The low-temperature (5 to 310 K) heat capacity and thermodynamic functions of cesium fluoroxysulfate (CsSO4F) and the standard potential at 298.15 K for the half-reaction: SO4F−(aq) + 2H+(aq) + 2e− = HSO4−(aq) + HF(aq)

The low-temperature (5 to 310 K) heat capacity of cesium fluoroxysulfate, CsSO₄F, has been measured by adiabatic calorimetry. At T = 298.15 K, the heat capacity C_p^o(T) and standard entropy S^o(T) are (163.46±0.82) and (201.89±1.01) J · K^?1 · mol^?1, respectively. Based on an earlier measurement of the standard enthalpy of formation ΔH_f^o the Gibbs energy of formation ΔG_f^o(CsSO₄F, c, 298.15 K) is calculated to be ?(877.6±1.6) kJ · mol^?1. For the half-reaction: SO₄F^?(aq)+2H⁺(aq)+2e^? = HSO₄^?(aq)+HF(aq), the standard electrode potential E at 298.15 K, is (2.47±0.01) V.     

Enthalpy of formation of aqueous tungstate ion and of crystalline tungstic acid (H2WO4)

Calorimetric measurements of the enthalpy of reaction of WO₃(c) with excess OH^?(aq) have been made at 85°C. Similar measurements have been made with MoO₃(c) at both 85 and 25°C, to permit estimation of ΔH°=?13.4 kcal mol^?1 for the reaction WO₃(c)+2OH^?(aq)=WO^2?₄(aq)+H₂O(liq) at 25°C. Combination of this ΔH° with ΔH°_f for WO₃(c) leads to ΔH°_f=?256.5 kcal mol^?1 for WO^2?₄(aq). We also obtain ΔH°_f=?269.5 kcal mol^?1 for H₂WO₄(c). Both of these values are discussed in relation to several earlier investigations.     

Nucleophilic and electrophilic promotion of ligand substitution reactions in oxo‐bridged,dinuclear chromium(III) complexes

Base hydrolysis reactions of [Cr(tmpa)(NCSe)]₂O²⁺, [Cr(tmpa)(N₃)]₂O²⁺, [Cr₂(tmpa)₂(μ−O)(μ−PhPO₄)]⁴⁺ and [Cr₂(tmpa)₂(μ−O)(μ−CO₃)]²⁺ follow the pseudo‐first‐order relationship (excess OH⁻): k_obsd=k_o+k_bQ_p[OH⁻]/(1+Q_p[OH⁻]). For the CO₃²⁻ complex, k_b(60°C)=(1.50±0.03)×10⁻² s⁻¹; ΔH‡=61±2 kJ/mol, ΔS‡=−99±7 J/mol K; Q_p(60°C)=(3.8±0.3)×10¹ M⁻¹; ΔH°=67±2 kJ/mol, ΔS°=230±7 J/mol K (I=1.0 M). An isokinetic relationship among k_OH(=k_bQ_p) activation parameters for five (tmpa)CrOCr(tmpa) complexes shows that all follow essentially the same pathway. Activated complex formation is thought to require nucleophilic attack of coordinated OH⁻ at the chromium‐leaving group bond in the k_b step, accompanied by reattachment of a tmpa pyridyl arm displaced by OH⁻ in the Q_p preequilibrium. Abstraction of both thiocyanate ligands was observed upon mixing [Cr(tmpa)(NCS)]₂O²⁺ with [Pd(CH₃CN)₄]²⁺ in CH₃CN solution. The proposed mechanism requires rapid complexation of both reactant thiocyanate ligands by Pd(II) (K_p(25°C)=(4.5±0.2)×10⁸ M⁻²; ΔH°=−32±6 kJ/mol, ΔS°=59±19 J/mol K) prior to rate‐limiting Cr NCS bond‐breaking (k₂(25°C)=(1.17±0.02)×10⁻³ s⁻¹; ΔH‡=98±2 kJ/mol, ΔS‡=27±5 J/mol K). Pd(II)‐assisted NCS⁻ abstraction is not driven by weakening of the Cr( )NCS⁻ bond through ligation of the sulfur atom to palladium, but rather by a favorable ΔS‡ resulting from the release of Pd(NCS)⁺ fragments and weak solvation of the activated complex in CH₃CN solution. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 351–356, 1999     

