Thermal decomposition of manganese(II)bis(oxalato)nickelate(II)tetrahydrate

Summary A mixed metal oxalate, manganese(II)bis(oxalato)nickelate(II)tetrahydrate, has been synthesized and characterized by elemental analysis, IR spectral and X-ray powder diffraction (XRD) studies. Thermal decomposition studies (TG, DTG and DTA) in air showed that the compound decomposed mainly to Mn₂O₃, MnO₂ and NiO at ca.1000°C, via. the formation of several intermediates. DSC study in nitrogen upto 500°C showed the endothermic decomposition. The tentative mechanism for the thermal decomposition in air is proposed.     

Cadmium(II)bis(oxalato)cobaltate(II)- pentahydrate

A mixed metal carboxylate, cadmium(II)bis(oxalato)cobaltate(II)pentahydrate, has been synthesized and characterized by elemental analysis, IR spectral, reflectance and X-ray powder diffraction studies. Thermal decomposition studies (TG, DTG and DTA) in air showed that the compound decomposed to CdCoO3 at 370°C through the formation of an anhydrous compound at ~194°C. Finally, CdCoO₂ is generated at 1000°C. DSC study in nitrogen up to 550°C showed the formation of a mixture of CdO and Co₃O₄ as end products. The kinetic parameters have been evaluated for the dehydration and decomposition steps using four non-mechanistic equations, i.e., Freeman and Carroll, Coats and Redfern, Flynn and Wall, MacCallum and Tanner equations. Using seven mechanistic equations, the rate controlling processes of the dehydration and decomposition mechanism are also inferred. The kinetic parameters, DH and DS obtained from DSC are discussed. IR and X-ray powder diffraction studies identified some of the decomposition products. A tentative mechanism for the decomposition in air is proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and the thermal decomposition of iron(III) tris(oxalato) ferrate(III) tetrahydrate

The paper describes the synthesis and thermal decomposition of Fe[Fe(C₂O₄)₃]4H₂O in air. The compound is completely dehydrated at 170°C and some reduction in the inner sphere iron(III) occurs. At 290°C, a mixture of ferric oxide and ferrous oxalate is obtained. Beyond 420°C, the decomposition is complete and final residue is ferric oxide. A probable reaction mechanism is proposed.     

Synthesis of cobalt nanoparticles from [bis(2-hydroxyacetophenato)cobalt(II)] by thermal decomposition

[Bis(2-hydroxyacetophenato)cobalt(II)] was used as a new precursor to prepare cobalt (Co) and tricobalt tetraoxide (Co₃O₄) nanoparticles of 15–25 nm in average diameter by thermal decomposition. The different combinations of triphenylphosphine, and oleylamine were added as surfactants to control the particle size. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared (FT-IR) spectroscopy. Time-dependent FT-IR studies indicate that oxidation of the as-synthesized cobalt nanoparticles in air is slow. The valence change of cobalt from the nanoparticle sample is not observed after it is kept in hexane under air for 30 days. The magnetic property was studied with vibrating sample magnetometer (VSM). The hysteresis loops of the obtained samples reveal the soft magnet behaviors the enhanced coercivity (H_c) and decreased saturation magnetization (M_s) in contrast to their respective bulk materials.     

Potassium trans-[bis(oxalato)diaquacobaltate(II)] tetrahydrate: synthesis, structure, potentiometric and thermal studies

The title compound, trans-K₂[Co(C₂O₄)₂(H₂O)₂]·4H₂O, was synthesised, and characterised by elemental analysis. Acid dissociation constants for the complex were determined by potentiometric titration and calculated by STOICHIO program. The crystal structure of trans-K₂[Co(C₂O₄)₂(H₂O)₂]·4H₂O was determined by X-ray diffraction studies. The asymmetric part of the unit cell contains one symmetric anion of oxalate and water molecule bound with Co(II) ion in crystallographic special position, one potassium cation and two molecules of water. Thermal properties of the complex were examined by thermogravimetric analysis (TGA). A decomposition mechanism is proposed on the basis of the results.     

