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Abstract  

The initial retentions (at ∼20°C) of (n, γ) activated rare earth bromates were studied using a252Cf fission neutron source with respect to80Br,80mBr and82Br. They lay over the ranges 19–23, 21–23 and 28–32%, respectively. On heating, retention progressively increases and closes on ∼100% for Sm-bromate while for other systems the optimum values reach <85%. Thus, cation effect becomes more pronounced during thermal annealing. The isothermal data show that the weight-loss is due to dehydration. The cation effect on retention is discussed in the light of various parameters like lanthanide contraction, crystal structure, lattice energy, crystal water, properties of anion and mode of thermal decomposition.

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Abstract  

10-Methylacridinium chloride, bromide and iodide were prepared in crystalline forms (the first two salts as monohydrates) and subjected to thermogravimetric investigations. Decomposition of the compounds is initially accompanied by the liberation of water (in case of monohydrates), halomethanes and acridine molecules. As decomposition proceeds, side reactions occur which are reflected in a complex pattern of thermogravimetric curves. TG traces corresponding to the initial decomposition stage were used to determine the kinetic characteristics of the thermal dissociation of the salts. MNDO/d, AM1 and PM3 methods were employed independently to examine reaction pathways and to predict thermodynamic and kinetic barriers for the thermal decomposition of the compounds. These data were subsequently supplemented with theoretically determined crystal lattice energies, which enabled the relevant characteristics for the decomposition of crystalline phases to be predicted. The theoretically predicted characteristics are qualitatively comparable with those originating from thermogravimetric investigations, which allows one to believe that both are valid.

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Abstract  

A brown and transparent ionic liquid (IL), [C4mim][FeCl4], was prepared by mixing anhydrous FeCl3 with 1-butyl-3-methylimidazolium chloride ([C4mim][Cl]), with molar ratio 1/1 under stirring in a glove box filled with dry argon. The molar enthalpies of solution, Δs H m, of [C4mim][FeCl4], in water with various molalities were determined by a solution-reaction isoperibol calorimeter at 298.15 K. Considering the hydrolyzation of anion [FeCl4] in dissolution process of the IL, a new method of determining the standard molar enthalpy of solution, Δs H m 0, was put forward on the bases of Pitzer solution theory of mixed electrolytes. The values of Δs H m 0 and the sum of Pitzer parameters:
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$(4\beta _{Fe,Cl}^{(0)L} + 4\beta _{C_4 mim,Cl}^{(0)L} + \Phi _{Fe,C_4 mim}^L )$$ \end{document}
and
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$(\beta _{Fe,Cl}^{(1)L} + \beta _{C_4 mim,Cl}^{(1)L} )$$ \end{document}
were obtained, respectively. In terms of thermodynamic cycle and the lattice energy of IL calculated by Glasser’s lattice energy theory of ILs, the dissociation enthalpy of anion [FeCl4], ΔH dis≈5650 kJ mol−1, for the reaction: [FeCl4](g)→Fe3+(g)+4Cl(g), was estimated. It is shown that large hydration enthalpies of ions have been compensated by large the dissociation enthalpy of [FeCl4] anion, Δd H m, in dissolution process of the IL.
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Abstract  

Crystal lattice energies of several organochlorine compounds—including pesticides, of known crystal structures were calculated on the basis of a model which takes into account electrostatic, dispersive and repulsive interactions—using three different sets of empirical parameters. These characteristics compare reasonably with experimental heats of volatilization, and it was subsequently shown how statistical and classical thermodynamics can be employed to evaluate dependencies of function of states of gaseous and solid compounds on temperature and how enthalpies and temperatures of sublimation at standard pressure, as well as vapour pressurevs. temperature dependencies can be predicted.

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Abstract  

Single crystals of the N,N-dimethylformamide (DMF) solvate (1:1) of flurbiprofen (FBP) were grown for the first time and characterised by X-ray diffraction, IR spectrophotometry, DSC and solution calorimetric methods. The structure may be characterised as a layer-structure, where DMF double-sheets are arranged between FBP double-sheets. The FBP and DMF molecules are linked to each other by a hydrogen bond, which is formed between the hydroxyl group of FBP and the carbonyl group of DMF. The conformation of FBP molecules in the DMF solvate differs from analogous enantiomers in the unsolvated form. The differences are discussed from the point of view of the influence of the nature of the solvent on selective crystallisation of the enantiomers. A peculiarity of the solvate is its low melting point, 37.30.2C, with respect to the unsolvated phase, 113.50.2C. Based on solution enthalpies of the solvated and unsolvated phases dissolved in DMF, the difference in crystal lattice energies, 9.8 kJ mol-1, was calculated and the difference in entropies, 33 J mol-1 K-1 estimated. A possible mechanism explaining the low melting point of the solvate is discussed.