Isopiestic Determination of the Osmotic and Activity Coefficients of Li2SO4(aq) at T=298.15 and 323.15 K, and Representation with an Extended Ion-Interaction (Pitzer) Model

Isopiestic vapor-pressure measurements were made for Li₂SO₄(aq) from 0.1069 to 2.8190 mol?kg^?1 at 298.15 K, and from 0.1148 to 2.7969 mol?kg^?1 at 323.15 K, with NaCl(aq) as the reference standard. Published thermodynamic data for this system were reviewed, recalculated for consistency, and critically assessed. The present results and the more reliable published results were used to evaluate the parameters of an extended version of Pitzer’s ion-interaction model with an ionic-strength dependent third-virial coefficient, as well as those of the standard Pitzer model, for the osmotic and activity coefficients at both temperatures. Published enthalpies of dilution at 298.15 K were also analyzed to yield the parameters of the ion-interaction models for the relative apparent molar enthalpies of dilution. The resulting models at 298.15 K are valid to the saturated solution molality of the thermodynamically stable phase Li₂SO₄?H₂O(cr). Solubilities of Li₂SO₄?H₂O(cr) at 298.15 K were assessed and the selected value of m(sat.)=3.13±0.04 mol?kg^?1 was used to evaluate the thermodynamic solubility product K _s(Li₂SO₄?H₂O, cr, 298.15 K) = (2.62±0.19) and a CODATA-compatible standard molar Gibbs energy of formation Δ_f G _m ^o (Li₂SO₄?H₂O, cr, 298.15 K) = ?(1564.6±0.5) kJ?mol^?1.     

Enthalpy of formation of wulfenite (natural lead molybdate)

A thermochemical study of wulfenite, i.e., natural lead molybdate PbMoO₄ (Kyzyl-Espe field deposit, Central Kazakhstan), is performed on a Setaram high-temperature heat-flux Tian-Calvet microcalorimeter (France). Enthalpies of the formation of wulfenite from oxides Δ_f H _ox ^o (298.15 K) = ?88.5 ± 4.3 kJ/mol and simple substances Δ_f H°(298.15 K) = ?1051.2 ± 4.3 kJ/mol were determined by means of melt calorimetry. The Δ_f G°(298.15 K) of wulfenite corresponding to ?949.1 ± 4.3 kJ/mol was calculated using data obtained earlier for S°(298.15 K) = 161.5 ± 0.27 J/(K mol).     

The kinetics and equilibrium of the gas-phase reaction CH3CF2Br + I2 = CH3CF2I + IBr the C-Br bond dissociation energy in 1,1-difluorobromoethane

The kinetics and equilibrium of the gas-phase reaction of CH₃CF₂Br with I₂ were studied spectrophotometrically from 581 to 662°K and determined to be consistent with the following mechanism: A least squares analysis of the kinetic data taken in the initial stages of reaction resulted in log k₁ (M^?1 · sec^?1) = (11.0 ± 0.3) - (27.7 ± 0.8)/θ where θ = 2.303 RT kcal/mol. The error represents one standard deviation. The equilibrium data were subjected to a “third-law” analysis using entropies and heat capacities estimated from group additivity to derive ΔH_r° (623°K) = 10.3 ± 0.2 kcal/mol and ΔH_rr (298°K) = 10.2 ± 0.2 kcal/mol. The enthalpy change at 298°K was combined with relevant bond dissociation energies to yield DH°(CH₃CF₂ - Br) = 68.6 ± 1 kcal/mol which is in excellent agreement with the kinetic data assuming that E₂ = 0 ± 1 kcal/mol, namely; DH°(CH₃CF₂ - Br) = 68.6 ± 1.3 kcal/mol. These data also lead to ΔH_f°(CH₃CF₂Br, g, 298°K) = -119.7 ± 1.5 kcal/mol.     

