Synthesis,Characterization, and Crystal Structures of Metal Amide Cage Complexes Containing a M<Subscript>4</Subscript>O<Subscript>4</Subscript> (M = Nb,Ta) Core Unit

Metal cage complexes [(Me₂N)₃MO]₄ (M = Nb, 3; Ta, 4) have been prepared from the reactions of M(NMe₂)₅ (M = Nb, 1; Ta, 2) with water. Single crystal X-ray diffraction studies of 3 and 4 reveal that they adopt cubane-like structures with M–O bridges. Variable-temperature NMR studies of –NMe_AMe_B rotations in 3 and 4 have been performed to give the following activation parameters for the exchanges: ΔH ^≠ = −1.4(1.1) kJ/mol, ΔS ^≠ = −209(8) J/mol K, \Updelta G _{30 8  \textK} ¹ = 6 4( 2)  \textkJ/\textmol \Updelta G_{{_{{ 30 8\;{\text{K}}}} }}^{{^{ \ne } }} = 6 4\left( 2\right)\;{\text{kJ}}/{\text{mol}} for 3, and ΔH ^≠ = −0.9(1.2) kJ/mol, ΔS ^≠ = −2.1(0.2) × 10² J/mol K, \Updelta G _{30 8  \textK} ¹ = 6 3( 6)  \textkJ/\textmol \Updelta G_{{ 30 8\;{\text{K}}}}^{{^{ \ne } }} = 6 3\left( 6\right)\;{\text{kJ}}/{\text{mol}} for 4.     

Thermochemical study on ternary complex of dysprosium <Emphasis Type="Italic">m</Emphasis>-nitrobenzoic acid with <Emphasis Type="Italic">o</Emphasis>-phenanthroline

A ternary binuclear complex of dysprosium chloride hexahydrate with m-nitrobenzoic acid and 1,10-phenanthroline, [Dy(m-NBA)₃phen]₂·4H₂O (m-NBA: m-nitrobenzoate; phen: 1,10-phenanthroline) was synthesized. The dissolution enthalpies of [2phen·H₂O(s)], [6m-HNBA(s)], [2DyCl₃·6H₂O(s)], and [Dy(m-NBA)₃phen]₂·4H₂O(s) in the calorimetric solvent (V_DMSO:V_MeOH = 3:2) were determined by the solution–reaction isoperibol calorimeter at 298.15 K to be \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [2phen·H₂O(s), 298.15 K] = 21.7367 ± 0.3150 kJ·mol⁻¹, \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [6m-HNBA(s), 298.15 K] = 15.3635 ± 0.2235 kJ·mol⁻¹, \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [2DyCl₃·6H₂O(s), 298.15 K] = −203.5331 ± 0.2200 kJ·mol⁻¹, and \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [[Dy(m-NBA)₃phen]₂·4H₂O(s), 298.15 K] = 53.5965 ± 0.2367 kJ·mol⁻¹, respectively. The enthalpy change of the reaction was determined to be \Updelta_\textr H_\textm^q = 3 6 9. 4 9 ±0. 5 6   \textkJ·\textmol ^{- 1} . \Updelta_{\text{r}} H_{\text{m}}^{\theta } = 3 6 9. 4 9 \pm 0. 5 6 \;{\text{kJ}}\cdot {\text{mol}}^{ - 1} . According to the above results and the relevant data in the literature, through Hess’ law, the standard molar enthalpy of formation of [Dy(m-NBA)₃phen]₂·4H₂O(s) was estimated to be \Updelta_\textf H_\textm^q \Updelta_{\text{f}} H_{\text{m}}^{\theta } [[Dy(m-NBA)₃phen]₂·4H₂O(s), 298.15 K] = −5525 ± 6 kJ·mol⁻¹.     

