THERMODESTRUCTION OF Lа(III) COORDINATION COMPOUNDS WITH ALIPHATIC Β-Keto­esters

Abstract

Mono- and mixed-ligand complexes of La (III) with aliphatic β-ketoesters were synthesized in the solid state. The complexes have the general formulas LаL2OH·H2O (L=meacac, etacac, alacac) and La(meacac)2X·nCH3OH(X = NO3, CH3COO; n = 1, 2). Their composition, structure, and thermal properties were established by chemical and thermal analysis, IR spectroscopy. It is shown that β-ketoesters are coordinated to the La (III) ion bidentate-cyclically into monoligand hydroxocomp­lexes. Ligand complexes with methylacetoacetate have an oligomeric structure. They consist of cationic fragments [La(meacac)2]+ with bridged connection of the nitrate or acetate anions.
 The thermal destructions of LaL2OH·H2O (L = meacac, etacac, alacac), La(meacac)2NO3· 2CH3OH and La(meacac)2(CH3COO)·CH3OH were studied for the first time in the helium dynamic atmosphere by TGA-MS in the temperature range of 25–900 °C. Depending on the ligand, dehydratation of the hydroxo-complexes takes place in the 120–180 (meacac), 120–190 (etacac) or 110–160 °C (alacac) temperature range, and the mass loss corresponds with the detachment of one water molecule. Decomposition of mixed-ligand complexes starts with the detachment of methanol in the 60–100 °C range. For La(meacac)2NO3·2CH3OH the decomposition process is attended with oxidation of methanol to carbon dioxide due to reduction of the nitrate-ion to nitrogen dioxide. Further heating to 300–400 °C leads to destruction of organic parts of the complexes attended with the release of low-molecular oxygen-containing organic compounds (aldehydes, ketones, alcohols), carbon dioxide and water. At ~500 °C all the La(III) complexes under study totally decompose, yielding the oxycarbonate La2O2CO3, which was fixed by IR spectroscopy. Under further heating to 850 °С oxycarbonate gradually decomposes to La2O3 liberating CO2.