New Layered Polymer [{Mn(H2O)3}2{Re6Se8(CN)6}] · 3.3H2O: Synthesis and Properties

The [{Mn(H₂O)₃}₂{Re₆Se₈(CN)₆}] · 3.3H₂O complex was produced on slow evaporation of an aqueous solution containing the salt of a cluster complex K₄Re₆Se₈(CN)₆ · 3.5H₂O and a 23-fold excess of Mn²⁺. The cluster complexes [Re₆Se₈(CN)₆]^4– are linked in a crystal into the charged coordination layers [{Mn(H₂O)₃}₄{Re₆Se₈(CN)₆}₃]^4– ₂ through the Mn²⁺ cations. The Mn²⁺ cations are coordinated in a layer by three cyano nitrogen atoms of the cluster complexes; the Mn–N bond lengths are 2.13(4) and 2.21(2) Å. Each [Re₆Se₈(CN)₆]^4– anion is bonded to three manganese cations Mn(1). The anions are bonded additionally to the Mn(2) cations disordered over two close positions.     

Dielectric properties and high-frequency conductivity of the sodium chloride-water system

An analysis has been performed of the dielectric characteristics and high-frequency (hf) electrical conductivity (EC) of aqueous solutions of NaCl. A method of the estimation of the static dielectric constant and of the time of dipole relaxation of concentrated aqueous solutions of NaCl in a wide range of concentrations and temperatures has been suggested. It has been shown that the limiting hf EC of the solutions and the hf EC at the frequency of 2455 MHz decrease with increasing salt concentration and differently change with increasing temperature: the limiting hf EC increases, whereas the hf EC at the frequency of 2455 MHz decreases. The decrease in the hf EC leads to a reduction of the rate of the hf heating of the NaCl solution with increasing salt concentration.     

Synthesis and crystal structure of Mo6−x Nb x I11 (x = 1–1.5)

A solid solution Mo_{6 ? x} Nb _x I₁₁ (x = 1.1–1.5) containing cluster cores {Mo₅NbI₈} is obtained by the high-temperature reaction of molybdenum, niobium, and iodine (550°C, 70 h, quartz ampule). According to the X-ray diffraction data, heating at 800°C in a molybdenum container results in the decomposition of the solution to Mo₆I₁₂ and Nb₆I₁₁. According to the X-ray structure analysis data, the compounds are isostructural to the high-spin modification Nb₆I₁₁ (space group Pccn). The presence of Nb atoms in the structure changes the structural type from the layered (Mo₆I₁₂) to framework structure, noticeably increases the metalmetal distances (2.661–2.716 Å, 2.695 Å) Mo₆ octahedron with the retention of the distance from the metal (M) to the μ₃-“capped” I atoms, and strongly elongates the M₆-I-M₆ bridges almost to the value observed in Nb₆I₁₁.     

Limiting equivalent electrical conductivity of inorganic salt solutions and dielectric properties of a polar solvent

A relation has been found to exist between the limiting equivalent electrical conductivity of inorganic salt solutions, viscosity, temperature, and dielectric properties of the solvent. As temperature rises, the limiting equivalent electrical conductivity of aqueous solution of an inorganic salt has been shown to increase in direct proportion to the ratio of the dielectric permittivity to the dipole dielectric relaxation time, i.e., the limiting high-frequency electrical conductivity of the polar solvent. Expressions have been derived to be used in ascertaining the limiting equivalent electrical conductivities of inorganic salt solutions proceeding from the dielectric properties of the solvent.     

Dielectric properties of solvents and their limiting high-frequency conductivity

The behavior of the limiting high-frequency (HF) conductivity of water, methanol, ethanol, and propanol in a wide temperature range is considered. As the temperature is increased to its critical value, the static permittivity and the dipole relaxation time of the polar solvents decrease monotonically; however, the limiting HF conductivity, which is determined by their ratio, passes through a maximum. The maximum is explained by differences in the behavior of the temperature dependences of the relative temperature coefficients (RTCs) of static permittivity and the dipole relaxation time. It is shown that the maximum on the temperature dependence of the limiting HF conductivity corresponds to the equality of the RTCs of static permittivity and the dipole relaxation time. It is noted that in the temperature range corresponding to the maximum limiting HF conductivities of water and alcohols, the temperature dependences of the ion product of water and the conductivity of the considered polar solvents and solutions of inorganic salts in them also pass through maxima.     

Electrical conductivity of associated electrolyte-water systems

The specific electrical conductivity (EC) of concentrated aqueous solutions of tartaric and oxalic acids was measured in the range 15–90°C. Specific electrical conductivity versus concentration and temperature relationships were analyzed for the acids studied in this work and for formic, acetic, propanoic, butanoic, chloroacetic, dichloroacetic, and trichloroacetic acids, as well as for aqueous ammonia. As the electrolyte concentration increases, the EC passes through a maximum whose position is independent of temperature. The maximal EC value of an aqueous solution of an associated electrolyte for a given temperature and the concentration corresponding to this maximal EC were used as generalizing parameters. Over the entire ranges of the temperatures and concentrations studied, normalized EC values (normalized EC is the ratio of the current EC to its maximal value for a given temperature) for all electrolytes considered fall on one curve provided that the argument is a normalized concentration (which is the ratio of the current solution concentration to its value at which specific EC has a maximal value).     

Colloidal dispersions of molybdenum disulfide with a narrow particle size distribution

Colloidal dispersions of MoS₂ in DMF were obtained, and a procedure for the preparation of the fraction of particles with the size distribution 1.5 times narrower than that in the original dispersion was developed. It was shown that for the gradual centrifugation of dispersions with an increase in the acceleration from 126g to 2016g the average thickness of nanosheets decreased from 35 to 8 nm and the average lateral sizes decreased from 250 nm to a constant value of 160 nm. A linear dependence of the absorbance of the dispersions on the concentration of MoS₂ was established.