t ⁰ [Co(4-Etpy)₄Cl]²⁺>–G _t ⁰ [Co(4-Etpy)₄Cl₂]⁺.     

Thermodynamics of transfer of non-ionic solutes between immiscible liquid phases. I. Transfer of normal alcohols fromn-octane to water at 25°C

A recently developed calorimetric method has been employed to estimate the thermodynamic functions for transfer of 1-propanol, 1-butanol, 1-pentanol, 1-hexanol and 1-heptanol from n-octane to water at 25°C. A linear correlation for G _t ^o as a function of the number of carbon atoms of the alchohol molecule has been found but for H _t ^o and S _t ^o the dependence gave well defined minima.     

Free energies of transfer of alkali halides from water to urea-water mixtures at 25°C from EMF measurements

The standard potentials_s E ^o of M/M⁺ (M=Li, Na, K, Rb, and Cs) electrodes in aqueous urea solutions containing 12, 20, 30 and 37% by weight of urea have been determined at 25°C from emf measurements on the cell M(Hg)/MCl (m), solvent/AgCl–Ag, from the activities of metals in amalgams by use of a similar type of cell in water, and from the values of_s E ^o of the Ag/AgCl electrode determined earlier. The standard free energies of transfer of MCl, G _t ^o (MCl), from water to the mixed solvents, computed by use of these values and those for the Ag–AgCl electrode, rise sharply from Li⁺ to Na⁺ but fall from Na⁺ to K⁺ and rather sharply from K⁺ to Cs⁺ with a maximum at Na⁺ in all the solvent compositions. This has been attributed to the superimposition of soft-soft interactions on the electrostatic interactions between the ions and the negative charge centers of the possible hydrogen-bonded solvent complexes in the mixed solvents. Comparison of G _t ^o (i) values for individual ions, obtained by a simultaneous extrapolation procedure, with those in aqueous mixtures of methanol,t-butanol, and dimethyl sulfoxide leads to the conclusion that the solvation of these ions in all these solvents is chiefly dictated by the acid-base type of ion-solvent interactions.     

Dampfdruckmessungen und Protonenresonanzuntersuchung an Hydriden der intermetallischen Phasen Ti2(Ni,Co) und Ti2(Ni,Fe)

NMR and hydrogen equilibrium pressure measurements were performed on hydrides of the intermetallic compounds Ti₂(Ni, Co) and Ti₂(Ni, Fe). The following values of enthalpy H and entropy S for the formation of the hydrides of the intermetallic phases Ti₂Co and Ti₂Ni were found: H(Ti₂CoH _y )=–47.6 kJ/mol H₂, H(Ti₂NiH _y )=–53.7 kJ/mol H₂; S(Ti₂CoH _y )=–119.8 J/(K·mol H₂), S(Ti₂NiH _y )=–127.5 J/(K·mol H₂). By substitution of Ni or Co by Fe, the values of H and S of the corresponding quaternary hydrides become less negative. An interpretation of the experimental results is tried by the model ofShaltiel and coworkers.Proton diffusion was investigated in a series of the intermetallic hydrides Ti₂(Ni, Co)H _x and Ti₂(Ni, Fe)H _x . The diffusion rate is lowered by increased Ni/Fe substitution. Substitution of Ni by Co scarcely effects the hopping process. The activation energies were found to be smaller for the Ti₂Ni-hydrides compared with the Ti₂Co-hydrides.

Herrn Prof. Dr.H. Nowotny zum 70. Geburtstag gewidmet.     

Heat-capacity changes and partial molal heat capacities of several amino acids in water

Integral enthalpies of solution of several amino acids in water at low concentrations have been determined at 25 and 35°C. These data have been used to derive the heat-capacity change C _p ^o on dissolution at 30°C. Partial molal heat capacities C _p2 ^o have been obtained by combining C _p ^o with C _p2 ^o (heat capacity of pure solid amino acids). The results indicate that the increments in C _p ^o and C _p2 ^o values per CH₂ group increment in the homologous series of -amino acids are constant and in agreement with those found for other homologous series of compounds containing monofunctional groups. However, this is not the case with amino acids having the NH ₃ ⁺ group at the terminal position. The present work also indicates that, as the NH ₃ ⁺ group is shifted away from the COO^– group, hydrophobic hydration decreases, as indicated by a decrease in C _p ^o and C _p2 ^o . the results on various isomers of amino acids show that branching of alkyl groups has no effect on C _p ^o and C _p2 ^o , indicating that hydrophobic hydration is unaffected by branching. The effect of substitution of H by OH and of CH₃ by groups in some amino acids has also been studied and discussed.     

Complex formation constants and thermodynamic parameters for La(III) and Y(III)L-serine complexes

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.

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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.

     

Volumetric Properties of Some α-Amino Acids in Aqueous Guanidine Hydrochloride at 5, 15, 25, and 35°C

The infinite-dilution apparent molar volumesV ₂ ^o for glycine, DL-alanine, DL--amino-n-butyric acid, DL-valine, DL-leucine, and L-serine in 6 mol-kg^–1 aqueous guanidine hydrochloride were determined at 5, 15, 25, and 35°C from precise density measurements. Using these data, the standard volumes of transfer, _t V°, from water to 6m> aqueous guanidine hydrochloride solution were calculated. A linear relationship was found between V ₂ ^o and temperature. Both V ₂ ^o and _t V° vary linearly with increasing number of carbon atoms in the alkyl chain of the amino acids. The results show that the apparent molar volumes at infinite dilution for (NH ₃ ⁺ ,COO^-) groups increase with increasing temperature and those for CH₂ and the other alkyl chains are almost constant. These results also shows that guanidine hydrochloride has stronger interactions with amino acids than urea. These phenomena are discussed in terms of the cosphere overlap model.     

