Protonation thermodynamics of some aminophenol derivatives in NaCl(aq) (0 ⩽ I ⩽3 mol · kg−1) at T = 298.15 K

The acid–base properties of four aminophenol derivatives, namely m-aminophenol (L1), 4-amino-2-hydroxytoluene (L2), 2-amino-5-ethylphenol (L3) and 5-amino-4-chloro-o-cresol (L4), are studied by potentiometric and titration calorimetric measurements in NaCl_(aq) (0 ? I ? 3 mol · kg^?1) at T = 298.15 K. The dependence of the protonation constants on ionic strength is modelled by the Debye–Hückel, SIT (Specific ion Interaction Theory) and Pitzer equations. Therefore, the values of protonation constants at infinite dilution and the relative interaction coefficients are calculated. The dependence of protonation enthalpies on ionic strength is also determined. Distribution (2-methyl-1-propanol/aqueous solution) measurements allowed us to determine the Setschenow coefficients and the activity coefficients of neutral species. Experimental results show that these compounds behave in a very similar way, and common class parameters are reported, in particular for the dependence on ionic strength of both protonation constants and protonation enthalpies.     

Study on the effect of Li doping in spinel Li4+xTi5−xO12 (0 ⩽ x ⩽ 0.2) materials for lithium-ion batteries

The effect of Li doping in spinel Li_4+xTi_5−xO₁₂ (0 ⩽ x ⩽ 0.2) materials on the structural and electrochemical properties were investigated. The ratio of the capacity in the voltage plateau (1.5 V) to the overall discharge capacity for Li_4.1Ti_4.9O₁₂ (x = 0.1) and Li_4.2Ti_4.8O₁₂ (x = 0.2) were higher than that of Li₄Ti₅O₁₂ especially at high current rates due to their enhanced lithium-ion and electronic conductivity by the substitution of Ti atoms by Li atoms. With the increasing of Li doping amount, lithium-ion and electronic conductivity of Li_4+xTi_5−xO₁₂ increased, however its cycling stability was depressed when the Li doping was of x = 0.2. The Li doping of x = 0.1, the appropriate Li doping amount, showed improved rate capability and better high rate performance comparing to undoped Li_4+xTi_5−xO₁₂ (x = 0).     

Hydrothermal synthesis and thermodynamic properties of 2ZnO · 3B2O3 · 3H2O

The important zinc borate of 2ZnO · 3B₂O₃ · 3H₂O has been synthesized and characterized by means of chemical analysis, XRD, FT-IR, and DTA–TG techniques. The molar enthalpies of solution of H₃BO₃(s) in HCl · 54.561H₂O, of ZnO(s) in the mixture of HCl · 54.561H₂O and calculated amount of H₃BO₃, and of 2ZnO · 3B₂O₃ · 3H₂O(s) in HCl · 54.604H₂O were measured, respectively. With the use of the standard molar enthalpies of formation for ZnO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of ?(5561.7 ± 4.9) kJ · mol^?1 for 2ZnO · 3B₂O₃ · 3H₂O(s) was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method.     

Relative permittivity increments for {xCH3OH + (1 − x)CH3OCH2(CH2OCH2)3CH2OCH3} fromT = 283.15 K toT = 323.15 K

Relative permittivities of { CH₃OH  +  CH₃OCH₂(CH₂OCH₂)₃CH₂OCH₃(2,5,8,11,14-pentaoxapentadecane, tegdme)} at temperatures from 283.15 K to 323.15 K and atmospheric pressure, were measured over the whole composition range. Experimental relative permittivities were fitted by a polynomial function in mole fraction. Values of relative permittivity were measured using a HP4284A precision LCR Meter together with the measuring cell HP16452A at 1 MHz. Relative permittivity increments were determined from experimental data and fitted to a variable-degree polynomial function. Different theoretical models were used to predict the permittivity of this mixture. The predictions are better when the volume change on mixing is considered.     

