Thermochemistry of Bu<Subscript>4</Subscript>NBr solutions in binary solvents containing formamide

The heats of solution of tetrabutylammonium bromide have been measured in mixtures of formamide (FA) with methanol (MeOH) and ethylene glycol (EG) at 313.15 K by calorimetric method. The standard enthalpies of solution in binary mixtures have been extrapolated to infinite dilution by Redlich–Rosenfeld–Meyer type equation using the literary data at 298.15 K and the present paper data at 313.15 K. The Debye–Hückel limiting law slope A _H required for calculation of the ∆_sol H ⁰ value has been obtained with application the new additive scheme of determination of the physic-chemical characteristics of binaries. The scheme is tested on the example of Bu₄NBr solutions in FA–MeOH mixture at 298.15 K. Its application yields the ∆_sol H ⁰ value very closed on the ones determined with the real (non-additive) characteristics of binaries. The standard enthalpies of solution extrapolated by Redlich–Rosenfeld–Meyer type equation are in a good agreement with the ones computed in terms of the Debye–Hückel theory in the second approximation. The heat capacities characteristics of Bu₄NBr have been calculated in H₂O–FA, MeOH–FA and EG–FA mixtures using the literary and present data. The sequence of solvents H₂O > FA > EG > MeOH located on their ability to solvophobic solvation found by us earlier for enthalpic characteristics is confirmed by the ∆C _p ⁰ values. The comparison of thermochemical characteristics of Bu₄NBr solutions in aqueous and non-aqueous mixtures containing FA has been carried out. The own structure of water remains in the region of small additions of formamide to co-solvents. It considerably differs the H₂O–FA mixture from the investigated non-aqueous systems.     

Thermal properties of <Emphasis Type="Italic">n</Emphasis>-R<Subscript>4</Subscript>NBr solutions in binary solvents containing formamide

The enthalpies of solution of tetraethyl- and tetra-n-hexylammonium bromides have been measured in mixtures of formamide with ethylene glycol at 298.15 and 313.15 K in the whole mole fraction range by the calorimetric method. The standard enthalpies of solution in binary mixtures have been calculated with Redlich–Rosenfeld–Meyer type equation. The enthalpy and heat capacity parameters of pair interaction of organic electrolytes with EG in FA and with FA in EG have been computed and discussed. The enthalpy interaction parameters of single ions with EG in FA medium have been evaluated and compared with those for ion–water and ion–MeOH interaction in FA. The standard heat capacities of solution have been evaluated. The excess enthalpies of solution, Δ_sol H ^E, of Et₄NBr, Bu₄NBr, and Hex₄NBr have been determined. The Δ_sol H ^E values are positive for Et₄NBr and negative for Bu₄NBr and Hex₄NBr and become more negative from Bu₄NBr to Hex₄NBr.     

Synthesis and structure of platinum complexes [Bu<Subscript>4</Subscript>P][PtBr<Subscript>6</Subscript>] and [Bu<Subscript>4</Subscript>P][PtBr<Subscript>5</Subscript>(DMSO-S)]

By the reaction of tetrabutylphosphonium bromide with potassium hexabromoplatinate (2: 1, mol) in acetone complex [Bu₄P]₂[PtBr₆] was obtained, which after crystallization from dimethyl sulfoxide gave complex [Bu₄P][PtBr₅(DMSO-S)]. Phosphorus atoms in both complexes have tetrahedral surrounding.     

The synthesis and properties of solid solutions based on Ba<Subscript>4</Subscript>Ca<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>11</Subscript>

(Ba_{1 ? x} Ca _x )₆Nb₂O₁₁ solid solutions were synthesized. The compositions were shown to be single-phase at 0.23 ≤ x ≤ 0.47 and have a double perovskite cubic structure with an incomplete oxygen sublattice. The interaction of solid solutions with water vapor and their electrical properties were studied. In dry atmosphere, these complex oxides were mixed oxygen-hole conductors. In humid atmosphere, they intercalated water and exhibited protonic conductivity. The influence of Ba/Ca isovalent substitution, the dynamics of the oxygen sublattice, and the concentration of intercalated water on the value and contribution of protonic and hole conductivity was analyzed.     