Formation of MSeO4(aq) complexes (M2+ = Mg2+, Co2+, Ni2+, Cu2+, Cd2+) studied as a function of temperature by affinity capillary electrophoresis

Complexation of divalent cations (Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺) by selenate ligand was studied by ACE (UV indirect detection) in 0.1 mol/L NaNO₃ ionic strength solutions at various temperatures (15, 25, 35, 45 and 55°C). For each solution, a unique peak was observed as a result of a fast equilibrium between the free ion and the complex (labile systems). The migration time corresponding to this peak changed as a function of the solution composition, namely the free and complexed metal concentrations, according to the complexation reactions. The results confirmed the formation of a unique 1:1 complex for each cation. The thermodynamic parameters were fitted to the experimental data at 0.1 mol/L ionic strength: (25°C) = ?(6.5 ± 0.3), ?(7.5 ± 0.3), ?(7.7 ± 0.3), ?(7.7 ± 0.3), and –(8.1 ± 0.3) kJ/mol and = 2.5 ± 0.2, 4.7 ± 0.4, 4.5 ± 0.6, 8.4 ± 1.1, and 7.2 ± 0.6 kJ/mol for M²⁺ = Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Cd²⁺, respectively. Complexes with alkaline earth and transition metal cations could be distinguished by their relative stabilities. The effect of the ionic medium was treated using the specific ion interaction theory and the thermodynamic parameters at infinite dilution were compared to previously published data on metal–selenate, metal–sulfate, and metal–chromate complexes.     

Apparent molar heat capacities and apparent molar volumes ofY2(SO4)3(aq),La2(SO4)3(aq),Pr2(SO4)3(aq),Nd2(SO4)3(aq),Eu2(SO4)3(aq),Dy2(SO4)3(aq),Ho2(SO4)3(aq), andLu2(SO4)3(aq)atT = 298.15 K andp = 0.1 MPa

The apparent molar heat capacities C_{p, φ} ^∘ and apparent molar volumes V_φ ^∘ of Y₂(SO₄)₃(aq), La₂(SO₄)₃(aq), Pr₂(SO₄)₃(aq), Nd₂(SO₄)₃(aq), Eu₂(SO₄)₃(aq), Dy₂(SO₄)₃(aq), Ho₂(SO₄)₃(aq), and Lu₂(SO₄)₃(aq) were measured at T =  298.15 K and p =  0.1 MPa with a Sodev (Picker) flow microcalorimeter and a Sodev vibrating-tube densimeter, respectively. These measurements extend from lower molalities of m =  (0.005 to 0.018) mol ·kg ^− 1to m =  (0.025 to 0.434) mol ·kg ^− 1, where the upper molality limits are slightly below those of the saturated solutions. There are no previously published apparent molar heat capacities for these systems, and only limited apparent molar volume information. Considerable amounts of the R SO₄ ⁺ (aq) and R(SO₄)₂ ⁻ (aq) complexes are present, where R denotes a rare-earth, which complicates the interpretation of these thermodynamic quantities. Values of the ionic molar heat capacities and ionic molar volumes of these complexes at infinite dilution are derived from the experimental information, but the calculations are necessarily quite approximate because of the need to estimate ionic activity coefficients and other thermodynamic quantities. Nevertheless, the derived standard ionic molar properties for the various R SO₄ ⁺ (aq) and R(SO₄)₂ ⁻ (aq) complexes are probably realistic approximations to the actual values. Comparisons indicate that V_φ ^∘ {RSO₄ ⁺ , aq, 298.15K}  =  − (6  ±  4)cm³· mol ^− 1and V_φ ^∘ {R(SO₄)₂ ⁻ , aq, 298.15K}  =  (35  ±  3)cm³· mol ^− 1, with no significant variation with rare-earth. In contrast, values of C_{p, φ} ^∘ { RSO₄ ⁺ , aq, 298.15K } generally increase with the atomic number of the rare-earth, whereas C_{p, φ} ^∘ { R(SO₄)₂ ⁻ , aq, 298.15K } shows a less regular trend, although its values are always positive and tend to be larger for the heavier than for the light rare earths.     