Thermochemistry of paracetamol

Combustion calorimetry, Calvet-drop sublimation calorimetry, and the Knudsen effusion method were used to determine the standard (p ^o = 0.1 MPa) molar enthalpies of formation of monoclinic (form I) and gaseous paracetamol, at T = 298.15 K: \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text cr I ) = - ( 4 10.4 ±1. 3)\text kJ  \textmol ^{- 1} \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ cr I}}} \right) = - ( 4 10.4 \pm 1. 3){\text{ kJ}}\;{\text{mol}}^{ - 1} and \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text g ) = - ( 2 80.5 ±1. 9)\text kJ  \textmol ^{- 1} . \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ g}}} \right) = - ( 2 80.5 \pm 1. 9){\text{ kJ}}\;{\text{mol}}^{ - 1} . From the obtained \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text cr I ) \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ cr I}}} \right) value and published data, it was also possible to derive the standard molar enthalpies of formation of the two other known polymorphs of paracetamol (forms II and III), at 298.15 K: \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text crII ) = - ( 40 8.4 ±1. 3)\text kJ  \textmol ^{- 1} \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ crII}}} \right) = - ( 40 8.4 \pm 1. 3){\text{ kJ}}\;{\text{mol}}^{ - 1} and \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text crIII ) = - ( 40 7.4 ±1. 3)\text kJ  \textmol ^{- 1} . \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ crIII}}} \right) = - ( 40 7.4 \pm 1. 3){\text{ kJ}}\;{\text{mol}}^{ - 1} . The proposed \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text g ) \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ g}}} \right) value, together with the experimental enthalpies of formation of acetophenone and 4′-hydroxyacetophenone, taken from the literature, and a re-evaluated enthalpy of formation of acetanilide, \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textON,\text g ) = - ( 10 9. 2 ± 2. 2)\text kJ  \textmol ^{- 1} , \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{ON}},{\text{ g}}} \right) = - ( 10 9. 2\,\pm\,2. 2){\text{ kJ}}\;{\text{mol}}^{ - 1} , were used to assess the predictions of the B3LYP/cc-pVTZ and CBS-QB3 methods for the enthalpy of a isodesmic and isogyric reaction involving those species. This test supported the reliability of the theoretical methods, and indicated a good thermodynamic consistency between the \Updelta_\textf H_\textm^\texto \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} (C₈H₉O₂N, g) value obtained in this study and the remaining experimental data used in the \Updelta_\textr H_\textm^\texto \Updelta_{\text{r}} H_{\text{m}}^{\text{o}} calculation. It also led to the conclusion that the presently recommended enthalpy of formation of gaseous acetanilide in Cox and Pilcher and Pedley’s compilations should be corrected by ~20 kJ mol⁻¹.     

Decomposition of KMnO<Subscript>4</Subscript> in different gases as a potential kinetics standard in thermal analysis

The assumption that potassium permanganate may serve as a kinetics standard in solid decomposition kinetics made a priori on the basis of the mechanism of the congruent dissociative vaporization of KMnO₄ and its crystal structure was successfully supported experimentally. As expected, the decomposition rate of KMnO₄ does not depend on the kind of foreign gas (He, air, CO₂ and Ar) and on the measurement technique (isothermal or dynamic). Other requirements for KMnO₄ as an ideal kinetics standard are satisfied as well. The use of the third-law method for determining the molar enthalpy of a reaction ( \Updelta_\textr H_\textT^\texto / n ) \left( {\Updelta_{\text{r}} H_{\text{T}}^{\text{o}} / \nu } \right) provides an excellent reproducibility of results. The mean value of \Updelta_\textr H_\textT^\texto / n \Updelta_{\text{r}} H_{\text{T}}^{\text{o}} / \nu from 12 experiments in different gases is 138.3 ± 0.6 kJ mol⁻¹, which coincides with the value of 138.1 kJ mol⁻¹ calculated from the isothermal measurements in different gases by the second-law method. As predicted by theory, the random errors of the second-law and Arrhenius plot methods are 10–20 times greater. In addition, the use of these methods in the case of dynamic measurements is related to large systematic errors caused by an inaccurate selection of the geometrical (contraction) model. The third-law method is practically free of these errors.     

