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Journal of Thermal Analysis and Calorimetry
Authors: G. Pokol, F. Tóth, I. Péter, J. Madarász, T. Kocsis, and S. Gál
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Journal of Thermal Analysis and Calorimetry
Authors: Ana Brăileanu, M. Răileanu, M. Crişan, D. Crişan, R. Bîrjega, V. Marinescu, J. Madarász, and G. Pokol

Abstract  

Two series of nanocomposites from the FexOy–SiO2 system, containing 20 mass% iron oxide were prepared by the alkoxide route of the sol–gel method, in the absence and presence of catalyst. The silica gel has been obtained using tetraethoxysilane. The iron(III) nitrate nonahydrate has been used as iron oxides source. The samples have been prepared in identical conditions, differing only by the gelation times, induced by different surface of evaporation/volume (S/V) ratios of sol let to gelify. Thermal analysis data have established the thermal treatments conditions of the prepared samples and were correlated with X-ray diffraction, IR spectroscopy and TEM results, in order to accomplish a complete structural characterization. The correlation between the structural modifications of the FexOy–SiO2 nanocomposites and different conditions of drying has been established.

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In the present study the solid and liquid phase behaviour of mandelic acid cyclodextrin systems were studied. The samples were prepared using dry grinding/kneading technique in the absence of any solvent. Thermoanalytical methods (TG, DSC, EGD) were used to characterise the solid compounds. In liquid phase the stoichiometry and the stability constants of the complexes formed were determined using UV spectrophotometry. Partial complex formation was found in case of all cyclodextrins used. The amount of uncomplexed mandelic acid varied between 10–20% of the total guest content.

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Transitionmetal complexes with pyrazole-based ligands

Part 21. Thermal decomposition of copper and cobalt halide complexes with 3,5-dimethyl-1-thiocarboxamidepyrazole

Journal of Thermal Analysis and Calorimetry
Authors: K. Mészáros Szécsényi, V. Leovac, A. Kovács, G. Pokol, and Ž. Jaćimović

Abstract  

The thermal decomposition of Cu2L2Cl4, Cu2L2Cl2, Cu2L2Br2 and Co2L2Cl4 complexes (L=3,5-dimethyl-1-thiocarboxamidepyrazole) is described. The influence of the central ion to ligand mole ratio on the course of complex formation is examined in reaction of L with copper(II) chloride. In Cu(II):L mole ratio of 1:1, in methanolic solution the reaction yields to yellow-green Cu2L2Cl4 crystals. In the filtrate a thermodynamically more stable orange Cu2L2Cl2 copper(I) complex is forming. With a Cu(II):L mole ratio of 1:2 only the latter compound is obtained. The composition and the structure of the compounds have been determined on the basis of customary methods. On the basis of FTIR spectrum of the intermediate which is forming during the thermal decomposition of Cu2L2Cl2 a decomposition mechanism is proposed.

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Abstract  

The coupling of a quadrupole mass spectrometer (QMS) via a heated capillary to a commercial thermogravimetric analyser is described. The amu and temperature ranges available were up to 1000 amu and 1500°C, respectively. The system was evaluated with test compounds, yielding gaseous species in the m/z range of 17-80, and then used for the study of thermal behaviour of scandium dipivaloyl methanate or Sc(thd)3 which is discussed in detail. Sc(thd)2 appears as the major Sc-containing species with m/z=411 in the gas phase at 200-300°C.

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Abstract  

Complexes represented by the general formula [MCl2L2] (M(II)=Zn, Mn, Co) and complexes of [Cu3Cl6L4] and CuSO4L24H2O, CoSO4L23H2O, [ZnSO4L3] where L stands for 3-amino-5-methylpyrazole were prepared. The complexes were characterized by elemental analysis, FT-IR spectroscopy, thermal (TG, DTG, DSC and EGA) methods and molar conductivity measurements. Except for the Zn-complexes, the magnetic susceptibilities were also determined. Thermal decomposition of the sulphato complexes of copper(II) and cobalt(II) and the chloro complexes of cobalt(II) and manganese(II) resulted in well-defined intermediates. On the basis of the IR spectra and elemental analysis data of the intermediates a decomposition scheme is proposed.