The enthalpies of formation of bis-(benzene)molybdenum and of bis-(toluene)tungsten

Microcalorimetric measurements at 520–523 K of the heats of thermal decomposition and of iodination of bis-(benzene)molybdenum and of bis-(toluene)tungsten have led to the values (kJ mol^?): ΔH^o_f[Mo(η-C₆H₆)₂, c] = (235.3 ± 8) and ΔH^o_f[W(η⁶-C₇H₈)₂, c] = (242.2 ± 8) for the standard enthalpies of formation at 25°C. The corresponding ΔH^o_f(g) values, using available and estimated enthalpies of sublimation, are (329.9 ± 11) and 352.2 ± 11) respectively, from which the metalligand mean bond-dissociation enthalpies, $\text{D}$(Mo—benzene) = (247.0 ± 6) and $\text{D}$(W—toluene) = (304.0 ± 6) kJ mol^?1, are derived.     

Equilibrium and Kinetic Studies on Ligand Substitution Reactions of Trans-[COIII(en)2(Me)H2O]2+: A Model for Coenzyme B12

Ligand substitution of trans-[Co^III(en)₂(Me)H₂O]²⁺ was studied for pyrazole, 1,2,4-triazole and N-acetylimidazole as entering nucleophiles. These displace the coordinated H₂O molecule trans to the methyl group to form trans-[Co(en)₂(Me)azole]. Stability constants at 18°C for the substitution of H₂O by pyrazole, 1,2,4-triazole and N-acetylimidazole are 0.7 ± 0.1, 13.8 ± 1.4 and 1.7 ± 0.2 M^?1, respectively. Second order rate constants at the same temperature for the reaction of trans-[Co^III(en)₂(Me)H₂O]²⁺ with pyrazole, 1,2,4-triazole and N-acetylimidazole are 161 ± 12, 212 ± 11 and 12.9 ± 1.6 M^?1 s^?1, respectively. Activation parameters (ΔH^≠, ΔS^≠) are 67 ± 6 kJ mol^?1, + 27 ± 19 J K^?1 mol^?1; 59 ± 2 kJ mol^?1, + 1 ± 6 J K^?1 mol^?1 and 72 ± 4 kJ mol^?1, + 23 ± 14 J K^?1 mol^?1 for reactions with pyrazole, 1,2,4-triazole and N-acetylimidazole, respectively. Substitution of coordinated H₂O by azoles follows an I_d mechanism.     

Conformational Analysis. XIX properties and reactions of 1,3-oxathianes VIII A 1H NMR conformational study of methyl-substituted derivatives

The addition of thioacetic acid to unsaturated alcohols or acids was utilized to obtain mercaptoalkanols which were condensed with suitable carybonyl compounds to prepare 24 methyl-substituted 1,3-oxathianes. The ¹H NMR spectra of the 1,3-oxathiane products were recorded at 60, 100 and/or 300 MHz and fully analysed. The results are best explained by a chair form which is completely staggered in the C-4? C-5? C-6 moiety ψ₄₅ or (ψ₅₆=60±1°). 1,3-Oxathianes having syn-axial 2,4- (and/or 2,6-) methyl-methyl interactions exist appreciably, if not exclusively, in twist forms. The vicinal coupling constants lead to the conformational free energies of axial methyl groups at C-4, ΔG°=7.4±0.4 kJ mol^?1, and at C-5, ΔG°=3.7±0.3 kJ mol^?1, in good agreement with previous estimates. They also show that both r-4,cis-5,trans-6- and r-4,trans-5,trans-6- trimethyl-1,3-oxathianes greatly favour the chiar form where the methyl group at C-4 is axial. The chair-twist energy parameters are reestimated at ΔH°_CT 27.0 kJ mol^?1, ΔS°_CT 11.6J mol^?1K^?1, and ΔG°_CT(298) 23.5 kJ mol^?1 for a 2,5-twist form.     