Kinetic and mechanistic studies on the substitution of aqua ligands from <Emphasis Type="Italic">cis</Emphasis>-diaqua-<Emphasis Type="Italic">bis</Emphasis>-(bypyridyl)-ruthenium(II) ion by vic-dioximes

Kinetics of aqua ligand substitution from cis-[Ru(bpy)₂(H₂O)₂]²⁺ by three vicinal dioximes, namely dimethylglyoxime (L¹H), 1,2-cyclohexane dionedioxime (L²H) and α-furil dioxime (L³H) have been studied spectrophotometrically in the 45–60 °C temperature range. The rate constants increase with increasing dioxime concentration and approach a limiting condition. We propose the following rate law for the reaction in the 3.5–5.5 pH range: where k ₂ is the interchange rate constant from outer sphere to inner sphere complex and K _E is the outer sphere association equilibrium constant. Activation parameters were calculated from the Eyring plots for all three systems: ΔH ^≠ = 59.2 ± 8.8, 63.1 ± 6.8 and 69.7 ± 8.5 kJ mol⁻¹, ΔS ^≠ = −122 ± 27, −117 ± 21 and −99 ± 26 J K⁻¹ mol⁻¹ for L¹H, L²H and L³H, respectively. An associative interchange mechanism is proposed for the substitution process. Thermodynamic parameters calculated from the temperature dependence of the outer sphere association equilibrium constants give negative ΔG ⁰ values for all the systems studied at all the temperatures (ΔH ⁰ = 30.05 ± 2.5, 18.9 ± 1.1 and 11.8 ± 0.2 kJ mol⁻¹; ΔS ⁰ = 123 ± 8, 94 ± 3 and 74 ± 1 J K⁻¹ mol⁻¹ for L¹H, L²H and L³H, respectively), which also support our proposition.     

Thermal decomposition kinetics of magnesite from thermogravimetric data

Thermal decomposition kinetics of magnesite were investigated using non-isothermal TG-DSC technique at heating rate (β) of 15, 20, 25, 35, and 40 K min⁻¹. The method combined Friedman equation and Kissinger equation was applied to calculate the E and lgA values. A new multiple rate iso-temperature method was used to determine the magnesite thermal decomposition mechanism function, based on the assumption of a series of mechanism functions. The mechanism corresponding to this value of F(a), which with high correlation coefficient (r-squared value) of linear regression analysis and the slope was equal to −1.000, was selected. And the Malek method was also used to further study the magnesite decomposition kinetics. The research results showed that the decomposition of magnesite was controlled by three-dimension diffusion; mechanism function was the anti-Jander equation, the apparent activation energy (E), and the pre-exponential term (A) were 156.12 kJ mol⁻¹ and 10^5.61 s⁻¹, respectively. The kinetic equation was

Determination of thermodynamic properties of YRhO3(s) by solid-state electrochemical cell and differential scanning calorimeter