Heats of solution of 1∶1 electrolytes in 1-propanol,and derived enthalpies of transfer from water

Heats of solution of 13 11 electrolytes in 1-propanol have been determined calorimetrically at various electrolyte concentrations, and extrapolated to zero concentration to give H _s ^o values for these electrolytes. Together with literature data on three additional 11 electrolytes, these measurements yield a self-consistent set of single-ion enthalpies of transfer from water to 1-propanol. Values are tabulated for 10 univalent cations and five univalent anions. It is shown that the H _t ^o (Ph ₄ As⁺)=H _t ^o (Ph ₄ B^–) assumption yields chemically reasonable single-ion values. Using this assumption, it may be deduced that all the univalent ions studied have about the same enthalpy in 1-propanol as in methanol.     

Enthalpies of solution of thymine and uracil in water and dimethylsulfoxide

Enthalpies of solution of thymine and uracil in water and in dimethylsulfoxide (DMSO) were measured calorimetrically in the temperature range 25–40°C. H _s ^o at 25°C for thymine and uracil in water were found to be 23.1±0.5 and 29.5±0.3 kJ-mol^–1, respectively. In DMSO, H _s ^o were 7.9±0.1 and 10.2±0.1 kJ-mol^–1, respectively. In aqueous solution C _p ^o for the two nucleic acid bases were relatively large and positive with C _p ^o of thymine being larger. Both transfer quantities H _t ^o and C _p,t ^o for the proceses H₂ODMSO for the two nucleic acid bases were negative. It is proposed that, the differences in the values obtained for the two bases is due principally to increased order in the water adjacent to the methyl group in thymine.     

Kinetic and mechanistic studies on the interaction of thymidine with the hydroxopentaaquarhodium(III) ion

The interaction of thymidine, a nucleoside, with hydroxopentaaquarhodium(III), [Rh(H₂O)₅(OH)]²⁺ ion in aqueous medium is reported and the possible mode of binding is discussed. The kinetics of interaction between thymidine and [Rh(H₂O)₅OH]²⁺ has been studied spectrophotometrically as a function of [Rh(H₂O)₅OH²⁺], [thymidine], pH and temperature. The reaction has been monitored at 298 nm, the _max of the substituted complex, and where the spectral difference between the reactant and product is a maximum. The reaction rate increases with [thymidine] and reaches a limiting value at a higher ligand concentration. From the experimental findings an associative interchange mechanism for the substitution process is suggested. The activation parameters (H=47.8 ± 5.7 kJ mol^–1, S=–173 ± 17 J K^–1 mol^–1) supports our proposition. The negative G⁰ (–13.8 kJ mol^–1) for the first equilibrium step also supports the spontaneous formation of the outer sphere association complex.     

The kinetics of the solvolysis of chloropentacyanocobaltate(III) ions in water containing 2-methoxyethanol or diethylene glycol: A contrast with the effect of more hydrophobic cosolvents

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)₅Cl^3– 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     

Activation thermodynamic parameters of binary mixtures of propionic acid ando-substituted anilines

Variations of densities and viscosities with temperature and composition are reported for binary liquid mixtures containing propionic acid+aniline (I),+o-toluidine (II),+o-anisidine (III), and+o-chloroaniline (IV). Entropies S _m and enthalpies H _m of activation as functions of the composition of the mixtures, as well as free energies of activation G _m at 10, 20, 30, 40, and 50°C and different compositions were calculated by means of Eyring's equation. The formation of activated complexes between the components of these binary mixtures is postulated and claimed to result from acid-base and hydrogen bonding exchange interactions.     

Effect of intramolecular rotational reorganization of reagents on the ratio between free energies of activation and reaction

Conclusions The relationship between the free energies of activation G and reaction G_o for proton transfer processes have been analyzed, taking into account the effect of hindered rotation of the reagents. We have shown that the considered effect can considerably affect the shape of the G=f(G_o) curve.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 77–81, January 1989.     

Kinetics of the thermal and photochemical decomposition of aquapentacyanoferrate(III) in aqueous solution

Summary The kinetics of the thermal and photochemical decomposition of aquapentacyanoferrate(III) ion in aqueous solution in the presence ofo-phenanthroline was studied spectrophotometrically. The first-order rate constant (k ) at 30° C [I=1 M(NaCl)] for the thermal reaction is (1.49±0.13)×10^–6 s^–1 with H =(158±7)kJ mol^–1 and S=(42±4) JK^–1 mol^–1. The initial quantum yield for the photochemical reaction at pH=7 is independent of the light intensity and is (1.49±0.33)×10^–2 mol einstein^–1.A communication on this subject was presented at the XVI Latinamerican Chemistry Congress held at Rio de Janeiro. Brasil, October 14–20, 1984.