Ion–Water Cooperative Interactions in Aqueous Solutions of MgCl2 by Dielectric Spectroscopy

The dielectric constant of aqueous MgCl₂ solution has been determined in the frequency range 0.2 MHz to 20 GHz at 298 K using the dielectric relaxation spectroscopy method. The behavior is well described according to four Cole-Cole terms whose evolution with composition is analyzed. The static dielectric constant and relaxation times decreases with the increasing aqueous MgCl₂ solution concentrations. Only one H-bonded water cluster with the aqueous MgCl₂ solution relaxes is reported during the cutoff relaxation time. A distinct ion–water cooperative interaction is observed, and water molecules perturbed by ion contribution on dielectric constant beyond the first hydration shell are obtained.     

Spin–Spin Relaxation in the 17O NMR Spectra of Na+ and K+ Water Clusters

Relaxation characteristics of Na⁺ and K⁺ water clusters were studied by ¹⁷O NMR spectroscopy. The influence of viscosity and pH of solution was taken into account; for both electrolytes in the concentration range -4 M, spin–spin relaxation times are greater than those for pure water. For K⁺ clusters, maxima of the concentration dependence of ¹⁷O spin–spin relaxation time have been found.     

A Study of the Relative Importance of Lipophilic, π–π and Dipole–Dipole Interactions on Cyanopropyl, Phenyl and Alkyl LC Phases Bonded onto the Same Base Silica

Cyano (CN), butyl (C₄), phenyl and octadecyl (C₁₈) phases prepared from the same base silica gel were chromatographically characterized in order to assess the relative importance of lipophilic, π–π and dipole–dipole interactions in governing retention on these differing phases. Dipole interactions of analytes (possessing dipole moments and low lipophilicity) with CN phases were primarily responsible for the elution order. However, as the analytes’ lipophilicity increased, the lipophilic interaction predominated over the dipole interaction. In comparison, retention on the phenyl phase appeared to be complex, being controlled by a mixture of lipophilic, π–π and dipole–dipole interactions. Retention on the C₄ and C₁₈ phases was dictated by the analyte’s lipophilicity and its accessibility into the phase.     

Directed Dehydration of Na4Sn2S6 ⋅ 5H2O Generates the New Compound Na4Sn2S6: Crystal Structure and Selected Properties

The new thiostannate Na₄Sn₂S₆ was prepared by directed crystal water removal from the hydrate Na₄Sn₂S₆ ⋅ 5H₂O at moderate temperatures. While the structure of the hydrate comprises isolated [Sn₂S₆]⁴⁻ anions, that of the anhydrate contains linear chains composed of corner-sharing SnS₄ tetrahedra, a structural motif not known in thiostannate chemistry. This structural rearrangement requires bond-breakage in the [Sn₂S₆]⁴⁻ anion, movements of the fragments of the opened [Sn₂S₆]⁴⁻ anion and Sn−S−Sn bond formation. Simultaneously, the coordination environment of the Na⁺ cations is significantly altered and the in situ formed NaS₅ polyhedra are joined by corner- and edge-sharing to form a six-membered ring. Time-dependent in situ X-ray powder diffraction evidences very fast rehydration into Na₄Sn₂S₆ ⋅ 5H₂O during storage in air atmosphere, but recovery of the initial crystallinity requires several days. Impedance spectroscopy demonstrates a mediocre room-temperature Na⁺ ion conductivity of 0.31 μS cm⁻¹ and an activation energy for ionic transport of E_a=0.75 eV.     

Effects of Hydrogen Bonding on the Transition Properties of Ethanol–Water Clusters: A TD-DFT Study

In this work, time-dependent density functional theory method was used to study the electronic transitions of hydrogen-bonded ethanol–water complexes Dimer-I, Dimer-II and Trimer. The intermolecular hydrogen bonds H₁···O₁ and O···H₂ were demonstrated by the optimized geometric structures of the three hydrogen-bonded ethanol–water complexes. It is demonstrated that the S₁-state electronic transitions for ethanol monomer and the hydrogen-bonded complex Dimer-I (through HB-I) should be of LE nature on the ethanol molecule, while those of complexes Dimer-II and Trimer should be of CT character from the hydrogen-bonded water molecule (through HB-II) to the ethanol moiety. The different electronic transition types should be the reasons for the tiny redshift of the S₁-state electronic energy for Dimer-I and the large blueshifts for Dimer-II and the Trimer compared with that of the ethanol monomer.     

