Conductivity, calorimetry and phase diagram of the NaHSO4–KHSO4 system

Physico-chemical properties of the binary system NaHSO₄–KHSO₄ were studied by calorimetry and conductivity. The enthalpy of mixing has been measured at 505 K in the full composition range and the phase diagram calculated. The phase diagram has also been constructed from phase transition temperatures obtained by conductivity for 10 different compositions and by differential thermal analysis. The phase diagram is of the simple eutectic type, where the eutectic is found to have the composition X(KHSO₄) = 0.44 (melting point ≈ 406 K). The conductivities in the liquid region have been fitted to polynomials of the form κ(X) = A(X) + B(X)(T − T_m) + C(X)(T − T_m)², where T_m is the intermediate temperature of the measured temperature range and X, the mole fraction of KHSO₄. The possible role of this binary system as a catalyst solvent is also discussed.     

Refined heat capacity of LaPO4 in the temperature range 0–1600 K

In the present work temperature dependence of heat capacity of cesium tantalum tungsten oxide has been measured first in the range from 7 to 350 K and then between 330 and 630 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity C_p° (T), enthalpy H°(T) − H°(0), entropy S°(T) − S°(0) and Gibbs function G°(T) − H°(0), for the range from T → 0 to 630 K. The structure of CsTaWO₆ is refined by the Rietveld method: space group F d3m, Z = 8, a = 10.3793(2) Å, V = 1118.14(4) Å³. The high-temperature X-ray diffraction was used for the determination of temperature of phase transition and coefficient of thermal expansion.     

Synthesis, structure and oxygen nonstoichiometry of La0.4Sr0.6Co1−yFeyO3−δ

The samples of La_0.4Sr_0.6Co_1−yFe_yO_3−δ (y = 0.2 and 0.4) were prepared using both conventional ceramic technique and nitrate–citrate precursors technique. The phase identification was made by X-ray diffraction method. The refinement of structural parameters from the XRD and neutron diffraction measurements was performed by full profile Rietveld analysis. Neutron diffraction showed that both samples possess distorted perovskite-type structure. Oxygen nonstoichiometry was measured by chemical analysis and thermogravimetry (TG) analysis in the range 20 ≤ T/°C ≤ 900 and 2E-5 ≤ pO₂/atm ≤ 4E-1. TG-experiments indicate a relatively fast and reversible oxygen exchange at pO₂ > 1E-2 atm. Mass saturation occurs at T < 300 °C upon cooling. The absolute value of oxygen nonstoichiometry was determined by iodometric titration measurements. It was found that both samples have practically stoichiometric composition at 300 °C in air and δ increases with increasing temperature and decreasing oxygen partial pressure.     

Solidification of metallic tin in dispersed phase

Differential scanning calorimetry (DSC) and particle size measurements were carried out on disproportionation products of pure SnO to investigate the fusion and solidification behaviour of Sn droplets and their catalytic nucleation on Sn oxides. If disproportionation reaction takes place at T ≥ 798 K, the products are metallic Sn and SnO₂; but for 523 < T < 798 K, SnO₂ is replaced by an intermediate oxide (IO) Sn_xO_(1+x). On melting, samples with IO show a drop of melting point of metallic tin due to Gibbs–Thomson effect; no lowering of melting point was observed in samples with SnO₂. On the other hand, if solidification occurs in the presence of IO, Tin droplets always displayed three distinct exothermic solidification peaks, but if it takes place in the presence of SnO₂, only one exothermic peak is observed. Undercooling values and contact angles were determined for each of the heterogeneous nucleation processes. The different behaviour of metallic Tin droplets was related to the different lattice symmetry of SnO₂ and IO, which act as nucleation catalysts.     

Structure analysis and the standard molar enthalpy of formation of a coordination polymer [Co(TO)2Cl2]n (TO = 1,2,4-triazole-5-one)

A coordination polymer was synthesized by the reaction of CoCl₂ with 1,2,4-triazole-5-one (TO) and charaterized by means of IR and TG–DTG. Single-crystal structure analysis showed that the complex crystallized in the monoclinic space group C2/c: a = 23.105(9) Å, b = 3.5683(2) Å, c = 13.589(6) Å,  = 90°, β = 124.038(4)°, γ = 90°, V = 928.4(7) Å³, Z = 4. The standard molar enthalpy of formation of the complex was determined to be (−1034.28 ± 0.95) kJ mol⁻¹.     

