Galvanostatic investigation of electrochemical processes at the LaF<Subscript>3</Subscript>/M (M: Ag,Bi) interface

The electrochemical processes at the interface between solid fluorine-conducting electrolyte LaF₃(Eu²⁺ 0.8 mol %) and silver or bismuth electrodes in the two-electrode cell with nonpolarizable reference electrode are studied using the galvanostatic method. The anodic galvanostatic transients of LaF₃: Eu²⁺/Ag and LaF₃: Eu²⁺/Bi interfaces are linearized on the log(η ? η_max), vs. t coordinates, i.e. the rate of LaF₃|MF _n |M electrode formation is limited by slow surface diffusion of metal adions. The initial portions of cathodic galvanostatic transients in the range of solid-electrolyte lanthanum reduction are approximated by the linear dependence of η on log(1 ? √t/τ). The plots of logI vs. 1/η are linear both for the lanthanum reduction and for silver and bismuth oxidation involving mobile fluoride ion of solid electrolyte, which is typical for two-dimensional growth of new phase.     

Oxygen isotope exchange in praseodymium nickelate

Oxygen surface exchange kinetics and diffusion were studied in Pr₂NiO_4?+?δ (PNO) by the isotope exchange method with gas phase equilibration in the temperature range of 600–800 °C and oxygen pressure range of 0.33–1.62 kPa. The oxygen heterogeneous exchange rate (r_H), oxygen diffusion coefficient (D), rates of oxygen dissociative adsorption (r_a), and oxygen incorporation (r_i) were calculated along with the apparent activation energies of oxygen surface exchange and diffusion processes. The temperature dependence of r_H was found to benon-linear in Arrhenius coordinates. The apparent activation energy changed from 1.4?±?0.2 eV at T?>?700 °C to 2.0?±?0.1 eV. This might be attributed to the change in the rate-determining stage of oxygen exchange for Pr₂NiO_4?+?δ at T ~?700 °C, because of a shift in the ratio between r_a and r_i caused by the difference in their activation energies. Possible reasons for the observed changes in the rate-determining stage are discussed.     

Molecular dynamics simulations of the characteristics of sodium carboxymethyl cellulose with different degrees of substitution in a salt solution

Sodium carboxymethyl cellulose (SCMC) with different degrees of substitution (DS) possesses structural characteristics and physicochemical properties that are important in broad areas of industrial applications. This reported work investigated the structural characteristics, including the effective length (L _ef), the radius of gyration (R _g), and the hydrodynamic radius (R _H), and the physicochemical properties, including intrinsic viscosity ([η]) and salt tolerance, of SCMC with a DS more than 1.0 in NaCl solution using molecular dynamics (MD) simulations. In the MD simulations, the DS of SCMC varied from 1.2 to 2.8, and the NaCl concentration varied from 0 to 1.4 mol/L. MD simulation results showed that with the increment of NaCl concentration, the L _ef (or R _g or R _H) of SCMC decreased; with the increment of the DS, the L _ef of SCMC increased. Also, the variation tendency of [η] in the NaCl solution was consistent with its L _ef (or R _g or R _H). It was noted that the salt tolerance (represented by D) of SCMC increased as the DS increased. In addition, the sharp variation of the D value of SCMC occurred in the range of DS of 1.6 to 2.0, which agreed with the reported experimental results. Radial distribution function analyses showed that the Na⁺ cations had a stronger interaction with the carboxyl groups in SCMC with lower DS when it was present in a salt solution of higher concentration, which also reasonably explained the variation of L _ef, R _g, R _H, [η], and D of SCMC in NaCl solution.     

Inclusion of the concentration dependence of the diffusion coefficient in the sand equation

The applications of the Sand equation in potentiometry of electrode and membrane systems for precise measurements of the transition time (τ) have been determined. An approach was suggested for choosing the diffusion coefficient of electrolyte (D) in the case when the concentration changes from its value in the agitated solution (where D = D_b) to the nearly zero value at the surface (D = D₀ corresponds to an infinitely dilute solution), D_b and D₀ being substantially different. The Nernst–Planck–Poisson nonstationary equations were numerically solved in a one-dimensional system including an ion-exchange membrane and two adjacent diffusion layers (for the electrode–solution system, the result is a particular case). An effective value D_ef was found, whose substitution in the Sand equation gave τ identical to that obtained by numerical solution. The neglect of the concentration dependence D(с) can lead to a nonadequate determination of the ion transport numbers in the membrane.     

