Low-temperature heat capacity and standard molar enthalpy of formation of the complex Zn(Thr)SO4·H2O (s)

Low-temperature heat capacities of the complex Zn(Thr)SO₄·H₂O (s) have been precisely measured with a small sample adiabatic calorimeter over the temperature range from 78 to 373 K. The initial dehydration temperature of the complex (T_d=325.50 K) has been obtained by analysis of the heat-capacity curve. The experimental values of molar heat capacities have been fitted to a polynomial equation by least square method. The standard molar enthalpy of formation of the complex has been determined from the enthalpies of dissolution (Δ_dH_m^Θ) of [ZnSO₄·7H₂O (s) +Thr (s)] and Zn(Thr)SO₄·H₂O (s) in 100 ml of 2 mol dm⁻³ HCl solvent as: Δ_fH_{m,Zn(Thr)SO4·H2O}^Θ=−2111.7±3.4 kJ mol⁻¹. These experiments were made by using an isoperibol solution calorimeter at 298.15 K.     

A calorimetrical study of the polynuclear Zn(II) and Pb(II) and the polymeric Ni(II) and Cd(II) complexes of 2-mercaptoethanol and 3-mercapto-1,2-propanediol

The ΔG, ΔH and ΔS values for the dissociation of 2-mercaptoethanol (MEL) and 3-mercapto-1,2-propanediol and for the formation of complexes between these ligands and the metal ions Ni²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ have been determined calorimetrically in 0.5 M KNO₃ and at 25°C.     

Mössbauer investigation on the crystal field splitting of Fe ion in zinc fluosilicate

The Mössbauer quadrupole interaction ΔE_Q of the Fe²⁺ ion has been measured with 2% at. ⁵⁷Fe in ZnSiF₆·6H₂O, between 1.3 and 20°K. The sign of ΔE_Q (< 0) has been determined by using a single crystal absorber. These results are interpreted in terms of a trigonal crystal field potential that splits the Fe²⁺ orbitals into a ground state singlet and a first excited doublet whose distance is much smaller than that reported for FeSiF₆·6H₂O, in reasonable agreement with previous EPR measurements.     

Thermochemical properties of Ln(Gly)4Im(ClO4)3·nH2O (Ln = Gd, Tb, Dy, Y)

The enthalpies of dissolution in water of new ternary complexes of four late trivalent lanthanide ions Ln(Gly)₄Im(ClO₄)₃·nH₂O (Ln=Gd, Tb, Dy, Y; Gly: glycine; Im: imidazole and n=1 or 2) were measured by means of a Calvet microcalorimeter. Empirical formulae for the calculation of the enthalpies of dissolution (Δ_dissH), relative apparent molar enthalpies (Δ_dissH (app)), relative partial molar enthalpies (Δ_dissH (partial)) and enthalpies of dilution (Δ_dilH_1,2) were obtained from the experimental data of the enthalpies of dissolution of these complexes. The plot of Δ_dissH_m^Θ, Δ_dissH (app) and Δ_dissH (partial) versus the values of the ionic radius of the lanthanide element (r) showed a grouping effect of the lanthanide elements, indicating that the coordinated bond between the lanthanide ions and the ligands has some covalent character. The unknown value of the standard enthalpy of dissolution for the similar complex: Ho(Gly)₄Im(ClO₄)₃·H₂O was estimated according to the plot of Δ_dissH_m^Θ versus r.     

Joint use of cyclodextrin additives in chiral discrimination by reversed-phase high-performance liquid chromatography: temperature effects

The temperature dependence of chiral separations was investigated in combined system of reversed-phase (RP) liquid chromatography using two chiral additives: single or β native cyclodextrins and their permethylated derivatives. The model tested compounds of pharmaceutical interest were: methylphenobarbital, mephenytoin, morsuximide and camphor. Taking the localization of a complexation process as a criterion – the combined system with two selectors has been rationalized as occurring in three stages. The influence of temperature (in narrow range of 20°C) on retention and enantioselectivity was studied in; System I (complexation occurs in the mobile phase), in System II (complexation on the stationary phase) and in System III (complexation in both phases together). In System III (as for System I) it has been found that the model compounds could be classified into three groups based on their retention dependence on temperature: retention decrease with temperature decrease, retention increase with temperature decrease or no influence of temperature on retention. For all the compounds investigated, decrease in temperature increases the selectivity. Standard enthalpy (ΔH⁰) and entropy (ΔS⁰) changes of solute transfer between the mobile and the stationary phase and standard enthalpy (ΔH⁰_CD) and entropy (ΔS⁰_CD) changes of complex formation were also calculated. In Systems I and III, if the complexation in the mobile phase is favored process compared with interaction with the stationary phases (RP or covered by permethylated cyclodextrin), the shortest retention time and the best selectivity is observed at low temperature.     