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Abstract  

The decomposition of the quaternary salts mentioned in the title was examined at the quantum mechanical Hartree-Fock level of theory employing pseudopotentials combined with a SBKJ** basis set. This enabled identification of intermediate and transition state species on the reaction pathway and prediction of the thermodynamic and kinetic barriers to the dissociation of the compounds in the gaseous phase. Application of classical methods permitted the lattice energies of salts, whose crystal structures had been established earlier, to be predicted. Combination of these latter characteristics with the heats of formation of gaseous halide ions (available from the literature) and the relevant cations (obtained at the density functional (B 3LYP)/6-31G**level of theory) provided heats of formation of the salts. On the basis of these values, the thermodynamic and kinetic barriers to the dissociation of the compounds were predicted. The characteristics thus obtained compare quite well with those available in the literature or determined in this work on the basis of TG or DSC measurements. These investigations have shed more light on the mechanism of the thermal dissociation of quaternary salts, and more generally on thermal processes involving solids.

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Abstract  

[Cd(NTO)4Cd(H2O)6]4H2O was prepared by mixing the aqueous solution of 3-nitro-1,2,4-triazol-5-one and cadmium carbonate in excess. The single crystal structure was determined by a four-circle X-ray diffractometer. The crystal is monoclinic, space group C2/c with crystal parameters of a=2.1229(3) nm, b=0.6261(8) nm, c=2.1165(3) nm, β=90.602(7), V=2.977(6) nm3, Z=4, Dc=2.055 gcm−3, μ=15.45 cm−1, F(000)=1824, λ(MoKα)=0.071073 nm. The final R is 0.0282. Based on the results of thermal analysis, the thermal decomposition mechanism of [Cd(NTO)4Cd(H2O)6]4H2O was derived. From measurements of the enthalpy of solution of [Cd(NTO)4Cd(H2O)6]4H2O in water at 298.15 K, the standard enthalpy of formation, lattice energy, lattice enthalpy and standard enthalpy of dehydration have been determined as -(1747.84.8), -2394, -2414 and 313.6 kJ mol−1 respectively.

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Abstract  

The single crystal of lead salt of 3-nitro-1,2,4-triazol-5-one (NTO), [Pb(NTO)2(H2O)] was prepared and its structure was determined by a four-circle X-ray diffractometer. The crystal is monoclinic, its space group is P21/n with crystal parameters of a=0.7262(1) nm, b=1.2129(2) nm, c=1.2268(3) nm, =90.38(2)°, V=1.0806(2) nm3, Z=4, D c=2.97 g cm–3, µ=157.83cm–1, F(000)=888. The final R is 0.027. By using SCF-PM3-MO method we obtained optimized geometry for [Pb(NTO)2 H2O] and particularly positions for hydrogen atoms. Through the analyses of MO levels and bond orders it is found that Pb atom bond to ligands mainly with its 6pz and 6py AOs. The thermal decomposition experiments are elucidated when [Pb(NTO)2 H2O] is heated, ligand water is dissociated first and NO2 group has priority of leaving. Based on the thermal analysis, the thermal decomposition mechanism of [Pb(NTO)2 H2O] has been derived. The lattice enthalpy and its lattice energy were also estimated.

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Ternary chlorides of the trivalent late lanthanides

Phase diagrams, crystal structures and thermodynamic properties

Journal of Thermal Analysis and Calorimetry
Author: H Seifert

Abstract  

A comprehensive review on phase diagrams, crystal structures and thermodynamic properties of ternary chlorides formed in the systems ACl/LnCl3 (A=Na, K, Rb, Cs) is presented. It continues an earlier review with the same contents on the lanthanides from La to Gd [1]. In both papers the author's own studies, published since 1985, together with original papers from other scientists are treated. With the three larger cations compounds of the composition A3LnCl6, A2LnCl5, ALn2Cl7 and beginning with holmium Cs3Ln2Cl9 are formed. With sodium the compounds Na3Ln5Cl18 (Ln=La to Sm) and NaLnCl4 (Ln=Eu to Lu) also exist. The stability of a ternary chloride in a system ACl/LnCl3 is given by the 'free enthalpy of synreaction', the formation of a compound from its neighbour compounds in its system. This must be negative. A surprising result is that the highest – melting compounds in the systems, A3LnCl6, are formed from ACl and A2LnCl5 with a loss of lattice energy, U. They exist as high-temperature compounds due to a sufficiently high gain in entropy at temperatures where the entropy term TΔS compensates the endothermic ΔH.

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Summary  

Although melting is a most familiar physical phenomenon, the nature of the structural changes that occur when crystals melt are not known in detail. The present article considers the structural implications of the changes in physical properties that occur at the melting points, T m, of the alkali halides. This group of solids was selected for comparative examination because the simple crystal lattices are similar and reliable data are available for this physical change. For most of these salts, the theoretical lattice energies for alternative, regular ionic packing in 4:4, 6:6 and 8:8 coordination arrangements are comparable. Density differences between each solid and liquid at T mare small. To explain the pattern of quantitative results, it is suggested that the melt is composed of numerous small domains, within each of which the ions form regular (crystal-type) structures (regliq). The liquid is portrayed as an assemblage of such domains representing more than a single coordination structure and between which dynamic equilibria maintain continual and rapid transfers of ions. T mis identified as the temperature at which more than a single (regular) structure can coexist. The interdomain (imperfect and constantly rearranging) material (irregliq) cannot withstand shear, giving the melt its fluid, flow properties. From the physical evidence, it is demonstrated that the structural changes on melting are small: these can accommodate only minor modifications of the dispositions of all, or most, ions or larger changes for only a small fraction. This proposed representation, the set/liq melt model, may have wider applicability.

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