Phosphasilaallenes >Si = C = P− and phosphagermaallenes >Ge = C = P−

Phosphasilaallene Tip(Ph)Si = C = PMes* (Tip = 2,4,6-triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl) and phosphagermaallene Mes₂Ge = C = PMes* (Mes = 2,4,6-trimethylphenyl) have been obtained by dehalogenation of their corresponding dihalophosphametallapropenes > E(X)-C(X′) = P? by tert-butyllithium. They dimerize above ?40 °C by a cycloaddition involving two E = C double bonds or the E = C and the P = C double bonds but can be characterized at low temperature by trapping reactions and by low field shifts in ³¹P, ²⁹Si and particularly ¹³C NMR for the sp carbon atom. Owing to a small increase in the steric hindrance, phosphagermaallene Tip(t-Bu)Ge = C = PMes* can be stabilized and isolated. The Ge = C double bond undergoes nearly quantitative [2 + 1] cycloadditions with chalcogens and [2 + 2] cycloadditions with aldehydes or ketones. The surprisingly stable lithiochlorosilane R(Cl₂)Si-C(Li) = PMes* (R = 9-methylfluorenyl) behaves as a synthetic equivalent of the phosphasilaallene R(Cl)Si = C = PMes*. With two alkyl groups (t-Bu) on the germanium atom, the phosphagermaallene t-Bu₂Ge = C = PMes* is not obtained but its formal dimers 1,3-digermacyclobutanes have been isolated.     

Measurements of the critical parameters for {xNH3 + (1 − x)H2O} with x = (0.9098, 0.7757, 0.6808)

Measurements of the critical parameters for {xNH₃ + (1 ? x)H₂O} with x = (0.9098, 0.7757, 0.6808) were carried out by using a metal-bellows variable volumometer with an optical cell. The expanded uncertainties (k = 2) in temperature, pressure, density, and composition measurements have been estimated to be less than 3.2 mK, 3.2 kPa, 0.3 kg · m^?3, and 8.8 · 10^?4, respectively. In each mole fraction, the critical temperature T_c was first determined on the basis of the intensity of the critical opalescence. The critical pressure p_c and critical density ρ_c were then determined as the point at which the meniscus disappears on the isotherm at T = T_c. The expanded uncertainties (k = 2) in the present critical parameters have also been estimated. Comparisons of the present values with the literature data as well as the calculated values afforded using the equation of state are also presented.     

The oxygen deficient cubic perovskite SrFe1−xScxO3−δ (x ≤ 0.5; 0.1 ≤ δ ≤ 0.5): Structural features and physical properties

Solid state synthesis method has been used to stabilize oxygen deficient perovskite phases SrFe_1?xSc_xO_3?δ (0 ≤ x ≤ 0.5). The good homogeneity of samples is confirmed by energy dispersive spectroscopy (EDS) analysis performed with a transmission electronic microscope (TEM). By combining X-ray and electronic diffraction (ED), it is demonstrated that the cationic substitution on the B site of the perovskite induces a decrease of the oxygen content but without inducing long range ordering phenomenon. On this basis, X-ray patterns of compounds were indexed in the cubic Pm3m space group. The oxidation states of iron evidenced by Mössbauer spectroscopy, are in good agreement with the oxygen stoichiometries determined by cerimetric titration. In the SrFe_1?xSc_xO_3?δ series, the Fe³⁺/Fe⁴⁺ origin of the electronic conductivity is clearly evidenced. The limit compound SrFe_0.5Sc_0.5O_2.5 is highly resistive and characterized by a cluster glass-like behaviour. Finally, negative magnetoresistivity properties are revealed for the x = 0.1 and x = 0.2 samples, reaching ?10% around the magnetic transition temperature in a 7T magnetic field.     

Inhomogeneous magnetism studied by ESR in La1-xSrxMnO3 (0.45 ≤ x ≤ 0.62)

The influence of strontium substitution on lanthanum site in La_1-xSr_xMnO₃ manganites has been investigated with x ranging from 0.55 to 0.62 in the 130–400 K temperature range. Powder X-ray diffraction reveals structural changes from rhomboedral to tetragonal and to orthorhombic structures upon increasing Sr substitution. Magnetic properties also show a rich variety of phases and behaviors, including coexistence of phases above Curie temperature. The electron spin resonance measurements allow quantifying paramagnetic phases and properties with randomly distributed spins and ferromagnetic phases or inclusions with oriented spins giving rise to a local magnetic field. When x = 0.55, 0.57, the ferromagnetic state is the minor phase embedded in a paramagnetic matrix. Conversely, when x increases, the ferromagnetic phase grows and becomes the only phase observed for x = 0.62.     