Kinetic study of trifluoromethylation with s-(trifluoromethyl) dibenzothiophenium salts

The kinetic parameters were determined for C-trifluoromethylation of aniline with S-(trifluoromethyl)dibenzothiophenium triflate (1), its 3,7-dinitro derivative (2) and S-(trifluoromethyl)diphenylsulfonium triflate (3) in DMF-d₇. The higher reactivity of heterocyclic 1 compared with non-heterocyclic 3 could be explained on the basis of its greatly enhanced activation entropy (ΔS^≠: −11.2 cal mol ⁻¹ K⁻¹ for 1; −47.1 for 3), but not its enhanced activation enthalpy (ΔH^≠: 21.2 kcal mol⁻¹ for 1; 12.1 for 3). The aromatic delocalization of the heterocyclic ring may thus be only slightly disturbed by the S-trifluoromethyl substituent. The high reactivity of 2 was attributed to the great electron deficiency caused by two nitro groups in addition to the heterocyclic salt system (ΔH^≠ 17.0 kcal mol⁻¹, ΔS^≠ −9.1 cal mol⁻¹ K⁻¹ for 2). The reaction mechanism is discussed; the conventional S_N2 attack mechanism was ruled out and a mechanism for a side-on attack to the CF₃-S bond may possibly be applicable.     

Solvent extraction of Fe(III) by dehydrated castor oil fatty acids

The effect of temperature on the extraction of FE(III) by dehydrated castor oil fatty acids (DCOFA) has been studied in the temperature range 283–313 K at 1.0M constant ionic strength (NaClO₄). The temperature dependence of the conditional constant of extraction is given in the form: ln K_ext=31.95 − 12800(1/T). Also, it was found that the average thermodynamic parameters, ΔH°_ext, ΔG°_ext, and ΔS°_ext are 106.5 kJ/mole, 27.3 kJ/mole, and 0.3 kJ. mole⁻¹.K⁻¹, respectively. The extracted species in toluene solution were identified as FeR₃.HR and Fe(OH)R₂, where HR represents the fatty acid used.     

Calorimetric study of the adducts CdBr2·nL (n = 1 and 2; L = ethyleneurea and propyleneurea)

A calorimetric study was performed for adducts of general formula CdBr₂·nL (n=1 and 2; L=ethyleneurea (eu) and propyleneurea (pu)). The standard molar reaction enthalpy in condensed phase: CdBr₂(c)+nL(c)=CdBr₂·nL(c); Δ_rH_m^θ, were obtained by reaction–solution calorimetry, to give the following values for mono- and bis-adducts: −19.54 and −34.59; −7.77 and −19.05 kJ mol⁻¹ for eu and pu adducts, respectively. Decomposition (Δ_DH_m^θ) and lattice (Δ_MH_m^θ) enthalpies, as well as the mean cadmium---oxygen bond dissociation enthalpy, DCd---O, were calculated for all adducts.     

Thermodynamic studies of the solvation of Ph4AsPh4B in mixed solvents (MeOH—DMF)

The thermodynamic data (ΔG⁰, ΔH⁰ and TΔS⁰) of the solvation of tetraphenylarsonium-tetraphenylborate (Ph₄AsPh₄B) and its neutral parts, tetraphenylgermanium (Ph₄Ge) and tetraphenylmethane (Ph₄C) in methanol—N,N-dimethylformamide mixed solvents are discussed.

The values of the free energy of transfer, Δ^s_MG⁰, are calculated from measurements of the solubilities of Ph₄AsPh₄B, Ph₄Ge and Ph₄C in the successive fractions of MeOH in DMF at three different temperatures (15, 25, 35°C). The values of Δ^s_MH⁰ and TΔ^s_MS⁰ for the derivatives are calculated from Δ^s_MG⁰ values.

The values of Δ^s_MG⁰, Δ^s_MH⁰ and TΔ^s_MS⁰ of tetraphenylarsonium and tetraphenylborate ions have also been carefully calculated. The ratios of Δ^s_MG⁰ values (Δ^s_MG⁰ = ΔG⁰(+)/ΔG⁰(−)) were found to be greater than unity. Similarly, the ratios of Δ^s_MH⁰ and TΔ^s_MS⁰ for the positive and negative ions were found to be greater than unity.     