Detailed Analysis of the Crystal Structures and Magnetic Properties of a Dysprosium(III) Phthalocyaninato Sextuple-Decker Complex: Weak f–f Interactions Suppress Magnetic Relaxation

In the research field of single-molecule magnets (SMMs), lanthanoid–lanthanoid interactions, so-called f–f interactions, are known to affect the SMM properties, although their magnitudes are small. In this article, an SMM with very weak f–f interactions is reported, and the effects of the interactions on the SMM properties are discussed. X-ray structural analysis of the Dy^III-Cd^II-phthalocyaninato sextuple-decker complex (Dy₂Cd₃) reveals that the intramolecular Dy−Dy length in Dy₂Cd₃ is more than 13 Å, which is longer than the intermolecular Dy−Dy length. Even though the two Dy^III ions are far apart, intermolecular ferromagnetic dipole–dipole interactions are observed in Dy₂Cd₃. From detailed analysis of ac magnetic susceptibilities, quantum tunneling of the magnetization (QTM) in Dy₂Cd₃ is partially suppressed owing to the existence of very weak Dy−Dy interactions. Our results show that even very weak Dy−Dy interactions act as a dipolar bias, suppressing QTM.     

Measurements of the Solid–Liquid Equilibria in the Quaternary System NaCl–NaBr–Na2SO4–H2O at 323 K

Phase equilibria of the quaternary NaCl–NaBr–Na₂SO₄–H₂O system at 323 K were studied by the isothermal dissolution equilibrium method. The solubilities of salts and densities of saturated solutions were determined. Solid solutions [Na(Cl, Br)] were found in the experiments. The phase diagram of the quaternary system has no invariant point, but has one univariant curve at the boundary of Na(Cl, Br) and Na₂SO₄ crystallization fields. The experimental results show that an increase of the NaBr concentration is accompanied by an obvious increase of the solution density and the decrease of the solubilities of NaCl and Na₂SO₄.     

Influence of NaI Additions on the Electrical,Dielectric, and Transport Properties in the GeS2–Ga2S3–NaI Glass System

Russian Journal of Electrochemistry - The vitreous system GeS2–Ga2S3 can incorporate a large amount of alkali salts, for example NaI, and such materials have a potential to be used as solid...     

Chalcogen Bonding “2S–2N Squares” versus Competing Interactions: Exploring the Recognition Properties of Sulfur

Chalcogen bonding (CB) is the focus of increased attention for its applications in medicinal chemistry, materials science, and crystal engineering. However, the origin of sulfur's recognition properties remains controversial, and experimental evidence for supporting theories is still emerging. Here, a comprehensive evaluation of sulfur CB interactions is presented by investigating 2,1,3-benzothiadiazole X-ray crystallographic structures gathered from the Cambridge Structure Database (CSD), Protein Data Bank (PDB), and own laboratory findings. Through the systematic analysis of substituent effects on a subset library of over thirty benzothiadiazole derivatives, the competing interactions have been categorized into four main classes, namely 2S–2N CB square, halogen bonding (XB), S ⋅⋅⋅ S, and hydrogen-bonding (HB). A geometric model is employed to characterize the 2S–2N CB square motifs and discuss the role of electrostatic, dipole, and orbital contributions toward the interaction.     

Thermophysical Properties of High-Temperature Reacting Mixtures of Carbon and Water in the Range 400–30,000 K and 0.1–10 atm. Part 1: Equilibrium Composition and Thermodynamic Properties

This paper is devoted to the calculation of the chemical equilibrium composition and thermodynamic properties of reacting mixtures of carbon and water at high temperature. Equilibrium particle concentrations and thermodynamic properties including mass density, molar weight, entropy, enthalpy and specific heat at constant pressure, sonic velocity, and heat capacity ratio are determined by the method of Gibbs free energy minimization, using species data from standard thermodynamic tables. The calculations, which assume local thermodynamic equilibrium, are performed in the temperature range from 400 to 30,000 K for pressures of 0.10, 1.0, 3.0, 5.0 and 10.0 atm. The properties of the reacting mixture are affected by the possible occurrence of solid carbon formation at low temperature, and therefore attention is paid to the influence of the carbon phase transition by comparing the results obtained with and without considering solid carbon formation. The results presented here clarify some basic chemical process and are reliable reference data for use in the simulation of plasmas in reacting carbon and water mixtures together with the need of transport coefficients computation.     

