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- Author or Editor: Z. Rzączyńska x
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Abstract
The complexes of yttrium and lanthanide with 1,1-cyclobutanedicarboxylic acid of the formula: Ln2(C6H6O4)3⋅nH2O, where n=4 for Y, Pr–Tm, n=5 for Yb,Lu, n=7 for La, Ce have been studied. The solid complexes have colours typical of Ln3+ ions. During heating in air they lose water molecules and then decompose to the oxides, directly (Y, Ce, Tm, Yb) or with intermediate formation. The thermal decomposition is connected with released water (313–353 K), carbon dioxide, hydrocarbons(538–598 K) and carbon oxide for Ho and Lu. When heated in nitrogen they dehydrate to form anhydrous salt and next decompose to the mixture of carbon and oxides of respective metals. IR spectra of the prepared complexes suggest that the carboxylate groups are bidentate chelating.
Rare earth elements 1,3,5-benzenetricarboxylates were prepared as solids of the general formula Ln(C9H3O6)·nH2O, where n=6 for La-Dy and n=4 for Ho-Lu,Y. Their solubilities in water at 293 K are of the order 10-4-10-6 mol dm-3. The IR spectra of the complexes indicate that the carboxylate groups are bridging and bidentate chelates. Hydrated 1,3,5-benzenetricarboxylates lose water molecules during heating in one step (La-Tb), two steps (Y, Ho-Tm) or three steps (Dy, Yb, Lu). The anhydrous complexes are stable up to 573-742 K and decompose to oxides (Ce-Lu) at higher temperatures.
The conditions of thermal decomposition of thep-aminosalicylates of Y, La and the lanthanides from Ce(III) to Lu have been studied. On heating, the hydrated complexes of La and the light lanthanides decompose to the oxides with the intermediate formation of Ln2[H2N·C6H3(O)COO]3. Only the complex of La decomposes to La2O3 through La2[H2N·C6H3(O)COO]3 and La2O2CO3. The anhydrous complexes of the heavy lanthanides decompose directly to the oxides, whereas the anhydrous complex of Y decomposes to Y2O3 via Y2[H2N·C6H3(O)COO]3 formation. During heating, the hydrated complexes lose crystallization water and decompose simultaneously, and the endothermic effect of dehydration is masked by the strong exothermic effect of burning of the organic ligand.
Abstract
Properties of lanthanide 1,2,4-benzenetricarboxylates and lanthanide 1,2,4,5-benzenetetracarboxylates obtained by a classical synthesis method and under hydrothermal conditions were compared. Solid 1,2,4-benzenetricarboxylates and 1,2,4,5-benzenetetracarboxylates of cerium, neodymium and erbium were prepared by a classical precipitation method. The same lanthanide compounds were obtained also from hydrothermal reaction. All obtained products were examined by elemental analysis. General formulae of complexes were: Ln(1,2,4-btc)xH2O and Ln4(1,2,4,5-btec)3 yH2O. The thermal analysis shows that hydrothermal conditions cause the coordination of less number of water molecules to complex molecule. Because lanthanide ions exhibit the most often the coordination number equal 8 or 9 one can conclude that the coordination ability of carboxylic groups under hydrothermal conditions is different from that under mild ones. Probably, in hydrothermal conditions the carboxylic groups of 1,2,4-benzenetricarboxylate ions are able to form more coordination bonds with lanthanide ions than under normal pressure.
Abstract
Rare earth complexes with 2,2′-biphenyldicarboxylic acid (diphenic acid = H2dpa) were obtained as hydrated precipitates of the general formula Ln2(C14H8O4)3∙nH2O, where n = 3 for the of Y(III) and Ce(III)–Er(III) and n = 6 for La(III), Tm(III), Yb(III) and Lu(III) complexes. On heating in air atmosphere complexes lose all water molecules in the temperature range 30–210 °C in one step and form anhydrous compounds, which are stable up to 315–370 °C. During further heating they decompose to oxides. The trihydrated compounds are crystalline powders whereas the hexahydrated are amorphous solids. The trihydrated complexes crystallize in the monoclinic (Pr(III) and Ce(III) complexes) and triclinic (Y(III) and Nd(III)–Er(III) complexes) crystal systems.
Abstract
The thermal decomposition behaviour of the manganese(II) complexes with glycine: Mn(gly)Cl2(H2O)2, Mn(gly)2Cl2, Mn(gly)Br2(H2O)2, Mn(gly)2Br2(H2O)2 was investigated by means of TG-DTG-DTA, Hi-Res-TA and DSC techniques. The evolved gas analysis was carried out by means of the coupled TG-FTIR system. Heating of the complexes results first in the release of water molecules. Next, the multi-stage decomposition process with degradation of glycine ligand occurs. Water, carbon dioxide and ammonia were detected in the gaseous products of the complexes decomposition. The temperature of NH3 evolution from the complexes is higher than from free glycine. The final residue in the air atmosphere is Mn2O3 which transforms into Mn3O4 at 930C. In a nitrogen atmosphere, the complexes decompose into MnO.
Abstract
The thermal decomposition reactions of manganese(II) complexes with L-proline and 4-hydroxy- L-proline were studied. The Mn(II) proline complex loses the water molecule at 40–95C and then, heated above 250C it decomposes in several steps to manganese oxide. The most appropriate kinetic equations for dehydration process are the geometrical R2 or R3 ones. They give a value of activation energy, E of about 95 kJmol–1. The Mn(II) hydroxyproline complex loses the water molecules in two stages (70–110 and 110–230C) and next it decomposes to manganese oxide in several steps. The R3 or D3 (three-dimensional diffusion) models are the most appropriate for the first stage of dehydration (E is about 155 kJ mol–1). The second step of dehydration is limited by D3 mechanism (E=52 kJ mol–1).