Kinetische und mechanistische untersuchungen von übergangsmetallkomplex-reaktionen : IX. Substitution von CO durch PPh3 in aminocarbinkomplexen: Präparative und kinetische untersuchungen

Pentacarbonyl(diethylaminocarbyne)chromium tetrafluoroborate, [(CO)₅₋ CrCNEt₂]BF₄ (I), reacts with PPh₃ with substitution of CO and formation of trans-tetracarbonyl(diethylaminocarbyne)triphenylphosphanechromium tetra-fluoroborate, trans-[PPh₃(CO)₄CrCNEt₂]BF₄ (III). Substitution of CO by PPh₃ in neutral trans-tetracarbonyl(halo)(diethylaminocarbyne)chromium complexes, trans-X(CO)₄CrCNEt₂ (IVa: X = Br, IVb: X = I), leads in a reversible reaction to the corresponding tricarbonyl complexes, mer-X(PPh₃)(CO)₃₋ CrNEt₂ (V), PPh₃ occupying the cis-position to the carbyne ligand. With PPh₃ in large excess both reactions follow a first-order rate law. This as well as the activation parameters (ΔH≠ = 104–113 kJ mol⁻¹, ΔS≠ = 64–71 J mol⁻¹ K⁻¹) indicate a dissociative mechanism.     

Formation of cobalt, nickel and copper complexes with murexide in ethanol-water mixtures

The complexation reactions between murexide and Co²⁺, Ni²⁺ and Cu²⁺ in C₂H₅OH-H₂O mixtures have been investigated spectrophotometrically. The formation constants of the 1:1 complexes formed increase in the order Co²⁺ < Ni²⁺ < Cu²⁺ for all solvent mixtures studied, and log K_f is a linear function of the mole fraction of ethanol. The heat of complexation was determined calorimetrically for the nickel and copper complexes. The values of ΔH° and ΔS° are solvent-dependent, and all three complexes have negative ΔH° and positive ΔS° values.     

Polymerization process of the silane coupling agent 3-aminopropyltriethoxy silane – H NMR spectra and kinetics of ethanol release

In the 3-aminopropyltriethoxy silane–deuterated ethanol–H₂O system, the rate of release of ethanol from the ethoxy groups, a reaction which occurs during the condensation process, has been followed by use of ¹H NMR spectroscopy at different temperatures. Two separate reaction processes have been identified, and values of the reaction rate constants and thermodynamic parameters (E_a, ΔH^‡ and ΔS^‡) have been calculated.     

CNDO/2 study of the mechanism and kinetics of the CIS-trans isomerization of N2F2(g) using the activated-complex theory

Complete optimization of the molecular geometry of N₂F₂ confirmed the two previously assumed activated complexes (AC's) for the title reaction. The contributions of both AC's were precisely weighed up in terms of the activated-complex theory. The possibility of an autocatalysed chain mechanism is discussed because of the disagreement of theoretical and experimental ΔH^‡_T and ΔS^‡_T values.     

Thermodynamic properties of solutions of benzoic and citric acids in formamide at different tempertures

The standard thermodynamic quantities, ΔG⁰, ΔH⁰, and ΔS⁰, associated with the ionization process of benzoic acid in formamide have been evaluated. The standard potentials of the Ag(s)/AgCNS(s)/CNS⁻ and the Ag(s)/Ag₃Ci(s)/Ci³⁻ electrode, and the standard thermodynamic quantities for the electrode processes have been calculated in formamide, at different temperatures.     

Influence of non-covalent interactions on the thermodynamic stereoselectivity of the protonation of some dipeptides

ΔG⁰, ΔH⁰ and ΔS⁰ protonation values of some pairs of diastereoisomeric dipeptides have been determined by potentiometry and calorimetry in aqueous solution at 25°C and I = 0.1 mol dm⁻³ (KNO₃). On the basis of the results obtained it has been possible to assess the role played by two different non-covalent interactions, namely the electrostatic interaction and the solvophobic interaction, on the thermodynamic stereoselectivity in the proton complex formation, shown by the systems investigated.     

