Abstract
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, LaCrOx (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.
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Deb, N. Thermal Investigations of M[La(C2O4)3]⋅xH2O (M=Cr(III) and Co(III)). Journal of Thermal Analysis and Calorimetry 67, 699–712 (2002). https://doi.org/10.1023/A:1014321309138
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DOI: https://doi.org/10.1023/A:1014321309138