Kinetics of the thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O

The thermal decomposition of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O was studied under isothermal conditions in flowing air and argon. Dissociation of the above complex occurs in three stages. The kinetics of the particular stages thermal decomposition have been evaluated. The R_N and/or A_M models were selected as those best fitting the experimental TG curves. The activation energies,E, and lnA were calculated with a conventional procedure and by a new method suggested by Kogaet al. [10, 11]. Comparison of the results have showed that the Arrhenius parameters values estimated by the use of both methods are very close. The calculated activation energies were in air: 96 kJ mol^–1 (R_1.575, stage I); 101 kJ mol^–1 (Ain1.725 stage II); 185 kJ mol^–1 (A _2.9, stage III) and in argon: 66 kJ mol^–1 (A _1.25, stage I); 87 kJ mol^–1 (A _1.825, stage II); 133 kJ mol^–1 (A _2.525, stage III).     

Low-temperature heat capacities and thermodynamic properties of rare-earth triisothiocyanate hydrates (III) —Sm(NCS)3 · 6H2O, Gd(NCS)3 · 6H20, Yb(NCS)3 · 6H20 and Y(NCS)3 · 6H20

The heat capacities of four RE isothiocyanate hydrates, Sm(NCS)₃, · 6H₂0, Gd(NCS)₃ · 6H₂0, Yb(NCS)₃, · 6H₂O and Y(NCS)₃, · 6H₂0, have been measured from 13 to 300 K with a fully-automated adiabatic calorimeter. No obvious thermal anomaly was observed for the above-mentioned compounds in the experimental temperature ranges. The polynomial equations for calculating the heat capacities of the four compounds in the range of 13–300 K were obtained by the least-squares fitting based on the experimentalC _P, data. TheC _P, values below 13 K were estimated by using the Debye-Einstein heat capacity functions. The standard molar thermodynamic functions were calculated from 0 to 300 K. Gibbs energies of formation were also calculated. Project supported by the National Natural Science Foundation of China.     

The effect of experimental methods and measurement conditions on values of the kinetic parameters of [Co(NH3)6]2(C2O4)3·4H2O

Using the thermal decomposition of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O as a basis, the paper presents results which show how computed values of kinetic parameters are influenced by experimental conditions (ambient atmosphere, sample mass, linear heating rate) when using the non-isothermal methods and the Coats-Redfern (CR) modified equation. It also illustrates the influence of the experimental methods i.e. non-isothermal and isothermal (conventional) methods and also a quasiisothermal-isobaric one which can be recognised as equivalent to Constant Rate Thermal Analysis (CRTA). The results obtained have confirmed the significant influence of the experimental parameters as well as that of the experimental method used on the estimated values of kinetic parameters. The correlation between activation energy (E) and sample mass (m) or heating rate (β) is generally of a linear nature:E=a+bx     

Reactivity investigations of some chosen peroxo-vanadium(V), manganese(III) and chromium(VI) compounds

An interpretative account of the results of reactions in aqueous medium of a highly peroxygenated vanadium(V) complex, K [V(O_{2 3}]·3H₂O, with different organic and inorganic substrates is presented. The reactions were monitored by solution EPR spectroscopy and isolation of products at different stages of the reactions. Redox reactions between diperoxide, K[VO(O₂)₂(H₂O)] and VOSO₄ were conducted. The results of the investigation suggest that secondary oxygen exchange-reaction occurs which not only depends on but also utilises the intermediates in the primary reaction during diperoxovanadate-dependent oxidation of VOSO₄. In an interesting reactiontris(acetylacetonato)-manganese(III), Mn(acac)₃, on being reacted with a hydrogen peroxide adduct, KF·H₂O₂, and bpy and phen afforded crystalline [Mn(acac)₂(bpy)] and [Mn(acac)₂(phen)], respectively. The X-ray structural analysis of [Mn(acac)₂(phen)] showed that the compound crystallised in orthorhombic space groupPbcn. The structure consists of a pseudooctahedral Mn(II) ion being bound to two acac⁻(C₅H₅O ₂ ⁻ ) and a phen ligand with the molecule lying on two-fold axis. Reactivity profiles of two new chromium(VI) reagents viz., pyridinium fluorochromate, C₅H₅NH[CrO₃F] (PFC), and quinolinium fluorochromate C₉H₇NH [CrO₃F] (QFC), have been presented. The compounds are capable of acting as both electron-transfer and oxygen-atom-transfer agents. The X-ray analysis of PFC crystals reveals that the compound crystallises in the orthorhombic space group CmcZ₁. The structure consists of discrete pyridinium cations and CrO₃ F anions with no significant hydrogen bonding. This results in total disorder of the pyridinium cation. The tetrahedral [CrO₃ F]⁻ ion lies on a crystallographic mirror plane.     

The thermal decomposition of (NH4)[VO(O2)2(NH3)]

The compound, (NH₄)[VO(O₂)₂(NH₃)], thermally decomposes to ammonium metavanadate, which then decomposes to vanadium pentoxide. Using a heating rate of 5 deg·min^–1, the first decomposition step occurs between 74° and 102°C. The transformation degree dependence of the activation energy (-E) is shown to follow a decreasing convex form, indicating that the first decomposition step is a complex reaction with a change in the limiting stage of the reaction. Infrared spectra indicated that the decomposition proceeds via the gradual reduction of the ratio of the (NH₄)₂O to V₂O₅ units from the original 11 ratio in ammonium metavanadate, which may be written as (NH₄)₂O·V₂O₅, to V₂O₅.The assistance of Professor A. M. Heyns (University of Pretoria) and Professor K. L. Range (University of Regensburg) is gratefully acknowledged as well as the financial assistance of the University of Pretoria and the FRD.     

Chromium(III)-Ettringite Formation and its Thermal Stability

Attempts have been made to replace aluminium(III) by chromium(III) in the ettringite structure because of practical importance of a waste treatment technology. The optimum conditions of Ca₆[Cr(OH)₆]₂(SO₄)₃⋅26H₂O formation and its thermal stability are reported. This revised version was published online in July 2006 with corrections to the Cover Date.     

A thermal and structural study on Lanthanum Hexacyanocobaltate(III) pentahydrate,La[Co(CN)6]·5H2O. Part III

On dehydration of La[Co(CN)₆]·5H₂O, the color of the complex, changes from white to pale blue at around 230°C. Heating the pale blue specimen, the color changes to deep blue at around 290°C. This deep blue specimen is easily rehydrated to a pink one. As reported previously, in the pale blue specimen, Co³⁺ ions are situated in the center of the D_4h crystal field formed by six CN^- ions. The deep blue specimen is due to the presence of [Co(CN)₄]^2- ions in which Co²⁺ was situated in a T_d coordination field formed by four CN^- ions and the Co-C bond length is 1.67 Ĺ. The pink species corresponded to trans-[Co(CN)₄(H₂O)₂]^2- and the bond lengths of Co-C and Co-O are 1.89 and 1.85 Ĺ, respectively. The Raman spectra of the complex observed at 25°C displays two bands at 2157 and 2176 cm^-1 associated with the vibration of C-N bond, and the band of 2157 cm^-1 was split into two bands, 2150 and 2156 cm^-1, at around 100°C. When the complex was heated to around 230°C, three new bands were observed at 2103, 2116 and 2141 cm-1. The bands of 2103 and 2116 cm^-1 were assigned to the stretching vibration of C=N bonding to Co²⁺. The band of 2141 cm^-1 was assigned to the stretching vibration of the inverted CN^- as follows: Co-C=N-La→Co-N=C-La. The activation energy for the inversion of CN^- was estimated as 67 kJ mol^-1. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tribochemistry and kinetics of Al2(SO4)3·xH2O decomposition

The thermal decomposition of tribochemically activated Al₂(SO₄)₃·xH₂O was studied by TG, DTA and EMF methods. For some of the intermediate solids, X-ray diffraction and IR-spectroscopy were applied to learn more about the reaction mechanism. Thermal and EMF studies confirmed that, even after mechanical activation of Al₂(SO₄)₃·xH₂O, Al₂O(SO₄)₂ is formed as an intermediate. Isothermal kinetic experiments demonstrated that the thermochemical sulphurization of inactivated Al₂(SO₄)₃·xH₂O has an activation energy of 102.2 kJ·mol^?1 in the temperature range 850–890 K. The activation energy for activated Al₂(SO₄)₃·xH₂O in the range 850–890 K is 55.0 kJ·mol^?1. The time of thermal decomposition is almost halved when Al₂(SO₄)₃·xH₂O is activated mechanically. The results permit conclusions concerning the efficiency of the tribochemical activation of Al₂(SO₄)₃·xH₂O and the chemical and kinetic mechanisms of the desulphurization process.     

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.     

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.     

On the electrochemical reduction of some Cr(III) complexes inDMSO investigated by cyclic voltammetry

The compounds investigated were: [Cr(en)₃]³⁺, [Cr(ur)₆]³⁺, [Cr(DMSO)₆]³⁺, [Cr(dien)₂]³⁺, [Cr(en)₂(acac)]²⁺, [Cr(en) (acac)₂]⁺ and Cr(acac)₃.A distinctly different behaviour is caused by the introduction of one or moreacac ligands into the molecule. The first step is much more cathodic and quite irreversible, while it is reversible or quasi reversible for the first group of ions. This is due to a -type interaction between theacac ligand and the central ion. This interaction is responsible for a third peak occurring for the second group of compounds and may be attributed to the reduction of the Cr(I) ion.Some correlations were found e.g. between the extinction of thed-d band of the first group of ions and the potential of the first peak, and the number ofacac groups introduced in the second group of compounds and the shift of the potential of the first peak.The determined electrochemical data are tabulated.

---

Untersuchungen zur elektrochemischen Reduktion einiger Cr(III)-Komplexe in DMSO mittels zyklischer Voltammetrie

Zusammenfassung Die elektrochemischen Daten einer Reihe von Cr(III)-Komplexen miten-, ur-, DMSO-, dien- undacac-Liganden werden präsentiert und einige Möglichkeiten der Korrelation der physikalischen Eigenschaften der Komplexe werden aufgezeigt.Die erste Stufe bei der Einführung vonacac-Liganden ist auf Grund einer -Wechselwirkung zwischen Ligand und Zentralion irreversibel.

     

TG/DTA/MS Study of the thermal decomposition of FeSO4·6H2O

The thermal decomposition of FeSO₄·6H₂O was studied by mass spectroscopy coupled with DTA/TG thermal analysis under inert atmosphere. On the ground of TG measurements, the mechanism of decomposition of FeSO₄·6H₂O is: i) three dehydration steps FeSO₄·6H₂O FeSO₄·4H₂O+2H₂O FeSO₄·4H₂O FeSO₄·H₂O+3H₂O FeSO₄·H₂O FeSO4+H₂O ii) two decomposition steps 6FeSO₄ Fe₂(SO₄)₃+2Fe₂O₃+2SO₂ Fe₂(SO₄)3 Fe₂O₃+3SO₂+3/2O₂ The intermediate compound was identified as Fe₂(SO₄)₃ and the final product as the hematite Fe₂O₃.     

Synthesis and thermal investigation of Na2Cd(SO4)2·2H2O

The synthesis and thermal decomposition of Na₂(SO₄)₂·2H₂O in both air and nitrogen are described. The synthesis was performed by two different procedures, but in both cases the same product was obtained, corresponding to the general formula given above. The crystals obtained were investigated by methods of X-ray powder diffraction, and chemical and thermal analysis. The differences in thermal decomposition in air and nitrogen are discussed.     

An efficient synthesis of 5-substituted 1H-tetrazoles via B(C6F5)3 catalyzed [3+2] cycloaddition of nitriles and sodium azide

A simple and efficient protocol is developed for the synthesis of 5-substituted 1H-tetrazole derivatives from various nitriles and sodium azide (NaN₃) via [3+2] cycloaddition reaction using B(C₆F₅)₃ as a catalyst. The present synthetic method displayed significant advantages such as low catalyst loading, mild reaction conditions, low toxicity, easy work-up, high yields, and compatibility with other functional groups.     

Cerium(III)-Catalyzed Synthesis of Schiff Bases: A Green Approach

The reaction of primary aromatic amines with aryl aldehydes is found to be catalyzed by cerium chloride heptahydrate under solvent-free conditions to give the corresponding Schiff bases in good yields.     

Effect of sample mass on the kinetics of thermal decomposition of a solid

Effects of sample mass on the kinetics of isothermal dehydration of crushed crystals of Li₂SO₄·H₂O were investigated using conventional TG. The process was characterized by a combination of Avrami-Erofeyev and contracting geometry models. Distribution of the fractional reaction, α, in particles within the sample assembly as well as the change in the rate of gross diffusion of the evolved water vapour appear responsible for the sample-mass-dependent kinetic parameters obtained for the system.     

Thermal decomposition of cobalt nitrato compounds: Preparation of anhydrous cobalt(II)nitrate and its characterisation by Infrared and Raman spectra

The thermal decomposition of Co(NO₃)₂·6H₂O (1) as well as that one of NO[Co(NO₃)₃] (Co(NO₃)₂·N₂O₄) (2) was followed by thermogravimetric (TG) measurements, X-ray recording and Raman and IR spectra. The stepwise decomposition reactions of 1 and 2 leading to anhydrous cobalt(II)nitrate (3) were established. In N₂ atmosphere, cobalt oxides are finally formed whereas in H₂/N₂ (10% H₂) cobalt metal is produced. Rapid heating of cobalt(II)nitrate hexahydrate causes melting (formation of a hydrate melt) and therefore side reactions in the hydrate melt by incoupled reactions and evolution/evaporation of different species as, e.g., HNO₃, NO₂, etc. In case of larger amounts in dense packing in the sample container, the formation of oxo(hydoxo)nitrates is possible at higher temperature. For 2, its thermal decomposition to 3 was followed and its decomposition mechanism is proposed.     

Trinuclear metal(III) trifluoroacetates

Hydrated and anhydrous trinuclear metal(III) trifluoroacetates of Cr and Fe were prepared by reaction of freshly precipitated metal oxides with trifluoroacetic acid, while manganese analogs by acid exchange. IR data show the presence of bidentate trifluoroacetate groups. The diffuse reflectance spectra suggest octahedral environment around metals.Mössbauer spectra show that iron atoms in the compounds are high spin hexacoordinated; two types of iron sites are suggested in hydrated iron compound. Low magnetic moment of chromium and iron compounds indicate antiferromagnetic coupling. Th anhydrous compounds decompose in single step with the evolution of (CF₃CO)₂O.M ₃O(O₂CCF₃)₇ form complexes [M ₃O(O₂CCF₃)₆·3Py]⁺ [O₂CCF₃]^– with pyridine.

---

Dreikernige Metall(III)-Trifluoracetate

Zusammenfassung Es wurden hydratisierte und wasserfreie dreikernige Metall(III)-Trifluoracetate von Cr und Fe mittels der Reaktion von frisch gefälltem Metalloxid und Trifluoressigsäure dargestellt; die Mangan-Analogen wurden über Säure-Austausch gewonnen. Die IR-Daten zeigen die Präsenz von zweizähnigen Trifluoracetat-Gruppen an. Die diffuse-reflectance-Spektren sprechen für eine octahedrale Umgebung rund um das Metall. DieMössbauer-Spektren zeigen, daß die Eisenatome in den entsprechenden Verbindungen high-spin hexakoordiniert sind; dabei werden in den hydratisierten Eisenverbindungen zwei Typen von Eisenatomen gezeigt. Ein niederes magnetisches Moment der Chrom- und Eisen-Verbindungen zeigen eine antiferromagnetische Kopplung an. Die wasserfreien Verbindungen zersetzen sich in einem einzigen Schritt unter Entwicklung von (CF₃CO)₂O. Mit Pyridin bilden die VerbindungenM ₃O(O₂CCF₃)₇ die Komplexe [M ₃O(O₂CCF₃)₆·3Py]⁺ [O₂CCF₃]^–.

     

Thiocyanate-selective membrane electrode based on cobalt(III) Schiff base as a charge carrier

A highly selective polyvinylchloride (PVC) membrane electrode based on Schiff base complex i.e. [Cobalt (Salpen) (PBu₃)] ClO4 · H2O (Salpen = bis(salycilaldehyde)propylene diamine) is reported as new carrier for thiocyanate selective electrode by incorporating the membrane ingredients on the surface of graphite electrodes. The proposed electrode possesses a very wide Nernestian linear range to thiocyanate from 1.0 × 10^?6 to 1.0 × 10^?1 M with slope of ?59.05 ± 0.91 mV per decade of thiocyanate concentration, very low detection limit (8.0 × 10^?7 M) and good thiocyanate selectivity over the wide variety of other anions. Fast and stable response, good reproducibility, long-term stability, applicability over a wide pH range (2.8–9.8) are advantages of the reported electrode. The sensor has a response time of <5 s and can be used for at least 14 weeks without any considerable change in respective potential response. The proposed electrode was used for the determination of thiocyanate in saliva, wastewater and human urine with satisfactory results and good agreement with colorimetric as reference method.     

Aromatization of Hantzsch 1,4-Dihydropyridines with Al(NO3)3·9H2O and/or Fe(NO3)3·9H2O in the Presence of Silica Sulfuric Acid Under Mild and Heterogeneous Conditions

A simple and convenient method for the aromatization of Hantzsch 1,4-dihydropyridines to the corresponding pyridines is achieved via combination of aluminum or ferric nitrates and silica sulfuric acid as environmentally friendly and novel oxidizing media. This oxidation was carried out in dichloromethane under heterogeneous conditions with good to excellent yields.