Mechanism of thermal decomposition of cobalt acetate tetrahydrate

The thermal decomposition of cobalt acetate tetrahydrate (Co(CH₃COO)₂ · 4H₂O) has been studied via thermogravimetric (TG) analysis, in situ X-ray powder diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The results of TG and XRD showed that the parent salt melted and then the dissolved crystalline water was vaporized in two steps. The dehydration process was followed by a major step concerning the decomposition of the acetate group, leading to basic acetate as an intermediate, which then produced CoO and Co in N₂ and H₂ atmosphere, respectively. Three decomposition intermediates Co(CH₃COO)₂ · 0.5H₂O, Co(CH₃COO)₂, and Co(OH)(CH₃COO) were presumed. In situ XRD experiments revealed that the intermediate basic acetate was poorly crystallized or even amorphous. Evolved gases analysis indicated that the volatile products of acetate decomposition were water vapor, acetic acid, ethylenone, acetone, and CO₂. A detailed thermal decomposition mechanism of Co(CH₃COO)₂ · 4H₂O was discussed.     

Solid-state thermal decomposition of heterobimetallic oxalate coordination compounds, zinc(II)tetraaquatris(oxalato)lanthanate(III)hexahydrate and cadmium(II)heptaaquatris(oxalato)lanthanate(III)tetrahydrate

Two heterobimetallic oxalate coordination compounds, zinc(II)tetraaquatris(oxalato)lanthanate(III)hexahydrate (ZnOLa) and cadmium(II)heptaaquatris(oxalato)lanthanate(III)tetrahydrate (CdOLa) were synthesized and characterized by elemental analysis, IR, electronic spectral and powder X-ray diffraction studies. Both the compounds were found to have monoclinic structure. Thermal decomposition studies by TG, DTG and DTA in air have proved that the aqua ligands are associated with metals in a stronger coordination mode. The temperatures for pyrolysis were adopted from the TG results chosen from the stable range of thermograms. In case of ZnOLa, it decomposes through two steps and the end product at 1000 °C was found to be consisting of mainly, La₂O_3, ZnO and La₂ZnO _x through the intermediate formation of several oxycarbonates of lanthanum at ca. 525 °C. In case of cadmium analogue, three steps decomposition were observed and the final products were confirmed as CdO₂, La₂O₃, LaCO and La₂CdO _x via the formation of several intermediates at 340 and 590 °C. The La₂C₃ and carbon are also found as part of the end product. The kinetic parameters, E ^*, lnk _o, ?H ^# and ?S ^# of all the deaquated and decomposition steps are investigated and discussed from the DSC study in nitrogen.     

Effect of gamma-radiation on thermal decomposition of bis(diethylene triamine)cobalt(II) nitrate and bis(diethylene triamine)zinc(II) nitrate

Effect of γ-radiation on non-isothermal decomposition kinetics of bis(diethylene triamine)cobalt(II) nitrate and bis(diethylene triamine)zinc(II) nitrate have been studied in nitrogen atmosphere at a heating rate of 10 °C/minute. The data were analyzed by Coats- Redfern, Freeman-Caroll and Horowitz-Metzeger methods. The result showed that irradiation enhanced thermal decomposition in both the complexes. Activation energy and associated kinetic parameters are lowered upon irradiation and the extent of lowering is higher in cobalt complex compared to zinc complex. Order of the reaction for each step was found to be unity. The mechanism for deamination and decomposition is controlled by R₂ function except for the deamination of unirradiated cobalt complex where the process is governed by R₃ function.     

Synthesis, thermal and calorimetric investigations of cobalt(ii) trihydrogen hexaoxoperiodate tetrahydrate

A new cobalt(II) trihydrogen hexaoxoperiodate tetrahydrate has been synthesized: CoH₃IO₆·4H₂O and has been characterized by quantitative analysis, TG, DTA, DSC and IR spectroscopy. Based on DTA and DSC data, a thermal decomposition scheme has been proposed for this complex.     

