Synthèse , étude structurale par diffraction des rayons X et caractérisation thermique de squartes de lanthanide à anions mixtes.

Abstract

This thesis deals with synthesis and characterization of new lanthanide squarates with anionic mixture of: sulfate, hydrogen squarate and oxalate. The structural study was done by X-ray single-crystal diffraction techniques. The hydrothermale reaction of novel phases unknown until now make the originality of this work. Two original phases of lanthanum sulfatosquarates: La2(H2O)4(SO4)2(C4O4) and La2(H2O)3(SO4)2(C4O4)2 was then synthesized which are the first rares earth sulfato-squarates. Another original phase of lanthanum squarate hydrogen squarate with free squaric acid and two water molecules: [La(H2O)3]5(HC4O4)(C4O4)4, H2C4O4, 2H2O. A novel family of lanthanide oxalate-squrarates: Ln2(H2O)2(C2O4)2(C4O4); (where Ln : La, Ce, Pr, Nd) was also synthesized. The TDXD (Thermal Dependent X-ray Diffraction), coupled to traditional methods of thermal analysis (TGA/DTA), has allowed us to describe the mechanism of thermal decomposition of these lanthanide squarates with anions mixture. In addition, Mass spectrometry has been coupled to the previous techniques at some stage in the study of lanthanide oxalate-squarates. The thermal decomposition mechanisms for the most investigated phases are straightforward and the final steps have conducted to oxides of La2O3 and CeO2.