Synthesis and properties of oxynitrides (La,Sr)Ti(O,N)3 thin films

We report on the synthesis, optical and electrical properties of thin films of La_xSr_(1−x)Ti(O,N)₃, x = 0, 0.25, 0.50, 0.75 and 1. The films were grown by a soft chemistry process from polymeric precursor solutions, which were deposited by spin coating on 100-oriented SrTiO₃ substrates. After drying, the organic matrix was burned at 400 °C. These steps were repeated six times to obtain a reasonable thickness of the films. Afterwards, the samples were heated in a tube furnace at 950 °C in flowing ammonia. The oxynitride films showed different colours from red-orange for LaTiO₂N to greenish-blue for SrTiO₃:N. The films were characterised by X-ray diffraction, scanning electron microscopy, atomic force microscopy, UV–vis spectroscopy, secondary ion mass spectrometry and electrical measurements. The results show that the films are polycrystalline and have the perovskite structure. Their thickness is about 440 nm and the average roughness value is 7.5 nm. UV–vis transmittance measurements showed a strong decrease in the band gap values for the oxynitrides compared to the respective oxides. The values change from approximately 3.2 eV for the oxides to an average value of 2.4 eV for the oxynitrides. The electrical measurements indicate a change in the electrical behaviour from insulator for LaTiO₂N to semiconductor for SrTiO₃:N.     

Three interpenetrated frameworks constructed by long flexible N,N′-bipyridyl and dicarboxylate ligands

Three interpenetrated polymeric networks, {[Co(bpp)(OH-BDC)] · H₂O}_n (1) [Ni(bpp)_1.5(H₂O)(OH-BDC)]_n (2) and {[Cd(bpp)(H₂O)(OH-BDC)] · 2H₂O}_n (3), have been prepared by hydrothermal reactions of 1,3-bis(4-pyridyl)propane (bpp), 5-hydroxyisophthalic acid (OH-H₂BDC), with Co(NO₃)₂ · 6H₂O, Ni(NO₃)₂ · 6H₂O and Cd(NO₃)₂ · 4H₂O, respectively. Single-crystal X-ray diffraction analyses reveal that the three compounds all exhibit interpenetrated but entirely different structures. Compound 1 is a fourfold interpenetrated adamantanoid structure with water molecules as space fillers, in which bpp adopts a TG conformation (T = trans, G = gauche). Compound 2 is an interdigitated structure from the interpenetrated long arms of one-dimensional molecular ladders, while bpp in 2 adopts both TT and TG conformations. Compound 3 is a twofold interpenetrated three-dimensional network from a one-dimensional metal-carboxylate chain bridged by TG conformational bpp. The hydrogen bonding interactions in 1–3 further stabilize the whole structural frameworks and play critical roles in their constructions.     

Interaction of sodium cholate with dioctadecyldimethylammonium chloride vesicles in aqueous dispersion

Mixtures of dioctadecyldimethylammonium chloride (DODAC) cationic vesicle dispersions with aqueous micelle solutions of the anionic sodium cholate (NaC) were investigated by differential scanning calorimetry, DSC, turbidity and light scattering. Within the concentration range investigated (constant 1.0 mM DODAC and varying NaC concentration up to 4 mM), vesicle → micelle → aggregate transitions were observed. The turbidity of DODAC/NaC/water depends on time and NaC/DODAB molar concentration ratio R. At equilibrium, turbidity initially decreases smoothly with R to a low value (owing to the vesicle–micelle transition) when R = 0.5–0.8 and then increases steeply to a high value (owing to the micelle–aggregate transition) when R = 0.9–1.0. DSC thermograms exhibit a single and sharp endothermic peak at T_m ≈ 49 °C, characteristic of the melting temperature of neat DODAC vesicles in water. Upon addition of NaC, T_m initially decreases to vanish around R = 0.5, and the main transition peak broadens as R increases. For R > 1.0 two new (endo- and exothermic) peaks appear at lower temperatures indicating the formation of large aggregates since the dispersion is turbid. All samples are non-birefringent. Dynamic light scattering (DLS) data indicate that both DODAC and DODAC/NaC dispersions are highly polydisperse, and that the mean size of the aggregates tends to decrease as R increases.     

