Thermal studies on oxalate complexes. II. Complexes of iron (III) and chromium (III)

The decomposition of solid K₃[Fe(C₂O₄)₃] · 2 H₂O and K₃[Cr(C₂O₄)₃] · 3 H₂O has been studied using TGA and DSC. After dehydration, the chromium compound was found to decompose by the loss of CO in two steps, the loss of CO₂ and additional CO, and finally the loss of CO₂. The final product appears to be either K₃CrO₃ or the mixed oxides of chromium and potassium. Kinetic parameters and enthalpy data are presented for these reactions. In the case of K₃[Fe(C₂O₄)₃] · 2 H₂O, dehydration is followed by the loss of CO₂ and CO, CO₂ alone, and finally CO. The final product appears to be a basic carbonate of the type K₃[FE(O)₂(CO₃)]. Kinetic and thermal data are presented for most of these decomposition reactions.     

Thermal studies on oxalate complexes. IV. Potassium bis(oxalato)cuprate(II) dihydrate

The dehydration and decomposition of K₂[Cu(C₂O₄)₂] · 2 H₂O have been studied using TG. The dehydration reaction gave the best fit to a second-order rate equation and has an activation energy of 411.5 ± 41.1 kJ mole^?1. Three distinct decomposition patterns were observed for the anhydrous complex. In the first case, K₂[Cu(C₂O₄)₂] decomposes to K₂CO₃ and CuO by loss of CO₂ and 2 CO. In the second case, decomposition leads to K₂C₂O₄ and Cu by loss of 2 CO₂. In the third case, the basic carbonate K₂[Cu(CO₃)_3/2O_1/2] is produced by loss of 2 CO and 0.5 CO₂. In the last case additional loss of CO₂ leads to the formation of K₂CO₃ and CuO in a separate reaction. Kinetic parameters are reported and discussed for all these reactions.     

Complex Carbonates of Iron(III)

The complex carbonates of iron(III) are shown to be anionic in nature. The solutions containing these complexes show a maximum absorbance at 460 nm. The complex carbonates of iron(III), viz., (i) K₆[Fe₂(OH)₂(CO₃)₅] · H₂O, — (ii) Na₂[Fe₃O₂(OH)₃(CO₃)₂], — (iii) K[Co(NH₃)₆]₂[Fe₃(OH)₄(CO₃)₆], — (iv) K₅[Co(NH₃)₆]₃[Fe₃(OH) ₄(CO₃)₆]₂, — (v) K[Co(NH₃)₆][Fe₂(OH)₄(CO₃)₃], and (vi) NH₄[Co(NH₃)₆][Fe₂(OH)₄(CO₃)₃] are isolated and studied by thermogravimetry. The infrared spectra of these compounds are recorded and probable band assignments made. Besides, the reaction between KHCO₃ and Fe(NO₃)₃ was studied through chemical and physicochemical methods.     

Kinetics of thermal decomposition of iron(III) dicarboxylate complexes

Summary Tris(dicarboxylate) complexes of iron(III) with oxalate, maleate, malonate and phthalate viz. K₃[Fe(C₂O₄)₃]×3H₂O (1), K₃[Fe(OOCCH₂COO)₃]×3H₂O (2), K₃[Fe(OOCCH=CHCOO)₃]×3H₂O (3), K₃[Fe(OOC-1,2-(C₆H₄)-COO)₃]×3H₂O (4) have been synthesized and characterized using a combination of physicochemical techniques. The thermal decomposition behaviour of these complexes have been investigated under dynamic air atmosphere upto 800 K. All these complexes undergo a three-step dehydration/decomposition process for which the kinetic parameters have been calculated using Freeman-Carrol model as well as using different mechanistic models of the solid-state reactions. The trisoxalato and trismalonato ferrate(III) complexes undergo rapid dehydration at lower temperature below 470 K. At moderately higher temperatures (i.e. >600 and 500 K, respectively) they formed bis chelate iron(III) complexes. The trismalonato and trismaleato complexes dehydrate with almost equal ease but the latter is much less stable to decomposition and yields FeCO₃ below 760 K. The cis-dicarboxylate complexes particularly with maleate(2-) and phthalate(2-) ligands are highly prone to the loss of cyclic anhydrides at moderately raised temperatures. The thermal decomposition of the tris(dicarboxylato)iron(II) to iron oxide was not observed in the investigated temperature range up to 800 K. The dehydration processes generally followed the first or second order mechanism while the third decomposition steps followed either three-dimensional diffusion or contracting volume mechanism.     