Synthesis and crystal structure of polymer cobalt(II) complex, 1,2,4,5-benzenetetracarboxylate hexaimidazole tetraaqua cobalt (II) tetrahydrate

The crystal structure of the title complex {[Co(TCB)2/2-(IMI)2(H2O)2][Co(IMI)4(H2O)2] } (H2O)4 (where TCB = 1,2,4,5-benzenetetracarboxylic anion; IMI = imidazole) has been determined by X-ray diffraction method. Crystal data for {[Co(TCB)2/2(IMI)2(H2O)2][Co(IMI)4(H2O)2]}-(H2O)4: triclinic, space group P 1, a = 1.0647(2) nm, b = 1.1165(1)nm,c = 1.00361(1)nm,α = 91.56(1)°,β = 111.34(1)°, γ = 115.642(10)°, V = 0.9772(3) nm5, Z = 1. The polymer cobalt (II) complex has a novel three-dimension network structure. Co(1) atom and Co(2) atom both are coordinated in an octahedral arrangement and located in the center of the coordination anion and the center of the coordination cation, respectively. Moreover four carboxyl groups of TCB are divided into two types, two para-carboxyl groups bridge Co(1) atom in monodentate fashion and other two para-carboxyl groups are in free.     

Synthesis, structural and magnetic studies of imidazolium bis(oxalato)cuprate(II)

Imidazoliumm bis(oxalato)cuprate(II) has been synthesized and its structure determined by X-ray crystallography. Variable temperature magnetic susceptibility measurements, as well as EPR and UV-vis spectroscopic studies, have been carried out. The results show that in the solid state the compound exists in a chain-like structure, with an asymmetric one-atom weak oxalate bridge joining adjacent Cu^II centres. Of the two oxygen atoms of each coordinated oxalate only one participates in bridging; thus, each oxalate ultimately achieves three-point coordination. Each of the imidazolium ions participates in two hydrogen through the N—H moieties. The compound exhibits a weak antiferromagnetic interaction (J = −0.40 cm⁻¹).EPR spectra reveal that the triplet state is appreciably populated at both room and liquid nitrogen temperatures.     

Solid-phase thermal decomposition of polynuclear nickel(II) and cobalt(II) complexes

Solid-phase thermal decomposition of polynuclear Ni^II and Co^II pivalate complexes was studied by differential scanning calorimetry and thermogravimetry. The decomposition of the polynuclear (from bi-to hexanuclear) Co^II carboxylate complexes is accompanied by aggregation to form a volatile octanuclear complex. Thermolysis of the polynuclear NiII carboxylates results in their destructure, and the phase composition of the decomposition products is determined by the nature of coordinated ligands. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 250—260, February, 2006.     

Thermal decomposition kinetics of bis(thiophene-2-carboxaldehyde thiosemicarbazonato) cobalt(II)

The thermal decomposition kinetics of thiophene-2-carboxaldehyde thiosemicarbazone complex of cobalt(II) has been studied using TG, DTG and DTA techniques. Its decomposition was subjected to critical evaluation using the equations of Freeman-Carroll, Horowitz-Metzger and Coats-Redfern and the kinetic parameters have been evaluated for each step of decomposition by the method of weighted least squares.

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Co(II) -2- , . -, - -. .

     

Synthesis,spectroscopic and thermal characterization of Co(II) tetrahydrogen hexaoxoiodate tetrahydrate

A new cobalt(II) tetrahydrogen hexaoxoiodate tetrahydrate Co(H₄IO₆)₂·4H₂O is prepared by crystallization from an acidic aqueous solution. This compound is identified by quantitative analysis, TG, DTA, DSC and IR spectra. A thermal decomposition scheme is proposed. Some phase transitions are identified and the corresponding enthalpy changes are determined.     