Reaction of transsilylation of <Emphasis Type="Italic">N</Emphasis>-methyl-<Emphasis Type="Italic">N</Emphasis>-trimethylsilylacetamide with silanes ClCH<Subscript>2</Subscript>SiR<Superscript>1</Superscript>R<Superscript>2</Superscript>Cl

The reaction of N-methyl-N-trimethylsilylacetamide with silanes ClCH₂SiR¹R²Cl (R¹, R² = H, Me; H, Ph; Ph₂) leads to the formation of (O→Si) chelate compounds with pentacoordinate silicon: N-[chloro(methyl)-silyl]methyl-, N-[chloro(phenyl)silyl]methyl-, and N-[chloro(diphenyl)silyl]methyl-N-methylacetamides. From the data of multinuclear NMR spectroscopy, the intermediates of the reaction of N-methyl-N-trimethylsilylacetamide with ClCH₂SiPhHCl and ClCH₂SiPh²Cl are stable in CDCl₃ solution at room temperature during several days and slowly rearrange to the final (O–Si) chelate compounds.     

Structure and dynamics of eight-membered <Emphasis Type="Italic">P,N</Emphasis>-heterocycles in solution

Conformational analysis of eight-membered P,N-heterocycles (P₂^NR₂^R') in the solution has been performed by means of NMR spectroscopy and quantum chemical calculations. The equilibrium of the С₂-symmetrical (crown, major) and С_s-symmetrical (chair-boat, minor) forms of the compounds has been revealed, the transition barriers being of about 12 kcal/mol. The presence of an aromatic substituent at the nitrogen atom significantly shifts the equilibrium towards the dominating form.     

Binuclear copper(II) complexes with acyldihydrazones of saturated carboxylic acids and pyruvic acid

Copper(II) binuclear complexes with acyldihydrazones of saturated carboxylic acids and pyruvic acid in which the coordination polyhedra are connected by polymethylene chains of different length (1 to 5 units) were synthesized and studied by chemical and thermogravimetric analysis, IR spectroscopy, and EPR. The structure of binuclear copper(II) complex with succinic acid acyldihydrazone [Cu₂L · 4Py] · 2Py was determined by X-ray diffraction. The crystals are monoclinic: a = 14.3795(6), b = 8.8736(4), c = 15.9147(7) Å, β = 101.062(3)°, space group P2₁/c, Z = 2. The number of independent reflections with I > 2σ(I) = 2804, R = 0.042, R _w = 0.087. The copper atoms are spaced by a chain of seven σ bonds at 8.922 Å. The coordination polyhedron can be described as a tetragonal pyramid highly distorted toward a trigonal bipyramid. The EPR spectra of solutions of complexes based on malonic, succinic, glutaric, and adipinic acids exhibit a poorly resolved signal of seven HFS lines with a constant of (26.3–27.0) × 10^?4 cm^?1, which attests to the presence of weak exchange interactions between paramagnetic centers. An increase in the length of the polymethylene spaur suppresses exchange interactions, and the EPR spectrum of the complex based on pimelic acid acyldihydrazone shows a signal of four HFS lines with a constant of 43.8 × 10^?4 cm^?1 typical of monomeric copper(II) complexes.     

Binuclear copper(II) complexes with acyldihydrazones of 4-formyl-5-hydroxy-3-methyl-1-phenylpyrazoles

The synthesis of copper(II) binuclear complexes with acyldihydrazones of saturated carboxylic acids and 4-formyl-5-hydroxy-3-methyl-1-phenylpyrazoles in which the coordination polyhedra are connected by polymethylene chains of different length (two to five units) is described. The complexes were studied by chemical and thermal analysis, IR spectroscopy, and EPR. The molecular and crystal structure of the copper(II) complex with glutaric acid and 1-(4′-chlorophenyl)-4-formyl-5-hydroxy-3-methylpyrazole acyldihydrazone (H₄L) described as [Cu₂L·2Py] · Py · 4H₂O was determined by X-ray diffraction. The crystals are orthorhombic: a = 24.789(7) Å, b = 39.319(9) Å, c = 4.6336(14) Å, space group Pnma, Z = 4. The number of symmetrically unrelated reflections is 4716, R = 0.0606, R _w = 0.1307. The central atoms are separated by a chain of eight σ bonds and are located at a distance of 8.939 Å. The copper coordination polyhedron is a square. A specific feature of the crystal structure is the stacking interaction involving chelate rings and the pyrazole ring, resulting in stacks of molecular complexes. The EPR spectrum of a solution of the complex based on the acyldihydrazone of succinic acid and 4-formyl-5-hydroxy-3-methyl-1-phenylpyrazole recorded at room temperature exhibits seven HFS lines with an intensity ratio of 1: 2: 3: 4: 3: 2: 1 and a constant of 33.3 G as a result of exchange coupling of the unpaired electrons to the two equivalent copper nuclei. An increase in the length of the polymethylene chain to 3–5 units or introduction of the para-chlorine atom into the benzene ring hampers the exchange interactions, and the EPR spectrum shows a signal of four HFS lines with a constant of 55–70 G typical of monomeric copper(II) complexes.     

Hall effect,electrical and magnetic resistance in Cd<Subscript>3</Subscript>As<Subscript>2</Subscript> + MnAs (30%) composite at high pressures

Electrical resistivity ρ, Hall factor R _H, magnetic resistance (R _m–R ₀)/R ₀, and magnetic-field-dependent resistances were measured in 70 mol % Cd₃As₂ + 30 mol % MnAs composite at fixed values of high hydrostatic pressures (up to p ≤ 9 GPa). The ρ, R _H, and (R _m–R ₀)/R ₀ versus pressure curves feature a phase transition at p = 4–4.3 GPa. Field-dependent magnetic resistance features a negative pressure-induced trend.     

Rhodium(I) bisaldimine complexes in transfer hydrogenation

The reactions of hydrogen transfer from 2-propanol on acetophenone in the presence of the system [Rh(cod)Cl]₂–L] (L is bisaldimine ligands based on (R,R)-1,2-cyclohexanediimine and pyridine-, quinoline-, and thiophenecarboxaldehyde) were studied. Rhodium(I) complexes with optically active ligand showed a high catalytic activity (up to 345 h^–1) and moderate enantioselectivity [up to 55% ee of (R)-1-phenyethanol]. The structure of rhodium complex with N,N'-(1R,2R)-cyclohexane-1,2-diyl-bis[1-(pyridine-2-yl)methanimine] was determined on the basis of the data of ¹H and ¹³C NMR spectroscopy and quantum chemical calculations.     

Molecular Dynamics Study on Carbon Dioxide Absorbed Potassium Glycinate Aqueous Solution

Molecular dynamics (MD) simulations have been performed to investigate the effects on structure, transport properties, and dynamical properties in the potassium glycinate aqueous solution caused by carbon dioxide (CO₂) absorption. The optimized structure and charges of constituents of the solution, such as the glycine zwitterion, have been determined by Gaussian09 using the density functional theory. The obtained pair distribution functions, g _ij (r)’s, show the significant distribution difference of bicarbonate ion, \({\text{HCO}}_{3}^{ - }\), around the glycine anion and glycine zwitterion. The shear viscosity and diffusion coefficient obtained by MD show different CO₂ concentration dependences. The frequency dependent diffusion coefficient D _i (ν) for N and C in glycine ions are mainly influenced by the cage effect of surrounding water molecules, whereas D _i (ν) for H show the characteristic vibration due to the structure difference of the glycine ions.     

Cobalt—Sandwiched lindqvist hexaniobate dimer [Co(III)H<Subscript>5</Subscript>(Nb<Subscript>6</Subscript>O<Subscript>19</Subscript>)<Subscript>2</Subscript>]<Superscript>8− 1</Superscript>

A new polyoxoniobate K₆Na₂[Co_IIIH₅(Nb₆O₁₉)₂] · 26.5H₂O (I) has been synthesized by a diffusion strategy and structurally characterized by IR spectrum, UV spectroscopy, TG analysis, and single crystal X-ray diffraction. Compound I crystallizes in the cubic Pa \(\bar 3\) space group with a = 17.969(8)Å V = 5802.6(4) ų, Z = 4, R ₁ = 0.0383 and wR ₂ = 0.1187. Compound I consists of the Lindqvist hexaniobate dimer [Co_IIIH₅(Nb₆O₁₉)₂]^8? in which the Co³⁺ cations sare andwiched between and face-shared with two Lindqvist-type [Nb₆O₁₉]^8? subunits. In situ UV spectra display that compound I can stably exist in an aqueous solution.     

Synthesis and crystal structure of the π copper(I) cyanide complex with N,N′-diallyl thiocarbamide 2CuCN · (C<Subscript>3</Subscript>H<Subscript>5</Subscript>NH)<Subscript>2</Subscript>CS

Crystals of the π copper(I) cyanide complex with N,N′-diallyl thiocarbamide, 2CuCN · (C₃H₅NH)₂CS (I), are synthesized from an aqueous-methanol solution of potassium nitroprusside, diallyl thiocarbamide on a copper electrode using the method of alternating-current electrochemical synthesis. The crystals are monoclinic: space group P2₁/n, a = 6.9440(5) Å, b = 13.760(1)) Å, c = 12.733(1) Å, β = 97.280(9)°, V = 1206.8(2) ų, Z = 4, R = 0.0361, R _w = 0.0362 for 2836 independent reflections with F ≥ 4σ(F). A unique polymeric structure is built due to the Cu(I)-(C=C) π bond and the bridging function of the thioamide S atom of the ligand molecule and one of the two independent cyano groups.     

Extensional rheology of cellulose/NaOH/urea/H<Subscript>2</Subscript>O solutions

The extensional flow behaviors of cellulose/NaOH/urea/H₂O solution were investigated by using capillary breakup extensional rheometry (CaBER). The effects of temperature, storage time and cellulose concentrations on both the storage modulus G′ and the loss modulus G″ were also analyzed. For 2 wt% cellulose solution, the G′, G″ and filament lifetime remained unchanged after long storage time. While, for 4 wt% cellulose solution, physical gels could form at either higher temperature or for longer storage time, and the filament lifetime, the relaxation time (λ _e ) and the initial extensional viscosity (η _e0) first increased and then decreased with increase of the storage time. The transition points of the filament lifetime shifted to lower storage time with the increase of the temperature. The η _e0 is proportional to λ _e . The results presented suggest that the extensional properties of the cellulose/NaOH/urea/H₂O solution first increase and then decrease during the gelation process, and the spinning time, which decreases linearly with the increase in the storage temperature, must be controlled below the time that η _e0 starts to decrease.     

Reactivity of dinuclear ruthenium complex containing two 1,2-dicarba-<Emphasis Type="Italic">closo</Emphasis>-dodecaborane-1,2-dithiolate ligands toward HC≡CCH(OH)(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>

The reaction of (p-cymene)Ru₂(μ-S₂)(S₂C₂B₁₀H₁₀)₂ (I) with HC≡CCH(OH)(CH₃)₂ in dichloromethane led to addition complexes, (p-cymene)Ru₂(μ-S₂)(S₂C₂B₁₀H₁₀)₂(R₁C=CR₂) (R₁ = H, R₂ = C(OH)(CH₃)₂ (II); R₁ = C(OH)(CH₃)₂, R₂ = H (III)). In boiling chloroform both complexes II and III spontaneously lose water to generate two geometrical isomers (p-cymene)Ru₂(μ-S₂)(S₂C₂B₁₀H₁₀)₂(R₁C=CR₂) (R₁ = H, R₂ = C(CH₃)=CH₂ (IV); R₁ = C(CH₃)=CH₂, R₂ = H (V)), respectively. Complexes IV and V could be interconverted in boiling toluene. All these complexes were characterized by elemental analysis, mass spectrometry, and NMR spectroscopy. The molecular structure of complex IV has been determined by X-ray crystallography (CIF file CCDC no. 1443964). Complex IV crystallizes in monoclinic system, space group P2₁/c with a = 10.3717(9), b = 20.3982(17), c = 18.6428(13) Å, β = 111.096(4)°, C₁₉H₄₀B₂₀Ru₂S₆, M _r = 879.27, V = 3679.8(5) ų, ρ _c = 1.587 g/cm³, Z = 4, F(000) = 1752, μ(MoK _α) = 1.179 mm^–1, R = 0.0416 and wR = 0.0848 for 4602 observed reflections (I > 2σ(I)).     

Crystal structure of nickel paratungstate B Ni<Subscript>5</Subscript>[W<Subscript>12</Subscript>O<Subscript>40</Subscript>(OH)<Subscript>2</Subscript>]·37H<Subscript>2</Subscript>O

From the solution of the system Na₂WO₄-HNO₃-Ni(NO₃)₂-H₂O acidified to Z = ν(H⁺)/ν(WO ₄ ^2? ) = 1.29, the green crystals of nickel paratungstate B Ni₅[W₁₂O₄₀(OH)₂]·37H₂O are isolated. By FTIR spectroscopy the isopoly anion is shown to belong to the structural type of paratungstate B. Using single crystal X-ray analysis, the structure of Ni₅[W₁₂O₄₀(OH)₂]·37H₂O is solved (M _r = 3840.36, monoclinic, P2₁/c space group, a = 21.9061(6) Å, b = 14.9297(4) Å, c = 22.1391(6) Å, β = 107.609(3)°, V = 6901.4(3)ų at T = 293 K, Z = 4, d_x = 3.696 g/cm³, F ₀₀₀ = 6944, μ = 21.368 mm^?1, ?33 ≤ h ≤ 33, ?22 ≤ k ≤ 22, ?33 ≤ l ≤33; the final uncertainty values for the observed reflections are R _F = 0.0532, wR ² = 0.0831 (R _F = 0.1088, wR ² = 0.0894 over all independent reflections), S = 0.978; CSD-421468).     

Properties of gold electrode modified with dimercaptosuccinic acid and electrochemical behavior of copper histidine complex

A self-assembled monolayer of meso-2,3-dimercaptosuccinic acid was prepared on the surface of gold disc electrode. The modified electrode was characterized using cyclic voltammetry in copper(II) solution and cyclic voltammetry and electrochemical impedance spectroscopy in the presence of potassium hexacyanoferrate( II)/(III) and hexaammineruthenium (II)/(III) chloride. Binding of copper(II) histidine complex (Cu–His) onto the electrode was successfully achieved for a wide range of tested concentrations, as shown with adsorption transfer stripping voltammetry. Electrode response (logΔI_p) was linearly proportional to logc(Cu–His) with correlation coefficient R³² = 0.9839.     

Vanadium separation with activated carbon and iron/activated carbon nanocomposites in fixed bed column: experimental and modelling study

In this work, iron nanoparticles were impregnated onto a commercial activated carbon surface to produce a novel adsorbent called iron-activated carbon nanocomposite (I-AC). Commercial activated carbon (CAC) and I-AC were used for vanadium separation in a fixed-bed column. The effects of various operating parameters such as inlet vanadium ion concentration, adsorbent dose and volumetric flow rate on vanadium separation performance of CAC were investigated. The performance of both adsorbents was compared in three adsorption/desorption cycles. The experimental breakthrough curves of vanadium ions in the fixed-bed column were modeled using the film-pore-surface diffusion model (FPSDM). The four mass transfer parameters characterizing this model, namely the external mass-transfer coefficient (k _f ), pore and surface diffusion coefficients (D _p and D _s ), and axial dispersion coefficient (D _L ) were evaluated through the model. Modelling and experimental results showed that the I-AC nanocomposite has a better performance for vanadium separation in comparison to AC. Sensitivity analysis on the FPSDM showed that the pore and surface diffusion, external mass transfer and axial dispersion play a significant role in vanadium separation using the I-AC. On the other hand, surface diffusion resulted to be relatively less important when CAC was used.     

Crystal structure of Iron(III) hydrogen diphosphate FeHP<Subscript>2</Subscript>O<Subscript>7</Subscript>

The crystal structure of the β modification of iron(III) hydrogen diphosphate FeHP₂O₇ has been refined by the Rietveld method using powder X-ray diffraction data. The compound crystallizes in the monoclinic system, space group P2₁/n, Z = 4, a = 7.9756(1) Å, b = 12.8260(2) Å, c = 4.8664(6) Å, β = 98.6404(8)°, V = 492.16(1) ų. The structure was refined in the isotropic approximation (pseudo-Voigt function), R _p = 0.024, R _wp = 0.033, R _Bragg = 0.091, R _F = 0.067, and compared with the structures of other compounds M^IIIHP₂O₇ (M^III is a trivalent metal).