The standard molar Gibbs free energy of formation of YRhO₃(s) has been determined using a solid-state electrochemical cell wherein calcia-stabilized zirconia was used as an electrolyte. The cell can be represented by: ( - )\textPt - Rh/{ \textY₂\textO_\text3( \texts ) + \textYRh\textO₃( \texts ) + \textRh( \texts ) }//\textCSZ//\textO₂( p( \textO₂ ) = 21.21  \textkPa )/\textPt - Rh( + ) \left( - \right){\text{Pt - Rh/}}\left\{ {{{\text{Y}}_2}{{\text{O}}_{\text{3}}}\left( {\text{s}} \right) + {\text{YRh}}{{\text{O}}_3}\left( {\text{s}} \right) + {\text{Rh}}\left( {\text{s}} \right)} \right\}//{\text{CSZ//}}{{\text{O}}_2}\left( {p\left( {{{\text{O}}_2}} \right) = 21.21\;{\text{kPa}}} \right)/{\text{Pt - Rh}}\left( + \right) . The electromotive force was measured in the temperature range from 920.0 to 1,197.3 K. The standard molar Gibbs energy of the formation of YRhO₃(s) from elements in their standard state using this electrochemical cell has been calculated and can be represented by: D_\textfG^\texto{ \textYRh\textO₃( \texts ) }/\textkJ  \textmo\textl ^{- 1}( ±1.61 ) = - 1,147.4 + 0.2815  T  ( \textK ) {\Delta_{\text{f}}}{G^{\text{o}}}\left\{ {{\text{YRh}}{{\text{O}}_3}\left( {\text{s}} \right)} \right\}/{\text{kJ}}\;{\text{mo}}{{\text{l}}^{ - 1}}\left( {\pm 1.61} \right) = - 1,147.4 + 0.2815\;T\;\left( {\text{K}} \right) . Standard molar heat capacity C^o_p,m C^{o}_{{p,m}} (T) of YRhO₃(s) was measured using a heat flux-type differential scanning calorimeter in two different temperature ranges from 127 to 299 K and 305 to 646 K. The heat capacity in the higher temperature range was fitted into a polynomial expression and can be represented by: $ {*{20}{c}} {\mathop C\nolimits_{p,m}^{\text{o}} \left( {{\text{YRh}}{{\text{O}}_3},{\text{s,}}T} \right)\left( {{\text{J}}\;{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}} \right)} & { = 109.838 + 23.318 \times {{10}^{ - 3}}T\left( {\text{K}} \right)} & { - 12.5964 \times {{10}^5}/{T^2}\left( {\text{K}} \right).} \\ {} & {\left( {305 \leqslant T\left( {\text{K}} \right) \leqslant 646} \right)} & {} \\ $ \begin{array}{*{20}{c}} {\mathop C\nolimits_{p,m}^{\text{o}} \left( {{\text{YRh}}{{\text{O}}_3},{\text{s,}}T} \right)\left( {{\text{J}}\;{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}} \right)} & { = 109.838 + 23.318 \times {{10}^{ - 3}}T\left( {\text{K}} \right)} & { - 12.5964 \times {{10}^5}/{T^2}\left( {\text{K}} \right).} \\ {} & {\left( {305 \leqslant T\left( {\text{K}} \right) \leqslant 646} \right)} & {} \\ \end{array} The heat capacity of YRhO₃(s) was used along with the data obtained from the electrochemical cell to calculate the standard enthalpy and entropy of formation of the compound at 298.15 K.     

The kinetics of the reduction of tetraoxoiodate(VII) by <Emphasis Type="Italic">n</Emphasis>-(2-hydroxylethyl)ethylenediaminetriacetatocobaltate(II) ion in aqueous perchloric acid

The stoichiometries, kinetics and mechanism of the reduction of tetraoxoiodate(VII) ion, IO₄ ⁻ to the corresponding trioxoiodate(V) ion, IO₃ ⁻ by n-(2-hydroxylethyl)ethylenediaminetriacetatocobaltate(II) ion, [CoHEDTAOH₂]⁻ have been studied in aqueous media at 28 °C, I = 0.50 mol dm⁻³ (NaClO₄) and [H⁺] = 7.0 × 10⁻³ mol dm⁻³. The reaction is first order in [Oxidant] and [Reductant], and the rate is inversely dependent on H⁺ concentration in the range 5.00 × 10⁻³ ≤ H⁺≤ 20.00 × 10⁻³ mol dm⁻³ studied. A plot of acid rate constant versus [H⁺]⁻¹ was linear with intercept. The rate law for the reaction is:

Standard enthalpies of formation of Li,Na, K,and Cs thiolates

The standard enthalpies of formation of alkaline metals thiolates in the crystalline state were determined by reaction-solution calorimetry. The obtained results at 298.15 K were as follows: \Updelta_\textf H_\textm^\texto (\textMSR,  \textcr) \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} ({\text{MSR,}}\;{\text{cr}}) /kJ mol⁻¹ = −259.0 ± 1.6 (LiSC₂H₅), −199.9 ± 1.8 (NaSC₂H₅), −254.9 ± 2.4 (NaSC₄H₉), −240.6 ± 1.9 (KSC₂H₅), −235.8 ± 2.0 (CsSC₂H₅). These results where compared with the literature values for the corresponding alkoxides and together with values for \Updelta_\textf H_\textm^\texto ( \textMSH,  \textcr) \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{MSH}},\;{\text{cr}}}\right) were used to derive a consistent set of lattice energies for MSR compounds based on the Kapustinskii equation. This allows the estimation of the enthalpy of formation for some non-measured thiolates.     