Studies on the composition and kinetics of chromium(III)-alanine system

Kinetics of the complex formation of chromium(III) with alanine in aqueous medium has been studied at 45, 50, and 55°C, pH 3.3–4.4, and μ = 1 M (KNO₃). Under pseudo first-order conditions the observed rate constant (k_obs) was found to follow the rate equation: Values of the rate parameters (k_an, k, K_IP, and K) were calculated. Activation parameters for anation rate constants, ΔH^≠(k_an) = 25 ± 1 kJ mol^?1, ΔH^≠(k) = 91 ± 3 kJ mol^?1, and ΔS^≠(k_an) = ?244 ± 3 JK^?1 mol^?1, ΔS^≠(k) = ?30 ± 10 JK^?1 mol^?1 are indicative of an (I_a) mechanism for k_an and (I_d) mechanism for k routes (‥substrate Cr(H₂O) is involved in the k route whereas Cr(H₂O)₅OH²⁺ is involved in k′ route). Thermodynamic parameters for ion-pair formation constants are found to be ΔH°(K_IP) = 12 ± 1 kJ mol^?1, ΔH°(K) = ?13 ± 3 kJ mol^?1 and ΔS°(K_IP) = 47 ± 2 JK^?1 mol^?1, and ΔS°(K) = 20 ± 9 JK^?1 mol^?1.     

Solvent extraction of barium picrate by p-tert-butylcalix[4]arene-tetrakis (N,N-diethylacetamide)

Summary From extraction experiments andg-activity measurements, the extraction constant of the Ba²⁺(aq)+2A^-(aq)+L(nb)?BaL²⁺(nb)+2A^-(nb) equilibrium in the two-phase water-nitrobenzene system (L = p-tert-butylcalix[4]arene-tetrakis (N,N-diethylacetamide); aq = aqueous phase, nb = nitrobenzene phase) was evaluated as logK_ex(BaL²⁺,2A^-)=6.5±0.1. Furthermore, the stability constant of the p-tert-butylcalix[4]arene-tetrakis (N,N-diethylacetamide)̵barium complex in nitrobenzene saturated with water was calculated for at 25 °C as logb_nb(BaL²⁺)=15.4±0.1.     

The platinumcarbon bond strength in Pt(PPh3)2(CH3)I

The enthalpies of reaction 1–3 have been determined

as ΔH(1) = ?176.6 ± 5.4, ΔH(2) = ?107.8 ± 6.0, and ΔH(3) = ?78.9 ± 2.0 kJ mol^?1. The bond dissociation energy difference D₁(PtCH₃) ? D₁(PtI) = +6 ± 5 kJ mol^?1 is calculated, which indicates that the two bonds have very similar strengths.     

Electrochemical kinetics of the hydrogen reaction on platinum in concentrated HCl(aq)

The hydrogen reaction in concentrated HCl(aq) solutions is a key reaction for the CuCl(aq)/HCl(aq) electrolytic cell. Here, electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) were used to obtain new data for the hydrogen reaction on platinum submerged in highly concentrated acidic solutions at 25 °C and 0.1 MPa. LSV and EIS data were collected for Pt in 0.5 mol/L H₂SO₄(aq), 1 mol/L HCl(aq) and 7.71 mol/L HCl(aq) solutions. It was found that exchange current density (j₀) values varied between 1 and 2 mA/cm². An equivalent circuit model was used to obtain comparable j₀ and limiting current density values from EIS data relative to values obtained with LSV data. It was found that as the concentration of acid increased, a noticeable decrease in the performance was observed.     

Low-Temperature Heat Capacities of Terbium Molybdate Phosphates M 2 I Tb(MoO4)(PO4) (MI = Na or K)

The heat capacities of Na₂Tb(MoO₄)(PO₄) and K₂Tb(MoO₄)(PO₄) were measured by adiabatic calorimetry at low temperatures (6.34–333.74 and 7.20–341.17 K, respectively). Smoothed thermal-capacities values were used to calculate the entropy, enthalpy increments, and reduced Gibbs energy. The respective values at 298.15 K are as follows: for Na₂Tb(MoO₄)(PO₄), C _p ⁰ (298.15 K) = 240.1 ± 0.2 J/(K mol), ⁰ (298.15 K) = 307.4 ± 0.4 J/(K mol), H ⁰(298.15 K) ? H ⁰(0) = 44.95 ± 0.03 kJ/mol, and Φ⁰(298.15 K) = 156.6 ± 0.5 J/(K mol); and for K₂Tb(MoO₄)(PO₄): C _p ⁰ (298.15 K) = 245.1 ± 0.1 J/(K mol), S ⁰(298.15 K) = 322.9 ± 0.1 J/(K mol), H ⁰(298.15 K) ? H ⁰(0) = 46.58 ± 0.02 kJ/mol, and Φ⁰(298.15 K) = 166.6 ± 0.2 J/(K mol). The noncooperative magnetic component of the heat capacity was estimated.     

