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Abstract  

Enthalpies of sublimation of acridine, 9-acridinamine, N-methyl-9-acridinamine, 10-methyl-9-acridinimine, N,N-dimethyl-9-acridinamine and N-methyl-10-methyl-9-acridinimine were determined by fitting to thermogravimetric curves with the Clausius-Clapeyron relationship. These values compare well with crystal lattice energies predicted theoretically as the sum of electrostatic, dispersive and repulsive interactions. Partial charges for these calculations were obtained on an ab initio level, while atomic parameters were taken from literature.

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Abstract

Volatile palladium(II) β-iminoketonates of the general formula Pd(R–C(NH)–CH–CO–R1),where R and R1 are CH3, CF3, C(CH3)3 in various combinations, were synthesized and identified. Thermal properties of the resulting palladium(II) complexes in the solid phase were studied by thermogravimetric analysis under an argon atmosphere. The temperature dependence of the saturated vapor pressure was measured for the compounds by the flow method and thermodynamic characteristics of vaporization processes, enthalpy ΔH T and entropy ΔS T o, were determined. The atom-atomic potential calculation of the van der Waals energy (E cryst) of the crystal lattice was performed and the results were compared to the experimental values of the sublimation enthalpy for the complexes under study.

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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  

MNDO/d and PM3 quantum chemistry methods were used to examine reaction pathways and predict thermodynamic and kinetic barriers for the thermal dissociation of isolated conglomerates of N,N,N-trimethylmethanaminium cations (TMA+) and halide anions (X = Cl, Br and I). Theoretically obtained changes in enthalpy and entropy for the above-mentioned process were subsequently supplemented with theoretically determined crystal lattice energies, that enabled prediction of relevant characteristics for the dissociation of crystalline phases. Data thus obtained compare only qualitatively with those available in literature and resulting predominantly from thermoanalytical investigations, although values of theoretical characteristics generally follow the same trends as experimental ones.

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A general approach to the theoretical evaluation of the crystal lattice energy of ionic substances, particularly those composed of monoatomic ions, is outlined in detail. Subsequently, the possibilities of theoretical prediction of the lattice energy of complex organic and inorganic ionic substances are discussed. Lastly, the importance of the lattice energy in examinations of the properties and behaviour of solid-state systems, is treated, together with the prospects of developing a model describing the kinetics of solid-state processes.

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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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Thermal features and thermochemistry of hexachlorohafnates of nitrogen aromatic bases

Theoretical studies on the geometry and thermochemistry of HfCl 6 2−

Journal of Thermal Analysis and Calorimetry
Authors: T. Janiak, J. Rak, and J. Btażejowski

Abstract  

Hexachlorohafnates of pyridine and its three methyl-substituted derivatives were synthesized and examined by the thermoanalytical methods. The van't Hoff equation employed for the thermogravimetric αvs. T dependencies enabled evaluation of the heats of the thermal dissociation and subsequently enthalpies of formation and crystal lattice energies of the salts. Geometry and energy of formation of HfCl 6 2− was determined at the ab initio Hartree-Fock SCF level, using all electron MINI basis set augmented with standard polarization functions (MINI*). Electron correlation was considered at the MP2 level. Thermodynamic characteristics for the latter species were also obtained combining ab initio results with those of statistical thermodynamics. The usefulness of theoretical methods in examination of solid state energetics is briefly discussed.

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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  

The melting points and melting enthalpies of nine phenyl acridine-9-carboxylates—nitro-, methoxy- or halogen-substituted in the phenyl fragment—and their 9-phenoxycarbonyl-10-methylacridinium trifluoromethanesulphonate derivatives were determined by DSC. The volatilisation temperatures and enthalpies of phenyl acridine-9-carboxylates were either measured by DSC or obtained by fitting TG curves to the Clausius–Clapeyron relationship. For the compounds whose crystal structures are known, crystal lattice energies and enthalpies were determined computationally as the sum of electrostatic, dispersive and repulsive interactions. By combining the enthalpies of formation of gaseous phenyl acridine-9-carboxylates or 9-phenoxycarbonyl-10-methylacridinium trifluoromethanesulphonate ions, obtained by the DFT method, and the corresponding enthalpies of sublimation and/or crystal lattice enthalpies, the enthalpies of formation of the compounds in the solid phase were predicted. In the case of the phenyl acridine-9-carboxylates, the computationally predicted crystal lattice enthalpies correspond reasonably well with the experimentally obtained enthalpies of sublimation. The crystal lattices of phenyl acridine-9-carboxylates are stabilised predominantly by dispersive interactions between molecules, whilst the crystal lattices of their quaternary salts are stabilised by electrostatic interactions between ions.

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