Abstract:Thermal analytical techniques have been employed to characterise the rare‐earth metal oxalato halide‐hydrates. The results permit clear correlation of the degree of hydration to the nature of the lanthanide and halogen ions.
“…The present investigation was intended to study the effect, of substitution of CI by Br. The results show that the substitution does not have a profound effect, which is consistent with the almost identical thermal decomposition characteristics of LnCzO4C1 and LnCzO4Br [3][4][5].…”
The activation energy of the thermal decomposition of finely _~round LaC204Br was determined according to the method of Ozawa as Ea = 203.83 kJ tool-. As compared to the value for the parent oxalate La2(C204)3 Ea= 130 ~/mol), this value is higher by about 70 kJ/mol, which is consistent with the increased interaction between the metal and oxalate ions. The substitution of Br by C1 does not affect the decomposition kinetics profoundly.
“…The present investigation was intended to study the effect, of substitution of CI by Br. The results show that the substitution does not have a profound effect, which is consistent with the almost identical thermal decomposition characteristics of LnCzO4C1 and LnCzO4Br [3][4][5].…”
The activation energy of the thermal decomposition of finely _~round LaC204Br was determined according to the method of Ozawa as Ea = 203.83 kJ tool-. As compared to the value for the parent oxalate La2(C204)3 Ea= 130 ~/mol), this value is higher by about 70 kJ/mol, which is consistent with the increased interaction between the metal and oxalate ions. The substitution of Br by C1 does not affect the decomposition kinetics profoundly.
“…Crystalline NdC204C1.3H20 was obtained by gentle evaporation of a solution of neodymium oxalate in concentrated hydrochloric acid [31][32][33]54].…”
Section: Methodsmentioning
confidence: 99%
“…There is only a narrow temperature interval between (1) We have been interested in a theoretical framework with which to explain the variable patterns of thermal decomposition of oxalate [31][32][33]. The position of the lanthanide oxalates in respect of reactions (1) and (2) makes these compounds and their allied derivatives a natural choice for detailed study.…”
An activation energy Ea = 195 kJ mol-1 has been determined for the thermal decomposition of NdC204C1 to NdOCI with simultaneous expulsion of CO and CO2. As compared with the value (127 kJ mo1-1) predicted by the Kahwa-Mulokozi empirical expression (i) + for Ln2(C204)3 (Ln = light lanthanide), the presence of C1-in the coordination polyhedron appreciably raises the activation energy, which is consistent with a corresponding increase in the covalent strength of the Ln-oxalate bond. The same conclusion regarding the strength of this bond is drawn from a study of the infrared spectrum.Mechanistically, the breaking of the Ln-oxalate bond is suggested to occur in the kinetic ratedetermining step.The thermal decomposition behaviour of the lanthanide oxalates and their derivatives LnC204X (X = C1 or Br) has been widely investigated [1-37]. The course of the reaction displays pronounced sensitivity to the nature of the bonding, not only with regard to the metal-oxalate interaction, but also as concerns the donor property of X. Those observations are explained in a neat theoretical framework. decomposition of oxalate can proceed via three alternativeThe thermal pathways:
Die Oxalatochloride von La, Pr, Cl, Nd, Sm, Eu und Gd und die Oxalatobromide von La, Pr und Ce werden als Trihydrate, die Oxalatobromide von Nd, Sm, Eu und Gd als Pentahydrate erhalten.
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