A. M. Kolker

Structure of methanol-methanol associates in dilute methanol-water mixtures from molecular dynamics simulation

Abstract Molecular dynamics simulations have been performed for 8 methanol-water solutions using rigid and flexible potential models. The heat capacity, the radial distribution functions and potential mean force obtained by MD simulations were compared to previous simulations and experimental results. Special attention has been paid to the anomalous behaviour of the heat capacity of dilute aqueous solutions of methanol. This behaviour can be attributed to a cooperative effect resulting from methanol-methanol associations.

Volumes and heat capacities of binary non-aqueous mixtures. Part 2. The systems acetonitrile-N,N-dimethylformamide and acetonitrile-hexamethylphosphoric triamide

Abstract The densities and heat capacities of binary mixtures of acetonitrile with N,N -dimethylformamide and hexamethylphosphoric triamide were measured between 283.15 and 328.15 K. The excess and apparent molar volumes and heat capacities of the systems studied were calculated. The influence of the nature and composition of the substance and of the temperature on the thermodynamic characteristics of acetonitrile mixtures with N,N -dimethylformamide and hexamethylphosphoric triamide is analysed. The thermodynamic characteristic values obtained are compared with those for the solutions of the same amides in water.

Effect of pressure and temperature on volume properties of water-N, N, dimethylformamide mixtures

Abstract Specific volumes (ν), isothermal compressibility coefficients ( β T ) and thermal expansion coefficients (α) of the water-N,N-dimethylformamide (DMF) system have been calculated at temperatures T = 278.15 … 323.15 K and pressures up to P = 100 MPa using the data on densities (ϱ) and compressibility coefficients k = ( ν o − ν )/ ν o measured at the atmospheric pressure. It was found, that the composition dependencies ν ( x ), where x is the mole fraction of DMF, have maxima and minima, and their shape depends on the pressure. The composition dependencies of the isothermal compressibility coefficients β pass through minima at x ≈ 0.15 … 0.20 at all pressures, and the α ( x ) dependencies have inversion points at various pressures and constant temperatures. it is shown, that the thermodynamic properties of dilute aqueous solutions of DMF are defined by the features of water structure. An increase of pressure, temperature and concentration of a non-electrolyte in the H 2 O-DMF system reduces the regularity of the H-bond network of water.

Volumes and heat capacities of binary non-aqueous mixtures. Part 1. The systems acetonitrile—formamide and acetonitrile—N-methylformamide

Abstract The density and heat capacity of the binary mixtures acetonitrile—formamide and acetonitrile— N -methylformamide were measured over the entire range of compositions at 283.15–328.15 K. The excess and apparent molar volumes and heat capacities of the mixtures studied were calculated. An analysis of the experimental and calculated data was carried out. Relationships between the nature of the substances, and the temperature and composition on the thermodynamic properties of acetonitrile mixtures with formamide and N -methylformamide are revealed.

Iron(III) complexes on the basis of azomethine derived from 4,4′-dodecyloxybenzoyloxybenzoyl-4-oxy-2-hydroxybenzaldehyde

This work deals with the synthesis and investigation of phase behavior of iron(III)-containing complexes of linear azomethine derived from 4,4′-dodecyloxybenzoyloxybenzoyl-4-oxy-2-hydroxybenzaldehyde with NO3−, PF6−, Cl−, and BF4− counterions. All semiproducts and target substances are characterized by TLC, elemental analysis, IR and NMR spectroscopy, and melting points. It is established that the reaction of Schiff base with metal salts at room temperature leads to the formation of complexes having presumably the linear structure. Phase behavior of the compounds obtained depending on the nature of counterion was studied.

Molecular dynamic study of the anomalous behavior of heat capacity in a methanol-water mixture

The molecular dynamic (MD) method is used to study the anomalous behavior of heat capacity in the range of small concentrations of methanol-water solutions. The behavior of the concentration dependence of heat capacity as calculated by the MD method qualitatively coincides with the experimental values. The calculation of contributions from different types of interaction to heat capacity showed that the greatest contribution is made by the interaction between the methanol molecules. The reason for the anomalous behavior of heat capacity is discussed based on the calculation of the mean force potential, radial distribution functions, and hydrogen bond network parameters.