High-temperature transport and stability of SrFe1−xNbxO3 − δ

The conductivity is measured in the series of solid solutions SrFe_1 ? xNb_xO_3 ? δ, where x = 0.05, 0.1, 0.2, 0.3, 0.4, within the oxygen partial pressure limits 10^?18–0.5 atm and temperature range 650–950 °C. The contributions to the total conductivity from oxygen ions, electrons and electron holes are obtained based on their different pressure dependences. The doped derivative with x = 0.1 is found to be a singular composition where ion conductivity attains a maximal value while activation energy for ion transport is minimal. This peculiar behavior is attributed to formation of favorable microstructure in the oxide. The deeper doping results in deterioration of ion transport, which is explained by oxygen vacancy filling. It is shown that replacement of iron for niobium favors enhanced thermodynamic stability towards reduction. The oxygen permeability is evaluated from the conductivity data, and it achieves rather high values in the doped derivatives. These oxides can, therefore, be recommended for further evaluation as oxygen separating membrane materials for partial oxidation of natural gas.     

Structural variations and cation distributions in Mn3−xCoxO4 (0 ≤ x ≤ 3) dense ceramics using neutron diffraction data

Single phase ceramics of cobalt manganese oxide spinels Mn_3?xCo_xO₄ were structurally characterized by neutron powder diffraction over the whole solid solution range. For x < 1.75, ceramics obtained at room temperature by conventional sintering techniques are tetragonal, while for x ≥ 1.75 ceramics sintered by Spark Plasma Sintering are of cubic symmetry. The unit cells, metal–metal and metal–oxygen average bonds decrease regularly with increasing cobalt content. Rietveld refinements using neutron data show that cobalt is first preferentially substituted on the tetrahedral site for x < 1, then on the octahedral site for increasing x values. Structural methods (bond valence sum computations and calculations based on Poix's work in oxide spinels) applied to our ceramics using element repartitions and [M–O] distances determined after neutron data refinements allowed us to specify the cation distributions in all phases. Mn²⁺ and/or Co²⁺ occupy the tetrahedral site while Mn³⁺, Co²⁺, Co^III (cobalt in low-spin state) and Mn⁴⁺ occupy the octahedral site. The electronic conduction mechanisms in our highly densified ceramics of pure cobalt and manganese oxide spinels are explained by the hopping of polarons between adjacent Mn³⁺/Mn⁴⁺ and Co²⁺/Co^III on the octahedral sites.     

Synthesis,characterization and thermochemistry of Cs(ASP) · nH2O (n = 0, 1)

New compounds of aspartic acid Cs(ASP) · nH₂O (n = 0, 1) have been synthesized and characterized by XRD, IR and Raman spectroscopy as well as TG. The structural formula of this new compound was Cs(ASP) · nH₂O (n = 0, 1). The enthalpy of solution of Cs(ASP) · nH₂O (n = 0, 1) in water were determined. With the incorporation of the standard molar enthalpies of formation of CsOH(aq) and ASP(s), the standard molar enthalpy of formation of −(1202.9 ± 0.2) kJ · mol⁻¹ of Cs(ASP) and −(1490.7 ± 0.2) kJ · mol⁻¹ of Cs(ASP) · H₂O were obtained.     

Hyperconjugation versus back bonding in AH3−nXn species (A = Si and Ge; X = F,Cl and Br; and n = 1, 2 and 3)

In this research two competing phenomena, back bonding and hyperconjugation, have been investigated based on Natural Bond Orbital (NBO) and Atoms in Molecules (AIM) analyses for radical AH_3?nX_n species, where A = Si and Ge, and n = 1, 2 and 3. It is demonstrated in this article that both above phenomena will be occurred significantly, while back bonding is the only event in analogous compounds with carbon and hyperconjugation is rather negligible. It was also found that only one back bonding with the help of keyword $CHOOSE in NBO analysis can be found in this type of compounds with reasonable structure, while it can be sometimes detected in AH_3?nX_n without using keyword $CHOOSE. It is also shown that there is always an increase in bond length in comparison with reference molecules in mentioned species due to existing hyperconjugation, while if the central atom is carbon, we have always a decrease of bond length due to only having back bonding. Additionally, from AIM point of view, the delocalization indices for α-spin (majority spin) is more than β-spin (minority spin) in radical species for molecules without back bonding, while the situation in our compounds is quite reverse, which can be attributed to the π back bonding in the β-spin electrons.