Study on the Melting Process of Nitrocellulose by Thermal Analysis Method

The melting process of NC is studied by using modulated differential scanning calorimetry (MDSC) technique, the microscope carrier method for measuring the melting point and the simultaneous device of the solid reaction cell in situ/RSFT-IR. The results show that the endothermic process in the MDSC curve is reversible. It is caused by the phase change from solid to liquid of the mixture of initial NC, decomposition partly into condensed phase products. The values of the melting point, melting enthalpy (H_m), melting entropy (S_m), the enthalpy of decomposition (H_dec) and the heat-temperature quotient (S_dec) obtained by the MDSC curve of NC at a heating rate of 10 K min^–1 are 476.84 K, 205.6 J g^–1, 0.4312 J g^–1 K^–1, –2475.0 J g^–1 and –5.242 Jg^–1K^–1, respectively. The MDSC results of NC with different nitrogen contents show that with increasing the nitrogen content in NC, the absolute values of H_m, S_m, H_dec and S_dec increase.This revised version was published online in November 2005 with corrections to the Cover Date.     

Apparent molal volumes and adiabatic compressibilities of ethylene glycol derivatives in water at 5, 25, and 45°C

Density and ultrasonic velocity measurements were made on a series of dilute equeous solutions of H(OCH ₂ CH ₂ )_nOH, CH ₃ (OCH ₂ CH ₂ )_nOCH ₃ , H(CH ₂ )_nOCH ₂ CH ₂ OH (n=1–4), and poly(ethylene glycol) at 5, 25, and 45°C. The additivity of the limiting partial molal volumes ( ) and adiabatic compressibilities ( ) for CH ₂ and CH ₂ CH ₂ O groups was tested by using the observed and values of the solutes. The and values of the CH ₃ , CH ₂ , CH ₂ CH ₂ O, and CH ₂ OH groups were estimated and discussed in relation to hydration effects. The and values of alkoxyethanols calculated on the basis of the additivity of the group partial molal quantities were in good agreement with the observed values. The behavior of the limiting partial molal isothermal compressibility of alkoxyethanols was similar to that of the adiabatic compressibility.     

The Formation and Stability of the [FePy3Cl3]· Py Clathrate in the Pyridine–Iron(III) Chloride System: Phase Diagram and Solid–Gas Equilibria Study

The phase diagram of the pyridine–iron(III) chloride system has been studied for the 223–423 K temperature and 0–56 mass-% concentration ranges using differential thermal analysis (DTA) and solubility techniques. A solid with the highest pyridine content formed in the system was found to be an already known clathrate compound, [FePy₃Cl₃]·Py. The clathrate melts incongruently at 346.9 ± 0.3 K with the destruction of the host complex: [FePy₃Cl₃]·Py_(solid)=[FePy₂Cl₃]_(solid) + liquor. The thermal dissociation of the clathrate with the release of pyridine into the gaseous phase (TGA) occurs in a similar way: [FePy₃Cl₃]·Py_(solid)=[FePy2Cl₃]_(solid) + 2 Py_(gas). Thermodynamic parameters of the clathrate dissociation have been determined from the dependence of the pyridine vapour pressure over the clathrate samples versus temperature (tensimetric method). The dependence experiences a change at 327 K indicating a polymorphous transformation occurring at this temperature. For the process in the range 292–327 K, ΔH =70.8 ± 0.8 kJ/mol, ΔS =197 ± 3 J/(mol K), ΔG =12.2 ± 0.1 kJ/mol; in the range 327–368 K, ΔH =44.4 ± 1.3 kJ/mol, ΔS =116 ± 4 J/(mol K), ΔG =9.9 ± 0.3 kJ/mol.     

Crystal structure of Ba(VUO<Subscript>6</Subscript>)<Subscript>2</Subscript>

The crystal structure of Ba(VUO₆)₂ was determined by X-ray diffraction at 243 K: monoclinic crystal system, space group P2₁/c, unit cell parameters a=6.4992(6) Å, b=8.3803(8) Å, c=10.4235(9) Å, =104.749(2) °, Z=2. The structure contains close-packed [VUO₆] ₂ ^- layers formed by the dimers of the flattened U₂O₁₂ pentagonal bipyramids and by the dimers of V₂O₈ square pyramids. The neighboring layers are bound by the statistically distributed barium atoms.Original Russian Text Copyright © 2004 by E. V. Alekseev, E. V. Suleimanov, E. V. Chuprunov, and G. K. FukinTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 544–548, May–June 2004.     