The non-isothermal decomposition of cobalt acetate tetrahydrate

The non-isothermal decomposition of cobalt acetate tetrahydrate was studied up to 500°C by means of TG, DTG, DTA and DSC techniques in different atmospheres of N₂, H₂ and in air. The complete course of the decomposition is described on the basis of six thermal events. Two intermediate compounds (i.e. acetyl cobalt acetate and cobalt acetate hydroxide) were found to participate in the decomposition reaction. IR spectroscopy, mass spectrometry and X-ray diffraction analysis were used to identify the solid products of calcination at different temperatures and in different atmospheres. CoO was identified as the final solid product in N₂, and Co₃O₄ was produced in air. A hydrogen atmosphere, on the other hand, produces cobalt metal. Scanning electron microscopy was used to investigate the solid decomposition products at different stages of the reaction. Identification of the volatile gaseous products (in nitrogen and in oxygen) was performed using gas chromatography. The main products were: acetone, acetic acid, CO₂ and acetaldehyde. The proportions of these products varied with the decomposition temperature and the prevailing atmosphere. Kinetic parameters (e.g.E and lnA) together with thermodynamic functions (e.g. °H, C _p and °S) were calculated for the different decomposition steps. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Thermal decompostion studies on nickel(II) bis(oxalato)nickelate(II) pentahydrate

The paper describes the synthesis and thermal decomposition of nickel(II)bis(oxalato)nickelate(II)pentahydrate, Ni[Ni(C₂O₄)2].5H₂O. The complex was characterized by elemental analysis, infrared, electronic, e.s.r., magnetic moment measurement and X-ray powder diffraction studies. The thermal decompostion of the complex led to NiO in air at about 338° and in nitrogen at about 720°. The activation energies (E ^*) for the dehydration and decompostion reactions in air and nitrogen were evaluated. Tentative reaction mechanisms have been suggested for the termal decompostion of the complex in air and nitrogen.

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Zusammenfassung Es wird die Synthese und thermische Zersetzung von Nickel(II) -bis(oxalato)- nickelat(II) - pentahydrat beschrieben: Ni[Ni(C₂O₄)2].5H₂O. Dieser Komplex wurde mittels Elementaranalyse, IR-Spektroskopie, ESR-Spektroskopie, der Messung des magnetischen Momentes sowie mittels Pulverdiffraktionsuntersuchungen charakterisiert. Im Ergebnis der thermischen Zersetzung entsteht NiO, in Luft bei etwa 338°, in Stickstoffatmosphäre bei ca. 720°. Die Aktivierungsenergien (E^*) der Dehydratations- und Zersetzungsreaktionen in Luft und in Stickstoff wurden ermittelt. Für die thermische Zersetzung des Komplexes in Luft bzw. in Stickstoff wurde ein Reaktionsmechanismus entwickelt.

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The authors thank the RSIC, CDRI, Lucknow for microanalysis, RSIC, NEHU, Shillong for i.r. spectra, RSIC, IIT, Madras for far i.r. spectra, RSIC, Nagpur University for thermal analysis, Dr. S. K. Datta for Forensic Science Laboratory, Guwahati, Assam for DSC and Dr. K. L. Deori of Dibrugarh University for X-ray powder diffraction photographs.     

Reactions of tris(oxalato)cobaltate(III) with two-electron reductants

The tris(oxalato)cobaltate(III) complex [Co(C(2)O(4))(3)](3-), E(o)(Co)(III/II)=+0.57 V) is readily reduced by the 2e(-) reagents, Sn(II) and Ge(II), in contrast to (NH(3))(5)CoCl(2+) and (NH(3))(5)CoBr(2+), which are unreactive toward these donors. Rates for the oxalato oxidant are only 10(-3)-10(-2) as great as those for vitamin B(12a)(aquacob(III)alamin, E(o)+0.35 V at pH 1), in accord with the suggestion that reductions of corrin-bound cobalt(III) by Sn(II) and Ge(II) occur predominantly through an additional path involving Co(i). Reductions of the oxalato complex by 2e(-) donors are taken to proceed by initial formation of odd-electron intermediates (e.g., Sn(III) and Ge(III)) which react rapidly with Co(III). Such a two-step sequence is in keeping with the observed behavior of the rare reductant, Ti(II), which is found to be oxidized by [Co(C(2)O(4))(3)](3-) more slowly than (independently prepared) Ti(III) under comparable conditions.