Molecular Organization of Reagents in the Kinetics and Catalysis of Liquid-Phase Reactions: XI. Manifestation of the Structure of Solution in the Kinetics of Water Addition to Isocyanate in Water–Dioxane Mixtures

Evidence for the structural effect of liquids associated by hydrogen bonds on the kinetics of molecular reactions was experimentally found. The kinetics of hydrolysis of (phenylaza)phenyl isocyanate in water–dioxane mixtures was studied at various temperatures and in the presence of structure-making and structure-breaking additives. The apparent order of reaction with respect to water concentration increased with temperature because of the partial breaking of the H-bond solution structure. It was found that the value of was affected by salt additives, for which positive (Et₄NCl) or negative (KI) hydration is typical. This hydration resulted in strengthening or partially breaking the H-bond structure of water, respectively. It follows from the kinetic data that the addition of 0.1 mol/l Et₄NCl was equivalent to a decrease in the solution temperature by 6 to 7°, whereas the addition of 0.1 mol/l KI was equivalent to an increase in the temperature by 5 to 6°. The effect of poly(ethylene oxide) additives (which stabilize the structure of water) on the value of was similar to the effect of the tetraethylammonium salt, which is characterized by positive hydration.     

Functional and Comfort Properties of Textiles from TENCEL® Fibres Resulting from the Fibres' Water-Absorbing Nanostructure: A Review

Summary: The comfort in wear of textiles has been studied extensively on the level of textile construction. The influence of the fibre material is present in the experience of textile consumers, but objective assessment is rather difficult. Some recent works are reviewed here. TENCEL® is a man-made cellulosic fibre of the generic fibre type lyocell. The background of the special comfort in wear of textiles made from TENCEL® fibres is explained as a consequence of the fibres' water-absorbing nanostructure. The basis for these properties are found in the high absorption of water and water vapour, which leads to high heat capacity and heat balancing effect for thermoregulation, comparable with the action of phase change materials. The thermal wear properties resulting are the cool and dry touch, the active cooling effect in sports wear, and the warming properties when used as an insulation layer. These effects are to a certain extent adaptive to the environment, providing comfort in a wide range of climatic conditions. Moreover, neutral electric properties, retarded bacterial growth and good skin sensory perception add to the overall skin friendly properties, which were also shown in wear studies with patients suffering from skin diseases.     

Experimental and the Theoretical Studies of the Dielectric Properties of DMSO–H<Subscript>2</Subscript>O Mixtures

This paper focuses on the measurement of the permittivity of dimethyl sulfoxide (DMSO)–water (H₂O) mixture solutions, at 2.45 GHz by using a resonant cavity perturbation method. A specific phenomenon was found, in that the imaginary part of the permittivity for the mixture solution was larger than the imaginary part for each component. Theoretical calculation indicated that the reason for that phenomenon was that the high frequency friction of the mixture was larger than that of each component. When comparing the theoretical results with the experimental data, it was found that the classical Debye equation must be modified in order to calculate the complex permittivity.     

Determination of Vitamin A in Infant Milk-Based Formulas and Pharmaceutical Formulations Using Flow Injection with Ce(IV)–Na2SO3 Chemiluminescence Detection

A rapid and simple flow injection (FI) method is reported for the determination of vitamin A (retinol) based on its strong enhancing effect on the Ce(IV)–Na₂SO₃ chemiluminescence (CL) reaction in an acidic solution. The effect of key chemical and physical parameters (i.e., reagent concentrations, flow rate, and sample volume) was optimized and potential interferences examined. Under the selected experimental conditions, a linear calibration was obtained between the CL intensity and vitamin A concentration in the range 0.1–8.0 µg mL^?1 (r ²  = 0.9986, n = 8). The limit of detection (3 s x blank) was 0.01 µg mL^?1 retinol (n = 6) and the relative standard deviation (RSD) for 0.25 µg mL^?1 retinol was 2.3% (n = 10) with a sampling rate of 180 h^?1. The method was successfully applied to infant milk-based formulas and pharmaceutical formulations and the results were not significantly different at 95% confidence interval with those obtained by using a spectrophotometric reference method. The possible CL mechanism is also discussed briefly supporting with UV-visible, fluorescence, and CL spectra.     

Single and Double Threading of Congo Red into γ-Cyclodextrin. Solution Structures and Thermodynamic Parameters of 1:1 and 2:2 Adducts,as Obtained from NMR Spectroscopy and Microcalorimetry