The ν(OH/OD) band shape of strong hydrogen bonded dimers of phosphinic acids. Phenomenology and formation models

The infrared spectra of phosphinic acid R₂POOH dimers (R=CH₃, CH₂Cl, C₆H₅) have been studied in CCl₄ and CH₂Cl₂ solutions (T=300 K). The infrared spectra of deuterated R₂POOD dimers (R=CH₃, CH₂Cl) were also studied in the gas phase (T=400–550 K) and solid state (T=100–300 K). They are compared with previously studied spectra of the light (non-deuterated) dimers in the gas phase, in the solid state and in low-temperature argon matrices (T=12–30 K) in the 4000–400 cm⁻¹ spectral region. It is found that the strong and broad ν(OH) dimer bands have similar shapes, nearly equal values of bandwidth and low-frequency shift, and possess the Hadzi ABC structure irrespective of the type of acid, significant differences of dimerization enthalpies, influence of solvent, the type of H-bonded complexes (cyclic dimers in the gas phase, in solutions, and in inert matrices, and infinite chains in the solid state), and temperature in the range 12–600 K. Isotopic ratio of the first moments of light and deuterated acid bands has been measured. Analysis of the ν(OH/OD) band of hydrogen bonded dimers of phosphinic acids shows that the interaction between the two intermolecular bonds O–HOP in a cyclic complex plays virtually no role in the mechanism of the ν(OH/OD) band formation; the shape of ν(OH/OD) band is controlled mainly by the POOH(D)O fragment; and the band shape of strong hydrogen bonded complexes is formed by a number of vibrational transitions from the ground state to different combination levels in the region 3500–1500 cm⁻¹.     

Comparative characteristics of texture and properties of hybrid organic–inorganic adsorbents functionalized by amine and thiol groups

The structure and texture characteristics of the hybrid organic–inorganic adsorbents, which were obtained by using of two-component systems of “structure-forming agent/trifunctional silane”, are compared as follows: the first component is Si(OC₂H₅)₄ or (C₂H₅O)₃Si–A–Si(OC₂H₅)₃, where A = –(CH₂)₂– or –C₆H₄–; the second one is alkoxysilane with amine (–NH₂, NH, –NH(CH₂)₂NH₂) and thiol (–SH) groups. The adsorbents, derived from TEOS, have more accessible functional groups (2.6–4.2 mmol/g) than xerogels, which are based on bis(triethoxysilanes) (1.0–2.6 mmol/g). On another hand xerogels derived from bis(triethoxysilanes) have a more extended porous structure (S_sp =516–968 m²/g, V_s = 0.418–1.490 cm³/g, d = 2.5–15.0 nm) than those that are based on TEOS (S_sp = 4–631 m²/g, V_s = 0.005–1.382 cm³/g, d = 2.3–17.7 nm). The geometric dimensions of functional groups have a more essential effect on the parameters of porous structure in the case of TEOS-derived xerogels. Using solid-state NMR spectroscopy, it has been shown that in synthesis of xerogels with the use of TEOS, the molecular frame of globules is formed by structural units Qⁿ (n = 2,3,4), and the functional groups exist as structural units of Tⁿ (n = 2,3). The xerogels obtained with using bis(triethoxysilanes) consist only of structural units of Tⁿ-type (n = 1,2,3).     

Isothermal kinetic analysis of the thermal decomposition of magnesium hydroxide using thermogravimetric data

