Synthesis, characterization and the thermal decomposition of potassium tris(oxalato)lanthanum(III)nonahydrate

Abstract

Potassium tris(oxalato)lanthanum(III)nonahydrate, K 3[La(III)(C 2O 4) 3]·9H 2O, has been synthesized and characterized by elemental analysis and IR spectral studies. Thermal studies (TG, DTG and DTA) in air showed that the anhydrous compound formed at ca. 192°C. The final end product at 1000°C was shown to be a mixture of La 2O 3, K 2CO 3, K 2O, KLaO 2 and La 2C 3, through the formation of an intermediate mixture of K 2C 2O 4 and K[La(C 2O 4) x ] (where 1.5 < x < 2) at ca. 293°C, and K 2C 2O 4 and La 2O 2CO 3 at ca. 528°C. DSC study in nitrogen upto 650°C showed that the end product was a mixture of K 2C 2O 4 and La 2O 2CO 3. The kinetic parameters, mainly E * of the dehydration and decomposition steps in TG, were calculated using four non-mechanistic equations. The kinetic parameters, E *, Δ H, Δ S obtained from DSC study are discussed. Some of the decomposition products were identified by IR and X-ray powder diffraction studies. A tentative mechanism for the decomposition in air is proposed.