Solution enthalpies of hydrates LnCl3·xH2O (Ln=Ce–Lu)

Trichlorides of the lanthanide elements Ln=Ce–Lu form: (a) isotypic hexahydrates LnCl₃·6H₂O with a coordination number (CN) 8 for the Ln³⁺ ions. (b) Two isotypic groups of trihydrates LnCl₃·3H₂O, in the first group Ln=Ce-Dy the CN is 8; the structure of the second group Ln=Er–Lu is unknown. With Ho no trihydrate exists; a dihydrate is formed. (c) Two isotypic groups of monohydrates LnCl₃·H₂O with unknown structure – Ln=Ce–Dy and Ln=Ho–Lu. For all compounds and for anhydrous chlorides LnCl₃ solution enthalpies were measured with an isoperibolic calorimeter. The Δ_solH⁰ values do not depend only on the difference (lattice enthalpies/hydration enthalpies), but also on the state in solution. According to Spedding the CN of the Ln³⁺ ions against water changes from 9 to 8 between Nd and Sm, causing minima in the series of solution enthalpies. Dihydrates LnCl₃·2H₂O are found for Ln=Ce, Pr, Nd, Sm and presumably for Eu and Gd. They are not yet well characterised.     

Solubility and thermodynamic data of manganese hydrogen phosphate in the system MnO---P2O5---H2O at 35, 40, 45 and 50°C

Manganese hydrogen phosphate monohydrate, MnHPO₄·H₂O, a new phase, is synthesized. Its solubility is investigated in the temperature range 35–50°C and pH range 3.4–7.5. K_sp, ΔH⁰, ΔS⁰ and ΔG⁰ for the dissolution are reported. The decrease in solubility with increase in pH is explained as due to a surface coating of insoluble basic phosphate.     

Surface activity and thermodynamic of micellization and adsorption for isooctylphenol ethoxylates, phosphate esters and their mixtures with N-diethoxylated perfluorooctanamide

Three nonionic surfactants; p-isooctylphenol ethoxylates p-[i-OPE10], p-[i-OPE15], and p-[i-OPE20], were phosphorylated to produce three anionic phosphate ester surfactants. In addition, N-diethoxylated perfluorooctanamide (N-DEFOA) was also prepared. The surface and thermodynamic properties of the three types of surfactants and mixtures of the fluorocarbon surfactant (FC) with the hydrocarbon surfactants (HC) have been investigated. Surface tension as a function of concentration of the surfactant in aqueous solution was measured at 30, 40, 50 and 60°C, using the spinning drop technique. From these measurements the critical micelle concentration (CMC), the surface tension at the CMC (γ_CMC), the maximum surface excess concentration (Γ_max), the minimum area per molecule at the aqueous solution/air interface (A_min), and the effectiveness of surface tension reduction (π_CMC), were calculated. The thermodynamic parameters of micellization (ΔG_mic, ΔH_mic, ΔS_mic) and of adsorption (ΔG_ad, ΔH_ad, ΔS_ad) for these surfactants and their mixtures were also calculated. Structural effects on micellization, adsorption and effectiveness of surface tension reduction are discussed in terms of these parameters. The results show that the FC surfactant and its mixtures with HC surfactants enhance the efficiency in surface tension reduction and adsorption in the mixed monolayer at the aqueous solution/air interface, and also, reduce γ_CMC and the tendency towards micellization.     

Determination of thermodynamic parameters and equilibrium constants for complexation reactions involving lanthanon(III) ions with 1,2-naphthoquinone-2-semicarbazone-4-sulphonic acid (sodium salt) (NQS · 4S)

The thermodynamic parameters and equilibrium constants of complexation reactions of 1,2-naphthoquinone-2-semicarbazone-4-sulphonic acid (sodium salt) (NQS · 4S) involving lanthanon ions were evaluated by potentiometric estimation of [H⁺], in aqueous medium at various ionic strengths (0.02, 0.05, 0.10 and 0.20 M NaClO₄) and at different temperatures (20, 30, 40 and 50±0.5°C). The −n and pL values calculated by the method of Bjerrum and Calvin, as modified by Irving and Rossotti, were used for the calculation of the equilibrium constants on an HCL Busy Bee PC/AT computer using the weighted least-squares method. The values of S_min were also evaluated. The order of equilibrium constants was found to be Ho(III) > Dy(III) > Tb(III) > Y(III) > Eu(III) > Sm(III) > Gd(III) > Nd(III) > Pr(III) > Ce(III) > La(III). The thermodynamic parameters ΔG, ΔH and ΔS were also calculated at a fixed temperature (30±0.05°C) and ionic strength (0.10 M NaClO₄).