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Abstract  

The synthesis of copper(II) chloride complexes with 3,5-dimethylpyrazole, 1-carboxamidine-3,5-dimethylpyrazole, 5-amino-4-carboxamide-1-phenylpyrazole and 4-acetyl-3-amino-5-methylpyrazole is described. The compounds are characterized by elemental analysis, FT-IR spectroscopy, thermal methods, magnetic moment and molar conductivity measurements. Thermal decomposition of the dichloro-(3,5-dimethylpyrazole)-copper(II) complex results in an unstable intermediate with a stochiometric composition. The decomposition of the other compounds is continuous.

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Journal of Thermal Analysis and Calorimetry
Authors: I. Szilágyi, Judit Pfeifer, C. Balázsi, A. Tóth, Katalin Varga-Josepovits, J. Madarász, and G. Pokol

Abstract  

We studied the thermal stability of different hexagonal tungsten trioxide, h-WO3 samples, which were prepared either by annealing hexagonal ammonium tungsten bronze, (NH4)0.33−xWO3−y, or by soft chemical synthesis from Na2WO4. The structure and composition of the samples were studied by powder XRD, SEM-EDX, XPS and 1H-MAS NMR. The thermal properties were investigated by simultaneous TG/DTA, on-line evolved gas analysis (TG/DAT-MS), SEM and in situ powder XRD. The preparative routes influenced the thermal properties of h-WO3 samples, i.e. the course of water release, the exothermic collapse of the hexagonal framework and the phase transformations were all affected.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Zaharescu, A. Jitianu, A. Brãileanu, V. Bãdescu, G. Pokol, J. Madarász, and Cs. Novák

Abstract  

The hydrolysis-polycondensation of organically modified Si-alkoxides leads to the obtaining of inorganic-organic hybrid materials in which the organic moieties remain as permanent groups bonded to the inorganic network. The molecular species previously determinated by GC-MS during the gelation process have been significantly different according to the type of the alkoxide used. In the present work, thermal stability of SiO2-based inorganic-organic hybrid materials starting with TEOS (tetraethoxysilan), MTEOS (triethoxymethylsilan), VTEOS (triethoxyvinylsilan) and MTMOS (trimethoxymethylsilan) was studied. The molecular structure of the gels obtained determines differences in their thermal behaviour. Gels obtained starting with MTEOS show the highest thermal stability, while gels obtained using VTEOS the lowest, among the substituted alkoxides. A particular behaviour presents the gel obtained with MTMOS that decomposes in four steps. This could be explained by the presence in the gel of some prevalent types of molecular species with different thermal stability.

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Abstract  

Thermal stability and structural features of three newly synthesized 1:1 lattice compounds of theophylline (th) with ethylenediamine carbamate (enCO 2), 1,10-phenanthroline (phen), and 5-sulfosalicylic acid (sa-5-SO 3 H) have been studied in comparison with those of the theophylline compounds with ethanolamine (ea) and salicylic acid (sa). Simultaneous TG-DTA measurements, FTIR spectroscopy and X-ray diffraction have been carried out to get information on the various structural units of these solid inclusions, especially on the actual form (molecule, anion or cation) of theophylline moieties built in. Theophyllinate and theophyllinium ions have been found in the ethanolammonium-theophyllinate (1:1) (1, eaH + th -) and the theophyllinium salicylic acid 5-sulfonate monohydrate (1:1:1), (5, thH + saSO 3 H 2 O), respectively. Whilst the 1:1 complexes with 1,10-phenanthroline (2, thphen), ethylenediamine carbamate (3, thenCO 2), and salicylic acid (4, thsa) contain neutral theophylline moieties associated with H-bonds. In compound (3) the zwitterion of N-(2-ammonium-ethyl)carbamate (NH3 +-CH2-CH2-NH-CO- 2) is present.

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