Structure of Iron(III)-containing complexes based on the azomethine — 4,4′-dodecyloxy-benzoyloxybenzoyl-4-salicylidene-N′-Ethyl-N-ethylenediamine molecule

Iron(III)-containing complexes with an asymmetric tridentate azomethine 4,4′-dodecyloxybenzoyloxybenzoyl-4-salicylidene-N′-ethyl-N-ethylenediamine ligand with NO3−, PF6−, Cl−, and BF4− counterions are synthesized. The presence of the complexation ion is confirmed by the far FTIR spectra. The structure of the compounds is determined by the matrix-assisted laser desorption/ionizationtime of flight (MALDI-ToF) method. The results of mass-spectrometric studies are consistent with the elemental analysis data. The complexation of iron salts with the asymmetric tridentate ligand is found to yield compounds of the 1:1 composition with octahedral packing of iron in the complex.

Analysis of the thermodynamic characteristics of the solvation of ions in protic solvents at various temperatures using model concepts

Abstract Our laboratory of the Institute of Non-aqueous Solution Chemistry of the U.S.S.R. Academy of Sciences performs systematic investigations on the influence of low temperatures on the thermodynamic properties of non-aqueous solutions of electrolytes. The majority of non-aqueous solvents are known to have low melting points. However, for various reasons investigators do not pay much attention to this very important region of low temperatures though it is of great practical and scientific interest. The present paper will deal with the influence of low temperatures on the thermodynamic characteristics of the solvation of ions in protic solvents, particularly in monoatomic alcohols.

Thermodynamic characteristics of solvation of individual ions in ethanol at −50 to 55°C

Experimentally determined are the enthalpies of solution of 12 electrolytes (LiBr, LiI, NaBr, NaI, NaBPh4, Et4NCl, Et4NBr, Pr4Br, Bu4NBr, Am4NBr, Ph4PCl, Ph4PBr) in ethanol at −50 to 55°C. ΔsHo values obtained on the basis of four different extrapolation equations are analyzed. The effect of temperature changes on the thermodynamic parameters of solvation indindividual ions are calculated using thermodynamic data for the salt crystals (lattice) with the assumption that ΔsolvCpo(Ph4P+)=ΔsolvCpo(Ph4P-).

Conversion of low spin states in a monochelate complex of Fe(III) with an asymmetric tridentate azomethine ligand

An iron(III)-containing complex with the asymmetric tridentate azomethine ligand 4,4′-dodecyloxybenzoyloxybenzoyl-4-salicylidene-N′-ethyl-N-ethylenediamine with a PF6− counterion is obtained. The presence of the complexing ion is confirmed by far IR Fourier spectra. The structure of the compounds is determined by matrix-assisted laser desorption/ionization with a time-of-flight mass analyzer (MALDI-ToF). The results of mass spectrometric studies are consistent with the elemental analysis data. It is found that the complexation of iron salt with an asymmetric tridentate ligand results in the formation of compounds of the composition 1:1 with octahedral packing of a metal ion in the complex. The electrochemical behavior of the compound in organic solvents is examined. The EPR study shows that iron(III) ions are in both low spin (LS) and high spin (HS) states in the complex. The LS and HS iron(III) centers are coupled into dimers in which a water molecule and the PF6− counterion act as bridges. It is also found that for LS complexes in the lowtemperature phase (4.2–300 K), the (dxz,dyz)4(dxy)1 electronic state is the ground state. It is revealed that the conversion of the sample into a high-temperature liquid crystalline (387–405 K) phase is accompanied by the conversion of the LS states of the Fe(III) ion: (dxz,dyz)4(dxy)1 ↔ (dxy)2(dxz,dyz)3. The conversion of LS states is temperature reversible and is driven by the temperature. X-ray crystallographic data confirm that the compound obtained consists of dimer formed by a hydrogen (O-H...F) bond.