Dynamics of H+O2 collisions on anab initio potential energy surface

The dynamics of elementary rate processes for H+O₂ collisions on an ab initio potential energy surface have been simulated by quasiclassical trajectory theory (QCT). For H+O₂ (v=0,j=1), we have obtained the reaction probabilityP _r (E,b) as a function of collision energy E and impact parameterb, the reaction cross sectionS _r as a function ofE, and the average values of the product quantum numbers of OH.For H+0₂ (v=2,j=1, 20, 40, 60, 80, 100;v=1, 3, 4, 5,j=1) atE=0.3 eV, we have found thatb _max is about 4.5a ₀ and the impact parameter at whichP _r is maximum decreases asj increases. The reaction cross section increases asj andv become large. For inelastic collisions, whenb is small andj is large, the and are both small. For reactive collisions, almost equals zero, but the probability of being larger than zero increases with increasingj; and¯v _OH even shows population inversion forj=100. Additional details of the dynamics are shown in figures of interparticle distance and stereographs.     

New Data on the Crystal Structures of Colusites and Arsenosulvanites

The crystal structures of three minerals (arsenosulvanite, V,As-germanite, and colusite) of the general crystal chemical formula (As, Ge, Sn, Sb, V)₆S₃₂, where Cu^M, V^M are cations at interstitial positions, 0.2 x 2.0, 2.7 y 0, (space group , a = 10.527; 10.600; 10.653 ; R = 0.066; 0.046; 0.033) have been determined using single-crystal X-ray diffraction data. The minerals are the two structural modifications of the compound with the ideal formula V₂Cu₂₄As₆S₃₂; they differ from each other in the occupancy of the interstitial position 2a. In colusite, this position is occupied by the V⁵⁺ cations; in arsenosulvanite and V,As-germanite, by Cu²⁺. A characteristic feature of the structures is the presence of octahedral [ S₄]Cu₆ ( = V, Cu) complexes not directly interacting with each other and lying inside the Laves polyhedra. In the structures of arsenosulvanite and V,As-germanite, a sulvanite framework consisting of interpenetrating Laves polyhedra T₃S₄ ( = V, Cu; T = Cu, As, Ge) has been found. The sulvanite framework is statistically distributed over the sphalerite matrix. The variable composition of the minerals is due to heterovalent isomorphism in the sphalerite position 6c. Charge disbalance arising from substitution of the pentavalent arsenic cations by cations of lower valence is compensated by the appearance of additional Cu²⁺ cations. The nonstoichiometry of the compositions is explained by the presence of vacancies in the interstitial and sphalerite positions.     

Crystal Structures and Properties of New Mixed-Ligand Complexes of Nickel(II) Diisobutyldithiophosphinate with Imidazole and 3,5-Dimethylpyrazole

The reaction of Ni{(i-C₄H₉)₂PS₂}₂ with imidazole and 3,5-dimethylpyrazole in ethanol gave paramagnetic (_ef = 3.02 and 3.11 BM) mixed-ligand complex compounds [Ni(Im)₂{(i-C₄H₉)₂PS₂}₂] (I) and [Ni(Pyr){(i-C₄H₉)₂PS₂}₂] (II). Single crystals were grown and the crystal structures of I and II were determined from X-ray diffraction data (CAD-4 diffractometer, Mo radiation, 1483 , R = 0.0344 for I and 2630 , R = 0.0486 for II). The crystals are monoclinic with cell dimensions a = 12.845(2), b = 10.250(1), c = 13.431(1) , = 115.89(1)°, V = 1591(1) ³, Z = 2, d _calc = 1.281 g/cm³, space group (for I); a = 11.152(3), b = 12.483(2), c = 23.389(4) , = 100.78(1)°, V = 3199(2) ³, Z = 4, d _calc = 1.191 g/cm³, space group (for II). The structures consist of discrete monomer molecules. The coordination polyhedron of the Ni atom is a compressed octahedron NiN₂S₄ (in I) and a tetragonal pyramid NiNS₄ (in II) formed by four S atoms of the two cyclic bidentate ligands i-Bu₂ and the N atoms of two monodentate ligands (Im molecules in trans-positions) or the N atom of the monodentate Pyr ligand in complexes I and II, respectively. The character of interaction between molecules I and II and molecular packing modes are considered. The electronic spectra of the complexes are consistent with the symmetry of chromophores found from X-ray data.     

