F. De Jesus

Kinetic studies by DSC on the thermal decomposition of calcium oxalate

Abstract In the present paper, we have studied the kinetics of the thermal decomposition of calcium oxalate monohydrate, using a new method of kinetic study employing data obtained from differential scanning calorimetry, as previously proposed by us. Initial products and those obtained following decomposition have been identified by infrared spectroscopy and X-ray powder diffraction. A comparison between the results obtained in this paper and those reported in the literature has also been made.

Application of a new method to the kinetic study of the thermal decarbonylation of sodium oxalate

Abstract The application of a new method for studying the kinetic parameters of the thermal decarbonylation of sodium oxalate in dinitrogen using differential scanning calorimetry is described. The activation energy and the pre-exponential Arrhenius factor for the loss of carbon monoxide are calculated from the DSC curves and the reaction order and mechanism are also determined. A comparison is made between the results obtained using the proposed method and those reported in the literature.

Comparative study of tungsten(V) complexes with 8-quinolinol and 2-methyl-8-quinolinol

Abstract The present paper reports a comparative study of a number of oxo- and sulphido bridge tungsten(V) oxo-complexes with 8-quinolinol and 2-methyl-8-quinolinol as ligands. The results obtained permit us to assign the following formulae to the complexes: W 2 O 3 (LL) 4 , W 2 O 4 (LL) 2 , W 2 O 2 S 2 (LL) 2 and W 2 O 3 S(LL) 2 . All these complexes present very low values of the magnetic moment, according to a dimer structure with monoxo, dioxo, disulphido and oxo-sulphido bridges. We suggest that the low magnetic moments observed are due, at least in part, to intramolecular metal—metal interactions.

Thermal and kinetic studies on the adducts with pyridines of bis(acetylacetonate)oxovanadium(IV)

Abstract The kinetics of the thermal decomposition, under nitrogen, of several adducts with pyridine or substituted pyridines of bis(acetylacetonate)oxovanadium(IV), {[VO(acac) 2 ,B] where acac = acetylacetonate and B = pyridine (Py), 3-methyl-pyridine (3-MP), 4-methylpyridine (4-MP), 3,5-dimethylpyridine (3,5-DMP), 3-aminopyridine (3-AP) and 4-aminopyridine (4-AP)}, have been studied by differential scanning calorimetry (DSC). Activation energies and pre-exponential Arrhenius factors, for the endothermic process of the loss of one mole of coordinated base, have been calculated using a new method, and the mechanism of this reaction has been determined. A relationship between activation energies and the properties of the ligands has also been determined.

Tungsten(V) dimeric complexes with ethyl xanthate

The chemical, spectroscopic and magnetic properties of a number of oxo- and sulphido-bridged tungsten(V) oxo-complexes with ethyl xanthate as a ligand are described. The following formulae are assigned to the complexes: W2O3(LL)4, W2O4(LL)2, W2O2S2(LL)2, W2O3S(LL)2. IR and electronic spectra of these compounds are modified by the introduction of sulphur atoms into the bridge system. The low magnetic moments observed are due either to an interaction through the bridging atoms or to a direct spin-spin interaction, according to a dimer structure with monoxo, dioxo, disulphido and oxo-sulphido bridges. The thermal behaviour has also been studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results are discussed on the basis of the structural information available to tungsten complexes.

Study of Dimeric Molybdenum(V) Complexes of Piperidine Carbamate

Abstract We report a number of novel oxo and sulphido bridged molybdenum(V) complexes with piperidine carbamate (LLH) as ligand. These complexes were characterized by infrared and electronic spectra, magnetic susceptibility and analytical data, and we have assigned the formulae [Mo2O3(LL)4], [Mo2O4(LL)2], [Mo2O2S2(LL)2], [Mo2O3S(LL)2]. Infrared and electronic spectra of these compounds are sensitive to substitution of sulphur atoms into the bridge system. The low magnetic moments are attributed, at least in part, to intramolecular metal-metal interactions. We have compared the spectra of these complexes with those of analogous piperidine dithiocarbamate complexes.

Thermal and kinetic studies on the adducts with pyridines of bis(8-quinolinol) oxovanadium(IV)

Abstract The kinetic study by differential scanning calorimetry (DSC) of the thermal decomposition under nitrogen atmosphere is described for several adducts with pyridine or substituted pyridines of bis(8-quinolinol) oxovanadium(IV), whose assigned formula is VO(ox)2·B, where ox ≡ 8-quinolinol and B ≡ pyridine (Py), 3-methylpyridine (3-MP), 4-methylpyridine (4-MP), 3,5-dimethylpyridine (3,5-DMP), 3-aminopyridine (3-AP) or 4-aminopyridine (4-AP). From the DSC curves, the activation energies and pre-exponential Arrhenius factors, for the endothermic loss of one mole of coordinated base were calculated using a new method, and the mechanism of this reaction was determined. A relationship between the activation energies and the properties of the ligands has also been established.

Thermal decomposition of bis(5,7-dichloro-8-quinolinol)- oxovanadium(IV) complexes with pyridines

Abstract We describe a kinetic study by differential scanning calorimetry (DSC) of the thermal decomposition under a nitrogen atmosphere of several adducts with pyridine or substituted pyridines of bis(5,7-dichloro-8-quinolinol)oxovanadium(IV), to which the formula assigned is VO(clox)2· B, where clox = 5,7-dichloro-8-quinolinol and B = pyridine (Py), 3-methylpyridine (3-MP), 4-methylpyridine (4-MP), 3,5-dimethylpyridine (3,5-DMP), 3-aminopyridine (3-AP) or 4-aminopyridine (4-AP). For the endothermic process of the loss of coordinated base, we calculated activation energies using a new method, and the mechanism of this reaction was also determined. A relationship between activation energies and the properties of the ligands was established.

Thermal and kinetic parameters of phyllosilicate dehydration

Abstract This paper describes the application of differential scanning calorimetry (DSC), thermogravimetry and differential thermogravimetry to the analysis of the thermal dehydration of a natural phyllosilicate (Sierra del Segura, Spain). The thermal and kinetic parameters of the thermal dehydration, under nitrogen atmosphere, have also been determined by differential scanning calorimetry (DSC). From the DSC curve, activation energies and pre-exponential Arrhenius factors for the endothermic processes of the loss of water, have been calculated using a new method, and the mechanism of these reactions has been determined. The samples have been identified by IR spectroscopy and X-ray powder diffraction.

Oxyhalide Molybdenum(V) Complexes with Diamines

Abstract Salts of the d1 complex anion (MoOCl5)2- with diamines have been prepared and characterized by a range of physical measurements. The absorption spectra of the complexes have been measured and discussed on the basis of several molecular orbital schemes suggested by Gray and Hare. The formation of an hydrogen bond between the complex anion and the diamines have also been studied. By hydrolysis of these complexes we have isolated the dimeric complexes Mo2O4Cl2R2 (R = 1,3-propylenediamine, 1,2-cyclohexylenediamine and 1,2-phenylenediamine).