In the present study, the kinetics of the thermal decomposition of magnesium hydroxide is investigated, using isothermal methods of kinetic analysis. For this purpose, experiments in thermogravimetric analyser were carried out in standard values of temperature (350°, 400°, 450° and 500°C) which resulted in weight loss percent as a function of time. The data were further modified to give fraction reacted ‘' versus time to be tested in various forms of ‘' functions. In order to determine the mechanism of the magnesium hydroxide decomposition and the form of the conversion function which governs the dehydroxylation of Mg(OH)₂, four different methods of isothermal kinetic analysis were used. Applying each of these methods to the data, it was concluded that the nucleation mechanism predominates the Mg(OH)₂, decomposition for all values of temperature tested; at 350°C the kinetic model which represents the experimental data is that of reaction at phase boundaries (random nucleation), F₁: ln(1−)=kt) while for the higher temperatures 400°, 450° and 500°C the kinetic equation of nucleation and development in two dimensions, A₂: [−ln (1−)]^1/2=kt was found to fit better the experimental results. The activation energy was evaluated applying two alternative methods; the Arrhenius plot, using maximum rates of reaction, from which the activation energy was evaluated to be 20.54 kcal/mol. An alternative method based on plots of ln t versus 1/T corresponding to the same value of ‘' gave values of 10.72, 13.82 and 16.31 kcal/mol for ‘' values of 0.25, 0.50 and 0.75, respectively.     

Strong antiferromagnetism in the dinuclear 2-pyridone complex with N–C–O bridges: A paddle-wheel analogue of the dinuclear tetracarboxylates

A novel dinuclear complex [Cu₂(μ-L)₄(HL)₂] (1) was isolated from starting 2-pyridone (HL) via a resonance and a tautomeric transformation. Each copper centre is in a square-pyramidal coordination sphere, defined by two oxygen atoms (Cu–O4 1.978(5), Cu–O11 1.964(4) Å) and two nitrogen atoms (Cu–N2 2.003(5), Cu–N3 2.007(5) Å) of four bridging deprotonated pyridin-2-olates and an oxygen atom on the top from a neutral 2-pyridone (Cu–O2 2.227(5) Å), analogous to tetracarboxylate paddle-wheel complexes. Compound 1 was compared with mixed pyridin-2-olato/methanoato analogues [Cu₂(μ-HCO₂)₂(μ-L)₂(HL)₂] · 2CH₃CN (2) and [Cu₂(μ-HCO₂)₂(μ-L)₂(HL)₂] (2a) (2a is an air stable form obtained from 2 outside mother-liquid). The EPR spectra of air stable 1 and 2a show three signals H_z1, H₂ and H_z2, typical for the binuclear systems with spin S = 1, both revealing strong antiferromagnetism 2J = −334 (1) and −324 cm⁻¹ (2a). Interestingly, only for 1 additional H₁ signal at 100 mT is noticed (D(1) = 0.293 cm⁻¹ < hν = 0.320 cm⁻¹ < D(2a) = 0.347 cm⁻¹). On the other hand, several broad signals in the 100–450 mT region, only in the high temperature spectrum for 2a are observed. These results are in agreement with the magnetic susceptibility analysis.     

The molecular structure and the puckering potential function of silacyclobutane as determined by gas electron diffraction and relaxation constraints from ab initio calculations

Gas electron diffraction is applied to determine the geometric parameters of the silacyclobutane molecule using a dynamic model where the ring puckering was treated as a large amplitude motion. The structural parameters and the parameters of the potential function were refined taking into account the relaxation of the molecular geometry estimated from ab initio calculations at the MP2/6-311+G(d, p) level of theory. The potential function has been described as V() = V₀[(/_e)² − 1]² with the following parameters V₀ = 0.82 ± 0.60 kcal/mol and _e = 33.5 ± 2.7°, where is a puckering angle of the ring.

The geometric parameters at the minimum V() (r_a in Å, in degrees and uncertainties given as three times the standard deviations including a scale error) are: r(Si–H_ax) = 1.467(96), r(Si–H_eq) = 1.468(96), r(Si–C) = 1.885(2), r(C–C) = 1.571(3), r(C–H) = 1.100(3), CSiC = 77.2(9), HSiH = 108.3, SiCH_eq = 123.5(16), SiCH_ax = 111.9(16), CC₅H_eq = 118.4(24), CC₅H_ax = 112.3(24), HC₃H = 107.7, δ(HSiH) = 6.6, δ(HC₃H) = 7.0, where the tilts δ, HSiH, and HC₃H are estimated from ab initio constraints. The structural parameters are compared with those obtained for related compounds.     