Detailed NMR studies of aqueous solutions (pH 7) of γ-cyclodextrin (γCD) and the azo dye Congo Red (CR) show distinct, concentration-independent ¹H NMR signals for different species. A very stable 1:1 pseudorotaxane (K ¹¹=38,000±1100?M^-1) is formed. In addition, a second complex corresponding to a 2:2 adduct (K ²²=13±3?M^?-1) is produced by dimerisation of the 1:1 species. The structure of the 1:1 pseudorotaxane involves fast motion of the γCD ring along the CR backbone, leaving the outer naphthalene rings free. This entity undergoes structural reorganisation and dimerises to form the 2:2 adducts. Variable-temperature spectra did not lead to coalescence and allowed for the calculation of K ¹¹ and K ²² at each temperature and also of the corresponding thermodynamic parameters. Therefore, formation of the 1:1 complex is favourable (ΔG=-26.1±0.1?kJ/mol) and exothermic (ΔH=-21.7±1.0?kJ/mol), whereas formation of the 2:2 entity is also favourable (ΔG=-6.36±0.58?kJ/mol) but endothermic (ΔH=+43.3±8.7?kJ/mol). The corresponding values for entropy change are both positive (ΔS ¹¹=+14.5±0.7?J/mol, ΔS ²²=+166±33?J/mol). Isothermal titration calorimetry studies confirm the NMR findings. For the 1:1 complexation, the dependence of K upon the concentration is indicative of the dimerisation to form the 2:2 complex. When CR is in excess, aggregation processes involving 2:2 complexes and CR molecules are observed by NMR and calorimetry.     

Complex Formation of Crown Ethers with Cations in the Water–Organic Solvent Mixtures. Part VII. Thermodynamic of Interactions of Na+ Ion with 15-Crown-5 Ether in the Mixture of Water with N,N-Dimethylacetamide at 298.15 K

The thermodynamic functions of the complex formation of 15-crown-5 ether with sodium cation in mixtures of water with N,N-dimethylacetamide at 298.15K are calculated. The equilibrium constants of complex formation of 15-crown-5 ether with sodium cation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by a calorimetric method at 298.15K. The complexes are enthalpy-stabilized but entropy-destabilized in this mixed solvent. A quantitative dependence of the excess molar enthalpy and entropy of complex formation on the structural and energetic properties of interactions between water and organic solvent molecules in the mixtures of water with N,N-dimethylacetamide, N,N-dimethylformamide and dimethylsulfoxide has been found. The linear entropy–enthalpy relationship for complex formation is also presented. The solvation enthalpy of the complex in the water–N,N-dimethylacetamide mixtures is discussed.     

Theoretical studies of the g factors and local structures of the Ni3+ centers in Na2Zn(SO4)2·4H2O and K2Zn(SO4)2·6H2O crystals

The local structures and the g factors g_i (i = x, y, z) for Ni³⁺ centers in Na₂Zn(SO₄)₂·4H₂O (DPPH) and K₂Zn(SO₄)₂·6H₂O (PHZS) crystals are theoretically studied by using the perturbation formulas of the g factors for a 3d⁷ ion with low spin (S = 1/2) in orthorhombically compressed octahedra. In these formulas, the contributions to g factors from both the spin-orbit coupling interactions of the central ion and ligands are taken into account, and the required crystal-field parameters are estimated from the superposition model and the local geometry of the systems. Based on the calculations, the Ni-O bonds are found to suffer the axial compression δz (or Δz) of about 0.111 Å (or 0.036 Å) along the z-axis for Ni³⁺ centers in DPPH (or PHZS) crystals. Meanwhile, the Ni-O bonds may experience additional planar bond length variation δx (≈0.015 Å) along x- and y-axes for the orthorhombic Ni³⁺ center in DPPH. The theoretical g factors agree well with the experimental data. The obtained local structural parameters for both Ni³⁺ centers are discussed.     

Solid–liquid Equilibria in the Quaternary System Na+, Mg2+//Cl–, SO2–4–H2O at 25 and 30°C

The isoplethic sections in the diagram of the quaternary system Na⁺ , Mg²⁺ //Cl^– , SO^2– ₄ –H₂ O were established at 25 and 30oC by analytical and conductometric measurements. Three compounds can be observed in the isoplethic sections: NaCl, Na₂ SO₄ and MgNa₂ (SO₄ )₂ 4 H₂ O. Seven fields are determined, relating to the precipitation of one, two or three salts. The solubility range of MgNa₂ (SO₄ )₂ 4 H₂ O is wide, while the liquidus curve of Na₂ SO₄ is very short. The compositions, expressed in Jänecke coordinates, at the eutonic and peritonic points, respectively, were: 42.70% Cl^– and 745% H₂ O; 79.47% Cl^– and 787% H₂ O; 71.6% Cl^– and 744% H₂ O at 25°C; and 48.80% Cl^– and 715% H₂ O; 80.20% Cl^– and 778% H₂ O; 70.14% Cl^– and 707% H₂ O at 30°C.     

Solid–Liquid Stable Equilibrium of the Quaternary System LiCl + NaCl + Li2SO4 + Na2SO4 + H2O at 288.15 K

Journal of Solution Chemistry - In this study, the isothermal saturation method was applied to obtain the data for solid–liquid equilibria in a system consisting of four solids...