Complexation of the cesium cation with 1,3-alternate-25,27-bis(1-octyloxy)calix[4]arene-crown-6

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Cs⁺(aq) + I^?(aq) + 1(nb) ? 1·Cs⁺(nb) + I^?(nb) taking place in the two–phase water–nitrobenzene system (1 = 1,3-alternate-25,27-bis(1-octyloxy)calix[4]arene-crown-6; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (1·Cs⁺, I^?) = 2.9 ± 0.1. Further, the stability constant of the 1·Cs⁺ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β_nb (1·Cs⁺) = 8.8 ± 0.1. Finally, by using quantum–mechanical DFT calculations, the most probable structure of the resulting cationic complex species 1·Cs⁺ was derived.     

Substitution and Isomerization of Nitrite Ion at a Cobalt(III) Centre Having a Coordinated Pentadentate Ligand with Two Nitrogen and Three Sulfur Donor Atoms

The influence of placing thioether linkages trans to a site of nitrito substitution and spontaneous nitrito-tonitro isomerization is reported for the [CoQS(H₂O)]³⁺ cation where QS is 1,11-diamino-3,6,9-trithiaundecane. Preparation and characterization is described for the aqua and nitrito complexes. Rate data for the substitution process is presented at 17.7, 25.0 and 35.0°C. It is consistent with the mechanism first proposed by Basolo and Pearson in which N₂O₃ is the nitrosation agent. [CoQS(H₂O)]³⁺ is three hundred times more reactive than [Co(NH₃)₅H₂O]³⁺ under identical conditions. Isomerization is dramatically slower than the conversion of [CoQS(H₂O)³⁺ to [CoQS(ONO)]²⁺. The isomerization process was studied at 5 wavelengths, 3 temperatures and various conditions of acid and nitrite ion at an ionic strength of 0.11–0.60 M. Studies at 25°C give k_isom = 1.21 ± 0.12 × 10^?4 sec ^?1. Similar determinations at 17.7 and 35.0°C give k_isom = 3.84 ± 0.65 × 10^?5 sec^?1 and 3.59 ± 0.13 × 10^?4 sec^?1 respectively. The thermodynamic activation parameters ΔH^≠, ΔG^≠, and ΔS^≠ obtained from an Eyring plot gives ΔH^≠ = 111.3 kJ/mol, ΔS^≠ = + 53 J/molK and ΔG^≠ = 95.4 kJ/mol. These results are discussed in the context of present knowledge and experience with other cobalt(III) ligand systems.     

A kinetic study of the oxidation of L-ascorbic acid by chromium(VI)

The reaction between chromium(VI) and L-ascorbic acid has been studied by spectrophotometry in the presence of aqueous citrate buffers in the pH range 5.69–7.21. The reaction is slowed down by an increase of the ionic strength. At constant ionic strength, manganese(II) ion does not exert any appreciable inhibition effect on the reaction rate. The rate law found is where K_p is the equilibrium constant for protonation of chromate ion and k_r is the rate constant for the redox reaction between the active forms of the oxidant (hydrogenchromate ion) and the reductant (L-hydrogenascorbate ion). The activation parameters associated with rate constant k_r are E_a = 20.4 ± 0.9 kJ mol^?1, ΔH^≠ = 17.9 ± 0.9 kJ mol^?1, and ΔS^≠=?152 ± 3 J K^?1 mol^?1. The reaction thermodynamic magnitudes associated with equilibrium constant K_p are ΔH⁰ = 16.5 ± 1.1 kJ mol^?1 and ΔS⁰ = 167 ± 4 J K^?1 mol^?1. A mechanism in accordance with the experimental data is proposed for the reaction. © 1993 John Wiley & Sons, Inc.