Nitrogen Trichloride Decomposition in the Presence of Molecular Hydrogen: I. Promotion of Nitrogen Trichloride Decomposition by Molecular Hydrogen Additives Near the Lower Self-Ignition Limit

The promotion of the branched-chain decomposition of nitrogen trichloride by molecular hydrogen additives at room temperature and 20 torr manifests itself in a decrease in the induction period and the acceleration of reactant consumption with an increase in the hydrogen concentration in the NCl₃+ H₂+ He mixtures. The emission spectrum of the H₂+ NCl₃flame contains the intense bands of NCl (b ¹⁺– X ^3–, = 1 – 0, = 0 – 1, and = 0 – 0, where is the vibrational quantum number) and the bands of a hydrogen-free compound. The latter bands can be assigned to electronically excited NCl ₂radicals formed in the H + NCl₃reaction. The calculations restrict the number of elementary reactions favoring promotion. The promotion effect in the system studied should be due to the side reaction of linear branching. The occurrence of the H + NCl₃reaction via two pathways (NHCl + 2Cl and NCl ₂+ HCl) ensures the qualitative agreement between the experimental data and calculation.     

Komplexverbindungen von Germaniumsäure mit ÄDTE und ÄDTE-Analogen, 1. Mitt.: Äthylendiamintetraessigsäure

Zusammenfassung Die Verbindung GeY · 2 H₂O wird nach einem Verfahren dargestellt, das die Verwendung von flüchtigem GeCl₄ vermeidet und direkt von Germaniumsäure-Lösungen ausgeht. Der Komplex, der analysenrein anfällt, wird thermogravimetrisch untersucht. In Wasser gelöst, erweist er sich als einbasige Säure, H[Ge(OH)Y]. Die Dissoziationskonstante der komplexen Säure wird potentiometrisch bestimmt:K _c =3,99 · 10^–3 (pK _c =2,40). Die Stabilitätskonstanten der komplexen Säure sowie des komplexen Anions werden ermittelt: =6,27 · 10⁴ (log =4,80); =3,34 · 10⁴ (log =4,52) (25°C; Ionenstärke 0,1m).

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The complex compound GeY · 2 H₂O is prepared directly from germanic acid solutions, avoiding volatile GeCl₄. It has been submitted to thermogravimetric analysis. Dissolved in water, it proves to be a monobasic acid, H[Ge(OH)Y]. The dissoziation constant of the complex acid is determined potentiometrically:K _c =3,99 · 10^–3 (pK _c =2,40). The stability constants of the complex acid as well as of the complex anion are evaluated: =6,27 · 10⁴ (log =4,80); =3,34 · 10⁴ (log =4,52), at 25°C; ionic strength 0,1m.

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Mit 4 Abbildungen

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Herrn Prof. Dr.J. W. Breitenbach zum 60. Geburtstag gewidmet.     

Molecular Packing in the Crystal Structures of the Mixed-Ligand Complexes [CdPhen{(i-C4H9)2PS2}2] and [Cd(2,2′-Bipy){(i-C4H9)2PS2}2]

Single crystals of the mixed-ligand complex compounds of Cd(i-Bu₂PS₂)₂ with Phen and 2,2-Bipy have been obtained. The crystal structures of the complexes [CdPhen{(i-C₄H₉)₂PS₂}₂] (I) and [Cd(2,2-Bipy){(i-C₄H₉)₂PS₂}₂] (II) were determined by X-ray diffraction (CAD-4 diffractometer, MoK radiation, 1739 F _{F hkl} , R = 0.0417 for I and 2612 F _hkl , R = 0.0442 for II). Monoclinic crystals with unit cell parameters a = 15.640(3), b = 20.797(4), c = 11.559(2) , = 111.21(3)°, V = 3505(1) ³, Z = 4, d _calc = 1.348 g/cm³, space group (I); a = 14.737(3), b = 20.918(4), c = 11.517(2) , = 105.53(3)°, V = 3421(1) ³, Z = 4, d _calc = 1.334 g/cm³, space group (II). The structures consist of discrete monomer molecules. The coordination polyhedra of the Cd atoms are distorted octahedra formed by four S atoms of two cyclic bidentate ligands i-Bu₂ and two N atoms of the cyclic bidentate ligands — Phen or 2, -Bipy molecules. The interaction between molecules I and II in the structures and the packing modes are considered.     

Crystal structure of copper(II) bis-hexafluoroacetylacetonate

An X-ray diffraction investigation has performed for copper(II) bis-hexafluoroacetylacetonate (Bruker AXS P4 automatic diffractometer, MoK radiation, t = –25°C). Crystal data for C₁₀H₂CuF₁₂O₄: a = 5.530(1) Å, b = 6.038(1) Å, c = 11.266(2) Å, = 95.948(3)°, = 101.743(3)°, = 92.298(3)°, space group; P1, V = 365.6(1) ų, Z = 1, d _calc = 2.169 g/cm³. The square-planar environment of the copper atom (Cu-O_av 1.912 Å, O-Cu-O_av 93°) is completed to bipyramidal by two fluorine atoms of the neighboring molecules, Cu...F 2.71 Å and 2.75 Å.Original Russian Text Copyright © 2004 by S. A. Gromilov, I. A. Baidina, P. A. Stabnikov, and G. V. RomanenkoTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 502–507, May–June 2004.     