Dissolution properties of hexanitrohexaazaisowurtzitane (CL-20) in ethyl acetate and acetone

The enthalpies of dissolution in ethyl acetate and acetone of hexanitrohexaazaisowurtzitane (CL-20) were measured by means of a RD496-2000 Calvet microcalorimeter at 298.15 K, respectively. Empirical formulae for the calculation of the enthalpy of dissolution (Δ_diss H), relative partial molar enthalpy (Δ_diss H _partial), relative apparent molar enthalpy (Δ_diss H _apparent), and the enthalpy of dilution (Δ_dil H _1,2) of each process were obtained from the experimental data of the enthalpy of dissolution of CL-20. The corresponding kinetic equations describing the two dissolution processes were \frac\textda\textdt = 1.60 ×10 ^{- 2} (1 - a)^0.84 {\frac{{{\text{d}}\alpha }}{{{\text{d}}t}}} = 1.60 \times 10^{ - 2} (1 - \alpha )^{0.84} for dissolution process of CL-20 in ethyl acetate, and \frac\textda\textdt = 2.15 ×10 ^{- 2} (1 - a)^0.89 {\frac{{{\text{d}}\alpha }}{{{\text{d}}t}}} = 2.15 \times 10^{ - 2} (1 - \alpha )^{0.89} for dissolution process of CL-20 in acetone.     

Effect of the cathode structure on the electrochemical performance of anode-supported solid oxide fuel cells

The study elementarily investigated the effect of the cathode structure on the electrochemical performance of anode-supported solid oxide fuel cells. Four single cells were fabricated with different cathode structures, and the total cathode thickness was 15, 55, 85, and 85 μm for cell-A, cell-B, cell-C, and cell-D, respectively. The cell-A, cell-B, and cell-D included only one cathode layer, which was fabricated by ( \textLa_0.74 \textBi_0.10 \textSr_0.16 )\textMnO_{3 - d} \left( {{\text{La}}_{0.74} {\text{Bi}}_{0.10} {\text{Sr}}_{0.16} } \right){\text{MnO}}_{{3 - \delta }} (LBSM) electrode material. The cathode of the cell-C was composed of a ( \textLa_0.74 \textBi_0.10 \textSr_0.16 )\textMnO_{3 - d} - ( \textBi_0.7 \textEr_0.3 \textO_1.5 ) \left( {{\text{La}}_{0.74} {\text{Bi}}_{0.10} {\text{Sr}}_{0.16} } \right){\text{MnO}}_{{3 - \delta }} - \left( {{\text{Bi}}_{0.7} {\text{Er}}_{0.3} {\text{O}}_{1.5} } \right) (LBSM–ESB) cathode functional layer and a LBSM cathode layer. Different cathode structures leaded to dissimilar polarization character for the four cells. At 750°C, the total polarization resistance (R _p) of the cell-A was 1.11, 0.41 and 0.53 Ω cm² at the current of 0, 400, and 800 mA, respectively, and that of the cell-B was 1.10, 0.39, and 0.23 Ω cm² at the current of 0, 400, and 800 mA, respectively. For cell-C and cell-D, their polarization character was similar to that of the cell-B and R _p also decreased with the increase of the current. The maximum power density was 0.81, 1.01, 0.79, and 0.43 W cm⁻² at 750°C for cell-D, cell-C, cell-B, and cell-A, respectively. The results demonstrated that cathode structures evidently influenced the electrochemical performance of anode-supported solid oxide fuel cells.     

Extraction and DFT study on the complexation of the cesium cation with dibenzo-21-crown-7

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium \textCs ⁺ ( \textaq ) + \textA ^- ( \textaq ) + 1( \textnb )\underset \rightleftharpoons 1·\textCs ⁺ ( \textnb ) + \textA ^- ( \textnb ) {\text{Cs}}^{ + } \left( {\text{aq}} \right) + {\text{A}}^{ - } \left( {\text{aq}} \right) + {\mathbf{1}}\left( {\text{nb}} \right)\underset {} \rightleftharpoons {\mathbf{1}}\cdot{\text{Cs}}^{ + } \left( {\text{nb}} \right) + {\text{A}}^{ - } \left( {\text{nb}} \right) taking place in the two-phase water-nitrobenzene system (A⁻ = picrate, 1 = dibenzo-21-crown-7; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (1·Cs⁺, A⁻) = 4.4 ± 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⁺) = 6.3 ± 0.1. Finally, by using quantum mechanical DFT calculations, the most probable structure of the resulting cationic complex species 1·Cs⁺ was solved.     