Thermal decomposition of potassium carbonatooxoperoxovanadate(V)

The thermal decomposition of K₃[V(CO₃)O(O₂)₂] was studied under isothermal, dynamic and quasi-isobaric-isothermal condition. A mixture of K₄V₂O₇ and K₂CO₃ was identified as the primary product of thermal decomposition. Under experimental conditions not allowing a continuous loss of volatile products, the reaction of K₄V₂O₇ with CO₂ gives KVO₃ and K₂CO₃.

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Zusammenfassung Unter isothermen, dynamischen und quasi-isobaren Bedingungen wurde die thermische Zersetzung von K₃[V(CO₃)O(O₂)₂] untersucht. Als Primärprodukt der thermischen Zersetzungsreaktion wurde ein Gemisch aus K₄V₂O₇ und K₂CO₃ festgestellt. Wird unter experimentellen Bedingungen das Entweichen flüchtiger Produkte verhindert, so gibt die Reaktion von K₄V₂O₇ mit CO₂ die Produkte KVO₃ und K₂CO₃.

     

Thermal studies on the decomposition of aquopentamminecobalt(III) hexathiocyanatochromate(III)

The decomposition of [Co(NH₃)₅H₂O] [Cr(NCS)₆] has been studied using DSC and TG. The first step involves the loss of H₂O and NH₃ in a first-order process to produce [(NH₃)₅Co(SCN)₃Cr(NCS)₃]. A second step involves the loss of HSCN. Activation energies are presented and the mechanisms of the reactions are discussed in comparison to analogous cyanide complexes.     

Decomposition of cis-and trans- potassium diaquobis(oxalato)chromate(III)

The decomposition of cis- and trans-K[Cr(C₂O₄)₂](H₂O)₂] has been studied using differential scanning calorimetry. Dehydration occurs as the first step with activation energies being 27.5 and 13.9 mol^?1, respectively, for the cis and trans complexes. After dehydration, continued heating results in loss of CO amd CO₂. For the trans complex, an additional endothermic peak is seen and the mass loss indicated that CO has been lost in a single step. In both cases, the final product indicated by mass loss data is KCrO₂.     

Thermal decomposition of the [Co(NH3)6]Cl3, Co[(NH3)4Cl2]Cl,K3[Fe(C2O4)3]3H2O and Fe(CH3COO)3 in argon and air atmosphere

Kinetic parameters (apparent activation energy, reaction order, pre-exponential factor (Z) in the Arrhenius equation) for thermal decomposition of the [Co(NH₃)₆]Cl₃, Co[(NH₃)₄Cl₂]Cl, K₃[Fe(C₂O₄)₃]3H₂O and Fe(CH₃COO)₃ are reported. They have been calculated on the DTA and TG data according to Coats-Redfern's model. Both, decomposition data obtained in argon and in air atmosphere have been considered and the results are compared.

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Zusammenfassung Es werden die kinetischen Parameter (scheinbare Aktivierungsenergie, Reaktionsordnung, prÄexponentieller Faktor (Z) der Arrhenius-Gleichung) der thermischen Zersetzung von [Co(NH₃)₆]Cl₃, [Co(NH₃)₄Cl₂]Cl, K₃[Fe(C₂O₄)₃]3H₂O und Fe(CH₃COO)₃ beschrieben, die entsprechend dem Coats-Redfern-Modell auf der Basis der DTA- und TG-Daten errechnet wurden. Die Zersetzung wurde sowohl in Argon als auch in Luft durchgeführt und die erhaltenen Daten miteinander verglichen.

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Helpful comments from Professor W. Wojciechowski and financial support from Institute for Low Temperatures and Structure Research Polish Academy of Sciences (CPBP 01.12) are greatefully acknowledged.     

Polymeric bis­(glycolato)­cobalt(II)

In the title compound, poly­[cobalt(II)‐bis(μ‐hydroxy­acetato‐O¹,O²:O^1′)], [Co(C₂H₃O₃)₂]_n, units of [Co(C₂H₃O₃)₂] constitute a bidimensional sheet coordination polymer in which each Co^II atom lies on an inversion centre and is octahedrally coordinated to glycolate ligands in a trans configuration. Carbonyl O atoms from adjacent units complete the octahedral environment.     