Crystal Structure of the Mixed-Ligand Compound [HgPhen{(C2H5)2NCS2}2] and the Character of Intermolecular Interactions in [MPhen{(C2H5)2NCS2}2] (M = Zn, Cd, Hg)

Single crystals of the mixed-ligand complex compound [HgPhen(Et₂NCS₂)₂] were obtained. The crystal structure of the compound was determined by X-ray diffraction analysis (CAD-4 diffractometer, Mo radiation, 3640 F _hkl , R = 0.0280). Triclinic crystals with cell parameters a = 10.308(2), b = 11.171(3), c = 11.552(2) , = 94.16(2), = 96.66(1), = 105.17(2)°, V = 1267.8(5) ³, Z = 2, d _calc = 1.774 g/cm³, space group . The structure is composed of discrete monomer molecules. The coordination polyhedron of the Hg atom is a distorted octahedron formed by four S atoms of the two cyclic bidentate Et₂ ligands and two N atoms of the cyclic bidentate Phen ligand. The character of interactions between [MPhen(Et₂NCS₂)₂] (M = Zn, Cd, Hg) molecules and their packing in the structure are considered.     

Thermodynamic stability of the γ-Co1−x Se phase by CaF2 electrolyte galvanic cell method

The partial molar free enthalpy of cobalt, , and the molar free enthalpy of formation of Co _x Se alloy phase, G _f ⁰ (Co _x Se) at 873K, were determined by the solid CaF₂ electrolyte galvanic cell method forx=0.725 to 0.956. was observed to be a monotonic function of the mole fractionX _Co in the composition region of the investigation with an inflexion point atX _Co=0.455. The measurements were extended down to a temperature of 710 K and a partial Co–Se phase diagram was evaluated from the resultant data.

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Untersuchung der thermodynamischen Stabilität der -Co-_1–x Se Phase mittels galvanischer Zelle mit CaF₂ Elektrolyt

Zusammenfassung Die partiellen molaren freien Enthalpien von Kobalt ( ) und die molaren freien Bildungsenthalpien der Co _x Se Legierungsphase [G f/0 (Co _x Se) bei 873 K] wurden mittels galvanischer Zelle (CaF₂ Fest-Elektrolyt) fürx=0,725–0,956 bestimmt. wurde im untersuchten Bereich als monotone Funktion vom MolenbruchX _Co, mit einer Inflexion beiX=0,455, gefunden. Die Messungen wurden bis zu einer Temperatur von 710 K ausgedehnt und die Daten wurden zur Erstellung eines partiellen Co–Se-Phasendiagramms ausgewertet.

     

Apparent molal volumes of phosphonium halides at 15, 25 and 35°C

The densities of aqueous solutions of the phosphonium halides, Bu _4-n Ph _n PX(n=0–4), some of which were synthesized from the phosphines, were measured at 15, 25 and 35°C. Partial molal volumes at infinite dilution, , and B _v coefficients for the apparent molal volumes were determined at each temperature. For the first four cations varies little with n. For all salts B _v are negative but become less negative with increasing n. The temperature dependence of B _v is positive for butyl-rich salts (n<2) but negative for phenyl-rich salts (n>1). Also it appears that is relatively large for phenyl-rich cations in comparison with that for butyl-rich cations.     

Dissociation Constants of Protonated Cysteine Species in NaCl Media

The sulfur-containing biomolecule, cysteine has a role in physiological and natural environment because of its strong interactions with metals. To understand these interactions of metals with cysteine, one needs reliable dissociation constants for the protonated cysteine species [ CH(CH₂SH)COOH; H₃B⁺]. The values of dissociated constants, p , for protonated cysteine species (H₃B⁺ H⁺ + H₂B, K ₁; H₂B H⁺ + HB^–,K ₂; HB^– H⁺ + B^2–,K ₃) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.5–6.0 mol-(kgH₂O)^–1 and between 5, and 45°C. The equations

Thermokinetic Studies of the Process for Electrorefining Silver

In this work some calorimetric measurements were also carried out on the electrorefining silver by using different current densities with a Calvet type microcalorimeter at room temperature. The ratio (R) of the measured heat (