Thermodynamics of micelle formation of the ephedrine-based chiral cationic surfactant DMEB in water, and the intercalation of DMEB in montmorillonite

The solubility and the micelle formation of the chiral cationic surfactant (1R,2S)-(−)-N-dodecyl-N-methylephedrinium bromide (DMEB) in aqueous solution were investigated by conductometry and titration microcalorimetry in the temperature range of 278–328 K. The Krafft temperature of DMEB is T_K = 280 K and the solubility of the surfactant at this point is 4.5 mM. The cmc versus T curve passes through a shallow minimum close to room temperature. The micelle formation changes from endothermic to exothermic at this characteristic temperature. The apparent degree of dissociation of the micelles _app increases slightly as the temperature is raised. The isosteric enthalpies of micelle formation, ΔH_{st mic}, are close to the calorimetrically measured enthalpies, ΔH_mic, provided that the real degree of dissociation, _st = 1, is used in the calculations. ΔH_mic and the temperature dependence of ΔH_mic of DMEB are markedly similar to those of sodium dodecylsulfate and dodecyltrimethylammonium bromide. The micelle formation of DMEB is favored by both enthalpy and entropy at and above room temperature. The enthalpy–entropy compensation results in a slight decrease in the Gibbs free energy on increase of the temperature. Sodium montmorillonite (M) was rendered organophilic by DMEB via ion-exchange to produce the clay/organocomplex DME-M. The swelling properties of the organoclay were investigated by XRD measurements in a variety of organic solvents. The basal spacing of DME-M varied from 1.8 to 3.5 nm, depending on the nature of the solvent. DME-M is a heterogenized ephedrine derivative, which may be regarded as a potential catalyst for enantioselective organic syntheses.     

The pseudogap in LSCO-type high-temperature superconductors as seen by neutron crystal-field spectroscopy

We studied the isotope, pressure and doping effects on the pseudogap temperature T^* by neutron spectroscopic experiments of the relaxation rate of crystal-field excitations in La_1.96−xSr_xHo_0.04CuO₄ (x = 0.11, 0.15, 0.20, 0.25) on the high-resolution time-of-flight spectrometer FOCUS at SINQ, PSI. We found clear evidence for the opening of a pseudogap in the underdoped regime at T^*(x = 0.11) = (82.2 ± 1.2) K as well as in the overdoped and the heavily overdoped compounds at T^*(x = 0.2) = (49.2 ± 0.7) K and at T^*(x = 0.25) = (46.5 ± 0.5) K, respectively. Furthermore, we investigated the effect of oxygen isotope substitution on the pseudogap, the experiments revealed ΔT^*(x = 0.11) = (21.3 ± 5.2) K and ΔT^*(x = 0.2) = (4.5 ± 1.3) K. The application of hydrostatic pressure (0.8 and 1.2 GPa) on the optimally doped compound (x = 0.15) results in a downward shift of dT^*/dp = (−5.9 ± 1.6) K/GPa.     

Heat capacity of copper hydride

The heat capacity of copper hydride has been measured in the temperature range 2–60 and 60–250 K using two adiabatic calorimeters. Special procedure for the purification of CuH has been applied and a careful analysis of sample contamination has been performed. The experimental results have been extrapolated up to 300 K due to instability of the copper hydride at room temperature. From the temperature dependence of heat capacity the values of entropy S°(T), thermal part of enthalpy H°(T)−H°(0) and Gibbs function [−(G°(T)−H°(0))] have been calculated assuming S°(0)=0. The standard absolute entropy, standard entropy of formation from the elements and enthalpy of decomposition of copper hydride from the elements have been calculated and found to be 130.8 J K⁻¹ mol⁻¹ (H₂), −85.1 J K⁻¹ mol⁻¹ (H₂), −55.1 kJ mol⁻¹ (H₂), respectively. These new results gave the possibility of discussion on thermodynamic properties of copper hydride. Debye temperature has been for the first time determined experimentally.     