Thermal decomposition of the oxo-diperoxo-molibdenum (VI)-potassium oxalate

The oxo-diperoxo-molibdenum(VI)-potassium oxalate, K₂[MoO(O₂)₂(C₂O₄)] was synthesized using an adapted version of the method suggested by Dengel. The thermal behavior of the synthesized complex was investigated by simultaneous thermal analysis TG/DTG/DTA, in air or nitrogen atmosphere, to identify and characterize the mass-loss decomposition processes. In addition, for the characterization of the observed decomposition steps, the FT-IR spectra for the initial complex, evolved gaseous compounds and isolated complex at 230 and 430/383 °C in air/nitrogen atmosphere, were recorded. On the 35–500 °C temperature range, the K₂[MoO(O₂)₂(C₂O₄)] complex presented three main decomposition steps, accompanied by mass-loss. The first degradation step is due to the elimination of one oxygen molecule, by the breaking of the peroxo groups, with the formation of an intermediary, like [MoO₃L]. The other two degradation steps can be attributed to the decomposition of the organic ligand, with the final formation of a stable metallic oxide.     

IR and thermal studies on a new oxomolybdenum(VI) oxalato complex

A new molybdenum(VI) oxalato complex K₄(NH₄)₁₀[Mo₁₄O₄₂(C₂O₄)₇] (PAMO) was prepared and characterized by chemical analysis, IR spectral and X-ray studies. Its thermal decomposition was studied using TG, DTA and DTG techniques. The compound is anhydrous and decomposes between 235° and 335°C in three steps. The first and the second steps occur in the temperature ranges 235°–290°C and 290–310°C to give the intermediate compounds having the tentative compositions K₄(NH₄)₈[Mo₁₄O₄₂(C₂O₄)₆] and K₂(NH₄)₂[Mo₁₄O₄₂(C₂O₄)₃], respectively, the later than decomposing to give a mixture of potassium tetramolybdate and molybdenum trioxide at 335°C. DTA also shows a peak at 530°C which corresponds to the melting of potassium tetramolybdate. An examination of the products obtained at 340° and 535°C by chemical analysis, IR spectra and X-ray studies reveals them to be identical.The authors are grateful to Dr. M. C. Jain, Head of the Department of Chemistry, for providing research facilities.     

Investigation on the formation of potassium trimolybdate via thermal decomposition of a new oxomolybdenum(VI) oxalato complex

The complex K₄(NH₄)₂ [Mo₆O₁₅(C₂O₄)₆(H₂O)₄] (PAMO) was prepared and characterized on the basis of chemical analysis and IR spectral data. Its thermal decomposition was studied by using TG and DTA techniques. PAMO loses its water between 190 and 225°C followed by the decomposition of anhydrous PAMO, which takes place in three stages. The first two stages occur in the temperature ranges 225–245°C and 245–270°C, to give the intermediates with tentative compositions K₁₂(NH₄)₂ [Mo₁₈O₄₅(CO₃)₄(C₂O₄)₁₂ and K₁₂[Mo₁₈O₅₄(CO₃)₂(C₂O₄)₄] respectively, the latter then decomposing in the third stage between 270 and 335°C to give the end product, potassium trimolybadate (K₂Mo₃O₁₀). The end product was characterized by chemical analysis, IR spectral and X-ray studies.

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Zusammenfassung Die Komplexverbindung K₄(NH₄)₂[Mo₆O₁₅(C₂O₄)₆(H₂O)₄] (PAMO) wurde hergestellt und auf der Basis von chemischer Analyse und IR-Spektrum characterisiert. Mittels TG und DT Techniken wurde die thermische Zersetzung untersucht. Zwischen 190 und 225°C gibt PAMO alles Wasser ab, anschlieend erfolgt in drei Schritten eineZersetzung des dehydratierten PAMO. Die ersten zwei Schritte verlaufen in den Temperaturbereichen 225–245°C bzw. 245–270°C und liefern Zwischenprodukte der Zusammensetzung K₁₂(NH₄)₂[Mo₁₈O₄₅(CO₃)₄(C₂O₄)₁₂] bzw. K₁₂[Mo₁₈O₅₄(CO₃)₂(C₂O₄]. Letzteres zerfällt dann in einem dritten Schritt zwischen 270 und 335° C und liefert Kaliumtrimolybdat (K₂Mo₃O₁₀) als Endprodukt, welches mittels Elementaranalyse, IR- und Röntgendiffraktionsuntersuchungen

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The authors are thankful to Dr. M. C. Jain, Head of the Department and professor L. N. Mittal, Principal of the Institution for providing the research facilities. One of the authors (S. P. G.) is also thankful to U. G. C. for providing financial assistance.     