Thermochemical properties of two nitrothiophene derivatives

This article reports the values of the standard (p ^o = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, \Updelta_\textf H_\textm^\texto ( \textg ), {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} \left( {\text{g}} \right), at T = 298.15 K, of 2-acetyl-5-nitrothiophene and 5-nitro-2-thiophenecarboxaldehyde as −(48.8 ± 1.6) and (4.4 ± 1.3) kJ mol⁻¹, respectively. These values were derived from experimental thermodynamic parameters, namely, the standard (p ^o = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, \Updelta_\textf H_\textm^\texto ( \textcr ) , {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} \left( {\text{cr}} \right) , at T = 298.15 K, obtained from the standard molar enthalpies of combustion, \Updelta_\textc H_\textm^\texto , {{\Updelta}}_{\text{c}} H_{\text{m}}^{\text{o}} , measured by rotating bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from the temperature–vapour pressure dependence, obtained by the Knudsen mass loss effusion method. The results are interpreted in terms of enthalpic increments and the enthalpic contribution of the nitro group in the substituted thiophene ring is compared with the same contribution in other structurally similar compounds.     

The Estimation of Standard Molar Enthalpies of Solution for VOSO<Subscript>4</Subscript>⋅<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O(s) in Water and in Aqueous H<Subscript>2</Subscript>SO<Subscript>4</Subscript>

The molar enthalpies of solution of VOSO₄⋅3.52H₂O(s) at various molalities in water and in aqueous sulfuric acid (0.1 mol⋅kg⁻¹), Δ_sol H _m, were measured by a solution-reaction isoperibol calorimeter at 298.15±0.01 K. An improved Archer’s method to estimate the standard molar enthalpy of solution, D_solH⁰_m\Delta_{\mathrm{sol}}H^{0}_{\mathrm{m}}, was put forward. In terms of the improved method, the values of D_solH⁰_m=-24.12±0.03 kJ·mol^-1\Delta_{\mathrm{sol}}H^{0}_{\mathrm{m}}=-24.12\pm 0.03~\mbox{kJ}{\cdot}\mbox{mol}^{-1} of VOSO₄⋅3.52H₂O(s) in water and D_solH⁰_m=-15.38±0.06 kJ·mol^-1\Delta_{\mathrm{sol}}H^{0}_{\mathrm{m}}=-15.38\pm 0.06~\mbox{kJ}{\cdot}\mbox{mol}^{-1} in aqueous sulfuric acid were obtained, respectively. The data indicates that the energy state of VOSO₄ in aqueous H₂SO₄ is higher than that in pure water.     

Studies on electron transfer reactions: reduction of heteropoly 10-tungstodivanadophosphate by <Emphasis Type="SmallCaps">l</Emphasis>-cysteine in aqueous acid medium

l-cysteine undergoes facile electron transfer with heteropoly 10-tungstodivanadophosphate, [ \textPV^\textV \textV^\textV \textW _{1 0} \textO _{4 0} ]^{5 -} , \left[ {{\text{PV}}^{\text{V}} {\text{V}}^{\text{V}} {\text{W}}_{ 1 0} {\text{O}}_{ 4 0} } \right]^{5 - } , at ambient temperature in aqueous acid medium. The stoichiometric ratio of [cysteine]/[oxidant] is 2.0. The products of the reaction are cystine and two electron-reduced heteropoly blue, [PV^IVV^IVW₁₀O₄₀]⁷⁻. The rates of the electron transfer reaction were measured spectrophotometrically in acetate–acetic acid buffers at 25 °C. The orders of the reaction with respect to both [cysteine] and [oxidant] are unity, and the reaction exhibits simple second-order kinetics at constant pH. The pH-rate profile indicates the participation of deprotonated cysteine in the reaction. The reaction proceeds through an outer-sphere mechanism. For the dianion ⁻SCH₂CH(NH₃ ⁺)COO⁻, the rate constant for the cross electron transfer reaction is 96 M⁻¹s⁻¹ at 25 °C. The self-exchange rate constant for the ^- \textSCH₂ \textCH( \textNH₃ ⁺ )\textCOO ^- \mathord