Constructions of a set of novel hydrogen-bonded supramolecules from reactions of cobalt(II) salt with bis(3,5-dimethylpyrazolyl)methane and different carboxylic acids

Reactions of CoX₂·6H₂O (X = Cl⁻, ClO₄⁻) with bis(3,5-dimethylpyrazolyl)methane (dmpzm) and formic acid, acetic acid, benzoic acid, salicylic acid, maleic acid, or fumaric acid under the presence of KOH solution produced a new family of Co(II)/dmpzm complexes, [Co(dmpzm)₂L]X·nH₂O (1: L = O₂CH, X = Cl, n = 2; 2: L = OAc, X = Cl, n = 3; 3: L = benzoate, X = ClO₄, n = 1/3; 4: L = salicylate, X = ClO₄, n = 1/3) and [Co₂(dmpzm)₄L](ClO₄)₂·nSolv (5: L = maleate, n = 3, Solv = H₂O; 6: L = fumarate, n = 2, Solv = MeOH). These compounds were structurally characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. Compounds 1–4 are mononuclear while 5–6 are binuclear. Each cobalt atom of 1–6 is hexacoordinate, with a distorted octahedral CoN₄O₂ coordination geometry incorporating two N,N′-bidentate dmpzm ligands and one O,O′-bidentate carboxylate ligand. There are rich intra- and intermolecular hydrogen bonds in the crystals of 1–6, thereby forming either 2D hydrogen-bonded networks (1 and 2) or 3D hydrogen-bonded networks (3–6). In addition, the thermal behaviors of 1–6 were also investigated.     

Investigation of relaxations in polystyrene–polyoxyethylene copolymer by thermally stimulated current

The diblock copolymer containing 43.5 wt.% of polystyrene (PS) (M_w=15 000) and polyoxyethylene (POE) (M_w=19 500) was investigated by integral and by partial thermally stimulated depolarization current (TSDC) measurements in the temperature range of 173–293 K. The first peak P₁, widely distributed from 183 to 213 K, was a dipolar peak attributed to the initial stage of glass transition in POE. The second peak P₂, with a maximum at 273 K, was due to glass transition. The third peak P₃, with a maximum at about 263 K, was caused by the space charge relaxation localized at the interfaces between the ordered and nonordered phases in POE, Maxwell–Wagner relaxation, representing a precursor in melting of POE crystals. The results were supported by determination of activation energy E_a of the partial peaks, which covered the whole range of investigation, and by differential scanning calorimetry (DSC) measurements. The E_a(T) distribution showed a maximum in entropy change at 219±4 K. Some runs with samples containing different amounts of the PS component were considered. All the relaxations were coming from the POE block. The current due to PS slightly overlapped the total spectra without interaction. The influence of the repeated runs was observed and discussed.     

Synthesis of small crystal polycrystalline mordenite membrane

Mordenite membrane was prepared on -Al₂O₃ tube by in situ hydrothermal synthesis with tetraethylammonium bromide (TEABr) as template agent. By the application of aging process of the parent solution, the size of mordenite crystals could be remarkably reduced from 20–30 (without aging) to 4–5 μm. The small crystal mordenite membrane had higher performance of pure gas permeation than big crystal mordenite membrane. The ideal selectivity of H₂/N₂ was 9.80, much higher than 3.82 of big crystals mordenite membrane. The membrane displayed high water-permselective performance in pervaporation (PV) test toward water/organic liquid mixtures. The highest separation factors achieved toward water/methanol, water/ethanol, water/n-propanol and water/i-propanol were 2600 (X_W=50%, T=323 K), 5500 (X_W=50%, T=343 K), 6000 (X_W=15%, T=343 K) and 6800 (X_W=50%, T=343 K), respectively.     

Validation and application of an analytical method for monomethylmercury quantification in aquatic plant tissues

An analytical methodology for monomethylmercury (MMHg) determination in aquatic plant tissues with low detection limit (346 pg g⁻¹) is proposed. It consists of acid digestion (HBr/CuSO₄), cleanup step with a Na₂S solution, pre-concentration procedure using a dithizone solution in toluene and quantification by GC–ECD. The performance of the methodology has been tested by determining the MMHg concentrations in the certified reference material Fucus Sea Plant Homogenate—IAEA-140/TM (CRM) and in leaves, stems and roots of the salt marsh plants Sarcocornia fruticosa and Halimione portulacoides. The results obtained for CRM were not statistically different ( = 0.056) from the certified value and repeatability was lower than 2.5% for the plant samples analyzed. This coefficient of variation was similar to those obtained in the externally quality control using within-batch and between-batch (<1.4%).