Thermal decomposition study of the coordination compound [Fe(urea)6](NO3)3

The thermochemical behavior of the coordination compound [Fe(urea)₆](NO₃)₃ was studied by simultaneous CG–TG–DTG–DTA and mass spectrometry methods non-isothermal conditions. The compound decomposes at 200 °C into a mixture of spinel-type oxides and hematite. The nature and particle size of the final decomposition products are strongly associated with the conditions during the thermal treatments, in particular the heating rate and the calcination temperature. A certain fraction of the products are formed as nanometric particles; they show superparamagnetic behavior at room temperature. The comparably low temperature of the calcination treatments of this compound is a promising perspective to attain small sized magnetic powders.     

Synthesis,Characterization and Thermal Decompositions Studies of Some Malates Coordination CompoundsI. iron nickel compounds

The thermal behaviour of three coordination compounds, potential precursors of nickel ferrite [Fe₂Ni(C₄H₄O₅)_2.5(OH)₂]NO₃·5H₂O,[Fe₂Ni(C₄H₈O₃N₂)₄](NO₃)₈·24H₂O and (NH₄)[Fe₂Ni(C₄H₄O₅)₃(OH)₃]·3H₂O has been investigated to evaluate their suitability as precursors for nickel ferrite. For a complete and reliable assignment of the thermal transformations, the isolable solid intermediates and end products were characterized by IR, X-ray diffraction and Mössbauer investigations. A decomposition scheme is proposed.     

Thermal analysis of two types of dextran-coated magnetite

The thermal stability of two kinds of dextran-coated magnetite (dextran with molecular weight of 40,000 (Dex40) and 70,000 (Dex70)), obtained by dextran adsorption onto the magnetite surface is investigated in comparison with free dextran in air and argon atmosphere. The thermal behavior of the two free dextran types and corresponding coated magnetites is similar, but atmosphere dependent. The magnetite catalyzes the thermal decomposition of dextran, the adsorbed dextran displaying lower initial decomposition temperatures comparative with the free one in both working atmospheres. The dextran adsorbed onto the magnetite surface decomposes in air through a strong sharp exothermic process up to ~450 °C while in argon atmosphere two endothermic stages are identified, one in the temperature range 160–450 °C and the other at 530–800 °C.     

Thermal Behaviour of Some Polyhydrocarboxylic Coordination Compounds with Neodium

New Nd-Co based polynuclear coordination compounds containing as ligand polyhydrocarboxylic acid as tartaric, malic and gluconic acids were prepared, namely: [NdCo(tart)₃]·4H₂O, (NH₄)[NdCo_0.5Cu_0.5(tart)₃]·4H₂O, (NH₄)[NdCo(malic)₃]·4H₂O, (NH₄)[NdCo_0.5Cu_0.5(malic)₃]·4H₂O, [NdCo(gluc)₄]·4H₂O and [Nd₂CoCu(gluc)₇]·5H₂O. A comparison between the thermal behaviour of the studied polynuclear coordination compounds concerning thermal stability and thermal decomposition stoichiometry was inferred. Oxalic and malonic intermediates were identified at about 300°C in the thermal decomposition of tartaric and malic compounds. In all the decomposition processes at about 400°C the presence of oxocarbonate is shown. The residual products are mixed oxides of perovskite type. This revised version was published online in August 2006 with corrections to the Cover Date.     

The d4/d3 redox pairs [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp']z (z=0 and 1): structural consequences of electron transfer and implications for the inverse halide order

The d4 halide complexes [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp'] {X=F, Cl, Br or I; R=Me or Ph; M=Mo or W; Tp'=hydrotris(3,5-dimethylpyrazolyl)borate} undergo one-electron oxidation to the d3 monocations [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp']+, isolable for M=W, R=Me. X-Ray structural studies on the redox pairs [WX(CO)(eta-MeC[triple bond, length as m-dash]CMe)Tp']z (X=Cl and Br, z=0 and 1), the ESR spectra of the cations [WX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp']+ (X=F, Cl, Br or I; R=Me or Ph), and DFT calculations on [WX(CO)(eta-MeC[triple bond, length as m-dash]CMe)Tp']z (X=F, Cl, Br and I; z=0 and 1) are consistent with electron removal from a HOMO (of the d4 complexes) which is pi-antibonding with respect to the W-X bond, pi-bonding with respect to the W-C(O) bond, and delta-bonding with respect to the W-Calkyne bonds. The dependence of both oxidation potential and nu(CO) for [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp'] shows an inverse halide order which is consistent with an ionic component to the M-X bond; the small size of fluorine and its closeness to the metal centre leads to the highest energy HOMO and the lowest oxidation potential. In the cations [MX(CO)(eta-RC[triple bond, length as m-dash]CR)Tp']+ electronegativity effects become more important, leading to a conventional order for Cl, Br and I. However, high M-F pi-donation is still facilitated by the short M-F distance.     

Some Polynuclear Coordination Compounds Precursors of Chromites Synthesis,Physicochemical Characterization and Thermal Stability

The polynuclear coordination compounds LnCr(tartrate)₃·nH₂O where Ln(III)=La-Er, obtained through a precipitation method, were characterized on the basis of elemental analysis, their electronic and vibrational spectra and magnetic susceptibility measurements. The possibility of obtaining chromites through the transformations of the polynuclear coordination compounds in the solid state was considered. The thermal decompositions of these compounds, studied by TG and DTA methods, were found to follow an almost uniform pattern. The decompositions occurred in six-eight steps. The first two steps involved dehydration, and the third the transformation of tartrate anions to oxalate, followed by conversion to carbonate and oxocarbonate intermediates. The final product in each case was LnCrO₃. A non-isothermal kinetic analysis of the first decomposition steps was performed, the most probable decomposition mechanism being selected and the kinetic parameters evaluated. The final products of the transformations were characterized. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Bevaviour of the Coordination Compound [Mn(urea)6](NO3)2·2H2O

Thermoanalytical, mass spectrometric and X-ray diffraction data were associated with a reliable assignation of the thermal transformations of the coordination compound [Mn(urea)₆](NO₃)₂·2H₂O. This revised version was published online in August 2006 with corrections to the Cover Date.     

The synthesis of manganese-zinc ferrite through the transformation of polynuclear coordination compounds

The authors analyse the possibility of obtaining manganese-zinc ferrite through the transformations of polynuclear coordination compounds (pcc), either in the solid state or in a reaction medium. Polynuclear coordination compound precursors with the general molecular formula: [Fe(II)_xFe(III)_y(Mn_0.5Zn_0.5)(C₂O₄)₂(OH)_y+2(H₂O)₂] with 0.2相似文献   

Thermal behaviour of CuS (covellite) obtained from copper–thiosulfate system

Thermal behaviour of CuS (covellite) obtained from the Cu(CH₃COO)₂·H₂O and Na₂S₂O₃·5H₂O system, working at different molar ratio (1:6 and 1:4) in presence/absence of NH₄VO₃, was studied. It was established that the presence of vanadium in the system induces a densification of CuS nodules, but do not change the hexagonal CuS structure. It has an important influence in thermal behaviour of copper sulfide CuS obtained also. The morphological characteristics of CuS play an important role in the thermal stability and the stoichiometry of the thermal decompositions. Also, the possibility to obtain copper sulfides with greater cooper content was investigated.