Solubility Measurements of Crystalline NiO in Aqueous Solution as a Function of Temperature and pH

Results of solubility experiments involving crystalline nickel oxide (bunsenite) in aqueous solutions are reported as functions of temperature (0 to 350 °C) and pH at pressures slightly exceeding (with one exception) saturation vapor pressure. These experiments were carried out in either flow-through reactors or a hydrogen-electrode concentration cell for mildly acidic to near neutral pH solutions. The results were treated successfully with a thermodynamic model incorporating only the unhydrolyzed aqueous nickel species (viz., Ni²⁺) and the neutrally charged hydrolyzed species (viz., Ni(OH)₂⁰)\mathrm{Ni(OH)}_{2}^{0}). The thermodynamic quantities obtained at 25 °C and infinite dilution are, with 2σ uncertainties: log₁₀K_s0^o = (12.40 ±0.29),\varDelta_rG_m^o = -(70. 8 ±1.7)\log_{10}K_{\mathrm{s0}}^{\mathrm{o}} = (12.40 \pm 0.29),\varDelta_{\mathrm{r}}G_{m}^{\mathrm{o}} = -(70. 8 \pm 1.7) kJ⋅mol⁻¹; \varDelta_rH_m^o = -(105.6 ±1.3)\varDelta_{\mathrm{r}}H_{m}^{\mathrm{o}} = -(105.6 \pm 1.3) kJ⋅mol⁻¹; \varDelta_rS_m^o = -(116.6 ±3.2)\varDelta_{\mathrm{r}}S_{m}^{\mathrm{o}} =-(116.6 \pm 3.2) J⋅K⁻¹⋅mol⁻¹; \varDelta_rC_p,m^o = (0 ±13)\varDelta_{\mathrm{r}}C_{p,m}^{\mathrm{o}} = (0 \pm 13) J⋅K⁻¹⋅mol⁻¹; and log₁₀K_s2^o = -(8.76 ±0.15)\log_{10}K_{\mathrm{s2}}^{\mathrm{o}} = -(8.76 \pm 0.15); \varDelta_rG_m^o = (50.0 ±1.7)\varDelta_{\mathrm{r}}G_{m}^{\mathrm{o}} = (50.0 \pm 1.7) kJ⋅mol⁻¹; \varDelta_rH_m^o = (17.7 ±1.7)\varDelta_{\mathrm{r}}H_{m}^{\mathrm{o}} = (17.7 \pm 1.7) kJ⋅mol⁻¹; \varDelta_rS_m^o = -(108±7)\varDelta_{\mathrm{r}}S_{m}^{\mathrm{o}} = -(108\pm 7) J⋅K⁻¹⋅mol⁻¹; \varDelta_rC_p,m^o = -(108 ±3)\varDelta_{\mathrm{r}}C_{p,m}^{\mathrm{o}} = -(108 \pm 3) J⋅K⁻¹⋅mol⁻¹. These results are internally consistent, but the latter set differs from those gleaned from previous studies recorded in the literature. The corresponding thermodynamic quantities for the formation of Ni²⁺ and Ni(OH)₂⁰\mathrm{Ni(OH)}_{2}^{0} are also estimated. Moreover, the Ni(OH)₃ ^-\mathrm{Ni(OH)}_{3}^{ -} anion was never observed, even in relatively strong basic solutions (m_{OH ^-} = 0.1m_{\mathrm{OH}^{ -}} = 0.1 mol⋅kg⁻¹), contrary to the conclusions drawn from all but one previous study.     