The thermodynamic characteristics of solutions of Bu<Subscript>4</Subscript>NI in dimethylsulfoxide over a wide concentration range

The integral heats of solution of Bu₄NI in dimethylsulfoxide (DMSO) were measured at 298.15, 313.15, and 328.15 K and concentrations from dilute to saturation. The standard enthalpies and heat capacities of solution and solvation of Bu₄NI in DMSO at various temperatures and the \(\bar C_p^o (Bu_4 N^ + )\) value at 298.15 K were calculated. The obtained and literature data were used to consider the influence of the nature of solvents on Δ_sol H ^m (Bu₄NI) and of the electrolyte on Δ_sol H ^m in dimethylsulfoxide at 298.15 K. The dynamic viscosity and density of the Bu₄NI-DMSO system were determined at various concentrations and temperatures. The Eyring equation was used to calculate the activation energy of viscous flow at all the concentrations studied.     

Electrotransport properties of ions in aqueous solutions of H<Subscript>2</Subscript>SeO<Subscript>4</Subscript> and Na<Subscript>2</Subscript>SeO<Subscript>4</Subscript>

Coefficients of self-diffusion, absolute speeds of movement of ions and the activation energy of electrical conductivity are found from the conductance measurements of aqueous solutions of selenic acid and sodium selenate at different concentrations in a temperature range of 288–318 K. Both the Stokes and effective radii of ions and their hydrate numbers at 298 K are calculated. The obtained results are interpreted in the frames of Samoilov theory on positive and negative hydration of ions.     

Electrochemical reduction and flow detection of iodate on (Bu<Subscript>4</Subscript>N)<Subscript>2</Subscript>Mo<Subscript>6</Subscript>O<Subscript>19</Subscript> self-assembled monolayer

A stable monolayer of the inorganic–organic hybrid polyoxometalate (Bu₄N)₂Mo₆O₁₉, denoted as Mo₆O₁₉, was formed on a sodium-3-mercapto-1-propanesulfonate (MPPS)-covered gold electrode surface, interlaced with an anionic poly(dimethyldiallylammonium chloride) (PDDA) binding layer based on the electrostatic self-assembled (ESA) technique. Electrochemical characterization of the Mo₆O₁₉ self-assembled thin films on the solid surface by cyclic voltammetry and AC impedance spectroscopy revealed a stable and sensitive electrocatalytic response to the reduction of iodate. Iodate was determined amperometrically through a flow injection cell at the modified electrode in the concentration range of 1.0×10^–6 to 1.0×10^–1 M with a detection limit of 8×10^–8 M (signal-to-noise ratio = 3). Performance was improved to meet practical needs compared with previously reported analogues.     

Crystal structure and EPR spectra of (Bu<Subscript>4</Subscript>N)<Subscript>2</Subscript>[V(dmit)<Subscript>3</Subscript>]

The tris-chelate complex of vanadium(IV) (Bu₄N)₂[V(dmit)₃] is prepared from VCl₃ and (Bu₄N)₂[Zn(dmit)₂] (dmit = isotrithionedithiolate C₃S₅ ^2–) and characterized by single crystal XRD and mass spectrometry. The complex crystallizes in the space group Pna2₁ and has a distorted octahedral environment of vanadium. The complex is paramagnetic and gives a characteristic EPR spectrum in both solution and solid phase. The g factors and hyperfine interaction constants are determined.     

Electrochemical properties of solid electrolytes based on BaSm<Subscript>2</Subscript>S<Subscript>4</Subscript>

Solid solutions based on BaSm₂S_{4 ? x} mol % BaS (Sm₂S₃) are obtained. Oxide intermediates were homogenized using chemical and mechanical mixing methods. The solid solution region is determined. Complex conductivity is studied and conductivity activation energy is calculated for samples with different history. Electrolytic properties of phases based on barium thiosamarate are studied. Vacancy mechanism of defect formation is suggested.     

Whitlockite solid solutions in the Ca<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript>-K<Subscript>3</Subscript>VO<Subscript>4</Subscript>-NdVO<Subscript>4</Subscript> system

Phase equilibria in the Ca₃(VO₄)₂-K₃VO₄-NdVO₄ system have been studied. An extensive calcium orthovanadate-based solid solution was found to form with the boundary compositions as follows: Ca₃(VO₄)₂-Ca₉Nd(VO₄)₇-Ca_9.33K_2.33(VO₄)₇-Ca_7.88K_2.63Nd_0.87(VO₄)₇. The unit cell parameters of the whit-lockite vanadates synthesized increase as the potassium and neodymium contents increase. Phase transitions from the low-temperature β phase to the β′ centrosymmetrical structure in Ca_{9.33 − 5z} K_{2.33 + z} Nd_3z (VO₄)₇ vanadates have been studied dilatometrically. The increase in the β ai β′ transition temperature caused by potassium is interpreted as arising from the filling in of vacant cation positions M(4) and M(6).     

Structure and properties of solid solutions based on bismuth niobate Bi<Subscript>3</Subscript>NbO<Subscript>7</Subscript>

Solid solutions Bi₃Nb_1–yW_yO_{7 ± δ}, Bi₃Nb_1–yV_yO_{7 ± δ}, Bi₃Nb_1–yFe_yO_{7 ± δ} (y = 0.1–0.5; Δy = 0.1), and Bi_3–xY_xNb_1–yW_yO_{7 ± δ} (x = 0.05, 0.1; y = 0–0.3; Δy = 0.1) have been studied. The homogeneity ranges of the solid solutions and crystal-chemical parameters have been determined by means of X-ray powder diffraction. The electrical conductivity of sintered samples has been studied by impedance spectroscopy. The joint introduction of yttrium and tungsten into the niobium sublattice does not lead to an increase in the conductivity of solid solutions, and the change of the dopant type has no noticeable effect on this conductivity.     

Molecular dynamics simulation of Bu<Subscript>4</Subscript>N<Superscript>+</Superscript> in dimethylformamide: Solvation-induced volume changes

The structure of the Bu₄N⁺-dimethylformamide system in the condensed and gas phases was studied by molecular dynamics simulation and quantum-chemical calculations. The calculation results were used to reveal the role played by steric effects in the volumetric characteristics of ion solvation.     

Synthesis and speciation of zirconium tetrafluoride complexes with phosphoryl-containing bases Ph<Subscript>3</Subscript>PO,Bu<Subscript>3</Subscript>PO and (Me<Subscript>2</Subscript>N)<Subscript>3</Subscript>PO in solutions

Zirconium fluoro complexes with phosphoryl-containing bases (L) have been synthesized by the reaction of a suspension of ZrF₄(dmso)₂ in toluene with an excess of Ph₃PO or Bu₃PO, as well as (Me₂N)₃PO in CH₂Cl₂. The composition and structure of the complexes in CH₂Cl₂ solutions have been studied by ¹⁹F NMR in the temperature range 293–203 K. Phosphine oxides are substituted for dmso to form mainly cis-tetrafluoro species, insignificant amounts of trans-tetrafluoro species, and mer- and fac-[ZrF₃L₃]⁺ complexes. In addition to these species, the reaction with Bu3PO yields the dimeric oxo complex (µ-O)[ZrF₃(Bu₃PO)₂]₂. Hydrolysis of fluoro complexes in CH₂Cl₂ with the use of an NBu₄OH solution in iso-PrOH does not lead to oxo and hydroxo complexes: first, the [ZrF₅L]^– complex is formed, and the final hydrolysis product is ZrF₆^2-. The fine structure of ¹⁹F NMR resonance lines for the zirconium fluoride compounds [ZrF5L]^–, cis- [ZrF₄L₂], dimeric oxo complex, and mer-[ZrF₃L₃]⁺ in organic solvents has been observed for the first time, which makes it possible to reliably identify the composition and structure of the zirconium coordination polyhedron in the complexes under consideration.     

Synthesis and colour properties of pigments based on terbium-dopped Mg<Subscript>2</Subscript>SnO<Subscript>4</Subscript>

The main aim of this work was to synthesize the magnesium orthostannate doped by terbium cations and tested whether these materials can be used for colouring of the different materials, e.g. organic binder and ceramic glazes. Initial composition of pigments was counted according the general formula 2MgO(1 − x)SnO₂–xTbO₂, where values of x varied from 0.1 to 0.5 in 0.1 steps. The simultaneous TG/DTA measurements of mixture containing tin oxide, magnesium carbonate hydroxide and terbium oxide showed that the formation of a new compound started at temperature 1,029 °C, but single-phase system was not prepared. Granulometric compositions of samples that were prepared by calcining at temperatures 1,300–1,400 °C are characterized by values of median (d ₅₀) in range 4–8 μm. The calcining temperature 1,500 °C caused the increase of the particle sizes at around 12 μm. The composition of sample 2MgO–1.5SnO₂–0.5TbO₂ and heating temperature 1,500 °C are the most suitable conditions for preparation of colourfully interesting pigment that can be recommended also for colouring of ceramic glazes. Especially, for colouring of decorative lead containing glaze G 07091 containing 5 wt% of PbO and 8 wt% of Al₂O₃.     

Synthesis and equilibria in solutions of hafnium fluoro complexes with phosphoryl-containing bases Ph<Subscript>3</Subscript>PO,Bu<Subscript>3</Subscript>PO,and (Me<Subscript>2</Subscript>N)<Subscript>3</Subscript>PO

The composition and equilibria in solutions of the products of reaction of HfF₄(dmso)₂ with monodentate phosphoryl-containing bases L = Ph₃PO, Bu₃PO, and (Me₂N)₃PO in CH₂Cl₂ are studied by ¹⁹F NMR. Octahedral molecular complexes cis-[HfF₄L₂] and minor amounts of trans-[HfF₄L₂] and fac-[HfF₃L₃]⁺ cations were the main products for all ligands. The oxytrifluoride complex (μ-O)[HfF₃(Bu₃PO)₂]₂ and the [HfF₅(Bu₃PO)]^– anion were identified in the case of Bu₃PO. The conclusion about the formation of the hafnium oxytrifluoro complex was verified via hydrolysis of the product of reaction between HfF₄ and Ph₃PO upon exposure to air. As a result, (μ-O)[HfF₃(Ph₃PO)₂]₂ were detected; fine-structure ¹⁹F NMR resonance lines were obtained and the spin–spin coupling constant J_FF was measured for the first time. Hydrolysis via adding a Bu₄NOH solution in i-PrOH to the HfF₄L₂ solutions in CH₂Cl₂ did not yield the expected zirconium oxyfluoro complexes with the smaller number of fluorine atoms. Due to deeper hydrolysis, equilibrium in fluoride complexes shifted towards species with higher fluorine contents, [ZrF₅L]^– and [ZrF₆]^2–, resulting in the formation of Hf(O)_x(OH)_у(i-PrOH)_z complexes that were not observed in the ¹⁹F NMR spectra and the substitution of the released fluoride ions for molecular ligands in HfF₄L₂ complexes.     

Electrochemical dissolution of Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> in acid solutions

The present study deals with the electrochemical reductive dissolution of Mn₃O₄, which was added to carbon-paste electroactive electrodes (CPEEs) in acid solutions. It was found that in the experimental conditions the thermodynamically stable form of manganese was . Kinetic features of the electrochemical reductive dissolution of Mn₃O₄, which was realized under potential cycling conditions (+1.0 V→−0.7 V→+1.0 V), were determined by the electrode polarization direction. It was shown that the cathodic reduction of Mn₃O₄ was accomplished in three stages. Manganese was dissolved in the supporting solution only at the third stage. The first two stages involved solid-phase reactions. The anodic cycling stage included an active dissolution of Mn₃O₄ and the lower manganese oxide (MnO) accumulated on the electrode surface during the cathodic reduction.     

Electrochemical dissolution of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> in acidic solutions

The cyclic voltammetry method was used to study the regularities of the electrochemical behavior of cobalt cobaltite in an acidic medium. It is shown that cathodic reduction of Co₃O₄ in the studied range of potentials of +1.0 to −0.8 V is a multistage process occurring according to the scheme:      

Synthesis and properties of nanocrystalline materials based on LaPO<Subscript>4</Subscript>

A study of the processes in which lanthanum orthophosphate nanocrystalline powders with rhabdophane and monazite structure and crystallite size of about 10 nm are formed demonstrated that, at temperatures of up to 500°C, nanocrystalline lanthanum orthophosphate with rhabdophane structure loses crystal hydrate water and is transformed at 520–540°C to a nanocrystalline phase with monazite structure. This transition is not associated with as change in the crystallite size because nanocrystals of the anhydrous lanthanum orthophosphate phase with monazite structure retain a size of about 10 nm both at the instant of the structural transformation and up to temperatures of 600–700°C. The technological modes were determined in which nanocrystalline lanthanum orthophosphate powders with monazite structure can be obtained and the powders are used for sintering of ceramic materials with porosity on the level of 5–7%.