Thermal Investigations of M[La(C2O4)3]⋅xH2O (M=Cr(III) and Co(III))

The complexes M[La(C₂O₄)₃]⋅xH₂O (x=10 for M=Cr(III) and x=7 forM=Co(III)) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR, reflectance and powder X-ray diffraction (XRD) studies. Thermal investigations using TG, DTG and DTA techniques in air of chromium(III)tris(oxalato)lanthanum(III)decahydrate, Cr[La(C₂O₄)₃]⋅10H₂O showed the complex decomposition pattern in air. The compound released all the ten molecules of water within ∼170°C, followed by decomposition to a mixture of oxides and carbides of chromium and lanthanum, i.e. CrO₂, Cr₂O₃, Cr₃O₄, Cr₃C₂, La₂O₃, La₂C₃, LaCO, LaCrO_x (2<x<3) and C at ∼1000°C through the intermediate formation of several compounds of chromium and lanthanum at ∼374, ∼430 and ∼550°C. Thecobalt(III)tris(oxalato)lanthanum(III)heptahydrate, Co[La(C₂O₄)₃]⋅7H₂O becomes anhydrous around 225°C, followed by decomposition to Co₃O₄, La₂(CO₃)₃ and C at ∼340°C and several other mixture species of cobalt and lanthanum at∼485°C. The end products were identified to be LaCoO₃, Co₃O₄, La₂O₃, La₂C₃, Co₃C, LaCO and C at ∼ 2>1000°C. DSC studies in nitrogen of both the compounds showed several distinct steps of decomposition along with ΔH and ΔSvalues. IR and powder XRD studies have identified some of the intermediate species. The tentative mechanisms for the decomposition in air are proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

STUDIES ON THE BACTERIAL ACTIVITY OF COBALT(III) COMPLEXES. PART III. COBALT(III) CARBOXYLATE COMPLEXES

Abstract

Cobalt(III) complexes of the type [Co(en)₂(chel)]X.nH₂O where en = ethylenediamine, chel = phthalato = C₆H₄CO₂)^2? ₂, maleato = (O₂CCH = CHCO₂)^2?, succinato = (O₂CCH₂CH₂CO₂)^2?, homophthalato = (O₂CC₆H₄(CH₂)CO₂)^2?, citraconato = (O₂CC(CH₃) = CHCO₂)^2?, itaconato = (CH₂ = C(CO₂)CH₂CO₂)^2?, X = NO^? ₃, Br^?, (O₂CC₆H₄CO₂H)^?, (O₂CHC = CHCO₂H)^?, (O₂C(CH₂)₂CO₂H)^?, (O₂CC₆H₄(CH₂)CO₂H)^?, (O₂CHC = C(CH₂)-CO₂H)^?, and (O₂C-CH₂?C(= CH₂)-CO₂H)^?, [Co(en)₂(malonato)]X.2H₂O (where malonato = (O₂CCH₂CO₂)^2?, X = Cl^?, Br^?, and NO^? ₃) and [Co(en)₂CO₃]Cl.2H₂O have been investigated for their bacterial activity against Escherichia coli B growing on EMB agar and in minimal glucose media both in lag and log phases. Among the most active are where chel = phthalato and homophthalato. The effects are distinct from those known for compounds of Pt, e.g., cis?[Pt(NH₃)₂Cl₂] and rhodium, e.g., trans?[Rh(C₅H₅N)₄,Cl₂].6H₂O. Antagonisms are reported.     

Oxo-peroxokomplexe des Vanadiums(V)

Oxo-peroxocomplexes of Vanadium(V) The complexes K[VO(O₂)₂H₂O], K₃[VO(O₂)₂CO₃], K₃[VO(O₂)₂C₂O₄], and K₃[VO(O₂)(C₂O₄)₂] · H₂O have been prepared. On the basis of the composition and the IR spectra it is supposed, that the anions are monomeric with the pentagonal pyramidal or pentagonal bipyramidal structure.     

Molten potassium pyrosulfate: The reactions of seven metal oxalates

The reactions of Li₂C₂O₄, Na₂C₂O₄, K₂C₂·H₂O, CaC₂·H₂O, ZnC₂O₄, La₂(C₂O₄)₃ and K₂TiO(C₂O₄)₂· 2H₂O with K₂S₂O₇ were investigated using thermal methods of analysis. Reaction products were analysed by various techniques. It was found that anhydrous oxalates reacted with K₂S₂O₇, evolving a mixture of CO₂ and CO with the formation of K₂SO₄ and the corresponding metal sulfates, which, in the reactions of ZnC₂O₄ and K₂TiO(C₂O₄)₂ 2H₂O, probably existed as K₂[Zn(SO₄)₂] and K₄[Ti(SO₄)₄], respectively. Water was found to be an additional product in the hydrated metal oxalate reactions. The stoichiometries of these reactions have been established from the thermogravimetric and acidimetric results.     

Solid-state decomposition studies on fluoroperoxo species of transition metals: Part XIII. Kinetics of isothermal decomposition of K2[V2O3(O2)F2] and K3[Ta(O2)2F4]

The kinetics of isothermal decomposition of K₂[V₂O₃(O₂)₂] and K₃[Ta(O₂)₂F₄] have been investigated in the temperature range 413–493 K using a constant volume apparatus. The α vs. time plots for both these solids are sigmoidal in nature. The kinetics obey the Avrami-Erofeev equation (n = 2) for the initial stage of the decomposition. The contracting volume equation fits well for the deceleratory region. The activation energies are 164.8 and 105.4 kJ mol⁻¹ for K₂[V₂O₃(O₂)₂F₂], and 85.2 and 76.6 kJ mol⁻¹ for K₃[Ta.(O₂)₂F₄].The absence of lattice water in these two solids may be responsible for the appearance of a short induction, followed by an acceleratory region in pristine solids, in contrast to hydrated fluoroperoxo zirconates, wherein the dehydration step preceding peroxide decomposition leads to facile nucleation and a deceleratory nature of decomposition.The kinetic characteristics of the decomposition of fluoroperoxo species so far studied are summarized and discussed.     

Reactions of coordinated ligands,Part III(1). Kinetics of lodination of malonate and pyruvate in malonato(pentaammine)-cobalt(III), malonato-bis-(ethylenediamine)cobalt(III) and pyruvato(pentaammine)cobalt(III) ions

Summary The kinetics of iodination of malonate and pyruvate in the title complexes are reported at 35.0 °C and I=0.3 M. The reaction is first order in substrate and zeroth order in [I₂]. This result is commensurate with rate determining enolisation of the active methylene and methyl groups of the malonate and pyruvate respectively. The reaction is catalysed by H₂O, OH^– and by the buffer anions used. The rate data suggest that the malonate methylene group in the [Co(en)₂-O₂CCH₂CO₂]²⁺ chelate is considerably more active towards electrophilic substitution than is the case in [Co(NH₃)₅O₂CCH₂CO₂]²⁺.     

Thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O: II. Identification of the gaseous products

The main goal of the presented work was to verify the previously assumed decomposition stages of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O (HACOT) [Thermochim. Acta 354 (2000) 45] under different atmospheres (inert, oxidising and reducing). The gaseous products of the decomposition were qualitatively and quantitatively analysed by mass spectrometry (MS) and Fourier-transformed infrared spectroscopy (FT-IR). It was confirmed that the gaseous products of HACOT decomposition under studied atmospheres there were H₂O (stage I) and NH₃, CO₂ (stage II). The main gaseous products in the third stage in argon and hydrogen (20 vol.% H₂/Ar) were CO and CO₂, whereas in air (20 vol.% O₂/Ar) only CO₂ was identified. Under the oxidising as well as reducing atmospheres the influence of secondary reactions on the composition of both, solid and gaseous products was found particularly strong during the third stage of the process. The studies of the multistage decomposition of HACOT, additionally complicated by many secondary reactions, required application of the hyphenated TA-MS or TA-FT-IR techniques combined with the pulse thermal analysis PTA^® allowing quantification of the spectroscopic signals and investigation of gas-solid and gas-gas reactions in situ.     

Crystal structure and spectroscopic behavior of three new tris-oxalatoferrate(III) salts

A new general synthetic procedure for preparation of Na₃[Fe(C₂O₄)₃]·5H₂O (1), Rb₃[Fe(C₂O₄)₃]·3H₂O (2), and Cs₃[Fe(C₂O₄)₃]·2H₂O (3) was developed. The crystal structures of these salts have been determined by single crystal X-ray diffraction. Salt 1 crystallizes in the monoclinic space group C2/c with Z = 8, salt 2 in P2₁/c with Z = 4, and salt 3 in P2₁/n with Z = 4. The three new salts and K₃[Fe(C₂O₄)₃]·3H₂O, prepared for comparative purposes, were further characterized by infrared and ⁵⁷Fe-Mössbauer spectroscopy. These spectra are discussed in comparison with those of related oxalato complexes.