Hydrogen peroxide as a reductant of hexacyanoferrate(III) in alkaline solutions: kinetic studies

The kinetics of hexacyanoferrate(III) reduction by hydrogen peroxide in strongly alkaline media leading to hexacyanoferrate(II) ion have been studied spectrophotometrically within the wavelength range 300–500 nm. The reaction obeys a simple pseudo-first-order rate expression under the applied conditions, namely, a large excess of the reductant and OH⁻ anion concentrations, and a low oxidant concentration. The linear dependences of the pseudo-first-order rate constant on OH⁻ and H₂O₂ concentrations are consistent with the rate law of the form: where and are the second- and the pseudo-third-order rate constants for the electron transfer from HO₂ ⁻ and O₂ ²⁻ to [Fe(CN)₆]³⁻, respectively. The apparent activation parameters determined at 0.4 M NaOH are as follows: ΔH ^# = (18.0 ± 1.0) kJ mol⁻¹ and ΔS ^# = (−155 ± 3.5) J K⁻¹ mol⁻¹. The possible mechanism of the reaction is discussed.     

Standard molar enthalpies of formation of some methylfuran derivatives

The standard (p ^o = 0.1 MPa) molar enthalpies of formation \Updelta_\textf H_\textm^\texto ( \textl), {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} ( {\text{l),}} of the liquid 2-methylfuran, 5-methyl-2-acetylfuran and 5-methyl-2-furaldehyde were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpies of vaporization of the three compounds. The standard (p ^o = 0.1 MPa) molar enthalpies of formation of the compounds, in the gaseous phase, at T = 298.15 K have been derived from the corresponding standard molar enthalpies of formation in the liquid phase and the standard molar enthalpies of vaporization. The results obtained were −(76.4 ± 1.2), −(253.9 ± 1.9), and −(196.8 ± 1.8) kJ mol⁻¹, for 2-methylfuran, 5-methyl-2-acetylfuran, and 5-methyl-2-furaldehyde, respectively.     

Base hydrolysis of <Emphasis Type="Italic">mer</Emphasis>-trispicolinatoruthenium(III): kinetics and mechanism

The mer-[Ru(pic)₃] isomer, where pic is 2-pyridinecarboxylic acid, undergoes base hydrolysis at pH > 12. The reaction was monitored spectrophotometrically within the UV–Vis spectral range. The product of the reaction, the [Ru(pic)₂(OH)₂]⁻ ion, is formed via a consecutive two-stage process. The chelate ring opening is proceeded by the nucleophilic attack of OH⁻ ion at the carbon atom of the carboxylic group and the deprotonation of the attached hydroxo group. In the second stage, the fast deprotonation of the coordinated OH⁻ ligand leads to liberation of the monodentato bonded picolinate. The dependence of the observed pseudo-first-order rate constant on [OH⁻] is given by k_\textobs1 = \frack ₊ k₁ [\textOH ^- ] + k ₊ k₂ K₁ [\textOH ^- ]² k _- + k₁ + ( k ₊ + k₂ K₁ )[\textOH ^- ] + k ₊ K₁ [\textOH ^- ]² k_{{{\text{obs}}1}} = \frac{{k_{ + } k_{1} [{\text{OH}}^{ - } ] + k_{ + } k_{2} K_{1} [{\text{OH}}^{ - } ]^{2} }}{{k_{ - } + k_{1} + \left( {k_{ + } + k_{2} K_{1} } \right)[{\text{OH}}^{ - } ] + k{}_{ + }K_{1} [{\text{OH}}^{ - } ]^{2} }} and ( k_\textobs2 = \frack_ca + k_cb K₂ [\textOH ^- ]1 + K₂ [\textOH ^- ] ) \left( {k_{{{\text{obs}}2}} = \frac{{k_{ca} + k_{cb} K_{2} [{\text{OH}}^{ - } ]}}{{1 + K_{2} [{\text{OH}}^{ - } ]}}} \right) for the first and the second stage, respectively, where k ₁, k ₂, k _-, k _ca , k _cb are the first-order rate constants and k ₊ is the second-order one, K ₁ and K ₂ are the protolytic equilibria constants.     

Kinetics and mechanism of oxidation of aquaethylenediaminetetraacetatocobaltate(II) by <Emphasis Type="Italic">N</Emphasis>-bromosuccinimide in aqueous acidic solution

The oxidation of aquaethylenediaminetetraacetatocobaltate(II) [Co(EDTA)(H₂O)]⁻² by N-bromosuccinimide (NBS) in aqueous solution has been studied spectrophotometrically over the pH 6.10–7.02 range at 25 °C. The reaction is first-order with respect to complex and the oxidant, and it obeys the following rate law: